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Letter
Cathodoluminescence Nanoscopy of 3D Plasmonic NetworksClick to copy article linkArticle link copied!
- Racheli RonRacheli RonDepartment of Chemistry, Institute of Nanotechnology and Advanced Materials (BINA), Bar-Ilan University, Ramat-Gan 5290002, IsraelMore by Racheli Ron
- Marcin Stefan ZielinskiMarcin Stefan ZielinskiAttolight AG, EPFL Innovation Park, Building D, 1015 Lausanne, SwitzerlandMore by Marcin Stefan Zielinski
- Adi Salomon*Adi Salomon*Email: [email protected]Department of Chemistry, Institute of Nanotechnology and Advanced Materials (BINA), Bar-Ilan University, Ramat-Gan 5290002, IsraelSaints-Pères Paris Institute for the Neurosciences, Universite de Paris, CNRS, 75270 Paris, FranceMore by Adi Salomon
Abstract
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Nanoporous metallic networks are endowed with the distinctive optical properties of strong field enhancement and spatial localization, raising the necessity to map the optical eigenmodes with high spatial resolution. In this work, we used cathodoluminescence (CL) to map the local electric fields of a three-dimensional (3D) silver network made of nanosized ligaments and holes over a broad spectral range. A multitude of neighboring hotspots at different frequencies and intensities are observed at subwavelength distances over the network. In contrast to well-defined plasmonic structures, the hotspots do not necessarily correlate with the network morphology, emphasizing the complexity and energy dissipation through the network. In addition, we show that the inherent connectivity of the networked structure plays a key optical role because a ligament with a single connected linker shows localized modes whereas an octopus-like ligament with multiple connections permits energy propagation through the network.
Copyright © 2020 American Chemical Society
Introduction
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Nanoporous metallic networks constitute a new class of advanced materials comprising multimodal nanosized blobs connected to each other to form a disordered 3D structure. Their distinct structural properties, including high surface-to-volume ratio, ability to host guest materials, pure solid connectivity, and high surface curvature, endow them with optical properties that can be found neither in conventional (well-defined) plasmonic structures nor in bulk metals. (1−14)
It has been previously shown by us (15−17) and others (18−33) that this class of connected metallic nanomaterials (two-dimensional (2D) networks as well) exhibit strong local fields over a broad optical range. These fields are confined to subwavelength volumes and are termed hotspots. The associated strong electric fields that exist in these hotspots lead to exceptional enhancement of the nonlinear optical properties of the network (13,16,20−23,33−38) and even to the occurrence of photochemical processes and reactions inside and on the network. (1,2,15,39−41) Both phenomena are outcomes of the high local density of optical states (LDOS) expected on the basis of the strong field enhancement and spatial localization, (18,31,38,42−44) raising the necessity to map the optical eigenmodes with high spatial resolution.
Diffraction-limited far-field optical measurements are not adapted for characterizing these local effects, as field fluctuations and spectral resonances are averaged and result in a broad spectral response. (4,15,45−47) Even near-field techniques, like near-field optical microscopy, are limited in their ability to retrieve spatial confinement in these highly topographic networks at a broad range of frequencies. (45,46,48)
On the other hand, electron microscopy techniques such as electron energy loss spectroscopy (EELS) and CL can meet those challenges because in these techniques the excitation results from an interaction with a highly localized (subnanometer) electron beam. (29,45,46,48−54) Additionally, the beam is considered as a “white source” comprising a broad range of frequencies and is therefore able to excite all available modes in the sample.
In a raster-scanning geometry, it is possible to retrieve the full spectrum from each pixel of the entire scanned sample with nanometer resolution. In EELS, one measures the energy transfer from electrons to plasmons by calculating the energy loss of electrons that have passed through the sample. In CL, on the other hand, photons scattered by the sample are directly collected, reflecting the efficiency of the decay of plasmons into radiation. Thus, in either technique it is possible to map the local electric fields with nanoscale resolution (for further information, see the Supporting Information). (29,50,52,53,55) As EELS is measured in transmission, it is not suitable for thick 3D samples such as those studied here (with a thickness of a few micrometers).
In this work, we used CL to map the local electric fields of a nanoporous silver network over a broad spectral range spanning the ultraviolet (UV), visible (VIS), and near-infrared (NIR) regions. A multitude of hotspots at different frequencies and intensities were observed at subwavelength scales. In contrast to well-defined plasmonic structures, the hotspots do not necessarily correlate with the network morphology, reflecting the complexity of the network and possible interactions between the building blocks as well as energy dissipation through the network. (9−13,35) However, accidental large cracks in the studied network could be distinguished by collecting CL emission in the NIR. (24) In addition, we show that silver ligaments that are multiply connected (“hubs”) permit energy flow through the network and therefore show different optical behavior compared with ligaments that are linked to the network presumably via a single string.
Results and Discussion
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The polychromatic optical response of the nanoporous silver network and its corresponding scanning electron microscopy (SEM) image are shown in Figure 1a,b, respectively. The CL emission is due to excitation of surface plasmon (SP) modes of the 3D silver network. The emission pattern is rich in localized spots spanning the VIS–NIR regime (Figure 1c) demonstrating the functional potential of the network and in agreement with its reported transmission spectrum. (15−17) The observed hotspots are mixed modes of different frequencies, reflecting energy dissipation as well as coupling through the 3D network. (18,28,30,32,47,56,57) Furthermore, modes with different energies and intensities over subwavelength distances are observed, a possible indication of light localization. (24)
Figure 1
Figure 1. Polychromatic CL emission from a 3D nanoporous silver network. (a) Overlay of three monochromatic CL maps of the network in (b) at λCL = 460 ± 10, 600 ± 10, and 775 ± 10 nm, color-coded in blue, green, and red, respectively (see Figure S1). (b) SEM image (1.8 μm × 1.6 μm) of the studied 3D silver network taken simultaneity with CL acquisition. (c) Point CL spectra extracted from various probe positions on the silver network, which are indicated by the corresponding colored crosses in (b). (d) Panchromatic CL (PanCL) map of the network in (b) over the range of 250–790 nm. (e) Monochromatic CL map of the network in (b) at 4.13 eV (λ = 330 ± 10 nm). The mode at 330 nm is attributed to the bulk plasmon frequency of silver. (f) Red-color-coded monochromatic CL image and (g) quantified intensity map of the network in (b) at λCL = 775 ± 10 nm. A comparison of the intensities of the monochromatic CL maps is shown in Figure S1. The identical white contour lines in (a), (e), and (f) indicate the rim of the structural crack shown in the SEM image in (b).
Modes appear from both metal ligaments and hole regions (see Figure 1b,c), and no clear correspondence between the network morphology and hotspot locations is observed (see Figure 1d for the panchromatic CL image and Movie S1). This observation is in agreement with previous studies on 2D metallic networks, (4,18,20−23,26,29,34) wherein it was attributed to the topological complexity of the 2D network. The network topography is revealed by the selection of a spectral range of 330 ± 10 nm, the silver bulk plasmon wavelength (Figure 1e).
Additional interesting features are detectable in Figure 1a. For example, the rim of a large crack (see the white curved contour line) is characterized by red-shifted emission that can be distinguished upon selection of the 775 ± 10 nm band from the hyperspectral CL map (see Figure 1f,g). Plasmon coupling between nearby ligaments and particles along the crack lowers the mode energy and is therefore expressed as a red-shifted CL emission area. (24,56) Coupling between plasmonic modes is an inherent property of this type of solid interconnected 3D network that contributes to the complex multimodal CL emission observed from the studied network.
To better understand the optical outcome of the inherent structural connectivity of the network and its optical robustness, we studied in detail the CL emission from two prototypical network structural elements (see Figure 2). One structural element is characterized by single connectivity, as it is linked at its bottom to the rest of the network (Figure 2a). Contrarily, the second prototypical element is an octopus-like fragment that is characterized by high-connectivity, with at least seven connection points to the whole network structure (Figure 2b). The SEM image in Figure 2c shows such prototypical network features at the same scan.
Figure 2
Figure 2. Effects of the network’s building block connectivity on the CL response. (a, b) Illustration of (a) low- and (b) high-connectivity network ligaments (marked in yellow). The low-connectivity ligament in (a) possesses one bottom connection point to rest of the network and has two disconnected ∼250 nm wings. Contrarily, the high-connectivity ligament in (b) is a nodal ligament with an octopus-like shape having at least seven connection points to the whole 3D network structure. (c) SEM image in which both low- and high-connectivity network ligaments appear (see the upper and lower dotted-line squares, respectively), as illustrated in (a) and (b), respectively. (d, e) Polychromatic CL images of the ligaments marked in (c). The polychromatic CL images are made of overlapped monochromatic CL maps at λCL= 460 ± 10, 500 ± 15, and 620 ± 15 nm. The discrete monochromatic CL maps color-coded according to the emitted color (blue, green, and red, respectively) are shown in Figure S2. (f, g) Local CL spectra corresponding to the probe positions indicated in (c) and in the insets in (f) and (g). The difference in the CL intensity scale bars in (f) and (g) should be noted.
Differences between the two prototypical optical elements are demonstrated by their overlaid polychromatic CL images at λCL= 460 ± 15, 500 ± 15, and 620 ± 15 nm. Whereas localized modes can be assigned at the low-connectivity ligament (Figure 2d), the CL emission detected from the octopus-like fragment is relatively weak and diffuse (Figure 2e).
CL spectra extracted from the low-connectivity ligament quantitatively reflect the ample number of localized modes owned by this single network ligament (Figure 2f); intense CL emissions at different wavelengths (e.g., 400, 420, and 500 nm) are observed from three spots located at subwavelength distances from each other on the ligament. On the other hand, similar spectra are observed from spots located on the octopus-like ligament with about a half order of magnitude less intensity (Figure 2g).
Next, we studied the spatial distribution of plasmonic modes of the two prototype ligaments mentioned above. Six monochromatic CL emission maps over the range of 400–650 nm are presented in Figure 3 for both the singly connected ligament and the octopus-like ligament.
Figure 3
Figure 3. CL emission patterns of low- and high-connectivity network ligaments. All scale bars denote 200 nm. (a) Monochromatic CL emission patterns of a ligament characterized by low-connectivity to the 3D silver network at λ = 400, 450, 470, 500, 600, and 650 nm (all ±5 nm). (b) 3D presentation of the CL maps in (a). (c) Overlaid SEM and CL images of the low-connectivity ligament. (d) Overlaid SEM and CL images of the multiply connected nodal network ligament at the same center wavelengths and bandwidth as in (a–c). The monochromatic CL maps of the nodal ligament and their 3D representation are shown in Figure S3. The black contour lines in (a), (c), and (d) mark the position of the ligaments as retrieved from the SEM image (see Figure 2c).
For the singly connected ligament, a clear spatial confinement of the modes located on the ligament is revealed within the range of 400–500 nm, indicating energy localization. At relatively high mode energies (400–500 nm), the CL emission patterns are spatially localized, and the localized modes fluctuate in energy and intensity. At lower mode energies (600 and 650 nm), the CL emission is delocalized along the ligament and is less intense. In all of the maps, the emission is lowest at the ligament center, where the metallic morphology is narrower and thinner. Such ligaments of low-connectivity support high-intensity modes that are spatially confined to deep subwavelength volumes. In addition, intense CL emission is observed from the gap between the upper neighboring tip and the low-connectivity ligament (Figure 3). The emission peak is observed at about 500 nm and is probably related to coupling of this neighboring tip to the ligament coming into expression by green light emission (see Figure 2d).
Figure 3d maps the CL emission of the octopus-like ligament. Here, unlike the low-connectivity ligament, little emission is observed, and it is diffused around the “hub” (also see Figure S3).
Hotspot Fluctuations
Enhancements of local fields at different frequencies are observed, as shown in Figure 4. Monochromatic CL maps extracted from two different locations are presented in Figure 4a,b. The observed hotspots (high CL intensities) are wavelength-dependent, and their intensities fluctuate, in agreement with our former studies on nonlinear responses of nanoporous 3D metallic networks. (16)Figure 4c shows three sets of point CL spectra from proximate network locations (∼150 nm). The observed spectra of the plasmonic modes fluctuate in both energy and intensity at subwavelength distances. Modes fluctuate from about 420 to 580 nm at a distance of about 100 nm. Figure S4 shows three additional sets of point CL spectra from locations on the network in Figure 1b that are distanced by ∼50 nm. However, at far field the different resonances are averaged out, giving rise to a very broad spectrum as was reported previously. (15,16)
Figure 4
Figure 4. Fluctuations of network hotspots. (a) Monochromatic CL emission patterns from two different network locations (415 nm diameter) indicated on the SEM image in (b) at the noted center wavelengths (20 nm bandwidth). The CL response of each location is strongly wavelength-dependent. (c) Point CL spectra extracted from close spatial positions (∼100 nm apart) on the silver network in (b) demonstrating strong variations in energy and intensity at proximal locations. The probe positions are indicated by the corresponding colored crosses and capital letters on the SEM image in (b). Figure S5 shows the panchromatic CL image of (b).
In the context of strong coupling photochemistry, molecules deposited in and on such a metallic network will experience very strong fields, which may alter their emission rates and directionality as well as their physical and chemical properties. (58−63) Such localized hotspots can lead to modification of the surface potential energy along a given reaction coordinate and open new pathways for energy redistribution that are not accessible through homogeneous catalysis, for example. In addition, the excited plasmonic modes of the network may induce crosstalk between remote molecules deposited on and inside the network, resulting in a supramolecular hybrid system with outstanding optical and chemical properties. We think that the metallic network offers a broadband spectral range for strong interactions and the possibility to host molecules in the large pores, forming a large-scale 3D molecular plasmonic network. Strong coupling between molecules and the network plasmonic modes should result in hybrid states with longer dephasing times and therefore should lead to enhancement of nonlinear optical phenomena such as Raman and second harmonic generation. (15,16) Raman spectra of C60 deposited on the 3D silver network and their reduction process with up to five or six electrons have been shown previously. (15)
Conclusion
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We have experimentally mapped local fields of a 3D silver network by CL nanoscopy. The disorder in such materials is characterized by mixed eigenmodes with fluctuating frequencies and intensities at subwavelength distances, reflecting the topological complexity of the network. A correspondence between the network morphology and the hotspots was found only in the presence of a large crack, where the observed hotspots at the rim of the crack are intense and in the IR regime. The network connectivity prominently affects the LDOS, such that high-connectivity leads to energy propagation through the network. To the best of our knowledge, this is the first experimental demonstration of CL properties of a 3D metallic networked system with a thickness of a few micrometers.
The large-scale lateral dimensions of the networks together with the random localized hotspots suggest that 3D plasmonic networks can exhibit superior performance in a range of technological fields including photonics, optoelectronic devices, photocatalysis, sensing, bioimaging, and quantum information. They can as well be used as fruitful systems for fundamental science endeavors.
Experimental Methods
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3D Silver Network Preparation
Samples of 3D nanoporous silver networks were prepared by sputtering on a silica aerogel substrate as detailed elsewhere. (15) In brief, sample preparation comprises two steps: (1) aerogel substrate synthesis and (2) physical vapor deposition. Silica aerogels were synthesized by a one-step base-catalyzed sol–gel process followed by drying with supercritical CO2 (K850, Quorum). Metals were sputtered (682, Gatan) from pure targets (99.99%, Kurt J. Lesker).
CL Measurements
CL studies were performed on an Attolight Rosa 4634 CL microscope (Attolight AG, Switzerland), which tightly integrates a high numerical aperture (N.A. = 0.72) achromatic reflective lens within the objective lens of a field-emission-gun scanning electron microscope (FEG-SEM). The focal plane of the light lens matches the FEG-SEM optimum working distance. CL was spectrally resolved with a Czerny–Turner spectrometer (320 mm focal length, 150 grooves/mm grating) and measured with a high quantum-efficiency CCD camera (Andor Newton 920) suitable for UV–VIS and NIR spectroscopy. The acceleration voltage and emission current of the electron beam were 7 kV and 20 nA, respectively. The CL data were analyzed using Mountains v.8 (Digital Surf) and MATLAB.
Supporting Information
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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.0c03317.
Monochromatic components of the polychromatic CL image in Figure 1a (Figure S1); monochromatic components of the polychromatic CL images in Figure 2d,e shown at a higher magnification and presenting both low- and high-connectivity structural elements of the 3D silver network (Figure S2); CL response of a highly connected nodal network ligament (Figure S3); demonstration of hotspot fluctuations at an additional 3D silver network scan (Figure 1b) by point CL spectra extracted from proximal probe positions (∼50 nm apart) (Figure S4); panchromatic CL map of the network in Figure 4b over the range of 250–790 nm (Figure S5); resolution of CL imaging (PDF)
Monochromatic CL images (250–790 nm) of the network in Figure 1b (MP4)
Terms & Conditions
Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.
Author Information
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- Adi Salomon - Department of Chemistry, Institute of Nanotechnology and Advanced Materials (BINA), Bar-Ilan University, Ramat-Gan 5290002, Israel; Saints-Pères Paris Institute for the Neurosciences, Universite de Paris, CNRS, 75270 Paris, France;
http://orcid.org/0000-0002-5643-0478;
- Racheli Ron - Department of Chemistry, Institute of Nanotechnology and Advanced Materials (BINA), Bar-Ilan University, Ramat-Gan 5290002, Israel;http://orcid.org/0000-0001-7133-3660
Acknowledgments
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R.R. thanks the Charles Clore Foundation for a fellowship for Ph.D students. This work was supported by the Energy and Water Resources Ministry of Israel (Grant 016-11-216) and the Israel Science Foundation (ISF) (Grant 1231/19).
| CL | cathodoluminescence |
| 2D | two-dimensional |
| LDOS | local density of optical states |
| EELS | energy electron loss spectroscopy |
| UV | ultraviolet |
| VIS | visible |
| NIR | near-infrared |
| SEM | scanning electron microscope |
| SP | surface plasmon |
| PanCL | Panchromatic CL |
| FEG-SEM | field-emission-gun scanning electron microscope |
References
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This article references 63 other publications.
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- 9Galanty, M.; Shavit, O.; Weissman, A.; Aharon, H.; Gachet, D.; Segal, E.; Salomon, A. Second Harmonic Generation Hotspot on a Centrosymmetric Smooth Silver Surface. Light: Sci. Appl. 2018, 7 (1), 49, DOI: 10.1038/s41377-018-0053-6Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3cbgvF2ksQ%253D%253D&md5=c24c3f11e5ef35719fb1e6d76b43a7b1Second harmonic generation hotspot on a centrosymmetric smooth silver surfaceGalanty Matan; Shavit Omer; Weissman Adam; Aharon Hannah; Segal Elad; Salomon Adi; Gachet DavidLight, science & applications (2018), 7 (), 49 ISSN:.Second harmonic generation (SHG) is forbidden for materials with inversion symmetry, such as bulk metals. Symmetry can be broken by morphological or dielectric discontinuities, yet SHG from a smooth continuous metallic surface is negligible. Using non-linear microscopy, we experimentally demonstrate enhanced SHG within an area of smooth silver film surrounded by nanocavities. Nanocavity-assisted SHG is locally enhanced by more than one order of magnitude compared to a neighboring silver surface area. Linear optical measurements and cathodoluminescence (CL) imaging substantiate these observations. We suggest that plasmonic modes launched from the edges of the nanocavities propagate onto the smooth silver film and annihilate, locally generating SHG. In addition, we show that these hotspots can be dynamically controlled in intensity and location by altering the polarization of the incoming field. Our results show that switchable nonlinear hotspots can be generated on smooth metallic films, with important applications in photocatalysis, single-molecule spectroscopy and non-linear surface imaging.
- 10Weissman, A.; Galanty, M.; Gachet, D.; Segal, E.; Shavit, O.; Salomon, A. Spatial Confinement of Light onto a Flat Metallic Surface Using Hybridization between Two Cavities. Adv. Opt. Mater. 2017, 5 (10), 1700097, DOI: 10.1002/adom.201700097Google ScholarThere is no corresponding record for this reference.
- 11Segal, E.; Weissman, A.; Gachet, D.; Salomon, A. Hybridization between Nanocavities for a Polarimetric Color Sorter at the Sub-Micron Scale. Nanoscale 2016, 8 (33), 15296– 15302, DOI: 10.1039/C6NR03528KGoogle Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1ers7jK&md5=04bd3483bf34987ba8f094b3937367c1Hybridization between nanocavities for a polarimetric color sorter at the sub-micron scaleSegal, Elad; Weissman, Adam; Gachet, David; Salomon, AdiNanoscale (2016), 8 (33), 15296-15302CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)Metallic hole arrays have been recently used for color generation and filtering due to their reliability and color tunability. However, color generation is still limited to several microns. Understanding the interaction between the individual elements of the whole nanostructure may push the resoln. to the sub-micron level. Herein, we study the hybridization between silver nanocavities in order to obtain active color generation at the micron scale. To do so, we use five identical triangular cavities which are sepd. by hundreds of nanometers from each other. By tuning either the distance between the cavities or the optical polarization state of the incoming field, the transmitted light through the cavities is actively enhanced at specific frequencies. Consequently, a rainbow of colors is obsd. from a sub-micron scale unit. The reason for this is that the metallic surface plays a vital role in the hybridization between the cavities and contributes to higher frequency modes. Cathodoluminescence measurements have confirmed this assumption and have revealed that these five triangular cavities act as a unified entity surrounded by the propagated surface plasmons. In such plasmonic structures, multi-color tuning can be accomplished and may open the possibility to improve color generation and high-quality pixel fabrication.
- 12Segal, E.; Galanty, M.; Aharon, H.; Salomon, A. Visualization of Plasmon-Induced Hot Electrons by Scanning Electron Microscopy. J. Phys. Chem. C 2019, 123 (50), 30528– 30535, DOI: 10.1021/acs.jpcc.9b08202Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXit1WktL%252FM&md5=907c451bbf63e7555e4c9843ba5dd088Visualization of Plasmon-Induced Hot Electrons by Scanning Electron MicroscopySegal, Elad; Galanty, Matan; Aharon, Hannah; Salomon, AdiJournal of Physical Chemistry C (2019), 123 (50), 30528-30535CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)SEM imaging can indicate hot-electron formation in Al plasmonic nanostructures composed of 5 triangular cavities. A very strong secondary electron emission was obsd., ≤150 nm from the plasmonic structure. The secondary electron emission depends on the acceleration voltage, the distance between the plasmonic cavities, the metal type, and the roughness of the surface. The formation of hot electrons was used to increase the efficiency of an optoelectronic device.
- 13Salomon, A.; Zielinski, M.; Kolkowski, R.; Zyss, J.; Prior, Y. Size and Shape Resonances in Second Harmonic Generation from Silver Nanocavities. J. Phys. Chem. C 2013, 117 (43), 22377– 22382, DOI: 10.1021/jp403010qGoogle Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXovFWnurg%253D&md5=ece3cc2ffa57dc8250eced85a1009609Size and Shape Resonances in Second Harmonic Generation from Silver NanocavitiesSalomon, Adi; Zielinski, Marcin; Kolkowski, Radoslaw; Zyss, Joseph; Prior, YehiamJournal of Physical Chemistry C (2013), 117 (43), 22377-22382CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The nonlinear response of subwavelength nanocavities in thin Ag films are studied. Significant enhancements are reported of the 2nd harmonic generation (SHG) when the fundamental wavelength matches dimensional resonances within the nanocavities. The nonlinear polarization properties of the nanocavities are studied as well and are correlated with the cavity shape and symmetry. In some nanocavities with internal nanocorrugations, giant field enhancements are obsd., making them excellent candidates for high sensitivity spectroscopy.
- 14Biener, J.; Nyce, G. W.; Hodge, A. M.; Biener, M. M.; Hamza, A. V.; Maier, S. A. Nanoporous Plasmonic Metamaterials. Adv. Mater. 2008, 20 (6), 1211– 1217, DOI: 10.1002/adma.200701899Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXlt1Wmu7w%253D&md5=4e39b160bdb8c3b5b5935ba791170592Nanoporous plasmonic metamaterialsBiener, Juergen; Nyce, Gregory W.; Hodge, Andrea M.; Biener, Monika M.; Hamza, Alex V.; Maier, Stefan A.Advanced Materials (Weinheim, Germany) (2008), 20 (6), 1211-1217CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)A review of different routes for the generation of nanoporous metallic foams and films exhibiting well-defined pore size and short-range order. Dealloying and templating gave both 2D and 3D structures that promise a plasmonic response detd. by material constituents and porosity. Viewed in the context of metamaterials, the ease of fabrication of samples covering macroscopic dimensions is highly promising, and suggests more in-depth studies of the plasmonic and photonic properties of this material system for photonic applications.
- 15Ron, R.; Gachet, D.; Rechav, K.; Salomon, A. Direct Fabrication of 3D Metallic Networks and Their Performance. Adv. Mater. 2017, 29 (7), 1604018, DOI: 10.1002/adma.201604018Google ScholarThere is no corresponding record for this reference.
- 16Ron, R.; Shavit, O.; Aharon, H.; Zielinski, M.; Galanty, M.; Salomon, A. Nanoporous Metallic Network as a Large-Scale 3D Source of Second Harmonic Light. J. Phys. Chem. C 2019, 123 (41), 25331– 25340, DOI: 10.1021/acs.jpcc.9b06300Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsl2htrfE&md5=dadca0b7188a82b9873a98fe8eac8518Nanoporous Metallic Network as a Large-Scale 3D Source of Second Harmonic LightRon, Racheli; Shavit, Omer; Aharon, Hannah; Zielinski, Marcin; Galanty, Matan; Salomon, AdiJournal of Physical Chemistry C (2019), 123 (41), 25331-25340CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)We introduce a large-scale nanoporous metallic network whose building-blocks are assembled into an effective nonlinear conductive material, with a considerable conversion efficiency in a wide-range of optical wavelengths. The high nonlinear response results from the complexity of the three-dimensional (3D) network structure having a large surface area as well as hot-spots in deeper focal plans of the metallic network. Broadband responses of the metallic network are obsd. both by second harmonic generation (SHG) and cathodoluminescence (CL). The large-scale dimension and generation of randomized hot-spots make this 3D metallic network a promising platform for applications like photocatalysis, sensing, or in optical imaging such as structured illumination microscopy.
- 17Ron, R.; Haleva, E.; Salomon, A. Nanoporous Metallic Networks: Fabrication, Optical Properties, and Applications. Adv. Mater. 2018, 30 (41), 1706755, DOI: 10.1002/adma.201706755Google ScholarThere is no corresponding record for this reference.
- 18Losquin, A.; Camelio, S.; Rossouw, D.; Besbes, M.; Pailloux, F.; Babonneau, D.; Botton, G. A.; Greffet, J.-J. J.; Stéphan, O.; Kociak, M. Experimental Evidence of Nanometer-Scale Confinement of Plasmonic Eigenmodes Responsible for Hot Spots in Random Metallic Films. Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 115427, DOI: 10.1103/PhysRevB.88.115427Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhslCjtb7K&md5=f12a00360d9e1200386b438186e7132aExperimental evidence of nanometer-scale confinement of plasmonic eigenmodes responsible for hot spots in random metallic filmsLosquin, Arthur; Camelio, Sophie; Rossouw, David; Besbes, Mondher; Pailloux, Frederic; Babonneau, David; Botton, Gianluigi A.; Greffet, Jean-Jacques; Stephan, Odile; Kociak, MathieuPhysical Review B: Condensed Matter and Materials Physics (2013), 88 (11), 115427/1-115427/7CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We report on the identification and nanometer scale characterization over a large energy range of random, disorder-driven, surface plasmons in silver semicontinuous films embedded in silicon nitride. By performing spatially resolved electron energy loss spectroscopy expts., we exptl. demonstrate that these plasmons eigenmodes arise when the films become fractal, leading to the emergence of strong elec. fields ("hot spots") localized over few nanometers. We show that disorder-driven surface plasmons strongly depart from those usually found in nanoparticles, being strongly confined and randomly and densely distributed in space and energy. Beyond that, we show that they have no obvious relation with the local morphol. of the films, in stark contrast with surface plasmon eigenmodes of nanoparticles.
- 19Li, C.; Dag, Ö.; Dao, T. D.; Nagao, T.; Sakamoto, Y.; Kimura, T.; Terasaki, O.; Yamauchi, Y. Electrochemical Synthesis of Mesoporous Gold Films toward Mesospace-Stimulated Optical Properties. Nat. Commun. 2015, 6 (1), 6608, DOI: 10.1038/ncomms7608Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXosFegur0%253D&md5=db3f15d3f482ec686be4f22024a67798Electrochemical synthesis of mesoporous gold films toward mesospace-stimulated optical propertiesLi, Cuiling; Dag, Omer; Dao, Thang Duy; Nagao, Tadaaki; Sakamoto, Yasuhiro; Kimura, Tatsuo; Terasaki, Osamu; Yamauchi, YusukeNature Communications (2015), 6 (), 6608CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)Mesoporous gold (Au) films with tunable pores are expected to provide fascinating optical properties stimulated by the mesospaces, but they have not been realized yet because of the difficulty of controlling the Au crystal growth. Here, we report a reliable soft-templating method to fabricate mesoporous Au films using stable micelles of diblock copolymers, with electrochem. deposition advantageous for precise control of Au crystal growth. Strong field enhancement takes place around the center of the uniform mesopores as well as on the walls between the pores, leading to the enhanced light scattering as well as surface-enhanced Raman scattering (SERS), which is understandable, for example, from Babinet principles applied for the reverse system of nanoparticle ensembles.
- 20Zayats, a V; Smolyaninov, I. I.; Davis, C. C. Observation of Localized Plasmonic Excitations in Thin Metal Films with Near-Field Second-Harmonic Microscopy. Opt. Commun. 1999, 169 (1–6), 93– 96, DOI: 10.1016/S0030-4018(99)00420-4Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXnt1ylu78%253D&md5=5f4093a8cdc2de565fb5503573f562bcObservation of localized plasmonic excitations in thin metal films with near-field second-harmonic microscopyZayats, Anatoly V.; Smolyaninov, Igor I.; Davis, Christopher C.Optics Communications (1999), 169 (1-6), 93-96CODEN: OPCOB8; ISSN:0030-4018. (Elsevier Science B.V.)Specific localized surface plasmons which exist at rough thin metal films were obsd. using near-field microscopy of 2nd-harmonic generation. The 2nd-harmonic field distribution over a pit on the film surface was imaged and compared to model predictions. The technique of near-field microscopy of 2nd-harmonic generation will be useful for studies of localized electromagnetic excitations at disordered surfaces.
- 21Beermann, J.; Bozhevolnyi, S. I. Microscopy of Localized Second-Harmonic Enhancement in Random Metal Nanostructures. Phys. Rev. B: Condens. Matter Mater. Phys. 2004, 69 (15), 155429, DOI: 10.1103/PhysRevB.69.155429Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXktVKjt7c%253D&md5=3a2c09f8e6c930d92d7b54e60aa81fbeMicroscopy of localized second-harmonic enhancement in random metal nanostructuresBeermann, Jonas; Bozhevolnyi, Sergey I.Physical Review B: Condensed Matter and Materials Physics (2004), 69 (15), 155429/1-155429/9CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)Using second-harmonic (SH) scanning optical microscopy in reflection we study the effect of localized SH enhancement in random metal nanostructures. With a tightly focused tunable (750-830 nm) laser beam, we obtain SH images of a 55-nm-thick gold film surface covered with randomly distributed 70-nm-high gold bumps showing small (∼0.7 μm) and very bright (∼103 times the background) spots. Wavelength and polarization dependencies of both positions and intensities of these SH bright spots as well as their statistics are investigated and compared for two areas having different nominal densities of scatterers, i.e., 25 and 50 μm-2. For relatively large signals, it is found that, the probability d. function of the SH signal follows the power-law dependence with the index being in the range of 2.5-3 for both values of the scattering d. We observe that, for incident laser powers in the range 3-40 mW, the SH bright spots exhibit, as expected, quadratic dependencies of the max. signal on the incident power. However, for higher power levels, the interrogating laser beam causes nonlocal modifications of SH images, i.e., some SH bright spots disappear and others emerge even outside of the area that was exposed to a high power radiation. We relate the obsd. feature to surface plasmon polariton contribution in the process of multiple scattering, resulting in the formation of resonant eigenmodes (at fundamental and SH frequency) whose excitation in turn gives rise to the SH bright spots.
- 22Breit, M.; Podolskiy, V. A.; Grésillon, S.; von Plessen, G.; Feldmann, J.; Rivoal, J. C.; Gadenne, P.; Sarychev, A. K.; Shalaev, V. M. Experimental Observation of Percolation-Enhanced Nonlinear Light Scattering from Semicontinuous Metal Films. Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 64 (12), 125106, DOI: 10.1103/PhysRevB.64.125106Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXmsl2ktr0%253D&md5=705f292cfe0c9748f04ad68990b334bfExperimental observation of percolation-enhanced nonlinear light scattering from semicontinuous metal filmsBreit, M.; Podolskiy, V. A.; Gresillon, S.; von Plessen, G.; Feldmann, J.; Rivoal, J. C.; Gadenne, P.; Sarychev, Andrey K.; Shalaev, Vladimir M.Physical Review B: Condensed Matter and Materials Physics (2001), 64 (12), 125106/1-125106/5CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)Strongly enhanced 2nd-harmonic generation (SHG), which is characterized by a nearly isotropic intensity distribution, is obsd. for Au-glass films near the percolation threshold. The diffuse-like SHG scattering, which can be thought of as nonlinear crit. opalescence, is in sharp contrast with highly collimated linear reflection and transmission from these nanostructured semicontinuous metal films. Observations, which can be explained by giant fluctuations of local nonlinear sources for SHG due to plasmon localization, verify recent predictions of percolation-enhanced nonlinear scattering.
- 23Stockman, M. I.; Bergman, D. J.; Anceau, C.; Brasselet, S.; Zyss, J. Enhanced Second-Harmonic Generation by Metal Surfaces with Nanoscale Roughness: Nanoscale Dephasing, Depolarization, and Correlations. Phys. Rev. Lett. 2004, 92 (5), 057402, DOI: 10.1103/PhysRevLett.92.057402Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXhtVGrt70%253D&md5=530bbc02895df2cba433e6ded077daaaEnhanced Second-Harmonic Generation by Metal Surfaces with Nanoscale Roughness: Nanoscale Dephasing, Depolarization, and CorrelationsStockman, Mark I.; Bergman, David J.; Anceau, Cristelle; Brasselet, Sophie; Zyss, JosephPhysical Review Letters (2004), 92 (5), 057402/1-057402/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)From spectral-expansion Green's function theory, the authors theor. describe the topog., polarization, and spatial-coherence properties of the 2nd-harmonic (SH) local fields at rough metal surfaces. The spatial distributions of the fundamental frequency and SH local fields are very different, with highly enhanced hot spots of the SH. The spatial correlation functions of the amplitude, phase, and direction of the SH polarization all show spatial decay on the nanoscale in the wide range of the metal fill factors. This implies that SH radiation collected from even nanometer-scale areas is strongly depolarized and dephased, i.e., has the nature of hyper-Rayleigh scattering, in agreement with recent expts. The present theory is applicable to nanometer-scale nonlinear-optical illumination, probing, and modification.
- 24Shalaev, V. M.; Safonov, V. P.; Poliakov, E. Y.; Markel, V. A.; Sarychev, A. K. Fractal-Surface-Enhanced Optical Nonlinearities. ACS Symp. Ser. 1997, 679, 88– 107, DOI: 10.1021/bk-1997-0679.ch008Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXntF2isrY%253D&md5=45f40cb930ca4c77fd9b953962ece3faFractal-surface-enhanced optical nonlinearitiesShalaev, V. M.; Safonov, V. P.; Poliakov, E. Y.; Markel, V. A.; Sarychev, A. K.ACS Symposium Series (1997), 679 (Nanostructured Materials), 88-107CODEN: ACSMC8; ISSN:0097-6156. (American Chemical Society)Optical excitations of nanomaterials with fractal structure result in highly localized areas of large fields leading to strong enhancements of optical nonlinearities. The localized modes of fractals cover a broad spectral range, from the visible to the far-IR.
- 25Lee, W. K.; Yu, S.; Engel, C. J.; Reese, T.; Rhee, D.; Chen, W.; Odom, T. W. Concurrent Design of Quasi-Random Photonic Nanostructures. Proc. Natl. Acad. Sci. U. S. A. 2017, 114 (33), 8734– 8739, DOI: 10.1073/pnas.1704711114Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Ckur7N&md5=c80fcf1fa8ae92366a563cf7ee8fb0ddConcurrent design of quasi-random photonic nanostructuresLee, Won-Kyu; Yu, Shuangcheng; Engel, Clifford J.; Reese, Thaddeus; Rhee, Dongjoon; Chen, Wei; Odom, Teri W.Proceedings of the National Academy of Sciences of the United States of America (2017), 114 (33), 8734-8739CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Nanostructured surfaces with quasi-random geometries can manipulate light over broadband wavelengths and wide ranges of angles. Optimization and realization of stochastic patterns have typically relied on serial, direct-write fabrication methods combined with real-space design. However, this approach is not suitable for customizable features or scalable nanomanufg. Moreover, trial-and-error processing cannot guarantee fabrication feasibility because processing-structure relations are not included in conventional designs. Here, we report wrinkle lithog. integrated with concurrent design to produce quasi-random nanostructures in amorphous silicon at wafer scales that achieved over 160% light absorption enhancement from 800 to 1,200 nm. The quasi-periodicity of patterns, materials filling ratio, and feature depths could be independently controlled. We statistically represented the quasi-random patterns by Fourier spectral d. functions (SDFs) that could bridge the processing-structure and structure-performance relations. Iterative search of the optimal structure via the SDF representation enabled concurrent design of nanostructures and processing.
- 26Galinski, H.; Fratalocchi, A.; Döbeli, M.; Capasso, F. Light Manipulation in Metallic Nanowire Networks with Functional Connectivity. Adv. Opt. Mater. 2017, 5 (5), 1600580, DOI: 10.1002/adom.201600580Google ScholarThere is no corresponding record for this reference.
- 27Galinski, H.; Favraud, G.; Dong, H.; Gongora, J. S. T.; Favaro, G.; Döbeli, M.; Spolenak, R.; Fratalocchi, A.; Capasso, F. Scalable, Ultra-Resistant Structural Colors Based on Network Metamaterials. Light: Sci. Appl. 2017, 6 (5), e16233 DOI: 10.1038/lsa.2016.233Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXntFahtr0%253D&md5=0097f0a31fdc90a0e81b575f34a1687fScalable, ultra-resistant structural colors based on network metamaterialsGalinski, Henning; Favraud, Gael; Dong, Hao; Gongora, Juan S. Totero; Favaro, Gregory; Dobeli, Max; Spolenak, Ralph; Fratalocchi, Andrea; Capasso, FedericoLight: Science & Applications (2017), 6 (5), e16233CODEN: LSAIAZ; ISSN:2047-7538. (Nature Publishing Group)Structural colors have drawn wide attention for their potential as a future printing technol. for various applications, ranging from biomimetic tissues to adaptive camouflage materials. However, an efficient approach to realize robust colors with a scalable fabrication technique is still lacking, hampering the realization of practical applications with this platform. Here, we develop a new approach based on large-scale network metamaterials that combine dealloyed subwavelength structures at the nanoscale with lossless, ultra-thin dielec. coatings. By using theory and expts., we show how subwavelength dielec. coatings control a mechanism of resonant light coupling with epsilon-near-zero regions generated in the metallic network, generating the formation of satd. structural colors that cover a wide portion of the spectrum. Ellipsometry measurements support the efficient observation of these colors, even at angles of 70°. The network-like architecture of these nanomaterials allows for high mech. resistance, which is quantified in a series of nano-scratch tests. With such remarkable properties, these metastructures represent a robust design technol. for real-world, large-scale com. applications.
- 28Gaio, M.; Castro-Lopez, M.; Renger, J.; van Hulst, N.; Sapienza, R. Percolating Plasmonic Networks for Light Emission Control. Faraday Discuss. 2015, 178 (0), 237– 252, DOI: 10.1039/C4FD00187GGoogle Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslGrtLjI&md5=2c16114822e86e39278d2383ce0c419ePercolating plasmonic networks for light emission controlGaio, Michele; Castro-Lopez, Marta; Renger, Jan; van Hulst, Niek; Sapienza, RiccardoFaraday Discussions (2015), 178 (Nanoplasmonics), 237-252CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)Optical nanoantennas have revolutionised the way we manipulate single photons emitted by individual light sources in a nanostructured photonic environment. Complex plasmonic architectures allow for multiscale light control by shortening or stretching the light wavelength for a fixed operating frequency, meeting the size of the emitter and that of propagating modes. Here, we study self-assembled semi-continuous gold films and lithog. gold networks characterised by large local d. of optical state (LDOS) fluctuations around the elec. percolation threshold, a regime where the surface is characterised by large metal clusters with fractal topol. We study the formation of plasmonic networks and their effect on light emission from embedded fluorescent probes in these systems. Through fluorescence dynamics expts. we discuss the role of global long-range interactions linked to the degree of percolation and to the network fractality, as well as the local near-field contributions coming from the local electro-magnetic fields and the topol. Our expts. indicate that local properties dominate the fluorescence modification.
- 29Bosman, M.; Anstis, G. R.; Keast, V. J.; Clarke, J. D.; Cortie, M. B. Light Splitting in Nanoporous Gold and Silver. ACS Nano 2012, 6 (1), 319– 326, DOI: 10.1021/nn203600nGoogle Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhs1Smu7%252FM&md5=97cf64bb64d24e7e78b30c24f5ae7711Light Splitting in Nanoporous Gold and SilverBosman, Michel; Anstis, Geoffrey R.; Keast, Vicki J.; Clarke, Jackson D.; Cortie, Michael B.ACS Nano (2012), 6 (1), 319-326CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Nanoporous Au and Ag exhibit strong, omnidirectional broad-band absorption in the far-field. Even though they consist entirely of Au or Ag atoms, these materials appear black and dull, in great contrast with the familiar luster of continuous Au and Ag. The nature of these anomalous optical characteristics is revealed here by combining nanoscale EELS with discrete dipole and boundary element simulations. The strong broad-band absorption finds its origin in nanoscale splitting of light, with great local variations in the absorbed color. This nanoscale polychromaticity results from the excitation of localized surface plasmon resonances, which are imaged and analyzed here with deep sub-wavelength, nanometer spatial resoln. With this insight, it is possible to customize the absorbance and reflectance wavelength bands of thin nanoporous films by only tuning their morphol.
- 30Teulle, A.; Bosman, M.; Girard, C.; Gurunatha, K. L.; Li, M.; Mann, S.; Dujardin, E. Multimodal Plasmonics in Fused Colloidal Networks. Nat. Mater. 2015, 14 (1), 87– 94, DOI: 10.1038/nmat4114Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvVSqtr%252FJ&md5=90ba20d7693ce89f2aaaa310d93bd632Multimodal plasmonics in fused colloidal networksTeulle, Alexandre; Bosman, Michel; Girard, Christian; Gurunatha, Kargal L.; Li, Mei; Mann, Stephen; Dujardin, ErikNature Materials (2015), 14 (1), 87-94CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Harnessing the optical properties of noble metals down to the nanometer scale is a key step towards fast and low-dissipative information processing. At the 10-nm length scale, metal crystallinity and patterning as well as probing of surface plasmon properties must be controlled with a challenging high level of precision. Here, ultimate lateral confinement and delocalization of surface plasmon modes are simultaneously achieved in extended self-assembled networks comprising linear chains of partially fused gold nanoparticles. The spectral and spatial distributions of the surface plasmon modes assocd. with the colloidal superstructures are evidenced by performing monochromated EELS with a nanometer-sized electron probe. The authors prep. the metallic bead strings by electron-beam-induced interparticle fusion of nanoparticle networks. The fused superstructures retain the native morphol. and crystallinity but develop very low-energy surface plasmon modes that are capable of supporting long-range and spectrally tunable propagation in nanoscale waveguides.
- 31Krachmalnicoff, V.; Castanié, E.; De Wilde, Y.; Carminati, R. Fluctuations of the Local Density of States Probe Localized Surface Plasmons on Disordered Metal Films. Phys. Rev. Lett. 2010, 105 (18), 183901, DOI: 10.1103/PhysRevLett.105.183901Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlKhsL%252FP&md5=053178dbbf080abe4ad7396207c60a31Fluctuations of the Local Density of States Probe Localized Surface Plasmons on Disordered Metal FilmsKrachmalnicoff, V.; Castanie, E.; De Wilde, Y.; Carminati, R.Physical Review Letters (2010), 105 (18), 183901/1-183901/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We measure the statistical distribution of the local d. of optical states (LDOS) on disordered semicontinuous metal films. We show that LDOS fluctuations exhibit a max. in a regime where fractal clusters dominate the film surface. These large fluctuations are a signature of surface-plasmon localization on the nanometer scale.
- 32Detsi, E.; Salverda, M.; Onck, P. R.; De Hosson, J. T. M. On the Localized Surface Plasmon Resonance Modes in Nanoporous Gold Films. J. Appl. Phys. 2014, 115 (4), 044308, DOI: 10.1063/1.4862440Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXjslyjsro%253D&md5=4fa2d28b1feb6f9d383b3fae58b43215On the localized surface plasmon resonance modes in nanoporous gold filmsDetsi, Eric; Salverda, Mart; Onck, Patrick R.; De Hosson, Jeff Th. M.Journal of Applied Physics (Melville, NY, United States) (2014), 115 (4), 044308/1-044308/8CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)This work concs. on the relation between plasmonic modes and the microstructure of nanoporous Au films. Based on expts. and computational analyses, we conclude that ligament as well as pore sizes need to be taken into account for an adequate phys. description of the optical performance of a disordered nanoporous metal film as a function of its detailed microstructure. (c) 2014 American Institute of Physics.
- 33Wokaun, A.; Bergman, J. G.; Heritage, J. P.; Glass, A. M.; Liao, P. F.; Olson, D. H. Surface Second-Harmonic Generation from Metal Island Films and Microlithographic Structures. Phys. Rev. B: Condens. Matter Mater. Phys. 1981, 24 (2), 849– 856, DOI: 10.1103/PhysRevB.24.849Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXlt1elt7c%253D&md5=7173bf8e99997e1a39854143467935fbSurface second-harmonic generation from metal island films and microlithographic structuresWokaun, A.; Bergman, J. G.; Heritage, J. P.; Glass, A. M.; Liao, P. F.; Olson, D. H.Physical Review B: Condensed Matter and Materials Physics (1981), 24 (2), 849-56CODEN: PRBMDO; ISSN:0163-1829.Enhanced 2nd-harmonic generation is obsd. from Ag and Au island films, and from regular arrays of Ag particles produced by microlithog. techniques. Enhancements are interpreted in terms of an electromagnetic model involving localized surface-plasma oscillations. The regular arrays allow the sepn. of fundamental and 2nd-harmonic beams by a novel grating effect.
- 34Smolyaninov, I.; Zayats, A.; Davis, C. Near-Field Second Harmonic Generation from a Rough Metal Surface. Phys. Rev. B: Condens. Matter Mater. Phys. 1997, 56 (15), 9290– 9293, DOI: 10.1103/PhysRevB.56.9290Google ScholarThere is no corresponding record for this reference.
- 35Salomon, A.; Prior, Y.; Fedoruk, M.; Feldmann, J.; Kolkowski, R.; Zyss, J. Plasmonic Coupling between Metallic Nanocavities. J. Opt. 2014, 16 (11), 114012, DOI: 10.1088/2040-8978/16/11/114012Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslGqtLc%253D&md5=40c9b46a57401473794d4ce4c8ab9726Plasmonic coupling between metallic nanocavitiesSalomon, Adi; Prior, Yehiam; Fedoruk, Michael; Feldmann, Jochen; Kolkowski, Radoslaw; Zyss, JosephJournal of Optics (Bristol, United Kingdom) (2014), 16 (11), 114012/1-114012/7, 7 pp.CODEN: JOOPCA; ISSN:2040-8978. (IOP Publishing Ltd.)We demonstrate strong coupling of nanocavities in metal films, sparked by propagating surface plasmons. Unlike the coupling of metallic nanoparticles which decays over distances of tens of nanometers, the metallic nanocavities display long range coupling at distances of hundreds of nanometers for the properly selected metal/wavelength combinations. Such strong coupling drastically changes the symmetry of the charge distribution around the nanocavities as is evidenced by the nonlinear optical response of the medium. We show that when strongly coupled, equilateral triangular nanocavities lose their individual symmetry to adopt the lower symmetry of the coupled system and respond like a single dipolar entity. A quant. model is suggested for the transition from individual to strongly coupled nanocavities.
- 36Wang, D.; Schaaf, P. Plasmonic Nanosponges. Adv. Phys. X 2018, 3 (1), 1456361, DOI: 10.1080/23746149.2018.1456361Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXht1OmsbfF&md5=0597999749f9592fc8b5d51cdcdf80e1Plasmonic nanospongesWang, Dong; Schaaf, PeterAdvances in Physics: X (2018), 3 (1), 1456361/1-1456361/19CODEN: APXDAR; ISSN:2374-6149. (Taylor & Francis Ltd.)Gold nanosponges, or nanoporous gold nanoparticles, possess a percolated nanoporous structure over the entire nanoparticles. The optical and plasmonic properties of gold nanosponges and its related hybrid nanosponges are very fascinating due to the unique structural feature, and are controllable and tuneable in a large scope by changing the structural parameters like pore/ligament size, porosity, particle size, particles form, and hybrid structure. The nanosponges show the strong polarization dependence and multiple resonances behavior. Besides, the nanosponges exhibit a significantly higher local field enhancement than the solid nanoparticles. Strong nonlinear optical properties are confirmed by their high-order photoemission behavior, whereby long-lived plasmon modes are also clearly obsd. All this is very important and relevant for the applications in enhanced Raman scattering, fluorescence manipulation, sensing, and nonlinear photonics.
- 37Bozhevolnyi, S. I.; Beermann, J.; Coello, V. Direct Observation of Localized Second-Harmonic Enhancement in Random Metal Nanostructures. Phys. Rev. Lett. 2003, 90 (19), 197403, DOI: 10.1103/PhysRevLett.90.197403Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXjvVKrurs%253D&md5=7a6161daa81dcc501d1fdb12341145fcDirect Observation of Localized Second-Harmonic Enhancement in Random Metal NanostructuresBozhevolnyi, Sergey I.; Beermann, Jonas; Coello, VictorPhysical Review Letters (2003), 90 (19), 197403/1-197403/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Second harmonic (SH) scanning optical microscopy in reflection is used to image the Au film surface covered with randomly placed scatterers. SH images obtained with a tightly focused tunable (750-830 nm) laser beam show small (∼0.7 μm) and very bright (∼103 times the background) spots, whose locations depend on the wavelength and polarization of light. Comparing SH and fundamental harmonic (FH) images, the localized SH enhancement occurs due to the overlap of FH and SH eigenmodes. The probability d. function of the SH signal is found to follow the power-law dependence.
- 38Mascheck, M.; Schmidt, S.; Silies, M.; Yatsui, T.; Kitamura, K.; Ohtsu, M.; Leipold, D.; Runge, E.; Lienau, C. Observing the Localization of Light in Space and Time by Ultrafast Second-Harmonic Microscopy. Nat. Photonics 2012, 6 (5), 293– 298, DOI: 10.1038/nphoton.2012.69Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XlsFWnsLk%253D&md5=a0ddcf0f59e80ed776e82ac547570eeeObserving the localization of light in space and time by ultrafast second-harmonic microscopyMascheck, Manfred; Schmidt, Slawa; Silies, Martin; Yatsui, Takashi; Kitamura, Kokoro; Ohtsu, Motoichi; Leipold, David; Runge, Erich; Lienau, ChristophNature Photonics (2012), 6 (5), 293-298CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)Multiple coherent scattering and the constructive interference of certain scattering paths form the common scheme of several remarkable localization phenomena of classical and quantum waves in randomly disordered media. Prominent examples are electron transport in disordered conductors, the localization of excitons in semiconductor nanostructures, surface plasmon polaritons at rough metallic films or light in disordered dielecs. and amplifying media. However, direct observation of the fundamental spatiotemporal dynamics of the localization process remains challenging. This holds true, in particular, for the localization of light occurring on exceedingly short femtosecond timescales and nanometer length scales. Here, we combine 2nd harmonic microscopy with few-cycle time resoln. to probe the spatiotemporal localization of light waves in a random dielec. medium. We find lifetimes of the photon modes of several femtoseconds and a broad distribution of the local optical d. of states, revealing central hallmarks of the localization of light.
- 39Ding, Y.; Zhang, Z. Nanoporous Metals for Advanced Energy Technologies; Springer International Publishing: Cham, Switzerland, 2016.Google ScholarThere is no corresponding record for this reference.
- 40Atwater, H. A.; Polman, A. Plasmonics for Improved Photovoltaic Devices. Nat. Mater. 2010, 9 (3), 205– 213, DOI: 10.1038/nmat2629Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXitFGltbg%253D&md5=6975cd4e62047de19d45766d775b1a9cPlasmonics for improved photovoltaic devicesAtwater, Harry A.; Polman, AlbertNature Materials (2010), 9 (3), 205-213CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)In this review, we survey recent advances at the intersection of plasmonics and photovoltaics and offer an outlook on the future of solar cells based on these principles. The emerging field of plasmonics has yielded methods for guiding and localizing light at the nanoscale, well below the scale of the wavelength of light in free space. Now plasmonics researchers are turning their attention to photovoltaics, where design approaches based on plasmonics can be used to improve absorption in photovoltaic devices, permitting a considerable redn. in the phys. thickness of solar photovoltaic absorber layers, and yielding new options for solar-cell design.
- 41Favraud, G.; Gongora, J. S. T.; Fratalocchi, A. Evolutionary Photonics for Renewable Energy, Nanomedicine, and Advanced Material Engineering. Laser Photonics Rev. 2018, 12 (11), 1700028, DOI: 10.1002/lpor.201700028Google ScholarThere is no corresponding record for this reference.
- 42Schuller, J. A.; Barnard, E. S.; Cai, W.; Jun, Y. C.; White, J. S.; Brongersma, M. L. Plasmonics for Extreme Light Concentration and Manipulation. Nat. Mater. 2010, 9 (3), 193– 204, DOI: 10.1038/nmat2630Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXitFGltbk%253D&md5=aca2ba7abc0dc5442fbd3e804dea7064Plasmonics for extreme light concentration and manipulationSchuller, Jon A.; Barnard, Edward S.; Cai, Wenshan; Jun, Young Chul; White, Justin S.; Brongersma, Mark L.Nature Materials (2010), 9 (3), 193-204CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)A review. The unprecedented ability of nanometallic (i.e., plasmonic) structures to conc. light into deep-subwavelength vols. has propelled their use in a vast array of nanophotonics technols. and research endeavours. Plasmonic light concentrators can elegantly interface diffraction-limited dielec. optical components with nanophotonic structures. Passive and active plasmonic devices provide new pathways to generate, guide, modulate and detect light with structures that are similar in size to state-of-the-art electronic devices. With the ability to produce highly confined optical fields, the conventional rules for light-matter interactions need to be reexamd., and researchers are venturing into new regimes of optical physics. The authors will discuss the basic concepts behind plasmonics-enabled light concn. and manipulation, make an attempt to capture the wide range of activities and excitement in this area, and speculate on possible future directions.
- 43Solís, D. M.; Taboada, J. M.; Obelleiro, F.; Liz-Marzán, L. M.; García De Abajo, F. J. Toward Ultimate Nanoplasmonics Modeling. ACS Nano 2014, 8 (8), 7559– 7570, DOI: 10.1021/nn5037703Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1GlurjM&md5=88c1cd59565d7f6118088c7272441fd3Toward Ultimate Nanoplasmonics ModelingSolis, Diego M.; Taboada, Jose M.; Obelleiro, Fernando; Liz-Marzan, Luis M.; Garcia de Abajo, F. JavierACS Nano (2014), 8 (8), 7559-7570CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Advances in the field of nanoplasmonics are hindered by the limited capabilities of simulation tools in dealing with realistic systems comprising regions that extend over many light wavelengths. We show that the optical response of unprecedentedly large systems can be accurately calcd. by using a combination of surface integral equation (SIE) method of moments (MoM) formulation and an expansion of the electromagnetic fields in a suitable set of spatial wave functions via fast multipole methods. We start with a crit. review of vol. vs. surface integral methods, followed by a short tutorial on the key features that render plasmons useful for sensing (field enhancement and confinement). We then use the SIE-MoM to examine the plasmonic and sensing capabilities of various systems with increasing degrees of complexity, including both individual and interacting gold nanorods and nanostars, as well as large random and periodic arrangements of ∼1000 gold nanorods. We believe that the present results and methodol. raise the std. of numerical electromagnetic simulations in the field of nanoplasmonics to a new level, which can be beneficial for the design of advanced nanophotonic devices and optical sensing structures.
- 44Wolf, P. E.; Maret, G. Weak Localization and Coherent Backscattering of Photons in Disordered Media. Phys. Rev. Lett. 1985, 55 (24), 2696– 2699, DOI: 10.1103/PhysRevLett.55.2696Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28Xis1eisQ%253D%253D&md5=a7e853ebc8d28f33abe39b9eeb7ecdb7Weak localization and coherent backscattering of photons in disordered mediaWolf, Pierre Etienne; Maret, GeorgPhysical Review Letters (1985), 55 (24), 2696-9CODEN: PRLTAO; ISSN:0031-9007.Coherent backscattering of waves by a disordered scattering medium is responsible for weak localization. This effort was directly obsd. for the 1st time by using visible light and concd. aq. suspensions of submicron-size polystyrene spheres. The scattered intensity is enhanced by up to 75% within a narrow cone centered at the backscattering direction. As predicted by theory, the aperture of the cone is inversely proportional to the light mean-free path; the latter was controlled by the concn. of spheres. The importance of light polarization and particle size is discussed.
- 45Vesseur, E. J. R.; Aizpurua, J.; Coenen, T.; Reyes-Coronado, A.; Batson, P. E.; Polman, A. Plasmonic Excitation and Manipulation with an Electron Beam. MRS Bull. 2012, 37 (8), 752– 760, DOI: 10.1557/mrs.2012.174Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhvVertrfJ&md5=32c75c623a04c6782c7a90f07575ee05Plasmonic excitation and manipulation with an electron beamVesseur, Ernst Jan R.; Aizpurua, Javier; Coenen, Toon; Reyes-Coronado, Alejandro; Batson, Philip E.; Polman, AlbertMRS Bulletin (2012), 37 (8), 752-760CODEN: MRSBEA; ISSN:0883-7694. (Materials Research Society)When an electron beam passes through or near a metal structure, it will excite surface plasmons, providing a unique way to access surface plasmon behavior at the nanoscale. An electron beam focused to nanometer dimensions thus functions as a point source that is able to probe the local plasmonic mode structure at deep-subwavelength resoln. In this article, we show how well-controlled coupling between an electron beam and surface plasmons, combined with a far-field detection system, allows characterization and manipulation of plasmons on a variety of plasmonic devices. By mapping the spatial profile of inelastic scattering to resonant modes, the dispersion and losses of surface plasmons are resolved. The technique further allows probing of the confinement of plasmons within cavities and measuring the angular emission profile of nanoantennas. The coupling of electrons to surface plasmons allows the use of the electron beam as a dipole emitter that can be positioned at will. The beam position thereby can select between modes with different symmetries. This effect can be used to exert forces on plasmonic structures on the nanometer length scale with great control.
- 46Kneipp, K.; Kneipp, H.; Kneipp, J. Probing Plasmonic Nanostructures by Photons and Electrons. Chem. Sci. 2015, 6 (5), 2721– 2726, DOI: 10.1039/C4SC03508AGoogle Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXisVyhu7k%253D&md5=7ba8945c0710d60d1f9389aacaee30b8Probing plasmonic nanostructures by photons and electronsKneipp, Katrin; Kneipp, Harald; Kneipp, JaninaChemical Science (2015), 6 (5), 2721-2726CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)We discuss recent developments for studying plasmonic metal nanostructures. Exploiting photons and electrons opens up new capabilities to probe the complete plasmon spectrum including bright and dark modes and related local optical fields at subnanometer spatial resoln. This comprehensive characterization of plasmonic properties of metal nanostructures provides new basic insight into the fundamental physics of "surface enhanced" spectroscopy in hottest hot spots and enables us to optimize plasmon supported processes and devices.
- 47Esteban, R.; Taylor, R. W.; Baumberg, J. J.; Aizpurua, J. How Chain Plasmons Govern the Optical Response in Strongly Interacting Self-Assembled Metallic Clusters of Nanoparticles. Langmuir 2012, 28 (24), 8881– 8890, DOI: 10.1021/la300198rGoogle Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XjtVGgsLo%253D&md5=2f9790906887bf02e905967a1ccc754fHow Chain Plasmons Govern the Optical Response in Strongly Interacting Self-Assembled Metallic Clusters of NanoparticlesEsteban, Ruben; Taylor, Richard W.; Baumberg, Jeremy J.; Aizpurua, JavierLangmuir (2012), 28 (24), 8881-8890CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Self-assembled clusters of metallic nanoparticles sepd. by nanometric gaps generate strong plasmonic modes that support both intense and localized near fields. These find use in many ultrasensitive chem. and biol. sensing applications through surface enhanced Raman scattering (SERS). The inability to control at the nanoscale the structure of the clusters on which the optical response crucially depends, led to the development of general descriptions to model the various morphols. fabricated. Rigorous electrodynamic calcns. were used to study clusters formed by a hundred nanospheres that are sepd. by ∼1 nm distance, set by the dimensions of the macrocyclic mol. linker employed exptl. Three-dimensional (3D) cluster structures of moderate compactness are of special interest since they resemble self-assembled clusters grown under typical diffusion-limited aggregation conditions. Agreement between the simulated and measured far-field extinction spectra, supporting the equivalence of the assumed and exptl. morphologies were found. The main features of the optical response of 2- and 3-dimensional clusters can be understood in terms of the excitation of simple units composed of different length resonant chains. A qual. difference was obsd. between short- and long-chain modes in both spectral response and spatial distribution: dimer and short-chain modes are obsd. in the periphery of the cluster at higher energies, whereas inside the structure longer chain excitation occurs at lower energies. Different configurations of isolated 1-dimensional chains as prototypical building blocks for large clusters were studied, showing that the optical response of the chains is robust to disorder. This study provides an intuitive understanding of the behavior of complex aggregates and may be generalized to other types of aggregates and systems formed by large nos. of strongly interacting particles.
- 48Ye, F.; Merlo, J. M.; Burns, M. J.; Naughton, M. J. Optical and Electrical Mappings of Surface Plasmon Cavity Modes. Nanophotonics 2014, 3 (1–2), 33– 49, DOI: 10.1515/nanoph-2013-0038Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmsV2ht74%253D&md5=67a90541b99a1c483a38b5e52bd02e69Optical and electrical mappings of surface plasmon cavity modesYe, Fan; Merlo, Juan M.; Burns, Michael J.; Naughton, Michael J.; Lewis, AaronNanophotonics (2014), 3 (1-2), 33-49CODEN: NANOLP; ISSN:2192-8614. (Walter de Gruyter GmbH)A review. Plasmonics is a rapidly expanding field, founded in physics but now with a growing no. of applications in biol. (biosensing), nanophotonics, photovoltaics, optical engineering and advanced information technol. Appearing as charge d. oscillations along a metal surface, excited by electromagnetic radiation (e.g., light), plasmons can propagate as surface plasmon polaritons, or can be confined as standing waves along an appropriately-prepd. surface. Here, we review the latter manifestation, both their origins and the manners in which they are detected, the latter dominated by near field scanning optical microscopy (NSOM/SNOM). We include discussion of the "plasmonic halo" effect recently obsd. by the authors, wherein cavity-confined plasmons are able to modulate optical transmission through step-gap nanostructures, yielding a novel form of color (wavelength) selection.
- 49Polman, A.; Kociak, M.; García de Abajo, F. J. Electron-Beam Spectroscopy for Nanophotonics. Nat. Mater. 2019, 18 (11), 1158– 1171, DOI: 10.1038/s41563-019-0409-1Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtlOgu77K&md5=a5b06052d2a1e780a333145ef6d4d2c9Electron-beam spectroscopy for nanophotonicsPolman, Albert; Kociak, Mathieu; Garcia de Abajo, F. JavierNature Materials (2019), 18 (11), 1158-1171CODEN: NMAACR; ISSN:1476-1122. (Nature Research)A review. Progress in electron-beam spectroscopies has recently enabled the study of optical excitations with combined space, energy and time resoln. in the nanometer, millielectronvolt and femtosecond domain, thus providing unique access into nanophotonic structures and their detailed optical responses. These techniques rely on ∼1-300 keV electron beams focused at the sample down to sub-nanometer spots, temporally compressed in wavepackets a few femtoseconds long, and in some cases controlled by ultrafast light pulses. The electrons undergo energy losses and gains (also giving rise to cathodoluminescence light emission), which are recorded to reveal the optical landscape along the beam path. This Review portraits these advances, with a focus on coherent excitations, emphasizing the increasing level of control over the electron wavefunctions and ensuing applications in the study and technol. use of optically resonant modes and polaritons in nanoparticles, 2D materials and engineered nanostructures.
- 50Coenen, T.; Haegel, N. M. Cathodoluminescence for the 21st Century: Learning More from Light. Appl. Phys. Rev. 2017, 4 (3), 031103, DOI: 10.1063/1.4985767Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVKnsbbN&md5=760af61652674ef3086a76e4e3c2f44cCathodoluminescence for the 21st century: Learning more from lightCoenen, T.; Haegel, N. M.Applied Physics Reviews (2017), 4 (3), 031103/1-031103/14CODEN: APRPG5; ISSN:1931-9401. (American Institute of Physics)Cathodoluminescence (CL) is the emission of light from a material in response to excitation by incident electrons. The technique has had significant impact in the characterization of semiconductors, minerals, ceramics, and many nanostructured materials. Since 2010, there have been a no. of innovative developments that have revolutionized and expanded the information that can be gained from CL and broadened the areas of application. While the primary historical application of CL was for spatial mapping of luminescence variations (e.g., imaging dark line defects in semiconductor lasers or providing high resoln. imaging of compositional variations in geol. materials), new ways to collect and analyze the emitted light have expanded the science impact of CL, particularly at the intersection of materials science and nanotechnol. These developments include (1) angular and polarized CL, (2) advances in time resolved CL, (3) far-field and near-field transport imaging that enable drift and diffusion information to be obtained through real space imaging, (4) increasing use of statistical analyses for the study of grain boundaries and interfaces, (5) 3D CL including tomog. and combined work utilizing dual beam systems with CL, and (6) combined STEM/CL measurements that are reaching new levels of resoln. and advancing single photon spectroscopy. This focused review will first summarize the fundamentals and then briefly describe the state-of-the-art in conventional CL imaging and spectroscopy. We then review these recent novel exptl. approaches that enable added insight and information, providing a range of examples from nanophotonics, photovoltaics, plasmonics, and studies of individual defects and grain boundaries. (c) 2017 American Institute of Physics.
- 51García De Abajo, F. J. Optical Excitations in Electron Microscopy. Rev. Mod. Phys. 2010, 82 (1), 209– 275, DOI: 10.1103/RevModPhys.82.209Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXktlSht7w%253D&md5=0291ceb122e8ca75d967f00986722fd6Optical excitations in electron microscopyGarcia de Abajo, F. J.Reviews of Modern Physics (2010), 82 (1), 209-275CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)This review discusses how low-energy valence excitations created by swift electrons can render information on the optical response of structured materials with unmatched spatial resoln. Electron microscopes are capable of focusing electron beams on subnanometer spots and probing the target response either by analyzing electron energy losses or by detecting emitted radiation. Theor. frameworks suited to calc. the probability of energy loss and light emission (cathodoluminescence) are reconsidered and compared with exptl. results. More precisely, a quantum-mech. description of the interaction between the electrons and the sample is discussed, followed by a powerful classical dielec. approach that can be applied in practice to more complex systems. The conditions are assessed under which classical and quantum-mech. formulations are equiv. The excitation of collective modes such as plasmons is studied in bulk materials, planar surfaces, and nanoparticles. Light emission induced by the electrons is shown to constitute an excellent probe of plasmons, combining subnanometer resoln. in the position of the electron beam with nanometer resoln. in the emitted wavelength. Both electron energy-loss and cathodoluminescence spectroscopies performed in a scanning mode of operation yield snapshots of plasmon modes in nanostructures with fine spatial detail as compared to other existing imaging techniques, thus providing an ideal tool for nanophotonics studies.
- 52Coenen, T.; Brenny, B. J. M.; Vesseur, E. J.; Polman, A. Cathodoluminescence Microscopy: Optical Imaging and Spectroscopy with Deep-Subwavelength Resolution. MRS Bull. 2015, 40 (04), 359– 365, DOI: 10.1557/mrs.2015.64Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlvVGnu7Y%253D&md5=5cdcd4bf17423cb5a0b5ec5fc73b056cCathodoluminescence microscopy: Optical imaging and spectroscopy with deep-subwavelength resolutionCoenen, Toon; Brenny, Benjamin J. M.; Vesseur, Ernst Jan; Polman, AlbertMRS Bulletin (2015), 40 (4), 359-365CODEN: MRSBEA; ISSN:0883-7694. (Cambridge University Press)This article describes a new microscope, based on angle-resolved cathodoluminescence (CL) imaging spectroscopy, which enables optical imaging and spectroscopy at deep-subwavelength spatial resoln. We used a free electron beam in a scanning electron microscope as a direct excitation source for polarizable materials, and we collected the emitted coherent visible/IR CL radiation using a specially designed optical collection system that is integrated in the electron microscope. We have demonstrated the use of this new technique for the excitation of plasmons in single metal nanoparticles, surface plasmon polaritons at metal surfaces, resonant Mie modes in dielec. nanostructures, and cavity modes and Bloch modes in photonic crystals. Using angle-resolved detection, we are able to derive the nature of localized modes and the dispersion of propagation modes in dielec. and plasmonic geometries. An outlook about new directions and applications of CL imaging spectroscopy is also provided.
- 53Nelayah, J.; Kociak, M.; Stéphan, O.; García De Abajo, F. J.; Tencé, M.; Henrard, L.; Taverna, D.; Pastoriza-Santos, I.; Liz-Marzán, L. M.; Colliex, C. Mapping Surface Plasmons on a Single Metallic Nanoparticle. Nat. Phys. 2007, 3 (5), 348– 353, DOI: 10.1038/nphys575Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXkslyitr4%253D&md5=d37fa4b79f158365b9f4b27d98ff773dMapping surface plasmons on a single metallic nanoparticleNelayah, Jaysen; Kociak, Mathieu; Stephan, Odile; Garcia de Abajo, F. Javier; Tence, Marcel; Henrard, Luc; Taverna, Dario; Pastoriza-Santos, Isabel; Liz-Marzan, Luis M.; Colliex, ChristianNature Physics (2007), 3 (5), 348-353CODEN: NPAHAX; ISSN:1745-2473. (Nature Publishing Group)Understanding how light interacts with matter at the nanometer scale is a fundamental issue in optoelectronics and nanophotonics. In particular, many applications (such as bio-sensing, cancer therapy and all-optical signal processing) rely on surface-bound optical excitations in metallic nanoparticles. However, so far no exptl. technique has been capable of imaging localized optical excitations with sufficient resoln. to reveal their dramatic spatial variation over one single nanoparticle. Here, we present a novel method applied on silver nanotriangles, achieving such resoln. by recording maps of plasmons in the near-IR/visible/UV domain using electron beams instead of photons. This method relies on the detection of plasmons as resonance peaks in the energy-loss spectra of subnanometre electron beams rastered on nanoparticles of well-defined geometrical parameters. This represents a significant improvement in the spatial resoln. with which plasmonic modes can be imaged, and provides a powerful tool in the development of nanometer-level optics.
- 54Atre, A. C.; Brenny, B. J. M.; Coenen, T.; García-Etxarri, A.; Polman, A.; Dionne, J. A. Nanoscale Optical Tomography with Cathodoluminescence Spectroscopy. Nat. Nanotechnol. 2015, 10 (5), 429– 436, DOI: 10.1038/nnano.2015.39Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXmtF2rsbc%253D&md5=f03be9034649cbda183ea0ba67dc5292Nanoscale optical tomography with cathodoluminescence spectroscopyAtre, Ashwin C.; Brenny, Benjamin J. M.; Coenen, Toon; Garcia-Etxarri, Aitzol; Polman, Albert; Dionne, Jennifer A.Nature Nanotechnology (2015), 10 (5), 429-436CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Tomog. has enabled the characterization of the Earth's interior, visualization of the inner workings of the human brain, and three-dimensional reconstruction of matter at the at. scale. However, tomog. techniques that rely on optical excitation or detection are generally limited in their resoln. by diffraction. Here, we introduce a tomog. technique-cathodoluminescence spectroscopic tomog.-to probe optical properties in three dimensions with nanometer-scale spatial and spectral resoln. We first obtain two-dimensional cathodoluminescence maps of a three-dimensional nanostructure at various orientations. We then use the method of filtered back-projection to reconstruct the cathodoluminescence intensity at each wavelength. The resulting tomograms allow us to locate regions of efficient cathodoluminescence in three dimensions across visible and near-IR wavelengths, with contributions from material luminescence and radiative decay of electromagnetic eigenmodes. The exptl. signal can be further correlated with the radiative local d. of optical states in particular regions of the reconstruction. We demonstrate how cathodoluminescence tomog. can be used to achieve nanoscale three-dimensional visualization of light-matter interactions by reconstructing a three-dimensional metal-dielec. nanoresonator.
- 55Zielinski, M. S.; Vardar, E.; Vythilingam, G.; Engelhardt, E.-M.; Hubbell, J. A.; Frey, P.; Larsson, H. M. Quantitative Intrinsic Auto-Cathodoluminescence Can Resolve Spectral Signatures of Tissue-Isolated Collagen Extracellular Matrix. Commun. Biol. 2019, 2 (1), 69, DOI: 10.1038/s42003-019-0313-xGoogle Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3cfmtlGjsQ%253D%253D&md5=cb88783b1d3e6d11bebb32587c8b4151Quantitative intrinsic auto-cathodoluminescence can resolve spectral signatures of tissue-isolated collagen extracellular matrixZielinski Marcin S; Vardar Elif; Vythilingam Ganesh; Engelhardt Eva-Maria; Frey Peter; Larsson Hans M; Vardar Elif; Vythilingam Ganesh; Hubbell Jeffrey ACommunications biology (2019), 2 (), 69 ISSN:.By analyzing isolated collagen gel samples, we demonstrated in situ detection of spectrally deconvoluted auto-cathodoluminescence signatures of specific molecular content with precise spatial localization over a maximum field of view of 300 μm. Correlation of the secondary electron and the hyperspectral images proved ~40 nm resolution in the optical channel, obtained due to a short carrier diffusion length, suppressed by fibril dimensions and poor electrical conductivity specific to their organic composition. By correlating spectrally analyzed auto-cathodoluminescence with mass spectroscopy data, we differentiated spectral signatures of two extracellular matrices, namely human fibrin complex and rat tail collagen isolate, and uncovered differences in protein distributions of isolated extracellular matrix networks of heterogeneous populations. Furthermore, we demonstrated that cathodoluminescence can monitor the progress of a human cell-mediated remodeling process, where human collagenous matrix was deposited within a rat collagenous matrix. The revealed change of the heterogeneous biological composition was confirmed by mass spectroscopy.
- 56Chen, T.; Pourmand, M.; Feizpour, A.; Cushman, B.; Reinhard, B. M. Tailoring Plasmon Coupling in Self-Assembled One-Dimensional Au Nanoparticle Chains through Simultaneous Control of Size and Gap Separation. J. Phys. Chem. Lett. 2013, 4 (13), 2147– 2152, DOI: 10.1021/jz401066gGoogle Scholar56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXptlCgtr8%253D&md5=b5918d7d2ba32cb6f27709825211d4abTailoring Plasmon Coupling in Self-Assembled One-Dimensional Au Nanoparticle Chains through Simultaneous Control of Size and Gap SeparationChen, Tianhong; Pourmand, Mahshid; Feizpour, Amin; Cushman, Bradford; Reinhard, Bjorn M.Journal of Physical Chemistry Letters (2013), 4 (13), 2147-2152CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The authors studied the near- and far-field response of 1-dimensional chains of Au nanoparticles (NPs) fabricated with high structural control through template guided self-assembly. The d. of poly(ethylene glycol) ligands grafted onto the NP surface, in combination with the buffer conditions, facilitate a systematic variation of the av. gap width (g) at short sepns. of g < 1.1 nm. The overall size (n) of the individual clusters was controlled through the template. The ability to independently vary n and g allowed for a rational tuning of the spectral response in individual NP clusters over a broad spectral range. The authors used this structural control for a systematic study of the electromagnetic coupling underlying the superradiant cluster mode. Independent of the chain length, plasmon coupling is dominated by direct neighbor interactions. A decrease in coupling strength at sepns. .ltorsim.0.5 nm indicates nonlocal or quantum-mech. coupling mechanisms.
- 57Lin, S.; Li, M.; Dujardin, E.; Girard, C.; Mann, S. One-Dimensional Plasmon Coupling by Facile Self-Assembly of Gold Nanoparticles into Branched Chain Networks. Adv. Mater. 2005, 17 (21), 2553– 2559, DOI: 10.1002/adma.200500828Google Scholar57https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXht1Cgt7vO&md5=b004311bcbea859f6ae29d005bc2f6c3One-dimensional plasmon coupling by facile self-assembly of gold nanoparticles into branched chain networksLin, Shan; Li, Mei; Dujardin, Erik; Girard, Christian; Mann, StephenAdvanced Materials (Weinheim, Germany) (2005), 17 (21), 2553-2559CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)Short chains and complex networks of interconnected Au nanoparticle chains are produced by a simple template-free approach. Optical spectroscopy and computer simulations show that surface plasmons from individual non-contacting nanoparticles are strongly coupled in the resulting 1D superstructures. These chains may provide a unique way to fabricate complex subwavelength optical waveguides.
- 58Salomon, A.; Genet, C.; Ebbesen, T. W. Molecule-Light Complex: Dynamics of Hybrid Molecule-Surface Plasmon States. Angew. Chem., Int. Ed. 2009, 48 (46), 8748– 8751, DOI: 10.1002/anie.200903191Google Scholar58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtlGju7%252FF&md5=f2563438012fdfedb50dfe038f273b4fMolecule-Light Complex: Dynamics of Hybrid Molecule-Surface Plasmon StatesSalomon, Adi; Genet, Cyriaque; Ebbesen, Thomas W.Angewandte Chemie, International Edition (2009), 48 (46), 8748-8751CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Hole arrays in Ag films are used to gain insight into the properties of hybrid states of tetra-Ph porphyrin tetrasulfonic acid J aggregates with visible spectra and transient optical absorption,. Hybrid mol.-surface plasmon states can be seen and populated with lifetimes comparable to the pure mol. excitonic states.
- 59Salomon, A.; Gordon, R. J.; Prior, Y.; Seideman, T.; Sukharev, M. Strong Coupling between Molecular Excited States and Surface Plasmon Modes of a Slit Array in a Thin Metal Film. Phys. Rev. Lett. 2012, 109 (7), 073002, DOI: 10.1103/PhysRevLett.109.073002Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtlehsLs%253D&md5=b4441b7c4b8e5424c9961c136735fc9fStrong coupling between molecular excited states and surface plasmon modes of a slit array in a thin metal filmSalomon, Adi; Gordon, Robert J.; Prior, Yehiam; Seideman, Tamar; Sukharev, MaximPhysical Review Letters (2012), 109 (7), 073002/1-073002/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We demonstrate strong coupling between mol. excited states and surface plasmon modes of a slit array in a thin metal film. The coupling manifests itself as an anticrossing behavior of the two newly formed polaritons. As the coupling strength grows, a new mode emerges, which is attributed to long-range mol. interactions mediated by the plasmonic field. The new, mol.-like mode repels the polariton states, and leads to an opening of energy gaps both below and above the asymptotic free mol. energy.
- 60Vasa, P.; Pomraenke, R.; Cirmi, G.; De Re, E.; Wang, W.; Schwieger, S.; Leipold, D.; Runge, E.; Cerullo, G.; Lienau, C. Ultrafast Manipulation of Strong Coupling in Metal-Molecular Aggregate Hybrid Nanostructures. ACS Nano 2010, 4 (12), 7559– 7565, DOI: 10.1021/nn101973pGoogle Scholar60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhsVensrrE&md5=4fa137b39892726c14136bceff06c731Ultrafast Manipulation of Strong Coupling in Metal-Molecular Aggregate Hybrid NanostructuresVasa, P.; Pomraenke, R.; Cirmi, G.; De Re, E.; Wang, W.; Schwieger, S.; Leipold, D.; Runge, E.; Cerullo, G.; Lienau, C.ACS Nano (2010), 4 (12), 7559-7565CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)An ultrafast manipulation is demonstrated of the Rabi splitting energy ΩR in a metal-mol. aggregate hybrid nanostructure. The fs excitation drastically alters the optical properties of a model system formed by coating a Au nanoslit array with a thin J-aggregated dye layer. Controlled and reversible transient switching from strong (ΩR ≃ 55 meV) to weak (ΩR ≈ 0) coupling on a sub-ps time scale is directly evidenced by mapping the nonequil. dispersion relations of the coupled excitations. Such a strong, externally controllable coupling of excitons and surface plasmon polaritons is of considerable interest for ultrafast all-optical switching applications in nanoscale plasmonic circuits.
- 61Ebbesen, T. W. Hybrid Light-Matter States in a Molecular and Material Science Perspective. Acc. Chem. Res. 2016, 49 (11), 2403– 2412, DOI: 10.1021/acs.accounts.6b00295Google Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslWhurfM&md5=112474dfc62bce8cf5ea2ba21fab9665Hybrid Light-Matter States in a Molecular and Material Science PerspectiveEbbesen, Thomas W.Accounts of Chemical Research (2016), 49 (11), 2403-2412CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review. The notion that light and matter states can be hybridized the way s and p orbitals are mixed is a concept that is not familiar to most chemists and material scientists. Yet it has much potential for mol. and material sciences that is just beginning to be explored. For instance, it has already been demonstrated that the rate and yield of chem. reactions can be modified and that the cond. of org. semiconductors and nonradiative energy transfer can be enhanced through the hybridization of electronic transitions. The hybridization is not limited to electronic transitions; it can be applied for instance to vibrational transitions to selectively perturb a given bond, opening new possibilities to change the chem. reactivity landscape and to use it as a tool in (bio)mol. science and spectroscopy. Such results are not only the consequence of the new eigenstates and energies generated by the hybridization. The hybrid light-matter states also have unusual properties: they can be delocalized over a very large no. of mols. (up to ca. 105), and they become dispersive or momentum-sensitive. Importantly, the hybridization occurs even in the absence of light because it is the zero-point energies of the mol. and optical transitions that generate the new light-matter states. The present work is not a review but rather an Account from the author's point of view that first introduces the reader to the underlying concepts and details of the features of hybrid light-matter states. It is shown that light-matter hybridization is quite easy to achieve: all that is needed is to place mols. or a material in a resonant optical cavity (e.g., between two parallel mirrors) under the right conditions. For vibrational strong coupling, microfluidic IR cells can be used to study the consequences for chem. in the liq. phase. Examples of modified properties are given to demonstrate the full potential for the mol. and material sciences. Finally an outlook of future directions for this emerging subject is given.
- 62Pustovit, V. N.; Shahbazyan, T. V. Resonance Energy Transfer near Metal Nanostructures Mediated by Surface Plasmons. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83 (8), 085427, DOI: 10.1103/PhysRevB.83.085427Google Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXis1Oqurg%253D&md5=5832815b9a41030f74a8321d36b8cacbResonance energy transfer near metal nanostructures mediated by surface plasmonsPustovit, Vitaliy N.; Shahbazyan, Tigran V.Physical Review B: Condensed Matter and Materials Physics (2011), 83 (8), 085427/1-085427/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The authors develop a unified theory of plasmon-assisted resonance energy transfer (RET) between mols. near a metal nanostructure that maintains energy balance between transfer, dissipation, and radiation. In a wide range of parameters, including in the near field, RET is dominated by plasmon-enhanced radiative transfer (PERT) rather than by a nonradiative transfer mechanism. Numerical calcns. performed for mols. near the Ag nanoparticle indicate that RET magnitude is highly sensitive to mols.' positions.
- 63Mao, P.; Liu, C.; Favraud, G.; Chen, Q.; Han, M.; Fratalocchi, A.; Zhang, S. Broadband Single Molecule SERS Detection Designed by Warped Optical Spaces. Nat. Commun. 2018, 9 (1), 5428, DOI: 10.1038/s41467-018-07869-5Google Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXktFWjug%253D%253D&md5=691edc68ecbd7338f33facb4153c43f8Broadband single molecule SERS detection designed by warped optical spacesMao, Peng; Liu, Changxu; Favraud, Gael; Chen, Qiang; Han, Min; Fratalocchi, Andrea; Zhang, ShuangNature Communications (2018), 9 (1), 5428CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)Engineering hotspots is of crucial importance in many applications including energy harvesting, nano-lasers, subwavelength imaging, and biomedical sensing. Surface-enhanced Raman scattering spectroscopy is a key technique to identify analytes that would otherwise be difficult to diagnose. In std. systems, hotspots are realized with nanostructures made by acute tips or narrow gaps. Owing to the low probability for mols. to reach such tiny active regions, high sensitivity is always accompanied by a large prepn. time for analyte accumulation which hinders the time response. Inspired by transformation optics, we introduce an approach based on warped spaces to manipulate hotspots, resulting in broadband enhancements in both the magnitude and vol. Expts. for single mol. detection with a fast soaking time are realized in conjunction with broadband response and uniformity. Such engineering could provide a new design platform for a rich manifold of devices, which can benefit from broadband and huge field enhancements.
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Abstract
Figure 1
Figure 1. Polychromatic CL emission from a 3D nanoporous silver network. (a) Overlay of three monochromatic CL maps of the network in (b) at λCL = 460 ± 10, 600 ± 10, and 775 ± 10 nm, color-coded in blue, green, and red, respectively (see Figure S1). (b) SEM image (1.8 μm × 1.6 μm) of the studied 3D silver network taken simultaneity with CL acquisition. (c) Point CL spectra extracted from various probe positions on the silver network, which are indicated by the corresponding colored crosses in (b). (d) Panchromatic CL (PanCL) map of the network in (b) over the range of 250–790 nm. (e) Monochromatic CL map of the network in (b) at 4.13 eV (λ = 330 ± 10 nm). The mode at 330 nm is attributed to the bulk plasmon frequency of silver. (f) Red-color-coded monochromatic CL image and (g) quantified intensity map of the network in (b) at λCL = 775 ± 10 nm. A comparison of the intensities of the monochromatic CL maps is shown in Figure S1. The identical white contour lines in (a), (e), and (f) indicate the rim of the structural crack shown in the SEM image in (b).
Figure 2
Figure 2. Effects of the network’s building block connectivity on the CL response. (a, b) Illustration of (a) low- and (b) high-connectivity network ligaments (marked in yellow). The low-connectivity ligament in (a) possesses one bottom connection point to rest of the network and has two disconnected ∼250 nm wings. Contrarily, the high-connectivity ligament in (b) is a nodal ligament with an octopus-like shape having at least seven connection points to the whole 3D network structure. (c) SEM image in which both low- and high-connectivity network ligaments appear (see the upper and lower dotted-line squares, respectively), as illustrated in (a) and (b), respectively. (d, e) Polychromatic CL images of the ligaments marked in (c). The polychromatic CL images are made of overlapped monochromatic CL maps at λCL= 460 ± 10, 500 ± 15, and 620 ± 15 nm. The discrete monochromatic CL maps color-coded according to the emitted color (blue, green, and red, respectively) are shown in Figure S2. (f, g) Local CL spectra corresponding to the probe positions indicated in (c) and in the insets in (f) and (g). The difference in the CL intensity scale bars in (f) and (g) should be noted.
Figure 3
Figure 3. CL emission patterns of low- and high-connectivity network ligaments. All scale bars denote 200 nm. (a) Monochromatic CL emission patterns of a ligament characterized by low-connectivity to the 3D silver network at λ = 400, 450, 470, 500, 600, and 650 nm (all ±5 nm). (b) 3D presentation of the CL maps in (a). (c) Overlaid SEM and CL images of the low-connectivity ligament. (d) Overlaid SEM and CL images of the multiply connected nodal network ligament at the same center wavelengths and bandwidth as in (a–c). The monochromatic CL maps of the nodal ligament and their 3D representation are shown in Figure S3. The black contour lines in (a), (c), and (d) mark the position of the ligaments as retrieved from the SEM image (see Figure 2c).
Figure 4
Figure 4. Fluctuations of network hotspots. (a) Monochromatic CL emission patterns from two different network locations (415 nm diameter) indicated on the SEM image in (b) at the noted center wavelengths (20 nm bandwidth). The CL response of each location is strongly wavelength-dependent. (c) Point CL spectra extracted from close spatial positions (∼100 nm apart) on the silver network in (b) demonstrating strong variations in energy and intensity at proximal locations. The probe positions are indicated by the corresponding colored crosses and capital letters on the SEM image in (b). Figure S5 shows the panchromatic CL image of (b).
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- 9Galanty, M.; Shavit, O.; Weissman, A.; Aharon, H.; Gachet, D.; Segal, E.; Salomon, A. Second Harmonic Generation Hotspot on a Centrosymmetric Smooth Silver Surface. Light: Sci. Appl. 2018, 7 (1), 49, DOI: 10.1038/s41377-018-0053-69https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3cbgvF2ksQ%253D%253D&md5=c24c3f11e5ef35719fb1e6d76b43a7b1Second harmonic generation hotspot on a centrosymmetric smooth silver surfaceGalanty Matan; Shavit Omer; Weissman Adam; Aharon Hannah; Segal Elad; Salomon Adi; Gachet DavidLight, science & applications (2018), 7 (), 49 ISSN:.Second harmonic generation (SHG) is forbidden for materials with inversion symmetry, such as bulk metals. Symmetry can be broken by morphological or dielectric discontinuities, yet SHG from a smooth continuous metallic surface is negligible. Using non-linear microscopy, we experimentally demonstrate enhanced SHG within an area of smooth silver film surrounded by nanocavities. Nanocavity-assisted SHG is locally enhanced by more than one order of magnitude compared to a neighboring silver surface area. Linear optical measurements and cathodoluminescence (CL) imaging substantiate these observations. We suggest that plasmonic modes launched from the edges of the nanocavities propagate onto the smooth silver film and annihilate, locally generating SHG. In addition, we show that these hotspots can be dynamically controlled in intensity and location by altering the polarization of the incoming field. Our results show that switchable nonlinear hotspots can be generated on smooth metallic films, with important applications in photocatalysis, single-molecule spectroscopy and non-linear surface imaging.
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- 11Segal, E.; Weissman, A.; Gachet, D.; Salomon, A. Hybridization between Nanocavities for a Polarimetric Color Sorter at the Sub-Micron Scale. Nanoscale 2016, 8 (33), 15296– 15302, DOI: 10.1039/C6NR03528K11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1ers7jK&md5=04bd3483bf34987ba8f094b3937367c1Hybridization between nanocavities for a polarimetric color sorter at the sub-micron scaleSegal, Elad; Weissman, Adam; Gachet, David; Salomon, AdiNanoscale (2016), 8 (33), 15296-15302CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)Metallic hole arrays have been recently used for color generation and filtering due to their reliability and color tunability. However, color generation is still limited to several microns. Understanding the interaction between the individual elements of the whole nanostructure may push the resoln. to the sub-micron level. Herein, we study the hybridization between silver nanocavities in order to obtain active color generation at the micron scale. To do so, we use five identical triangular cavities which are sepd. by hundreds of nanometers from each other. By tuning either the distance between the cavities or the optical polarization state of the incoming field, the transmitted light through the cavities is actively enhanced at specific frequencies. Consequently, a rainbow of colors is obsd. from a sub-micron scale unit. The reason for this is that the metallic surface plays a vital role in the hybridization between the cavities and contributes to higher frequency modes. Cathodoluminescence measurements have confirmed this assumption and have revealed that these five triangular cavities act as a unified entity surrounded by the propagated surface plasmons. In such plasmonic structures, multi-color tuning can be accomplished and may open the possibility to improve color generation and high-quality pixel fabrication.
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- 13Salomon, A.; Zielinski, M.; Kolkowski, R.; Zyss, J.; Prior, Y. Size and Shape Resonances in Second Harmonic Generation from Silver Nanocavities. J. Phys. Chem. C 2013, 117 (43), 22377– 22382, DOI: 10.1021/jp403010q13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXovFWnurg%253D&md5=ece3cc2ffa57dc8250eced85a1009609Size and Shape Resonances in Second Harmonic Generation from Silver NanocavitiesSalomon, Adi; Zielinski, Marcin; Kolkowski, Radoslaw; Zyss, Joseph; Prior, YehiamJournal of Physical Chemistry C (2013), 117 (43), 22377-22382CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The nonlinear response of subwavelength nanocavities in thin Ag films are studied. Significant enhancements are reported of the 2nd harmonic generation (SHG) when the fundamental wavelength matches dimensional resonances within the nanocavities. The nonlinear polarization properties of the nanocavities are studied as well and are correlated with the cavity shape and symmetry. In some nanocavities with internal nanocorrugations, giant field enhancements are obsd., making them excellent candidates for high sensitivity spectroscopy.
- 14Biener, J.; Nyce, G. W.; Hodge, A. M.; Biener, M. M.; Hamza, A. V.; Maier, S. A. Nanoporous Plasmonic Metamaterials. Adv. Mater. 2008, 20 (6), 1211– 1217, DOI: 10.1002/adma.20070189914https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXlt1Wmu7w%253D&md5=4e39b160bdb8c3b5b5935ba791170592Nanoporous plasmonic metamaterialsBiener, Juergen; Nyce, Gregory W.; Hodge, Andrea M.; Biener, Monika M.; Hamza, Alex V.; Maier, Stefan A.Advanced Materials (Weinheim, Germany) (2008), 20 (6), 1211-1217CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)A review of different routes for the generation of nanoporous metallic foams and films exhibiting well-defined pore size and short-range order. Dealloying and templating gave both 2D and 3D structures that promise a plasmonic response detd. by material constituents and porosity. Viewed in the context of metamaterials, the ease of fabrication of samples covering macroscopic dimensions is highly promising, and suggests more in-depth studies of the plasmonic and photonic properties of this material system for photonic applications.
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- 16Ron, R.; Shavit, O.; Aharon, H.; Zielinski, M.; Galanty, M.; Salomon, A. Nanoporous Metallic Network as a Large-Scale 3D Source of Second Harmonic Light. J. Phys. Chem. C 2019, 123 (41), 25331– 25340, DOI: 10.1021/acs.jpcc.9b0630016https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsl2htrfE&md5=dadca0b7188a82b9873a98fe8eac8518Nanoporous Metallic Network as a Large-Scale 3D Source of Second Harmonic LightRon, Racheli; Shavit, Omer; Aharon, Hannah; Zielinski, Marcin; Galanty, Matan; Salomon, AdiJournal of Physical Chemistry C (2019), 123 (41), 25331-25340CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)We introduce a large-scale nanoporous metallic network whose building-blocks are assembled into an effective nonlinear conductive material, with a considerable conversion efficiency in a wide-range of optical wavelengths. The high nonlinear response results from the complexity of the three-dimensional (3D) network structure having a large surface area as well as hot-spots in deeper focal plans of the metallic network. Broadband responses of the metallic network are obsd. both by second harmonic generation (SHG) and cathodoluminescence (CL). The large-scale dimension and generation of randomized hot-spots make this 3D metallic network a promising platform for applications like photocatalysis, sensing, or in optical imaging such as structured illumination microscopy.
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- 19Li, C.; Dag, Ö.; Dao, T. D.; Nagao, T.; Sakamoto, Y.; Kimura, T.; Terasaki, O.; Yamauchi, Y. Electrochemical Synthesis of Mesoporous Gold Films toward Mesospace-Stimulated Optical Properties. Nat. Commun. 2015, 6 (1), 6608, DOI: 10.1038/ncomms760819https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXosFegur0%253D&md5=db3f15d3f482ec686be4f22024a67798Electrochemical synthesis of mesoporous gold films toward mesospace-stimulated optical propertiesLi, Cuiling; Dag, Omer; Dao, Thang Duy; Nagao, Tadaaki; Sakamoto, Yasuhiro; Kimura, Tatsuo; Terasaki, Osamu; Yamauchi, YusukeNature Communications (2015), 6 (), 6608CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)Mesoporous gold (Au) films with tunable pores are expected to provide fascinating optical properties stimulated by the mesospaces, but they have not been realized yet because of the difficulty of controlling the Au crystal growth. Here, we report a reliable soft-templating method to fabricate mesoporous Au films using stable micelles of diblock copolymers, with electrochem. deposition advantageous for precise control of Au crystal growth. Strong field enhancement takes place around the center of the uniform mesopores as well as on the walls between the pores, leading to the enhanced light scattering as well as surface-enhanced Raman scattering (SERS), which is understandable, for example, from Babinet principles applied for the reverse system of nanoparticle ensembles.
- 20Zayats, a V; Smolyaninov, I. I.; Davis, C. C. Observation of Localized Plasmonic Excitations in Thin Metal Films with Near-Field Second-Harmonic Microscopy. Opt. Commun. 1999, 169 (1–6), 93– 96, DOI: 10.1016/S0030-4018(99)00420-420https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXnt1ylu78%253D&md5=5f4093a8cdc2de565fb5503573f562bcObservation of localized plasmonic excitations in thin metal films with near-field second-harmonic microscopyZayats, Anatoly V.; Smolyaninov, Igor I.; Davis, Christopher C.Optics Communications (1999), 169 (1-6), 93-96CODEN: OPCOB8; ISSN:0030-4018. (Elsevier Science B.V.)Specific localized surface plasmons which exist at rough thin metal films were obsd. using near-field microscopy of 2nd-harmonic generation. The 2nd-harmonic field distribution over a pit on the film surface was imaged and compared to model predictions. The technique of near-field microscopy of 2nd-harmonic generation will be useful for studies of localized electromagnetic excitations at disordered surfaces.
- 21Beermann, J.; Bozhevolnyi, S. I. Microscopy of Localized Second-Harmonic Enhancement in Random Metal Nanostructures. Phys. Rev. B: Condens. Matter Mater. Phys. 2004, 69 (15), 155429, DOI: 10.1103/PhysRevB.69.15542921https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXktVKjt7c%253D&md5=3a2c09f8e6c930d92d7b54e60aa81fbeMicroscopy of localized second-harmonic enhancement in random metal nanostructuresBeermann, Jonas; Bozhevolnyi, Sergey I.Physical Review B: Condensed Matter and Materials Physics (2004), 69 (15), 155429/1-155429/9CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)Using second-harmonic (SH) scanning optical microscopy in reflection we study the effect of localized SH enhancement in random metal nanostructures. With a tightly focused tunable (750-830 nm) laser beam, we obtain SH images of a 55-nm-thick gold film surface covered with randomly distributed 70-nm-high gold bumps showing small (∼0.7 μm) and very bright (∼103 times the background) spots. Wavelength and polarization dependencies of both positions and intensities of these SH bright spots as well as their statistics are investigated and compared for two areas having different nominal densities of scatterers, i.e., 25 and 50 μm-2. For relatively large signals, it is found that, the probability d. function of the SH signal follows the power-law dependence with the index being in the range of 2.5-3 for both values of the scattering d. We observe that, for incident laser powers in the range 3-40 mW, the SH bright spots exhibit, as expected, quadratic dependencies of the max. signal on the incident power. However, for higher power levels, the interrogating laser beam causes nonlocal modifications of SH images, i.e., some SH bright spots disappear and others emerge even outside of the area that was exposed to a high power radiation. We relate the obsd. feature to surface plasmon polariton contribution in the process of multiple scattering, resulting in the formation of resonant eigenmodes (at fundamental and SH frequency) whose excitation in turn gives rise to the SH bright spots.
- 22Breit, M.; Podolskiy, V. A.; Grésillon, S.; von Plessen, G.; Feldmann, J.; Rivoal, J. C.; Gadenne, P.; Sarychev, A. K.; Shalaev, V. M. Experimental Observation of Percolation-Enhanced Nonlinear Light Scattering from Semicontinuous Metal Films. Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 64 (12), 125106, DOI: 10.1103/PhysRevB.64.12510622https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXmsl2ktr0%253D&md5=705f292cfe0c9748f04ad68990b334bfExperimental observation of percolation-enhanced nonlinear light scattering from semicontinuous metal filmsBreit, M.; Podolskiy, V. A.; Gresillon, S.; von Plessen, G.; Feldmann, J.; Rivoal, J. C.; Gadenne, P.; Sarychev, Andrey K.; Shalaev, Vladimir M.Physical Review B: Condensed Matter and Materials Physics (2001), 64 (12), 125106/1-125106/5CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)Strongly enhanced 2nd-harmonic generation (SHG), which is characterized by a nearly isotropic intensity distribution, is obsd. for Au-glass films near the percolation threshold. The diffuse-like SHG scattering, which can be thought of as nonlinear crit. opalescence, is in sharp contrast with highly collimated linear reflection and transmission from these nanostructured semicontinuous metal films. Observations, which can be explained by giant fluctuations of local nonlinear sources for SHG due to plasmon localization, verify recent predictions of percolation-enhanced nonlinear scattering.
- 23Stockman, M. I.; Bergman, D. J.; Anceau, C.; Brasselet, S.; Zyss, J. Enhanced Second-Harmonic Generation by Metal Surfaces with Nanoscale Roughness: Nanoscale Dephasing, Depolarization, and Correlations. Phys. Rev. Lett. 2004, 92 (5), 057402, DOI: 10.1103/PhysRevLett.92.05740223https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXhtVGrt70%253D&md5=530bbc02895df2cba433e6ded077daaaEnhanced Second-Harmonic Generation by Metal Surfaces with Nanoscale Roughness: Nanoscale Dephasing, Depolarization, and CorrelationsStockman, Mark I.; Bergman, David J.; Anceau, Cristelle; Brasselet, Sophie; Zyss, JosephPhysical Review Letters (2004), 92 (5), 057402/1-057402/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)From spectral-expansion Green's function theory, the authors theor. describe the topog., polarization, and spatial-coherence properties of the 2nd-harmonic (SH) local fields at rough metal surfaces. The spatial distributions of the fundamental frequency and SH local fields are very different, with highly enhanced hot spots of the SH. The spatial correlation functions of the amplitude, phase, and direction of the SH polarization all show spatial decay on the nanoscale in the wide range of the metal fill factors. This implies that SH radiation collected from even nanometer-scale areas is strongly depolarized and dephased, i.e., has the nature of hyper-Rayleigh scattering, in agreement with recent expts. The present theory is applicable to nanometer-scale nonlinear-optical illumination, probing, and modification.
- 24Shalaev, V. M.; Safonov, V. P.; Poliakov, E. Y.; Markel, V. A.; Sarychev, A. K. Fractal-Surface-Enhanced Optical Nonlinearities. ACS Symp. Ser. 1997, 679, 88– 107, DOI: 10.1021/bk-1997-0679.ch00824https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXntF2isrY%253D&md5=45f40cb930ca4c77fd9b953962ece3faFractal-surface-enhanced optical nonlinearitiesShalaev, V. M.; Safonov, V. P.; Poliakov, E. Y.; Markel, V. A.; Sarychev, A. K.ACS Symposium Series (1997), 679 (Nanostructured Materials), 88-107CODEN: ACSMC8; ISSN:0097-6156. (American Chemical Society)Optical excitations of nanomaterials with fractal structure result in highly localized areas of large fields leading to strong enhancements of optical nonlinearities. The localized modes of fractals cover a broad spectral range, from the visible to the far-IR.
- 25Lee, W. K.; Yu, S.; Engel, C. J.; Reese, T.; Rhee, D.; Chen, W.; Odom, T. W. Concurrent Design of Quasi-Random Photonic Nanostructures. Proc. Natl. Acad. Sci. U. S. A. 2017, 114 (33), 8734– 8739, DOI: 10.1073/pnas.170471111425https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Ckur7N&md5=c80fcf1fa8ae92366a563cf7ee8fb0ddConcurrent design of quasi-random photonic nanostructuresLee, Won-Kyu; Yu, Shuangcheng; Engel, Clifford J.; Reese, Thaddeus; Rhee, Dongjoon; Chen, Wei; Odom, Teri W.Proceedings of the National Academy of Sciences of the United States of America (2017), 114 (33), 8734-8739CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Nanostructured surfaces with quasi-random geometries can manipulate light over broadband wavelengths and wide ranges of angles. Optimization and realization of stochastic patterns have typically relied on serial, direct-write fabrication methods combined with real-space design. However, this approach is not suitable for customizable features or scalable nanomanufg. Moreover, trial-and-error processing cannot guarantee fabrication feasibility because processing-structure relations are not included in conventional designs. Here, we report wrinkle lithog. integrated with concurrent design to produce quasi-random nanostructures in amorphous silicon at wafer scales that achieved over 160% light absorption enhancement from 800 to 1,200 nm. The quasi-periodicity of patterns, materials filling ratio, and feature depths could be independently controlled. We statistically represented the quasi-random patterns by Fourier spectral d. functions (SDFs) that could bridge the processing-structure and structure-performance relations. Iterative search of the optimal structure via the SDF representation enabled concurrent design of nanostructures and processing.
- 26Galinski, H.; Fratalocchi, A.; Döbeli, M.; Capasso, F. Light Manipulation in Metallic Nanowire Networks with Functional Connectivity. Adv. Opt. Mater. 2017, 5 (5), 1600580, DOI: 10.1002/adom.201600580There is no corresponding record for this reference.
- 27Galinski, H.; Favraud, G.; Dong, H.; Gongora, J. S. T.; Favaro, G.; Döbeli, M.; Spolenak, R.; Fratalocchi, A.; Capasso, F. Scalable, Ultra-Resistant Structural Colors Based on Network Metamaterials. Light: Sci. Appl. 2017, 6 (5), e16233 DOI: 10.1038/lsa.2016.23327https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXntFahtr0%253D&md5=0097f0a31fdc90a0e81b575f34a1687fScalable, ultra-resistant structural colors based on network metamaterialsGalinski, Henning; Favraud, Gael; Dong, Hao; Gongora, Juan S. Totero; Favaro, Gregory; Dobeli, Max; Spolenak, Ralph; Fratalocchi, Andrea; Capasso, FedericoLight: Science & Applications (2017), 6 (5), e16233CODEN: LSAIAZ; ISSN:2047-7538. (Nature Publishing Group)Structural colors have drawn wide attention for their potential as a future printing technol. for various applications, ranging from biomimetic tissues to adaptive camouflage materials. However, an efficient approach to realize robust colors with a scalable fabrication technique is still lacking, hampering the realization of practical applications with this platform. Here, we develop a new approach based on large-scale network metamaterials that combine dealloyed subwavelength structures at the nanoscale with lossless, ultra-thin dielec. coatings. By using theory and expts., we show how subwavelength dielec. coatings control a mechanism of resonant light coupling with epsilon-near-zero regions generated in the metallic network, generating the formation of satd. structural colors that cover a wide portion of the spectrum. Ellipsometry measurements support the efficient observation of these colors, even at angles of 70°. The network-like architecture of these nanomaterials allows for high mech. resistance, which is quantified in a series of nano-scratch tests. With such remarkable properties, these metastructures represent a robust design technol. for real-world, large-scale com. applications.
- 28Gaio, M.; Castro-Lopez, M.; Renger, J.; van Hulst, N.; Sapienza, R. Percolating Plasmonic Networks for Light Emission Control. Faraday Discuss. 2015, 178 (0), 237– 252, DOI: 10.1039/C4FD00187G28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslGrtLjI&md5=2c16114822e86e39278d2383ce0c419ePercolating plasmonic networks for light emission controlGaio, Michele; Castro-Lopez, Marta; Renger, Jan; van Hulst, Niek; Sapienza, RiccardoFaraday Discussions (2015), 178 (Nanoplasmonics), 237-252CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)Optical nanoantennas have revolutionised the way we manipulate single photons emitted by individual light sources in a nanostructured photonic environment. Complex plasmonic architectures allow for multiscale light control by shortening or stretching the light wavelength for a fixed operating frequency, meeting the size of the emitter and that of propagating modes. Here, we study self-assembled semi-continuous gold films and lithog. gold networks characterised by large local d. of optical state (LDOS) fluctuations around the elec. percolation threshold, a regime where the surface is characterised by large metal clusters with fractal topol. We study the formation of plasmonic networks and their effect on light emission from embedded fluorescent probes in these systems. Through fluorescence dynamics expts. we discuss the role of global long-range interactions linked to the degree of percolation and to the network fractality, as well as the local near-field contributions coming from the local electro-magnetic fields and the topol. Our expts. indicate that local properties dominate the fluorescence modification.
- 29Bosman, M.; Anstis, G. R.; Keast, V. J.; Clarke, J. D.; Cortie, M. B. Light Splitting in Nanoporous Gold and Silver. ACS Nano 2012, 6 (1), 319– 326, DOI: 10.1021/nn203600n29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhs1Smu7%252FM&md5=97cf64bb64d24e7e78b30c24f5ae7711Light Splitting in Nanoporous Gold and SilverBosman, Michel; Anstis, Geoffrey R.; Keast, Vicki J.; Clarke, Jackson D.; Cortie, Michael B.ACS Nano (2012), 6 (1), 319-326CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Nanoporous Au and Ag exhibit strong, omnidirectional broad-band absorption in the far-field. Even though they consist entirely of Au or Ag atoms, these materials appear black and dull, in great contrast with the familiar luster of continuous Au and Ag. The nature of these anomalous optical characteristics is revealed here by combining nanoscale EELS with discrete dipole and boundary element simulations. The strong broad-band absorption finds its origin in nanoscale splitting of light, with great local variations in the absorbed color. This nanoscale polychromaticity results from the excitation of localized surface plasmon resonances, which are imaged and analyzed here with deep sub-wavelength, nanometer spatial resoln. With this insight, it is possible to customize the absorbance and reflectance wavelength bands of thin nanoporous films by only tuning their morphol.
- 30Teulle, A.; Bosman, M.; Girard, C.; Gurunatha, K. L.; Li, M.; Mann, S.; Dujardin, E. Multimodal Plasmonics in Fused Colloidal Networks. Nat. Mater. 2015, 14 (1), 87– 94, DOI: 10.1038/nmat411430https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvVSqtr%252FJ&md5=90ba20d7693ce89f2aaaa310d93bd632Multimodal plasmonics in fused colloidal networksTeulle, Alexandre; Bosman, Michel; Girard, Christian; Gurunatha, Kargal L.; Li, Mei; Mann, Stephen; Dujardin, ErikNature Materials (2015), 14 (1), 87-94CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Harnessing the optical properties of noble metals down to the nanometer scale is a key step towards fast and low-dissipative information processing. At the 10-nm length scale, metal crystallinity and patterning as well as probing of surface plasmon properties must be controlled with a challenging high level of precision. Here, ultimate lateral confinement and delocalization of surface plasmon modes are simultaneously achieved in extended self-assembled networks comprising linear chains of partially fused gold nanoparticles. The spectral and spatial distributions of the surface plasmon modes assocd. with the colloidal superstructures are evidenced by performing monochromated EELS with a nanometer-sized electron probe. The authors prep. the metallic bead strings by electron-beam-induced interparticle fusion of nanoparticle networks. The fused superstructures retain the native morphol. and crystallinity but develop very low-energy surface plasmon modes that are capable of supporting long-range and spectrally tunable propagation in nanoscale waveguides.
- 31Krachmalnicoff, V.; Castanié, E.; De Wilde, Y.; Carminati, R. Fluctuations of the Local Density of States Probe Localized Surface Plasmons on Disordered Metal Films. Phys. Rev. Lett. 2010, 105 (18), 183901, DOI: 10.1103/PhysRevLett.105.18390131https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlKhsL%252FP&md5=053178dbbf080abe4ad7396207c60a31Fluctuations of the Local Density of States Probe Localized Surface Plasmons on Disordered Metal FilmsKrachmalnicoff, V.; Castanie, E.; De Wilde, Y.; Carminati, R.Physical Review Letters (2010), 105 (18), 183901/1-183901/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We measure the statistical distribution of the local d. of optical states (LDOS) on disordered semicontinuous metal films. We show that LDOS fluctuations exhibit a max. in a regime where fractal clusters dominate the film surface. These large fluctuations are a signature of surface-plasmon localization on the nanometer scale.
- 32Detsi, E.; Salverda, M.; Onck, P. R.; De Hosson, J. T. M. On the Localized Surface Plasmon Resonance Modes in Nanoporous Gold Films. J. Appl. Phys. 2014, 115 (4), 044308, DOI: 10.1063/1.486244032https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXjslyjsro%253D&md5=4fa2d28b1feb6f9d383b3fae58b43215On the localized surface plasmon resonance modes in nanoporous gold filmsDetsi, Eric; Salverda, Mart; Onck, Patrick R.; De Hosson, Jeff Th. M.Journal of Applied Physics (Melville, NY, United States) (2014), 115 (4), 044308/1-044308/8CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)This work concs. on the relation between plasmonic modes and the microstructure of nanoporous Au films. Based on expts. and computational analyses, we conclude that ligament as well as pore sizes need to be taken into account for an adequate phys. description of the optical performance of a disordered nanoporous metal film as a function of its detailed microstructure. (c) 2014 American Institute of Physics.
- 33Wokaun, A.; Bergman, J. G.; Heritage, J. P.; Glass, A. M.; Liao, P. F.; Olson, D. H. Surface Second-Harmonic Generation from Metal Island Films and Microlithographic Structures. Phys. Rev. B: Condens. Matter Mater. Phys. 1981, 24 (2), 849– 856, DOI: 10.1103/PhysRevB.24.84933https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXlt1elt7c%253D&md5=7173bf8e99997e1a39854143467935fbSurface second-harmonic generation from metal island films and microlithographic structuresWokaun, A.; Bergman, J. G.; Heritage, J. P.; Glass, A. M.; Liao, P. F.; Olson, D. H.Physical Review B: Condensed Matter and Materials Physics (1981), 24 (2), 849-56CODEN: PRBMDO; ISSN:0163-1829.Enhanced 2nd-harmonic generation is obsd. from Ag and Au island films, and from regular arrays of Ag particles produced by microlithog. techniques. Enhancements are interpreted in terms of an electromagnetic model involving localized surface-plasma oscillations. The regular arrays allow the sepn. of fundamental and 2nd-harmonic beams by a novel grating effect.
- 34Smolyaninov, I.; Zayats, A.; Davis, C. Near-Field Second Harmonic Generation from a Rough Metal Surface. Phys. Rev. B: Condens. Matter Mater. Phys. 1997, 56 (15), 9290– 9293, DOI: 10.1103/PhysRevB.56.9290There is no corresponding record for this reference.
- 35Salomon, A.; Prior, Y.; Fedoruk, M.; Feldmann, J.; Kolkowski, R.; Zyss, J. Plasmonic Coupling between Metallic Nanocavities. J. Opt. 2014, 16 (11), 114012, DOI: 10.1088/2040-8978/16/11/11401235https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslGqtLc%253D&md5=40c9b46a57401473794d4ce4c8ab9726Plasmonic coupling between metallic nanocavitiesSalomon, Adi; Prior, Yehiam; Fedoruk, Michael; Feldmann, Jochen; Kolkowski, Radoslaw; Zyss, JosephJournal of Optics (Bristol, United Kingdom) (2014), 16 (11), 114012/1-114012/7, 7 pp.CODEN: JOOPCA; ISSN:2040-8978. (IOP Publishing Ltd.)We demonstrate strong coupling of nanocavities in metal films, sparked by propagating surface plasmons. Unlike the coupling of metallic nanoparticles which decays over distances of tens of nanometers, the metallic nanocavities display long range coupling at distances of hundreds of nanometers for the properly selected metal/wavelength combinations. Such strong coupling drastically changes the symmetry of the charge distribution around the nanocavities as is evidenced by the nonlinear optical response of the medium. We show that when strongly coupled, equilateral triangular nanocavities lose their individual symmetry to adopt the lower symmetry of the coupled system and respond like a single dipolar entity. A quant. model is suggested for the transition from individual to strongly coupled nanocavities.
- 36Wang, D.; Schaaf, P. Plasmonic Nanosponges. Adv. Phys. X 2018, 3 (1), 1456361, DOI: 10.1080/23746149.2018.145636136https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXht1OmsbfF&md5=0597999749f9592fc8b5d51cdcdf80e1Plasmonic nanospongesWang, Dong; Schaaf, PeterAdvances in Physics: X (2018), 3 (1), 1456361/1-1456361/19CODEN: APXDAR; ISSN:2374-6149. (Taylor & Francis Ltd.)Gold nanosponges, or nanoporous gold nanoparticles, possess a percolated nanoporous structure over the entire nanoparticles. The optical and plasmonic properties of gold nanosponges and its related hybrid nanosponges are very fascinating due to the unique structural feature, and are controllable and tuneable in a large scope by changing the structural parameters like pore/ligament size, porosity, particle size, particles form, and hybrid structure. The nanosponges show the strong polarization dependence and multiple resonances behavior. Besides, the nanosponges exhibit a significantly higher local field enhancement than the solid nanoparticles. Strong nonlinear optical properties are confirmed by their high-order photoemission behavior, whereby long-lived plasmon modes are also clearly obsd. All this is very important and relevant for the applications in enhanced Raman scattering, fluorescence manipulation, sensing, and nonlinear photonics.
- 37Bozhevolnyi, S. I.; Beermann, J.; Coello, V. Direct Observation of Localized Second-Harmonic Enhancement in Random Metal Nanostructures. Phys. Rev. Lett. 2003, 90 (19), 197403, DOI: 10.1103/PhysRevLett.90.19740337https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXjvVKrurs%253D&md5=7a6161daa81dcc501d1fdb12341145fcDirect Observation of Localized Second-Harmonic Enhancement in Random Metal NanostructuresBozhevolnyi, Sergey I.; Beermann, Jonas; Coello, VictorPhysical Review Letters (2003), 90 (19), 197403/1-197403/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Second harmonic (SH) scanning optical microscopy in reflection is used to image the Au film surface covered with randomly placed scatterers. SH images obtained with a tightly focused tunable (750-830 nm) laser beam show small (∼0.7 μm) and very bright (∼103 times the background) spots, whose locations depend on the wavelength and polarization of light. Comparing SH and fundamental harmonic (FH) images, the localized SH enhancement occurs due to the overlap of FH and SH eigenmodes. The probability d. function of the SH signal is found to follow the power-law dependence.
- 38Mascheck, M.; Schmidt, S.; Silies, M.; Yatsui, T.; Kitamura, K.; Ohtsu, M.; Leipold, D.; Runge, E.; Lienau, C. Observing the Localization of Light in Space and Time by Ultrafast Second-Harmonic Microscopy. Nat. Photonics 2012, 6 (5), 293– 298, DOI: 10.1038/nphoton.2012.6938https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XlsFWnsLk%253D&md5=a0ddcf0f59e80ed776e82ac547570eeeObserving the localization of light in space and time by ultrafast second-harmonic microscopyMascheck, Manfred; Schmidt, Slawa; Silies, Martin; Yatsui, Takashi; Kitamura, Kokoro; Ohtsu, Motoichi; Leipold, David; Runge, Erich; Lienau, ChristophNature Photonics (2012), 6 (5), 293-298CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)Multiple coherent scattering and the constructive interference of certain scattering paths form the common scheme of several remarkable localization phenomena of classical and quantum waves in randomly disordered media. Prominent examples are electron transport in disordered conductors, the localization of excitons in semiconductor nanostructures, surface plasmon polaritons at rough metallic films or light in disordered dielecs. and amplifying media. However, direct observation of the fundamental spatiotemporal dynamics of the localization process remains challenging. This holds true, in particular, for the localization of light occurring on exceedingly short femtosecond timescales and nanometer length scales. Here, we combine 2nd harmonic microscopy with few-cycle time resoln. to probe the spatiotemporal localization of light waves in a random dielec. medium. We find lifetimes of the photon modes of several femtoseconds and a broad distribution of the local optical d. of states, revealing central hallmarks of the localization of light.
- 39Ding, Y.; Zhang, Z. Nanoporous Metals for Advanced Energy Technologies; Springer International Publishing: Cham, Switzerland, 2016.There is no corresponding record for this reference.
- 40Atwater, H. A.; Polman, A. Plasmonics for Improved Photovoltaic Devices. Nat. Mater. 2010, 9 (3), 205– 213, DOI: 10.1038/nmat262940https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXitFGltbg%253D&md5=6975cd4e62047de19d45766d775b1a9cPlasmonics for improved photovoltaic devicesAtwater, Harry A.; Polman, AlbertNature Materials (2010), 9 (3), 205-213CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)In this review, we survey recent advances at the intersection of plasmonics and photovoltaics and offer an outlook on the future of solar cells based on these principles. The emerging field of plasmonics has yielded methods for guiding and localizing light at the nanoscale, well below the scale of the wavelength of light in free space. Now plasmonics researchers are turning their attention to photovoltaics, where design approaches based on plasmonics can be used to improve absorption in photovoltaic devices, permitting a considerable redn. in the phys. thickness of solar photovoltaic absorber layers, and yielding new options for solar-cell design.
- 41Favraud, G.; Gongora, J. S. T.; Fratalocchi, A. Evolutionary Photonics for Renewable Energy, Nanomedicine, and Advanced Material Engineering. Laser Photonics Rev. 2018, 12 (11), 1700028, DOI: 10.1002/lpor.201700028There is no corresponding record for this reference.
- 42Schuller, J. A.; Barnard, E. S.; Cai, W.; Jun, Y. C.; White, J. S.; Brongersma, M. L. Plasmonics for Extreme Light Concentration and Manipulation. Nat. Mater. 2010, 9 (3), 193– 204, DOI: 10.1038/nmat263042https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXitFGltbk%253D&md5=aca2ba7abc0dc5442fbd3e804dea7064Plasmonics for extreme light concentration and manipulationSchuller, Jon A.; Barnard, Edward S.; Cai, Wenshan; Jun, Young Chul; White, Justin S.; Brongersma, Mark L.Nature Materials (2010), 9 (3), 193-204CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)A review. The unprecedented ability of nanometallic (i.e., plasmonic) structures to conc. light into deep-subwavelength vols. has propelled their use in a vast array of nanophotonics technols. and research endeavours. Plasmonic light concentrators can elegantly interface diffraction-limited dielec. optical components with nanophotonic structures. Passive and active plasmonic devices provide new pathways to generate, guide, modulate and detect light with structures that are similar in size to state-of-the-art electronic devices. With the ability to produce highly confined optical fields, the conventional rules for light-matter interactions need to be reexamd., and researchers are venturing into new regimes of optical physics. The authors will discuss the basic concepts behind plasmonics-enabled light concn. and manipulation, make an attempt to capture the wide range of activities and excitement in this area, and speculate on possible future directions.
- 43Solís, D. M.; Taboada, J. M.; Obelleiro, F.; Liz-Marzán, L. M.; García De Abajo, F. J. Toward Ultimate Nanoplasmonics Modeling. ACS Nano 2014, 8 (8), 7559– 7570, DOI: 10.1021/nn503770343https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1GlurjM&md5=88c1cd59565d7f6118088c7272441fd3Toward Ultimate Nanoplasmonics ModelingSolis, Diego M.; Taboada, Jose M.; Obelleiro, Fernando; Liz-Marzan, Luis M.; Garcia de Abajo, F. JavierACS Nano (2014), 8 (8), 7559-7570CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Advances in the field of nanoplasmonics are hindered by the limited capabilities of simulation tools in dealing with realistic systems comprising regions that extend over many light wavelengths. We show that the optical response of unprecedentedly large systems can be accurately calcd. by using a combination of surface integral equation (SIE) method of moments (MoM) formulation and an expansion of the electromagnetic fields in a suitable set of spatial wave functions via fast multipole methods. We start with a crit. review of vol. vs. surface integral methods, followed by a short tutorial on the key features that render plasmons useful for sensing (field enhancement and confinement). We then use the SIE-MoM to examine the plasmonic and sensing capabilities of various systems with increasing degrees of complexity, including both individual and interacting gold nanorods and nanostars, as well as large random and periodic arrangements of ∼1000 gold nanorods. We believe that the present results and methodol. raise the std. of numerical electromagnetic simulations in the field of nanoplasmonics to a new level, which can be beneficial for the design of advanced nanophotonic devices and optical sensing structures.
- 44Wolf, P. E.; Maret, G. Weak Localization and Coherent Backscattering of Photons in Disordered Media. Phys. Rev. Lett. 1985, 55 (24), 2696– 2699, DOI: 10.1103/PhysRevLett.55.269644https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28Xis1eisQ%253D%253D&md5=a7e853ebc8d28f33abe39b9eeb7ecdb7Weak localization and coherent backscattering of photons in disordered mediaWolf, Pierre Etienne; Maret, GeorgPhysical Review Letters (1985), 55 (24), 2696-9CODEN: PRLTAO; ISSN:0031-9007.Coherent backscattering of waves by a disordered scattering medium is responsible for weak localization. This effort was directly obsd. for the 1st time by using visible light and concd. aq. suspensions of submicron-size polystyrene spheres. The scattered intensity is enhanced by up to 75% within a narrow cone centered at the backscattering direction. As predicted by theory, the aperture of the cone is inversely proportional to the light mean-free path; the latter was controlled by the concn. of spheres. The importance of light polarization and particle size is discussed.
- 45Vesseur, E. J. R.; Aizpurua, J.; Coenen, T.; Reyes-Coronado, A.; Batson, P. E.; Polman, A. Plasmonic Excitation and Manipulation with an Electron Beam. MRS Bull. 2012, 37 (8), 752– 760, DOI: 10.1557/mrs.2012.17445https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhvVertrfJ&md5=32c75c623a04c6782c7a90f07575ee05Plasmonic excitation and manipulation with an electron beamVesseur, Ernst Jan R.; Aizpurua, Javier; Coenen, Toon; Reyes-Coronado, Alejandro; Batson, Philip E.; Polman, AlbertMRS Bulletin (2012), 37 (8), 752-760CODEN: MRSBEA; ISSN:0883-7694. (Materials Research Society)When an electron beam passes through or near a metal structure, it will excite surface plasmons, providing a unique way to access surface plasmon behavior at the nanoscale. An electron beam focused to nanometer dimensions thus functions as a point source that is able to probe the local plasmonic mode structure at deep-subwavelength resoln. In this article, we show how well-controlled coupling between an electron beam and surface plasmons, combined with a far-field detection system, allows characterization and manipulation of plasmons on a variety of plasmonic devices. By mapping the spatial profile of inelastic scattering to resonant modes, the dispersion and losses of surface plasmons are resolved. The technique further allows probing of the confinement of plasmons within cavities and measuring the angular emission profile of nanoantennas. The coupling of electrons to surface plasmons allows the use of the electron beam as a dipole emitter that can be positioned at will. The beam position thereby can select between modes with different symmetries. This effect can be used to exert forces on plasmonic structures on the nanometer length scale with great control.
- 46Kneipp, K.; Kneipp, H.; Kneipp, J. Probing Plasmonic Nanostructures by Photons and Electrons. Chem. Sci. 2015, 6 (5), 2721– 2726, DOI: 10.1039/C4SC03508A46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXisVyhu7k%253D&md5=7ba8945c0710d60d1f9389aacaee30b8Probing plasmonic nanostructures by photons and electronsKneipp, Katrin; Kneipp, Harald; Kneipp, JaninaChemical Science (2015), 6 (5), 2721-2726CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)We discuss recent developments for studying plasmonic metal nanostructures. Exploiting photons and electrons opens up new capabilities to probe the complete plasmon spectrum including bright and dark modes and related local optical fields at subnanometer spatial resoln. This comprehensive characterization of plasmonic properties of metal nanostructures provides new basic insight into the fundamental physics of "surface enhanced" spectroscopy in hottest hot spots and enables us to optimize plasmon supported processes and devices.
- 47Esteban, R.; Taylor, R. W.; Baumberg, J. J.; Aizpurua, J. How Chain Plasmons Govern the Optical Response in Strongly Interacting Self-Assembled Metallic Clusters of Nanoparticles. Langmuir 2012, 28 (24), 8881– 8890, DOI: 10.1021/la300198r47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XjtVGgsLo%253D&md5=2f9790906887bf02e905967a1ccc754fHow Chain Plasmons Govern the Optical Response in Strongly Interacting Self-Assembled Metallic Clusters of NanoparticlesEsteban, Ruben; Taylor, Richard W.; Baumberg, Jeremy J.; Aizpurua, JavierLangmuir (2012), 28 (24), 8881-8890CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Self-assembled clusters of metallic nanoparticles sepd. by nanometric gaps generate strong plasmonic modes that support both intense and localized near fields. These find use in many ultrasensitive chem. and biol. sensing applications through surface enhanced Raman scattering (SERS). The inability to control at the nanoscale the structure of the clusters on which the optical response crucially depends, led to the development of general descriptions to model the various morphols. fabricated. Rigorous electrodynamic calcns. were used to study clusters formed by a hundred nanospheres that are sepd. by ∼1 nm distance, set by the dimensions of the macrocyclic mol. linker employed exptl. Three-dimensional (3D) cluster structures of moderate compactness are of special interest since they resemble self-assembled clusters grown under typical diffusion-limited aggregation conditions. Agreement between the simulated and measured far-field extinction spectra, supporting the equivalence of the assumed and exptl. morphologies were found. The main features of the optical response of 2- and 3-dimensional clusters can be understood in terms of the excitation of simple units composed of different length resonant chains. A qual. difference was obsd. between short- and long-chain modes in both spectral response and spatial distribution: dimer and short-chain modes are obsd. in the periphery of the cluster at higher energies, whereas inside the structure longer chain excitation occurs at lower energies. Different configurations of isolated 1-dimensional chains as prototypical building blocks for large clusters were studied, showing that the optical response of the chains is robust to disorder. This study provides an intuitive understanding of the behavior of complex aggregates and may be generalized to other types of aggregates and systems formed by large nos. of strongly interacting particles.
- 48Ye, F.; Merlo, J. M.; Burns, M. J.; Naughton, M. J. Optical and Electrical Mappings of Surface Plasmon Cavity Modes. Nanophotonics 2014, 3 (1–2), 33– 49, DOI: 10.1515/nanoph-2013-003848https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmsV2ht74%253D&md5=67a90541b99a1c483a38b5e52bd02e69Optical and electrical mappings of surface plasmon cavity modesYe, Fan; Merlo, Juan M.; Burns, Michael J.; Naughton, Michael J.; Lewis, AaronNanophotonics (2014), 3 (1-2), 33-49CODEN: NANOLP; ISSN:2192-8614. (Walter de Gruyter GmbH)A review. Plasmonics is a rapidly expanding field, founded in physics but now with a growing no. of applications in biol. (biosensing), nanophotonics, photovoltaics, optical engineering and advanced information technol. Appearing as charge d. oscillations along a metal surface, excited by electromagnetic radiation (e.g., light), plasmons can propagate as surface plasmon polaritons, or can be confined as standing waves along an appropriately-prepd. surface. Here, we review the latter manifestation, both their origins and the manners in which they are detected, the latter dominated by near field scanning optical microscopy (NSOM/SNOM). We include discussion of the "plasmonic halo" effect recently obsd. by the authors, wherein cavity-confined plasmons are able to modulate optical transmission through step-gap nanostructures, yielding a novel form of color (wavelength) selection.
- 49Polman, A.; Kociak, M.; García de Abajo, F. J. Electron-Beam Spectroscopy for Nanophotonics. Nat. Mater. 2019, 18 (11), 1158– 1171, DOI: 10.1038/s41563-019-0409-149https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtlOgu77K&md5=a5b06052d2a1e780a333145ef6d4d2c9Electron-beam spectroscopy for nanophotonicsPolman, Albert; Kociak, Mathieu; Garcia de Abajo, F. JavierNature Materials (2019), 18 (11), 1158-1171CODEN: NMAACR; ISSN:1476-1122. (Nature Research)A review. Progress in electron-beam spectroscopies has recently enabled the study of optical excitations with combined space, energy and time resoln. in the nanometer, millielectronvolt and femtosecond domain, thus providing unique access into nanophotonic structures and their detailed optical responses. These techniques rely on ∼1-300 keV electron beams focused at the sample down to sub-nanometer spots, temporally compressed in wavepackets a few femtoseconds long, and in some cases controlled by ultrafast light pulses. The electrons undergo energy losses and gains (also giving rise to cathodoluminescence light emission), which are recorded to reveal the optical landscape along the beam path. This Review portraits these advances, with a focus on coherent excitations, emphasizing the increasing level of control over the electron wavefunctions and ensuing applications in the study and technol. use of optically resonant modes and polaritons in nanoparticles, 2D materials and engineered nanostructures.
- 50Coenen, T.; Haegel, N. M. Cathodoluminescence for the 21st Century: Learning More from Light. Appl. Phys. Rev. 2017, 4 (3), 031103, DOI: 10.1063/1.498576750https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVKnsbbN&md5=760af61652674ef3086a76e4e3c2f44cCathodoluminescence for the 21st century: Learning more from lightCoenen, T.; Haegel, N. M.Applied Physics Reviews (2017), 4 (3), 031103/1-031103/14CODEN: APRPG5; ISSN:1931-9401. (American Institute of Physics)Cathodoluminescence (CL) is the emission of light from a material in response to excitation by incident electrons. The technique has had significant impact in the characterization of semiconductors, minerals, ceramics, and many nanostructured materials. Since 2010, there have been a no. of innovative developments that have revolutionized and expanded the information that can be gained from CL and broadened the areas of application. While the primary historical application of CL was for spatial mapping of luminescence variations (e.g., imaging dark line defects in semiconductor lasers or providing high resoln. imaging of compositional variations in geol. materials), new ways to collect and analyze the emitted light have expanded the science impact of CL, particularly at the intersection of materials science and nanotechnol. These developments include (1) angular and polarized CL, (2) advances in time resolved CL, (3) far-field and near-field transport imaging that enable drift and diffusion information to be obtained through real space imaging, (4) increasing use of statistical analyses for the study of grain boundaries and interfaces, (5) 3D CL including tomog. and combined work utilizing dual beam systems with CL, and (6) combined STEM/CL measurements that are reaching new levels of resoln. and advancing single photon spectroscopy. This focused review will first summarize the fundamentals and then briefly describe the state-of-the-art in conventional CL imaging and spectroscopy. We then review these recent novel exptl. approaches that enable added insight and information, providing a range of examples from nanophotonics, photovoltaics, plasmonics, and studies of individual defects and grain boundaries. (c) 2017 American Institute of Physics.
- 51García De Abajo, F. J. Optical Excitations in Electron Microscopy. Rev. Mod. Phys. 2010, 82 (1), 209– 275, DOI: 10.1103/RevModPhys.82.20951https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXktlSht7w%253D&md5=0291ceb122e8ca75d967f00986722fd6Optical excitations in electron microscopyGarcia de Abajo, F. J.Reviews of Modern Physics (2010), 82 (1), 209-275CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)This review discusses how low-energy valence excitations created by swift electrons can render information on the optical response of structured materials with unmatched spatial resoln. Electron microscopes are capable of focusing electron beams on subnanometer spots and probing the target response either by analyzing electron energy losses or by detecting emitted radiation. Theor. frameworks suited to calc. the probability of energy loss and light emission (cathodoluminescence) are reconsidered and compared with exptl. results. More precisely, a quantum-mech. description of the interaction between the electrons and the sample is discussed, followed by a powerful classical dielec. approach that can be applied in practice to more complex systems. The conditions are assessed under which classical and quantum-mech. formulations are equiv. The excitation of collective modes such as plasmons is studied in bulk materials, planar surfaces, and nanoparticles. Light emission induced by the electrons is shown to constitute an excellent probe of plasmons, combining subnanometer resoln. in the position of the electron beam with nanometer resoln. in the emitted wavelength. Both electron energy-loss and cathodoluminescence spectroscopies performed in a scanning mode of operation yield snapshots of plasmon modes in nanostructures with fine spatial detail as compared to other existing imaging techniques, thus providing an ideal tool for nanophotonics studies.
- 52Coenen, T.; Brenny, B. J. M.; Vesseur, E. J.; Polman, A. Cathodoluminescence Microscopy: Optical Imaging and Spectroscopy with Deep-Subwavelength Resolution. MRS Bull. 2015, 40 (04), 359– 365, DOI: 10.1557/mrs.2015.6452https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlvVGnu7Y%253D&md5=5cdcd4bf17423cb5a0b5ec5fc73b056cCathodoluminescence microscopy: Optical imaging and spectroscopy with deep-subwavelength resolutionCoenen, Toon; Brenny, Benjamin J. M.; Vesseur, Ernst Jan; Polman, AlbertMRS Bulletin (2015), 40 (4), 359-365CODEN: MRSBEA; ISSN:0883-7694. (Cambridge University Press)This article describes a new microscope, based on angle-resolved cathodoluminescence (CL) imaging spectroscopy, which enables optical imaging and spectroscopy at deep-subwavelength spatial resoln. We used a free electron beam in a scanning electron microscope as a direct excitation source for polarizable materials, and we collected the emitted coherent visible/IR CL radiation using a specially designed optical collection system that is integrated in the electron microscope. We have demonstrated the use of this new technique for the excitation of plasmons in single metal nanoparticles, surface plasmon polaritons at metal surfaces, resonant Mie modes in dielec. nanostructures, and cavity modes and Bloch modes in photonic crystals. Using angle-resolved detection, we are able to derive the nature of localized modes and the dispersion of propagation modes in dielec. and plasmonic geometries. An outlook about new directions and applications of CL imaging spectroscopy is also provided.
- 53Nelayah, J.; Kociak, M.; Stéphan, O.; García De Abajo, F. J.; Tencé, M.; Henrard, L.; Taverna, D.; Pastoriza-Santos, I.; Liz-Marzán, L. M.; Colliex, C. Mapping Surface Plasmons on a Single Metallic Nanoparticle. Nat. Phys. 2007, 3 (5), 348– 353, DOI: 10.1038/nphys57553https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXkslyitr4%253D&md5=d37fa4b79f158365b9f4b27d98ff773dMapping surface plasmons on a single metallic nanoparticleNelayah, Jaysen; Kociak, Mathieu; Stephan, Odile; Garcia de Abajo, F. Javier; Tence, Marcel; Henrard, Luc; Taverna, Dario; Pastoriza-Santos, Isabel; Liz-Marzan, Luis M.; Colliex, ChristianNature Physics (2007), 3 (5), 348-353CODEN: NPAHAX; ISSN:1745-2473. (Nature Publishing Group)Understanding how light interacts with matter at the nanometer scale is a fundamental issue in optoelectronics and nanophotonics. In particular, many applications (such as bio-sensing, cancer therapy and all-optical signal processing) rely on surface-bound optical excitations in metallic nanoparticles. However, so far no exptl. technique has been capable of imaging localized optical excitations with sufficient resoln. to reveal their dramatic spatial variation over one single nanoparticle. Here, we present a novel method applied on silver nanotriangles, achieving such resoln. by recording maps of plasmons in the near-IR/visible/UV domain using electron beams instead of photons. This method relies on the detection of plasmons as resonance peaks in the energy-loss spectra of subnanometre electron beams rastered on nanoparticles of well-defined geometrical parameters. This represents a significant improvement in the spatial resoln. with which plasmonic modes can be imaged, and provides a powerful tool in the development of nanometer-level optics.
- 54Atre, A. C.; Brenny, B. J. M.; Coenen, T.; García-Etxarri, A.; Polman, A.; Dionne, J. A. Nanoscale Optical Tomography with Cathodoluminescence Spectroscopy. Nat. Nanotechnol. 2015, 10 (5), 429– 436, DOI: 10.1038/nnano.2015.3954https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXmtF2rsbc%253D&md5=f03be9034649cbda183ea0ba67dc5292Nanoscale optical tomography with cathodoluminescence spectroscopyAtre, Ashwin C.; Brenny, Benjamin J. M.; Coenen, Toon; Garcia-Etxarri, Aitzol; Polman, Albert; Dionne, Jennifer A.Nature Nanotechnology (2015), 10 (5), 429-436CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Tomog. has enabled the characterization of the Earth's interior, visualization of the inner workings of the human brain, and three-dimensional reconstruction of matter at the at. scale. However, tomog. techniques that rely on optical excitation or detection are generally limited in their resoln. by diffraction. Here, we introduce a tomog. technique-cathodoluminescence spectroscopic tomog.-to probe optical properties in three dimensions with nanometer-scale spatial and spectral resoln. We first obtain two-dimensional cathodoluminescence maps of a three-dimensional nanostructure at various orientations. We then use the method of filtered back-projection to reconstruct the cathodoluminescence intensity at each wavelength. The resulting tomograms allow us to locate regions of efficient cathodoluminescence in three dimensions across visible and near-IR wavelengths, with contributions from material luminescence and radiative decay of electromagnetic eigenmodes. The exptl. signal can be further correlated with the radiative local d. of optical states in particular regions of the reconstruction. We demonstrate how cathodoluminescence tomog. can be used to achieve nanoscale three-dimensional visualization of light-matter interactions by reconstructing a three-dimensional metal-dielec. nanoresonator.
- 55Zielinski, M. S.; Vardar, E.; Vythilingam, G.; Engelhardt, E.-M.; Hubbell, J. A.; Frey, P.; Larsson, H. M. Quantitative Intrinsic Auto-Cathodoluminescence Can Resolve Spectral Signatures of Tissue-Isolated Collagen Extracellular Matrix. Commun. Biol. 2019, 2 (1), 69, DOI: 10.1038/s42003-019-0313-x55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3cfmtlGjsQ%253D%253D&md5=cb88783b1d3e6d11bebb32587c8b4151Quantitative intrinsic auto-cathodoluminescence can resolve spectral signatures of tissue-isolated collagen extracellular matrixZielinski Marcin S; Vardar Elif; Vythilingam Ganesh; Engelhardt Eva-Maria; Frey Peter; Larsson Hans M; Vardar Elif; Vythilingam Ganesh; Hubbell Jeffrey ACommunications biology (2019), 2 (), 69 ISSN:.By analyzing isolated collagen gel samples, we demonstrated in situ detection of spectrally deconvoluted auto-cathodoluminescence signatures of specific molecular content with precise spatial localization over a maximum field of view of 300 μm. Correlation of the secondary electron and the hyperspectral images proved ~40 nm resolution in the optical channel, obtained due to a short carrier diffusion length, suppressed by fibril dimensions and poor electrical conductivity specific to their organic composition. By correlating spectrally analyzed auto-cathodoluminescence with mass spectroscopy data, we differentiated spectral signatures of two extracellular matrices, namely human fibrin complex and rat tail collagen isolate, and uncovered differences in protein distributions of isolated extracellular matrix networks of heterogeneous populations. Furthermore, we demonstrated that cathodoluminescence can monitor the progress of a human cell-mediated remodeling process, where human collagenous matrix was deposited within a rat collagenous matrix. The revealed change of the heterogeneous biological composition was confirmed by mass spectroscopy.
- 56Chen, T.; Pourmand, M.; Feizpour, A.; Cushman, B.; Reinhard, B. M. Tailoring Plasmon Coupling in Self-Assembled One-Dimensional Au Nanoparticle Chains through Simultaneous Control of Size and Gap Separation. J. Phys. Chem. Lett. 2013, 4 (13), 2147– 2152, DOI: 10.1021/jz401066g56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXptlCgtr8%253D&md5=b5918d7d2ba32cb6f27709825211d4abTailoring Plasmon Coupling in Self-Assembled One-Dimensional Au Nanoparticle Chains through Simultaneous Control of Size and Gap SeparationChen, Tianhong; Pourmand, Mahshid; Feizpour, Amin; Cushman, Bradford; Reinhard, Bjorn M.Journal of Physical Chemistry Letters (2013), 4 (13), 2147-2152CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The authors studied the near- and far-field response of 1-dimensional chains of Au nanoparticles (NPs) fabricated with high structural control through template guided self-assembly. The d. of poly(ethylene glycol) ligands grafted onto the NP surface, in combination with the buffer conditions, facilitate a systematic variation of the av. gap width (g) at short sepns. of g < 1.1 nm. The overall size (n) of the individual clusters was controlled through the template. The ability to independently vary n and g allowed for a rational tuning of the spectral response in individual NP clusters over a broad spectral range. The authors used this structural control for a systematic study of the electromagnetic coupling underlying the superradiant cluster mode. Independent of the chain length, plasmon coupling is dominated by direct neighbor interactions. A decrease in coupling strength at sepns. .ltorsim.0.5 nm indicates nonlocal or quantum-mech. coupling mechanisms.
- 57Lin, S.; Li, M.; Dujardin, E.; Girard, C.; Mann, S. One-Dimensional Plasmon Coupling by Facile Self-Assembly of Gold Nanoparticles into Branched Chain Networks. Adv. Mater. 2005, 17 (21), 2553– 2559, DOI: 10.1002/adma.20050082857https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXht1Cgt7vO&md5=b004311bcbea859f6ae29d005bc2f6c3One-dimensional plasmon coupling by facile self-assembly of gold nanoparticles into branched chain networksLin, Shan; Li, Mei; Dujardin, Erik; Girard, Christian; Mann, StephenAdvanced Materials (Weinheim, Germany) (2005), 17 (21), 2553-2559CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)Short chains and complex networks of interconnected Au nanoparticle chains are produced by a simple template-free approach. Optical spectroscopy and computer simulations show that surface plasmons from individual non-contacting nanoparticles are strongly coupled in the resulting 1D superstructures. These chains may provide a unique way to fabricate complex subwavelength optical waveguides.
- 58Salomon, A.; Genet, C.; Ebbesen, T. W. Molecule-Light Complex: Dynamics of Hybrid Molecule-Surface Plasmon States. Angew. Chem., Int. Ed. 2009, 48 (46), 8748– 8751, DOI: 10.1002/anie.20090319158https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtlGju7%252FF&md5=f2563438012fdfedb50dfe038f273b4fMolecule-Light Complex: Dynamics of Hybrid Molecule-Surface Plasmon StatesSalomon, Adi; Genet, Cyriaque; Ebbesen, Thomas W.Angewandte Chemie, International Edition (2009), 48 (46), 8748-8751CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Hole arrays in Ag films are used to gain insight into the properties of hybrid states of tetra-Ph porphyrin tetrasulfonic acid J aggregates with visible spectra and transient optical absorption,. Hybrid mol.-surface plasmon states can be seen and populated with lifetimes comparable to the pure mol. excitonic states.
- 59Salomon, A.; Gordon, R. J.; Prior, Y.; Seideman, T.; Sukharev, M. Strong Coupling between Molecular Excited States and Surface Plasmon Modes of a Slit Array in a Thin Metal Film. Phys. Rev. Lett. 2012, 109 (7), 073002, DOI: 10.1103/PhysRevLett.109.07300259https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtlehsLs%253D&md5=b4441b7c4b8e5424c9961c136735fc9fStrong coupling between molecular excited states and surface plasmon modes of a slit array in a thin metal filmSalomon, Adi; Gordon, Robert J.; Prior, Yehiam; Seideman, Tamar; Sukharev, MaximPhysical Review Letters (2012), 109 (7), 073002/1-073002/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We demonstrate strong coupling between mol. excited states and surface plasmon modes of a slit array in a thin metal film. The coupling manifests itself as an anticrossing behavior of the two newly formed polaritons. As the coupling strength grows, a new mode emerges, which is attributed to long-range mol. interactions mediated by the plasmonic field. The new, mol.-like mode repels the polariton states, and leads to an opening of energy gaps both below and above the asymptotic free mol. energy.
- 60Vasa, P.; Pomraenke, R.; Cirmi, G.; De Re, E.; Wang, W.; Schwieger, S.; Leipold, D.; Runge, E.; Cerullo, G.; Lienau, C. Ultrafast Manipulation of Strong Coupling in Metal-Molecular Aggregate Hybrid Nanostructures. ACS Nano 2010, 4 (12), 7559– 7565, DOI: 10.1021/nn101973p60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhsVensrrE&md5=4fa137b39892726c14136bceff06c731Ultrafast Manipulation of Strong Coupling in Metal-Molecular Aggregate Hybrid NanostructuresVasa, P.; Pomraenke, R.; Cirmi, G.; De Re, E.; Wang, W.; Schwieger, S.; Leipold, D.; Runge, E.; Cerullo, G.; Lienau, C.ACS Nano (2010), 4 (12), 7559-7565CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)An ultrafast manipulation is demonstrated of the Rabi splitting energy ΩR in a metal-mol. aggregate hybrid nanostructure. The fs excitation drastically alters the optical properties of a model system formed by coating a Au nanoslit array with a thin J-aggregated dye layer. Controlled and reversible transient switching from strong (ΩR ≃ 55 meV) to weak (ΩR ≈ 0) coupling on a sub-ps time scale is directly evidenced by mapping the nonequil. dispersion relations of the coupled excitations. Such a strong, externally controllable coupling of excitons and surface plasmon polaritons is of considerable interest for ultrafast all-optical switching applications in nanoscale plasmonic circuits.
- 61Ebbesen, T. W. Hybrid Light-Matter States in a Molecular and Material Science Perspective. Acc. Chem. Res. 2016, 49 (11), 2403– 2412, DOI: 10.1021/acs.accounts.6b0029561https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslWhurfM&md5=112474dfc62bce8cf5ea2ba21fab9665Hybrid Light-Matter States in a Molecular and Material Science PerspectiveEbbesen, Thomas W.Accounts of Chemical Research (2016), 49 (11), 2403-2412CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review. The notion that light and matter states can be hybridized the way s and p orbitals are mixed is a concept that is not familiar to most chemists and material scientists. Yet it has much potential for mol. and material sciences that is just beginning to be explored. For instance, it has already been demonstrated that the rate and yield of chem. reactions can be modified and that the cond. of org. semiconductors and nonradiative energy transfer can be enhanced through the hybridization of electronic transitions. The hybridization is not limited to electronic transitions; it can be applied for instance to vibrational transitions to selectively perturb a given bond, opening new possibilities to change the chem. reactivity landscape and to use it as a tool in (bio)mol. science and spectroscopy. Such results are not only the consequence of the new eigenstates and energies generated by the hybridization. The hybrid light-matter states also have unusual properties: they can be delocalized over a very large no. of mols. (up to ca. 105), and they become dispersive or momentum-sensitive. Importantly, the hybridization occurs even in the absence of light because it is the zero-point energies of the mol. and optical transitions that generate the new light-matter states. The present work is not a review but rather an Account from the author's point of view that first introduces the reader to the underlying concepts and details of the features of hybrid light-matter states. It is shown that light-matter hybridization is quite easy to achieve: all that is needed is to place mols. or a material in a resonant optical cavity (e.g., between two parallel mirrors) under the right conditions. For vibrational strong coupling, microfluidic IR cells can be used to study the consequences for chem. in the liq. phase. Examples of modified properties are given to demonstrate the full potential for the mol. and material sciences. Finally an outlook of future directions for this emerging subject is given.
- 62Pustovit, V. N.; Shahbazyan, T. V. Resonance Energy Transfer near Metal Nanostructures Mediated by Surface Plasmons. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83 (8), 085427, DOI: 10.1103/PhysRevB.83.08542762https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXis1Oqurg%253D&md5=5832815b9a41030f74a8321d36b8cacbResonance energy transfer near metal nanostructures mediated by surface plasmonsPustovit, Vitaliy N.; Shahbazyan, Tigran V.Physical Review B: Condensed Matter and Materials Physics (2011), 83 (8), 085427/1-085427/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The authors develop a unified theory of plasmon-assisted resonance energy transfer (RET) between mols. near a metal nanostructure that maintains energy balance between transfer, dissipation, and radiation. In a wide range of parameters, including in the near field, RET is dominated by plasmon-enhanced radiative transfer (PERT) rather than by a nonradiative transfer mechanism. Numerical calcns. performed for mols. near the Ag nanoparticle indicate that RET magnitude is highly sensitive to mols.' positions.
- 63Mao, P.; Liu, C.; Favraud, G.; Chen, Q.; Han, M.; Fratalocchi, A.; Zhang, S. Broadband Single Molecule SERS Detection Designed by Warped Optical Spaces. Nat. Commun. 2018, 9 (1), 5428, DOI: 10.1038/s41467-018-07869-563https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXktFWjug%253D%253D&md5=691edc68ecbd7338f33facb4153c43f8Broadband single molecule SERS detection designed by warped optical spacesMao, Peng; Liu, Changxu; Favraud, Gael; Chen, Qiang; Han, Min; Fratalocchi, Andrea; Zhang, ShuangNature Communications (2018), 9 (1), 5428CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)Engineering hotspots is of crucial importance in many applications including energy harvesting, nano-lasers, subwavelength imaging, and biomedical sensing. Surface-enhanced Raman scattering spectroscopy is a key technique to identify analytes that would otherwise be difficult to diagnose. In std. systems, hotspots are realized with nanostructures made by acute tips or narrow gaps. Owing to the low probability for mols. to reach such tiny active regions, high sensitivity is always accompanied by a large prepn. time for analyte accumulation which hinders the time response. Inspired by transformation optics, we introduce an approach based on warped spaces to manipulate hotspots, resulting in broadband enhancements in both the magnitude and vol. Expts. for single mol. detection with a fast soaking time are realized in conjunction with broadband response and uniformity. Such engineering could provide a new design platform for a rich manifold of devices, which can benefit from broadband and huge field enhancements.
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.0c03317.
Monochromatic components of the polychromatic CL image in Figure 1a (Figure S1); monochromatic components of the polychromatic CL images in Figure 2d,e shown at a higher magnification and presenting both low- and high-connectivity structural elements of the 3D silver network (Figure S2); CL response of a highly connected nodal network ligament (Figure S3); demonstration of hotspot fluctuations at an additional 3D silver network scan (Figure 1b) by point CL spectra extracted from proximal probe positions (∼50 nm apart) (Figure S4); panchromatic CL map of the network in Figure 4b over the range of 250–790 nm (Figure S5); resolution of CL imaging (PDF)
Monochromatic CL images (250–790 nm) of the network in Figure 1b (MP4)
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