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Nanoscale Three-Dimensional Charge Density and Electric Field Mapping by Electron Holographic TomographyClick to copy article linkArticle link copied!
- Fengshan Zheng*Fengshan Zheng*Email: [email protected]Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, GermanySpin-X Institute, Electron Microscopy Center, School of Physics and Optoelectronics, State Key Laboratory of Luminescent Materials and Devices, Guangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials, South China University of Technology, Guangzhou 511442, ChinaMore by Fengshan Zheng
- Vadim MigunovVadim MigunovErnst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, GermanyCentral Facility for Electron Microscopy (GFE), RWTH Aachen University, Ahornstrasse 55, 52074 Aachen, GermanyMore by Vadim Migunov
- Jan CaronJan CaronErnst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, GermanyMore by Jan Caron
- Hongchu DuHongchu DuErnst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, GermanyCentral Facility for Electron Microscopy (GFE), RWTH Aachen University, Ahornstrasse 55, 52074 Aachen, GermanyMore by Hongchu Du
- Giulio PozziGiulio PozziErnst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, GermanyDepartment FIM, University of Modena and Reggio Emilia, via G. Campi 213/a, 41125 Modena, ItalyMore by Giulio Pozzi
- Rafal E. Dunin-BorkowskiRafal E. Dunin-BorkowskiErnst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, GermanyMore by Rafal E. Dunin-Borkowski
Nano Letters
Cite this: Nano Lett. 2023, 23, 3, 843–849
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Abstract
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The operation of nanoscale electronic devices is related intimately to the three-dimensional (3D) charge density distributions within them. Here, we demonstrate the quantitative 3D mapping of the charge density and long-range electric field associated with an electrically biased carbon fiber nanotip with a spatial resolution of approximately 5 nm using electron holographic tomography in the transmission electron microscope combined with model-based iterative reconstruction. The approach presented here can be applied to a wide range of other nanoscale materials and devices.
This publication is licensed under
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You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:
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License Summary*
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Attribution (BY): Credit must be given to the creator.
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Copyright © 2023 The Authors. Published by American Chemical Society
Nanoscale electronic devices such as transistors and light-emitting diodes are widely used in high technology applications. In order to improve the working performance of such devices, it is important to understand the relationship between their local electrical properties and the presence of defects, dopants, interfaces, and surfaces. (1) For example, the emission performance of electron sources in electron microscopes (in particular, field emitters) is determined by geometrical factors, including local shape, curvature, and crystallographic orientation. (2−4) In atom probe tomography, (5) the shape, chemistry, and defect distribution of a needle-shaped sample determine the electric field around it, influencing the trajectories of field-evaporated ions and affecting the fidelity of reconstructed atom positions. (6) Similarly, tip-enhanced catalytic efficiency is influenced by the shape and species of the tip. (7,8)
Off-axis electron holography (9) in the transmission electron microscope (TEM) is a powerful technique that can be used to map projected and three-dimensional (3D) electrostatic potentials, (10−18) electric fields, (19−23) and charge density distributions (24−28) with nanometer to atomic spatial resolution. 3D electrostatic potentials have been measured from tilt series of electron holographic phase images to study dopant potentials in semiconductors, (11,12,14,15) and the morphologies of nanoscale materials (29−31) and 3D electric fields around specimens have been inferred from phase images based on the assumption of rotational symmetry (23,32) or have made use of simple analytical models. (22) Measurements of 3D charge density distributions in materials have also been proposed. (33,34) However, until now only empirical models for charge density distributions within samples have been fitted by comparing simulated projected potentials with experimental phase images, for example, by making use of a line-charge model and the assumption of cylindrical symmetry for reconstruction of the 3D electric field around a metallic atom probe needle. (22)
In general, the use of back-projection-based tomographic reconstruction to study 3D electrostatic potentials and electric fields is complicated by the fact that they are continuous functions that may vary significantly in magnitude within and outside both the specimen and the field of view (FOV). Reconstructions are then affected more significantly by artifacts than when using electron tomography to recover variations in morphology and composition in materials, especially if full 360° rotation cannot be achieved when recording an experimental tomographic tilt series of off-axis electron holograms. If electrostatic fringing fields are present outside the specimen, then direct tomographic reconstructions of potentials and fields are also affected by the so-called perturbed reference wave (PRW) effect in off-axis electron holography. (23,35)
In this paper, we show that these problems can be circumvented by not determining the 3D potential or field directly, but by combining electron holographic tomography with model-based iterative reconstruction (MBIR) (28,36) to first determine the 3D charge density in the specimen, i.e., the source of the potential and field. This approach allows a priori information, such as the shape of the object, the PRW effect, and the influence of charges that are located outside the FOV to be taken into account. (28) It is also more robust to noise and artifacts that originate from the use of a limited tilt range and can provide a quantitative number for the spatial resolution of the reconstructed charge density. (34,36) The reconstructed 3D charge distribution in the specimen can then be used to infer the 3D electrostatic potential and electric field both inside and around the specimen without the artifacts that would be present by reconstructing them from recorded phase images directly.
We illustrate the method through the experimental measurement of the 3D charge density in an electrically biased C fiber needle that has a long-range electric field outside it with a spatial resolution of approximately 5 nm. As a needle-shaped sample geometry is similar to that present in some nanoelectronic devices, such as semiconducting nanowires, nanoscale p–n junctions, and field emitters, (11,13,15,20,37) we believe that our results will also be useful in these research fields, in particular to understand the relationship between local electrical properties and the presence of defects, dopants, interfaces, and surfaces.
A C fiber needle was prepared using a standard focused ion beam (FIB) milling procedure in an FEI Helios Nanolab 460F1 workstation, as described elsewhere in detail. (38) An electrical bias was applied between the needle and a micrometer-sized Au counter electrode in the TEM using a Nanofactory scanning tunneling microscopy TEM specimen holder. Figure 1a shows a low-magnification bright-field TEM image of the experimental setup. The length of the C fiber needle is approximately 2.5 μm. The distance between the needle and the Au counter electrode is approximately 4.5 μm. The diameter of the apex of the needle is approximately 60 nm. A higher magnification bright-field TEM image is shown in Figure 1b.
Figure 1
Figure 1. (a) Low-magnification bright-field TEM image showing the experimental setup for electrical biasing of a C fiber needle in the TEM. (b) Higher magnification image of the end of the needle. (c) Electron holographic phase difference image with +40 V applied between the needle and the counter electrode at a 0° sample tilt angle. The mean inner potential contribution to the phase has been removed by subtracting an aligned phase image recorded without a bias applied to the needle. Equiphase contour lines (black) are superimposed. The phase contour spacing is 2π radians. A TEM image of the C fiber needle is overlaid to guide the eye.
As off-axis electron holography is sensitive to contributions to the electrostatic potential from both the mean inner potential (MIP) of the specimen and the applied electrical bias, two tomographic tilt series of electron holographic phase images were recorded over a tilt range of −52° to +48° with a tilt increment of 4°. The first tilt series was recorded without an electrical bias applied to the needle. On the assumption that the needle does not undergo electron-beam-induced charging, these phase images are sensitive only to the projected MIP of the specimen. They can be used to subtract the MIP contribution to the phase from subsequent images recorded at each tilt angle as well as to reconstruct the 3D shape of the needle. The second tilt series was recorded with +40 V applied between the needle and the counter electrode. The MIP contribution to the phase was removed by aligning and subtracting corresponding phase images at each tilt angle with and without the electrical bias applied to the needle. Figure S2 contains further details about this procedure.
The spatial resolution of the reconstruction presented below is limited to approximately 5 nm here primarily by the spatial resolution of the TEM and the aperture size used for hologram reconstruction. It can be improved in future studies by choosing an operating mode of the TEM that has higher spatial resolution, by using a larger aperture size for hologram reconstruction and by using approaches such as double-resolution or phase-shifting holography. (39,40)
Figure 1c shows a resulting phase difference image for a 0° sample tilt angle with equiphase contour lines superimposed. The asymmetry in the contours between the two sides of the needle is a consequence of the PRW effect, i.e., the influence on the holographic reference wave of the long-range electric field associated with the voltage applied to the needle. Figure S3 shows similar phase contour images for selected other sample tilt angles. The first data set alone was used to reconstruct the 3D shape of the needle using the ASTRA toolbox (41) (see Figure S4 for further details).
3D reconstruction of the charge density in the electrically biased needle was performed by applying the MBIR approach (28,36) to the aligned tomographic data set of phase difference images (after removal of the MIP contribution to the phase at each tilt angle). The 3D shape of the needle (reconstructed from the first data set) was used to define the volume in which charges can be placed during reconstruction, on the assumption that no charges are present in the vacuum region around the needle. A buffer region of voxels was also defined immediately outside the 3D reconstruction volume. This buffer region was also allowed to contain “artificial” charges, which are used to represent contributions from the PRW and from charges that are located outside the FOV. These charges can be removed after reconstruction when analyzing the charges in the needle alone. By varying the positions and magnitudes of the charges in the reconstruction volume and using them to obtain predicted phase images, the algorithm attempts to minimize the residual with the experimental phase difference images at each sample tilt angle. At the same time, it uses a Euclidean norm for regularization. This choice favors a solution that minimizes the norm of the charge density. In a conductor, charges are expected to be located on the specimen surface. Here, the total of the norm of the charge density is a measure of the total electrostatic potential energy. (42) Therefore, the algorithm converges to a solution that corresponds to a minimum in electrostatic energy. To an extent, this approach guarantees the physical uniqueness of the solution. A compromise between the two criteria is implemented by using a standard L-curve analysis. An optimized parameter for the regularization is chosen in order to balance the residual error between the experimental and reconstructed phase measurements and the minimum of the Euclidean norm of the reconstructed charges. Further details are available in Figure S5 and elsewhere. (28,36)
Figure 2a shows a visualization of the resulting reconstructed 3D charge density in the C fiber needle. As expected, the charge density is greatest at the apex of the needle, which has the highest curvature and is closest to the Au counter electrode. The maximum charge density is 2.94 × 1018 cm–3. The charge is distributed asymmetrically around the needle, which is not perfectly circular in cross section. Such an effect can also originate from the reconstruction algorithm if the mask that defines the sample surface is not chosen correctly or if the boundary buffer voxel approach that is used to represent charges outside the FOV and the PRW effect does not work effectively. We therefore verified the result by evaluating the influence on the reconstructed charge density of changing the size of the 3D mask manually as well as changing the thickness of the buffer region from 8 to 16, 32, and 64 voxels.
Figure 2
Figure 2. Visualization of 3D charge density in a C fiber needle reconstructed using electron holographic tomography and the MBIR approach. The needle is biased at +40 V with a distance of 4.5 μm from a Au counter electrode. (a) Side view of the 3D charge density. (b, c) 2D slices of charge density in the (b) xy and (c) yz planes, extracted from the 3D reconstructed charge density shown in (a). (d–f) Three representative slices of charge density in the xz plane extracted from the 3D reconstructed charge density shown in (a). The positions of the planes are marked by white arrows and numbers in (b). The white dashed lines mark the outline of the needle. See text for details.
Selected slices extracted from the reconstructed 3D charge density distribution are shown in Figures 2b–f. The xy plane (Figure 2b) reveals an asymmetry in the charge density (white arrow “1”), which is absent in the yz plane (Figure 2c) and may be associated with local differences in the shape of the needle. The fact that the majority of the charge is located close to the surface of the needle is visible in the yz plane (Figure 2c). On the one hand, this observation is consistent with the prediction (based on classical electrostatics) that charges reside on the outer surface of a conductor. (42) On the other hand, it is surprising that the charge penetrates several tens of nanometers into the surface, perhaps because the needle has a disordered or poorly conducting surface layer. As the spatial resolution of our method is currently about 5 nm, it does not provide unambiguous information about field penetration, band bending, or screening depth. (43) This information should be accessible in the future when the spatial resolution of the technique is improved.
A region with a local increase in charge density is marked by red dashed ellipses in Figures 2b,c. It may be associated with a local difference in damage to the needle during sample preparation (e.g., Ga+ bombardment). Figures 2d–f show three representative xz planes (labeled in Figure 2b), in which the charge can be seen to be located primarily at the surface of the needle. Plane “1” is thought to lie at the interface between a more insulating apex region and the more conductive shank of the needle. Plane “2” intersects a local maximum in charge density (marked by a white dashed ellipse in Figure 2b). Plane “3” corresponds to a plane that is at a greater distance from the apex. In planes “2” and “3”, the charge is localized at the outer surface of the needle.
Corresponding charge density profiles determined from the 3D reconstruction are shown in Figure 3. Figure 3a shows a line profile of the charge density in the xy plane along the axis of the needle (marked by a red arrow in Figure 2b). In addition to a maximum at the apex, there is a local maximum with a charge density of approximately 0.5 × 1018 cm–3. The charge density along the axis of the rest of needle is close to zero. For the three chosen xz planes, line profiles of the measured charge density are plotted in the z and x directions in Figures 3b and 3c, respectively. In the z direction (Figure 3b), the green and blue profiles from planes “2” and “3” are almost symmetrical with respect to the needle axis. The red profile from plane “1” is higher than those from planes “2” and “3” on the axis of the needle. In the x direction (Figure 3c), the red profile from plane “1” is again higher on the axis of the needle than the other two profiles. It should be noted that negative values in the reconstructed charge distribution fall within the errors that are present due to noise from the experimental data and the reconstruction.
Figure 3
Figure 3. Line profiles of charge density extracted from the 3D charge density shown in Figure 2a along the axis of the needle (y) in the central xy plane (marked by a red arrow in Figure 2b) and (b, c) along z and x in three different xz planes (1: red; 2: green; 3: blue) marked in Figure 2b. (d) Cumulative charge profile along the length of the needle.
The cumulative charge integrated along the length of the needle, which is shown in Figure 3d, follows an almost linear trend, suggesting that the line charge density along the needle is almost constant, as expected from analytical solutions. (21,35) The slope of the cumulative charge profile is slightly greater close to the apex of the needle than in the shank, indicating a greater line charge density in this region, perhaps because of its more insulating character or because of a local deviation from an ellipsoidal geometry. (44)
The 3D electrostatic potential and electric field can be calculated from the 3D reconstructed charge density by removing the artificial charges in the buffer voxel region and assuming that image charges in the counter electrode can be defined to have a norm vector with respect to the apex of the needle of (0,–4.5, 0) μm, as determined from the experimental setup (Figure 1b). It should be noted that charges outside the FOV also contribute to the electrostatic potential and electric field inside the FOV. However, as the electric field decays in a quadratic manner with distance and the charge density in the needle is negligible far from the apex (see Figure 3d), it is reasonable to assume that charges outside the FOV have a negligible contribution in this setup. This consideration is not in conflict with simulations performed by the atom probe community (e.g., (45,46)), as we are focusing here only on the local electric field within the FOV, whereas additional boundary conditions in an atom probe apparatus (further from the tip of the needle) affect ion trajectories to the detector.
Figure 4a show a 3D visualization of the magnitude of the electric field, while Figures 4b,c show slices of the magnitude of the electric field in the central xy and yz planes. The electric field is almost symmetrical about the needle axis. Residual slight asymmetry results from the asymmetry in the reconstructed charge density (as seen in the xy plane in Figure 4b). Figures 4b,c show that the electric field is strongest close to the apex and that it decays rapidly into the vacuum region with increasing distance from it. The maximum electric field strength measured in this study is approximately 0.25 GV/m. On the basis of a single projection model (6) used by the atom probe community, the geometric field factor here is predicted to be approximately 5.33, which falls within theoretical values that typically range between 2 and 14. (46) It should be noted that this factor is highly dependent on the radius and shape of the tip and on the distance to the counter electrode. Inside the needle (Figures 4b,c), the magnitude of the electric field is strongest in the region close to the surface, where it is thought to be less conducting.
Figure 4
Figure 4. 3D electric field determined from the reconstructed 3D charge density shown in Figure 2 for the electrically biased C fiber needle. (a) Magnitude of the electric field plotted on a logarithmic scale. (b, c) Magnitude of the electric field in the central xy and yz planes, respectively. The black dashed line shows the outline of the needle.
A combination of a streamline plot of the electric field and the electrostatic potential in the central xy plane is shown in Figure 5. The fact that the field lines are normal to the surface of the needle close to its apex suggests that charges outside the FOV do not influence the reconstruction in this region and that the electric field around the apex can be calculated reliably using the MBIR approach. In contrast, the field lines on the right of the image (close to the shank of the needle) are inclined with respect to the surface of the needle as a result of the influence of missing contributions to the electric field from charges outside the FOV.
Figure 5
Figure 5. Combination of a streamline plot of the electric field and a plot of the electrostatic potential in the central xy plane of the reconstructed volume of the C fiber needle. The interior of the needle is marked in blue. The scale bar is 50 nm.
In summary, the 3D charge density, electrostatic potential, and electric field of an electrically biased C fiber needle have been determined experimentally using electron holographic tomography combined with model-based iterative reconstruction of the charge density. Tomographic tilt series of holographic phase images with the needle biased at +40 V with respect to a Au counter electrode were used as input for the algorithm after subtracting the MIP contribution to the phase from each image in the tilt series. The reconstructed charge density is greatest at the apex of the needle and localized primarily close to its surface. The cumulative charge displays a close-to-linear behavior, which is consistent with a line charge density that is almost constant along the needle. Asymmetry in the reconstructed charge density results from changes in the local geometry of the needle or damage from FIB sample preparation. The 3D electric field and electrostatic potential can be calculated from the reconstructed 3D charge density based on an assumption for the positions of image charges in the Au counter electrode. The inferred electric field and electrostatic potential are both almost symmetrical about the needle axis. The strength of the electric field is greatest close to the apex of the needle and has a maximum value of 0.25 GV/m at an applied bias voltage of +40 V with a distance of 4.5 μm to the Au counter electrode. The results suggest that this approach can be used for 3D characterization of charge, electrostatic potential, and electric field from limited data sets recorded from a wide range of nanostructures and may provide guidance for designs and improvements of nanoscale electronic devices.
Methods
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C Fiber
A high-strength C fiber (T1000) was obtained from Toray Company (www.toray.jp). The fiber comprised primarily C (≥99%), with a small amount of N, in the form of a highly textured structure along the fiber axis, with turbostratic graphene as the basic structural unit. (47) This choice of material reduces the influence of changing diffraction conditions during tomographic tilt series acquisition.
Off-Axis Electron Holography
An FEI Titan G2 60-300 TEM equipped with an ultrabright-field emission electron gun (X-FEG) and two electrostatic biprisms was used for off-axis electron holography experiments. The operating voltage was set to 300 kV. In order to obtain a large field of view, experiments were performed in Lorentz mode with the conventional microscope objective lens switched off. A scanning tunneling microscopy TEM specimen holder (Nanofactory Instruments) was used for electrical biasing experiments. Off-axis electron holograms were recorded using an exposure time of 6 s on a 4k × 4k direct electron counting Gatan K2 IS camera. A representative hologram is shown in Figure S1. The holographic interference fringe spacing was approximately 1.7 nm, and the interference width was approximately 1.8 μm. Thirty holograms were recorded at each tilt angle to increase the signal-to-noise ratio. Reference holograms were recorded from a region of vacuum with the specimen removed from the field of view. Real-space phase and amplitude images were reconstructed from recorded electron holograms with a standard fast Fourier transform algorithm using Holoworks software (Holowerk LLC).
Supporting Information
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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.2c03879.
Representative off-axis electron hologram, reconstructed phase images, phase contour maps, reconstructed 3D shape of the needle and parameters used for model-based iterative reconstruction (PDF)
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Author Information
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- Fengshan Zheng - Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany; Spin-X Institute, Electron Microscopy Center, School of Physics and Optoelectronics, State Key Laboratory of Luminescent Materials and Devices, Guangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials, South China University of Technology, Guangzhou 511442, China;
https://orcid.org/0000-0001-7354-041X;
- Vadim Migunov - Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany; Central Facility for Electron Microscopy (GFE), RWTH Aachen University, Ahornstrasse 55, 52074 Aachen, Germany;https://orcid.org/0000-0002-6296-4492
- Hongchu Du - Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany; Central Facility for Electron Microscopy (GFE), RWTH Aachen University, Ahornstrasse 55, 52074 Aachen, Germany;https://orcid.org/0000-0002-4661-4644
- Rafal E. Dunin-Borkowski - Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany;https://orcid.org/0000-0001-8082-0647
Acknowledgments
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The authors thank Prof. Michael Farle and AG Farle at the University of Duisburg-Essen for technical help, Shasha Wang and Prof. Haifeng Du for focused ion beam preparation of the specimen, and Werner Pieper and Rolf Speen for technical assistance. The authors acknowledge the European Union for funding through the Marie Curie Initial Training Network SIMDALEE2 (Marie Curie Initial Training Network (ITN) Grant No. 606988 under FP7-PEOPLE-2013-ITN). V.M. and H.D. thank the Deutsche Forschungsgemeinschaft for funding within the framework of the SFB 917 project Nanoswitches. R.D.-B. thanks the Deutsche Forschungsgemeinschaft for a Deutsch-Israelische Projektkooperation (DIP) Grant and the European Union’s Horizon 2020 Research and Innovation Programme Q-SORT (Grant No. 766970 under H2020-FETOPEN-2016-2017). This project has received funding from the European Unions Horizon 2020 Research and Innovation Programme (Grant No. 823717, project “ESTEEM3”).
References
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- 2Zheng, X.; Chen, G.; Li, Z.; Deng, S.; Xu, N. Quantum-mechanical investigation of field-emission mechanism of a micrometer-long single-walled carbon nanotube. Phys. Rev. Lett. 2004, 92, 106803, DOI: 10.1103/PhysRevLett.92.106803Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXitFWgu70%253D&md5=8684ed9f0aa4fd778e3ec25cf53d4b02Quantum-mechanical investigation of field-emission mechanism of a micrometer-long single-walled carbon nanotubeZheng, Xiao; Chen, GuanHua; Li, Zhibing; Deng, Shaozhi; Xu, NingshengPhysical Review Letters (2004), 92 (10), 106803/1-106803/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)A quantum-mech. simulation is carried out to investigate the charge distribution and electrostatic potential along a 1 μm long (5,5) single-walled carbon nanotube under realistic field-emission exptl. conditions. A single layer of carbon atoms is found sufficient to shield most of the elec. field except at the tip where strong field penetration occurs. The penetration leads to a nonlinear decrease of potential barrier for emission, which is equally responsible for the low threshold voltage besides the well-known geometrical field enhancement factor.
- 3Zhang, H.; Tang, J.; Yuan, J.; Yamauchi, Y.; Suzuki, T. T.; Shinya, N.; Nakajima, K.; Qin, L.-C. An ultrabright and monochromatic electron point source made of a LaB6 nanowire. Nat. Nanotechnol. 2016, 11, 273, DOI: 10.1038/nnano.2015.276Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFemsb3L&md5=9119110fcf7b516095f76bc41855210bAn ultrabright and monochromatic electron point source made of a LaB6 nanowireZhang, Han; Tang, Jie; Yuan, Jinshi; Yamauchi, Yasushi; Suzuki, Taku T.; Shinya, Norio; Nakajima, Kiyomi; Qin, Lu-ChangNature Nanotechnology (2016), 11 (3), 273-279CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Electron sources as 1-dimensional nanotubes and nanowires are an essential tool for studies in a variety of fields, such as x-ray computed tomog., flexible displays, chem. sensors and electron optics applications. However, field emission instability and the need to work under high-vacuum or high-temp. conditions have imposed stringent requirements that are currently limiting the range of application of electron sources. Here the authors report the fabrication of a LaB6 nanowire with only a few La atoms bonded on the tip that emits collimated electrons from a single point with high monochromaticity. The nanostructured tip has a low work function of 2.07 eV (lower than that of Cs) while remaining chem. inert, two properties usually regarded as mutually exclusive. Installed in a scanning electron microscope (SEM) field emission gun, the authors' tip shows a c.d. gain that is ∼1,000 times greater than that achievable with W(310) tips, and no emission decay for tens of hours of operation. Using this new SEM, the authors acquired very low-noise, high-resoln. images together with rapid chem. compositional mapping using a tip operated at room temp. and at 10-times higher residual gas pressure than that required for W tips.
- 4Zhou, Y.; Liang, Y.; Fu, J.; Liu, K.; Chen, Q.; Wang, X.; Li, H.; Zhu, L.; Hu, J.; Pan, H.; Miyauchi, M.; Jiang, L.; Cortés, E.; Liu, M. Vertical Cu nanoneedle arrays enhance the local electric field promoting C2 Hydrocarbons in the CO2 electroreduction. Nano Lett. 2022, 22, 1963– 1970, DOI: 10.1021/acs.nanolett.1c04653Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XjsFSkur4%253D&md5=2c4a2879e044b69c4bfb1ec1247670d6Vertical Cu Nanoneedle Arrays Enhance the Local Electric Field Promoting C2 Hydrocarbons in the CO2 ElectroreductionZhou, Yajiao; Liang, Yanqing; Fu, Junwei; Liu, Kang; Chen, Qin; Wang, Xiqing; Li, Hongmei; Zhu, Li; Hu, Junhua; Pan, Hao; Miyauchi, Masahiro; Jiang, Liangxing; Cortes, Emiliano; Liu, MinNano Letters (2022), 22 (5), 1963-1970CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Electrocatalytic redn. of CO2 to multicarbon products is a potential strategy to solve the energy crisis while achieving C neutrality. To improve the efficiency of multicarbon products in Cu-based catalysts, optimizing the *CO adsorption and reducing the energy barrier for C-C (C-C) coupling are essential features. A strong local elec. field was obtained by regulating the arrangement of Cu nanoneedle arrays (CuNNAs). CO2 redn. performance tests indicate that an ordered nanoneedle array reaches a 59% Faraday efficiency for multicarbon products (FEC2) at -1.2 V (vs. RHE), compared to a FEC2 of 20% for a disordered nanoneedle array (CuNNs). As such, the very high and local elec. fields achieved by an ordered Cu nanoneedle array leads to the accumulation of K+ ions, which benefit both *CO adsorption and C-C coupling. The authors' results contribute to the design of highly efficient catalysts for multicarbon products.
- 5Gault, B.; Chiaramonti, A.; Cojocaru-Mirédin, O.; Stender, P.; Dubosq, R.; Freysoldt, C.; Makineni, S. K.; Li, T.; Moody, M.; Cairney, J. M. Atom probe tomography. Nature Reviews Methods Primers 2021, 1, 51, DOI: 10.1038/s43586-021-00047-wGoogle Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XjsVGnsL0%253D&md5=ac7361639febed57f478c11b293c3819Atom probe tomographyGault, Baptiste; Chiaramonti, Ann; Cojocaru-Miredin, Oana; Stender, Patrick; Dubosq, Renelle; Freysoldt, Christoph; Makineni, Surendra Kumar; Li, Tong; Moody, Michael; Cairney, Julie M.Nature Reviews Methods Primers (2021), 1 (1), 51CODEN: NRMPAT; ISSN:2662-8449. (Nature Portfolio)A review. Atom probe tomog. (APT) provides three-dimensional compositional mapping with sub-nanometer resoln. The sensitivity of APT is in the range of ppm for all elements, including light elements such as hydrogen, carbon or lithium, enabling unique insights into the compn. of performance-enhancing or lifetime-limiting microstructural features and making APT ideally suited to complement electron-based or X-ray-based microscopies and spectroscopies. Here, we provide an introductory overview of APT ranging from its inception as an evolution of field ion microscopy to the most recent developments in specimen prepn., including for nanomaterials. We touch on data reconstruction, anal. and various applications, including in the geosciences and the burgeoning biol. sciences. We review the underpinnings of APT performance and discuss both strengths and limitations of APT, including how the community can improve on current shortcomings. Finally, we look forwards to true at.-scale tomog. with the ability to measure the isotopic identity and spatial coordinates of every atom in an ever wider range of materials through new specimen prepn. routes, novel laser pulsing and detector technologies, and full interoperability with complementary microscopy techniques.
- 6Vurpillot, F.; Oberdorfer, C. Modeling atom probe tomography: A review. Ultramicroscopy 2015, 159, 202– 216, DOI: 10.1016/j.ultramic.2014.12.013Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVWisw%253D%253D&md5=c4ef728fed985c769409192c1108ba71Modeling Atom Probe Tomography: A reviewVurpillot, F.; Oberdorfer, C.Ultramicroscopy (2015), 159 (Part_2), 202-216CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)A review. Improving both the precision and the accuracy of Atom Probe Tomog. reconstruction requires a correct understanding of the imaging process. In this aim, numerical modeling approaches were developed for 15 years. The injected ingredients of these modeling tools are related to the basic physic of the field evapn. mechanism. The interplay between the sample nature and structure of the analyzed sample and the reconstructed image artifacts have pushed to gradually improve and make the model more and more sophisticated. This paper reviews the evolution of the modeling approach in Atom Probe Tomog. and presents some future potential directions to improve the method.
- 7Su, Y.; Liu, C.; Brittman, S.; Tang, J.; Fu, A.; Kornienko, N.; Kong, Q.; Yang, P. Single-nanowire photoelectrochemistry. Nat. Nanotechnol. 2016, 11, 609, DOI: 10.1038/nnano.2016.30Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XkvFGisrw%253D&md5=6734e926aad989ba71a1f2727759303aSingle-nanowire photoelectrochemistrySu, Yude; Liu, Chong; Brittman, Sarah; Tang, Jinyao; Fu, Anthony; Kornienko, Nikolay; Kong, Qiao; Yang, PeidongNature Nanotechnology (2016), 11 (7), 609-612CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Photoelectrochem. is one of several promising approaches for the realization of efficient solar-to-fuel conversion. Recent work has shown that photoelectrodes made of semiconductor nano-/microwire arrays can have better photoelectrochem. performance than their planar counterparts because of their unique properties, such as high surface area. Although considerable research effort has focused on studying wire arrays, the inhomogeneity in the geometry, doping, defects and catalyst loading present in such arrays can obscure the link between these properties and the photoelectrochem. performance of the wires, and correlating performance with the specific properties of individual wires is difficult because of ensemble averaging. Here, we show that a single-nanowire-based photoelectrode platform can be used to reliably probe the current-voltage (I-V) characteristics of individual nanowires. We find that the photovoltage output of ensemble array samples can be limited by poorly performing individual wires, which highlights the importance of improving nanowire homogeneity within an array. Furthermore, the platform allows the flux of photogenerated electrons to be quantified as a function of the lengths and diams. of individual nanowires, and we find that the flux over the entire nanowire surface (7-30 electrons/nm2 s) is significantly reduced as compared with that of a planar analog (∼1,200 electrons /nm2 s). Such characterization of the photogenerated carrier flux at the semiconductor/electrolyte interface is essential for designing nanowire photoelectrodes that match the activity of their loaded electrocatalysts.
- 8Liu, M. Enhanced electrocatalytic CO2 reduction via field-induced reagent concentration. Nature 2016, 537, 382, DOI: 10.1038/nature19060Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1yqsbzO&md5=11d8dcf8010b105587ba93d7035bc657Enhanced electrocatalytic CO2 reduction via field-induced reagent concentrationLiu, Min; Pang, Yuanjie; Zhang, Bo; De Luna, Phil; Voznyy, Oleksandr; Xu, Jixian; Zheng, Xueli; Dinh, Cao Thang; Fan, Fengjia; Cao, Changhong; Garcia de Arquer, F. Pelayo; Safaei, Tina Saberi; Mepham, Adam; Klinkova, Anna; Kumacheva, Eugenia; Filleter, Tobin; Sinton, David; Kelley, Shana O.; Sargent, Edward H.Nature (London, United Kingdom) (2016), 537 (7620), 382-386CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Electrochem. redn. of CO2 (CO2) to CO (CO) is the 1st step in the synthesis of more complex C-based fuels and feedstocks using renewable electricity. Unfortunately, the reaction suffers from slow kinetics owing to the low local concn. of CO2 surrounding typical CO2 redn. reaction catalysts. Alkali metal cations are known to overcome this limitation through noncovalent interactions with adsorbed reagent species, but the effect is restricted by the soly. of relevant salts. Large applied electrode potentials can also enhance CO2 adsorption, but this comes at the cost of increased H (H2) evolution. Here we report that nanostructured electrodes produce, at low applied overpotentials, local high elec. fields that conc. electrolyte cations, which in turn leads to a high local concn. of CO2 close to the active CO2 redn. reaction surface. Simulations reveal 10-fold higher elec. fields assocd. with metallic nm-sized tips compared to quasi-planar electrode regions, and measurements using Au nanoneedles confirm a field-induced reagent concn. that enables the CO2 redn. reaction to proceed with a geometric c.d. for CO of 22 mA per square centimeter at -0.35 V (overpotential of 0.24 V). This performance surpasses by an order of magnitude the performance of the best Au nanorods, nanoparticles and oxide-derived noble metal catalysts. Similarly designed Pd nanoneedle electrocatalysts produce formate with a faradaic efficiency of >90 per cent and an unprecedented geometric c.d. for formate of 10 mA per square centimeter at -0.2 V, demonstrating the wider applicability of the field-induced reagent concn. concept.
- 9Lichte, H.; Lehmann, M. Electron holography–basics and applications. Rep. Prog. Phys. 2008, 71, 016102, DOI: 10.1088/0034-4885/71/1/016102Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXitVSjt78%253D&md5=17f9da9c25d61f7328fc135530831e79Electron holography-basics and applicationsLichte, Hannes; Lehmann, MichaelReports on Progress in Physics (2008), 71 (1), 016102/1-016102/46CODEN: RPPHAG; ISSN:0034-4885. (Institute of Physics Publishing)A review. Despite the huge progress achieved recently by means of the corrector for aberrations, allowing now a true at. resoln. of 0.1 nm, hence making it an unrivalled tool for nanoscience, transmission electron microscopy (TEM) suffers from a severe drawback: in a conventional electron micrograph only a poor phase contrast can be achieved, i.e. phase structures are virtually invisible. Therefore, conventional TEM is nearly blind for elec. and magnetic fields, which are pure phase objects. Since such fields provoked by the at. structure, e.g. of semiconductors and ferroelecs., largely det. the solid state properties, hence the importance for high technol. applications, substantial object information is missing. Electron holog. in TEM offers the soln.: by superposition with a coherent ref. wave, a hologram is recorded, from which the image wave can be completely reconstructed by amplitude and phase. Now the object is displayed quant. in two sep. images: one representing the amplitude, the other the phase. From the phase image, elec. and magnetic fields can be detd. quant. in the range from micrometre down to at. dimensions by all wave optical methods that one can think of, both in real space and in Fourier space. Electron holog. is pure wave optics. Therefore, we discuss the basics of coherence and interference, the implementation into a TEM, the path of rays for recording holograms as well as the limits in lateral and signal resoln. We outline the methods of reconstructing the wave by numerical image processing and procedures for extg. the object properties of interest. Furthermore, we present a broad spectrum of applications both at mesoscopic and at. dimensions. This paper gives an overview of the state of the art pointing at the needs for further development. It is also meant as encouragement for those who refrain from holog., thinking that it can only be performed by specialists in highly specialized labs. In fact, a modern TEM built for at. resoln. and equipped with a field emitter or a Schottky emitter, well aligned by a skilled operator, can deliver good holograms. Running com. available image processing software and mathematics programs on a laptop-computer is sufficient for reconstruction of the amplitude and phase images and extg. desirable object information.
- 10Twitchett, A.; Dunin-Borkowski, R.; Midgley, P. Quantitative electron holography of biased semiconductor devices. Phys. Rev. Lett. 2002, 88, 238302, DOI: 10.1103/PhysRevLett.88.238302Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XktFGktb4%253D&md5=cc051b3903a6d33e3c09f3637a9fea4bQuantitative Electron Holography of Biased Semiconductor DevicesTwitchett, A. C.; Dunin-Borkowski, R. E.; Midgley, P. A.Physical Review Letters (2002), 88 (23), 238302/1-238302/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Electron holog. is used to measure electrostatic potential profiles across reverse-biased Si p-n junctions in situ in the transmission electron microscope. A novel sample geometry based on focused ion-beam milling is developed, and results are obtained for a range of sample thicknesses and bias voltages to allow the holog. contrast to be interpreted. The phys. and elec. nature of the sample surface, which is affected by sample prepn. and electron beam irradn., is discussed.
- 11Twitchett-Harrison, A. C.; Yates, T. J.; Newcomb, S. B.; Dunin-Borkowski, R. E.; Midgley, P. A. High-resolution three-dimensional mapping of semiconductor dopant potentials. Nano Lett. 2007, 7, 2020– 2023, DOI: 10.1021/nl070858nGoogle Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXmt12isbs%253D&md5=d57c0420e8a188bc2c229e634ea3c891High-resolution 3-dimensional mapping of semiconductor dopant potentialsTwitchett-Harrison, Alison C.; Yates, Timothy J. V.; Newcomb, Simon B.; Dunin-Borkowski, Rafal E.; Midgley, Paul A.Nano Letters (2007), 7 (7), 2020-2023CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Semiconductor device structures are becoming increasingly 3D at the nanometer scale. A key issue that must be addressed to enable future device development is the 3D mapping of dopant distributions, ideally under working conditions. Here we demonstrate how a combination of electron holog. and electron tomog. can be used to det. quant. the 3D electrostatic potential in an elec. biased semiconductor device with nanometer spatial resoln.
- 12Wolf, D.; Lichte, H.; Pozzi, G.; Prete, P.; Lovergine, N. Electron holographic tomography for mapping the three-dimensional distribution of electrostatic potential in III-V semiconductor nanowires. Appl. Phys. Lett. 2011, 98, 264103, DOI: 10.1063/1.3604793Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotV2hurk%253D&md5=fb1569935b9fc404b77e2b27156740d8Electron holographic tomography for mapping the three-dimensional distribution of electrostatic potential in III-V semiconductor nanowiresWolf, D.; Lichte, H.; Pozzi, G.; Prete, P.; Lovergine, N.Applied Physics Letters (2011), 98 (26), 264103/1-264103/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Electron holog. tomog. (EHT), the combination of off-axis electron holog. with electron tomog., is a technique, which can be applied to the quant. 3D mapping of electrostatic potential at the nanoscale. Here, we show the results obtained in the EHT investigation of GaAs and GaAs-AlGaAs core-shell nanowires grown by Au-catalyzed metalorg. vapor phase epitaxy. The unique ability of EHT of disentangling the materials mean inner potential (MIP) from the specimen projected thickness allows reconstruction of the nanowire 3D morphol. and inner compositional structure as well as the measurement of the MIP. (c) 2011 American Institute of Physics.
- 13Li, L.; Smith, D. J.; Dailey, E.; Madras, P.; Drucker, J.; McCartney, M. R. Observation of hole accumulation in Ge/Si core/shell nanowires using off-axis electron holography. Nano Lett. 2011, 11, 493– 497, DOI: 10.1021/nl1033107Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXmslCitg%253D%253D&md5=30537c2b68e304e6066258ff003d78e2Observation of hole accumulation in Ge/Si core/shell nanowires using off-axis electron holographyLi, Luying; Smith, David J.; Dailey, Eric; Madras, Prashanth; Drucker, Jeff; McCartney, Martha R.Nano Letters (2011), 11 (2), 493-497CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Hole accumulation in Ge/Si core/shell nanowires (NWs) was obsd. and quantified using off-axis electron holog. and other electron microscopy techniques. The epitaxial (110)-oriented Ge/Si core/shell NWs were grown on Si (111) substrates by chem. vapor deposition through the vapor-liq.-solid growth mechanism. High-angle annular-dark-field scanning transmission electron microscopy images and off-axis electron holograms were obtained from specific NWs. The excess phase shifts measured by electron holog. across the NWs indicated the presence of holes inside the Ge cores. Calcns. based on a simplified coaxial cylindrical model gave hole densities of (0.4 ± 0.2) /nm3 in the core regions.
- 14Wolf, D.; Lubk, A.; Lenk, A.; Sturm, S.; Lichte, H. Tomographic investigation of fermi level pinning at focused ion beam milled semiconductor surfaces. Appl. Phys. Lett. 2013, 103, 264104, DOI: 10.1063/1.4858957Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXitVWntL3K&md5=0a7759535556fc7e15994446951241e0Tomographic investigation of fermi level pinning at focused ion beam milled semiconductor surfacesWolf, D.; Lubk, A.; Lenk, A.; Sturm, S.; Lichte, H.Applied Physics Letters (2013), 103 (26), 264104/1-264104/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Electron holog. in the transmission electron microscope (TEM) offers the spatial and signal resoln. for studying effects like Fermi level pinning or dopant concn. variations important for the design of modern electronic devices. To overcome the loss of information along the projection direction, surface effects, and surface damage due to TEM specimen prepn., we apply electron holog. tomog. to analyze the 3D potential distribution of semiconductor samples prepd. by focused-ion-beam. We observe mid-band gap pinning of the Fermi level at Si surfaces but valence band pinning at Ge surfaces. The pinning extends over tens of nanometers into the bulk. (c) 2013 American Institute of Physics.
- 15Wolf, D.; Lubk, A.; Prete, P.; Lovergine, N.; Lichte, H. 3D mapping of nanoscale electric potentials in semiconductor structures using electron-holographic tomography. J. Phys. D: Appl. Phys. 2016, 49, 364004, DOI: 10.1088/0022-3727/49/36/364004Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFOqs7zJ&md5=40af8f3387e5a15b33acf7145e1d4e393D mapping of nanoscale electric potentials in semiconductor structures using electron-holographic tomographyWolf, Daniel; Lubk, Axel; Prete, Paola; Lovergine, Nico; Lichte, HannesJournal of Physics D: Applied Physics (2016), 49 (36), 364004/1-364004/9CODEN: JPAPBE; ISSN:0022-3727. (IOP Publishing Ltd.)Off-axis electron holog. (EH) is a powerful method for mapping projected elec. potentials, such as built-in potentials in semiconductor devices, in two dimensions (2D) at nanometer resoln. However, not well-defined thickness profiles, surface effects, and compn. changes of the sample under investigation complicate the interpretation of the projected potentials. Here, we demonstrate how these problems can be overcome by combining EH with tomog. techniques, i.e., electron holog. tomog. (EHT), reconstructing elec. potentials in 3D. We present EHT reconstructions of an n-type MOSFET including its dopant-related built-in potentials inside the device, as well as of a GaAs/AlGaAs core-multishell nanowire contg. a 5 nm thick quantum well tube.
- 16Gan, Z.; Perea, D.; Yoo, J.; He, Y.; Colby, R.; Barker, J.; Gu, M.; Mao, S.; Wang, C.; Picraux, S.; Smith, D.; McCartney, M. Characterization of electrical properties in axial Si-Ge nanowire heterojunctions using off-axis electron holography and atom-probe tomography. J. Appl. Phys. 2016, 120, 104301, DOI: 10.1063/1.4962380Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFWnurfL&md5=062fa88688fc755e18dd2f99c55ef8fbCharacterization of electrical properties in axial Si-Ge nanowire heterojunctions using off-axis electron holography and atom-probe tomographyGan, Zhaofeng; Perea, Daniel E.; Yoo, Jinkyoung; He, Yang; Colby, Robert J.; Barker, Josh E.; Gu, Meng; Mao, Scott X.; Wang, Chongmin; Picraux, S. T.; Smith, David J.; McCartney, Martha R.Journal of Applied Physics (Melville, NY, United States) (2016), 120 (10), 104301/1-104301/8CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)Nanowires (NWs) consisting of P-doped Si/B-doped Ge axial heterojunctions were grown via vapor-liq.-solid synthesis using a combination of Au and AuGa catalyst particles. Off-axis electron holog. (EH) was used to measure the electrostatic potential profile across the junction resulting from elec. active dopants, and atom-probe tomog. (APT) was used to map total dopant concn. profiles. A comparison of the electrostatic potential profile measured from EH with simulations that were based on the APT results indicates that Ga atoms unintentionally introduced during AuGa catalyst growth were mostly electronically inactive. This finding was also corroborated by in situ electron-holog. biasing expts. Electronic band structure simulations guided by the exptl. results helped to provide a much better explanation of the NW elec. behavior. Overall, this work demonstrates that the combination of EH, APT, in situ biasing, and simulations allows a more complete understanding of NW elec. properties to be developed. (c) 2016 American Institute of Physics.
- 17Chalasani, R.; Pekin, A.; Rabkin, A.; Abutbul, R. E.; Diéguez, O.; Kauffmann, Y.; Golan, Y.; Kohn, A. Mapping charge distribution in single PbS core-CdS arm nano-multipod heterostructures by off-axis electron holography. Nano Lett. 2017, 17, 2778– 2787, DOI: 10.1021/acs.nanolett.6b04957Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlslCjtr8%253D&md5=1277f0eba081351a9b16dec68cd1a964Mapping Charge Distribution in Single PbS Core - CdS Arm Nano-Multipod Heterostructures by Off-Axis Electron HolographyChalasani, Rajesh; Pekin, Alexander; Rabkin, Alexander; Abutbul, Ran E.; Dieguez, Oswaldo; Kauffmann, Yaron; Golan, Yuval; Kohn, AmitNano Letters (2017), 17 (5), 2778-2787CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The authors synthesized PbS core-CdS arm nanomultipod heterostructures (NMHs) that exhibit PbS{111}/CdS{0002} epitaxial relations. The PbS-CdS interface is chem. sharp as detd. by aberration cor. TEM and compared to d. functional theory (DFT) calcns. Ensemble fluorescence measurements show quenching of the optical signal from the CdS arms indicating charge sepn. due to the heterojunction with PbS. A finite-element three-dimensional (3D) calcn. of the Poisson equation shows a type-I heterojunction, which would prevent recombination in the CdS arm after optical excitation. To examine charge redistribution, the authors used off-axis electron holog. (OAEH) in the TEM to map the electrostatic potential across an individual heterojunction. Indeed, a built-in potential of 500 mV is estd. across the junction, though as opposed to the thermal equil. calcns. significant accumulation of pos. charge at the CdS side of the interface is detected. The NMH multipod geometry prevents efficient removal of generated charge carriers by the high energy electrons of the TEM. Simulations of generated electron-hole pairs in the insulated CdS arm of the NMH indeed show charge accumulation in agreement with the exptl. measurements. Thus, OAEH can be used as a complementary methodol. to ensemble measurements by mapping the charge distribution in single NMHs with complex geometries.
- 18Li, L.; Cheng, Y.; Liu, Z.; Yan, S.; Li, L.; Wang, J.; Zhang, L.; Gao, Y. Study of structure-property relationship of semiconductor nanomaterials by off-axis electron holography. Journal of Semiconductors 2022, 43, 041103, DOI: 10.1088/1674-4926/43/4/041103Google ScholarThere is no corresponding record for this reference.
- 19Cumings, J.; Zettl, A.; McCartney, M.; Spence, J. Electron holography of field-emitting carbon nanotubes. Phys. Rev. Lett. 2002, 88, 056804, DOI: 10.1103/PhysRevLett.88.056804Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XnsF2nsQ%253D%253D&md5=d446e4c240cc05504f9c407316acc09eElectron holography of field-emitting carbon nanotubesCumings, John; Zettl, A.; McCartney, M. R.; Spence, J. C. H.Physical Review Letters (2002), 88 (5), 056804/1-056804/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Electron holog. performed in situ inside a high resoln. transmission electron microscope was used to det. the magnitude and spatial distribution of the elec. field surrounding individual field-emitting C nanotubes. The elec. field (and hence the assocd. field emission current) is concd. precisely at the tips of the nanotubes and not at other nanotube defects such as sidewall imperfections. The elec. field magnitude and distribution are stable in time, even in cases where the nanotube field emission current exhibits extensive temporal fluctuations.
- 20Lubk, A.; Wolf, D.; Simon, P.; Wang, C.; Sturm, S.; Felser, C. Nanoscale three-dimensional reconstruction of electric and magnetic stray fields around nanowires. Appl. Phys. Lett. 2014, 105, 173110, DOI: 10.1063/1.4900826Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvVertrjF&md5=d7f41ebe44b5dcbbb635757db94482f1Nanoscale three-dimensional reconstruction of electric and magnetic stray fields around nanowiresLubk, A.; Wolf, D.; Simon, P.; Wang, C.; Sturm, S.; Felser, C.Applied Physics Letters (2014), 105 (17), 173110/1-173110/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Static electromagnetic stray fields around nanowires (NWs) are characteristic for a no. of important phys. effects such as field emission or magnetic force microscopy. Consequently, an accurate characterization of these fields is of high interest and electron holog. tomog. (EHT) is unique in providing tomog. 3D reconstructions at nm spatial resoln. However, several limitations of the exptl. setup and the specimen itself are influencing EHT. Here, we show how a deliberate restriction of the tomog. reconstruction to the exterior of the NWs can be used to mitigate these limitations facilitating a quant. 3D tomog. reconstruction of static electromagnetic stray fields at the nanoscale. As an example, we reconstruct the electrostatic stray field around a GaAs-AlGaAs core shell NW and the magnetic stray field around a Co2FeGa Heusler compd. NW. (c) 2014 American Institute of Physics.
- 21Beleggia, M.; Kasama, T.; Larson, D.; Kelly, T.; Dunin-Borkowski, R.; Pozzi, G. Towards quantitative off-axis electron holographic mapping of the electric field around the tip of a sharp biased metallic needle. J. Appl. Phys. 2014, 116, 024305, DOI: 10.1063/1.4887448Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFeqs7bM&md5=9a790b971d1a9d94d573dd4656d3b928Towards quantitative off-axis electron holographic mapping of the electric field around the tip of a sharp biased metallic needleBeleggia, M.; Kasama, T.; Larson, D. J.; Kelly, T. F.; Dunin-Borkowski, R. E.; Pozzi, G.Journal of Applied Physics (Melville, NY, United States) (2014), 116 (2), 024305/1-024305/9CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)We apply off-axis electron holog. and Lorentz microscopy in the transmission electron microscope to map the elec. field generated by a sharp biased metallic tip. A combination of exptl. data and modeling provides quant. information about the potential and the field around the tip. Close to the tip apex, we measure a max. field intensity of 82 MV/m, corresponding to a field k factor of 2.5, in excellent agreement with theory. In order to verify the validity of the measurements, we use the inferred charge d. distribution in the tip region to generate simulated phase maps and Fresnel (out-of-focus) images for comparison with exptl. measurements. While the overall agreement is excellent, the simulations also highlight the presence of an unexpected astigmatic contribution to the intensity in a highly defocused Fresnel image, which is thought to result from the geometry of the applied field. (c) 2014 American Institute of Physics.
- 22Migunov, V.; London, A.; Farle, M.; Dunin-Borkowski, R. Model-independent measurement of the charge density distribution along an Fe atom probe needle using off-axis electron holography without mean inner potential effects. J. Appl. Phys. 2015, 117, 134301, DOI: 10.1063/1.4916609Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlslCnurs%253D&md5=2da3dc2a8aee9b40892c7346624b519eModel-independent measurement of the charge density distribution along an Fe atom probe needle using off-axis electron holography without mean inner potential effectsMigunov, V.; London, A.; Farle, M.; Dunin-Borkowski, R. E.Journal of Applied Physics (Melville, NY, United States) (2015), 117 (13), 134301/1-134301/8CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)The one-dimensional charge d. distribution along an elec. biased Fe atom probe needle is measured using a model-independent approach based on off-axis electron holog. in the transmission electron microscope. Both the mean inner potential and the magnetic contribution to the phase shift are subtracted by taking differences between electron-optical phase images recorded with different voltages applied to the needle. The measured one-dimensional charge d. distribution along the needle is compared with a similar result obtained using model-based fitting of the phase shift surrounding the needle. On the assumption of cylindrical symmetry, it is then used to infer the three-dimensional elec. field and electrostatic potential around the needle with ∼10 nm spatial resoln., without needing to consider either the influence of the perturbed ref. wave or the extension of the projected potential outside the field of view of the electron hologram. The present study illustrates how a model-independent approach can be used to measure local variations in charge d. in a material using electron holog. in the presence of addnl. contributions to the phase, such as those arising from changes in mean inner potential and specimen thickness. (c) 2015 American Institute of Physics.
- 23Phatak, C.; De Knoop, L.; Houdellier, F.; Gatel, C.; Hÿtch, M.; Masseboeuf, A. Quantitative 3D electromagnetic field determination of 1D nanostructures from single projection. Ultramicroscopy 2016, 164, 24– 30, DOI: 10.1016/j.ultramic.2016.03.005Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlsFSkt78%253D&md5=9edcf6f872fc66b35bf6a10c93e21858Quantitative 3D electromagnetic field determination of 1D nanostructures from single projectionPhatak, C.; de Knoop, L.; Houdellier, F.; Gatel, C.; Hytch, M. J.; Masseboeuf, A.Ultramicroscopy (2016), 164 (), 24-30CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)One-dimensional (1D) nanostructures have been regarded as the most promising building blocks for nanoelectronics and nanocomposite material systems as well as for alternative energy applications. Although they result in confinement of a material, their properties and interactions with other nanostructures are still very much three-dimensional (3D) in nature. In this work, we present a novel method for quant. detn. of the 3D electromagnetic fields in and around 1D nanostructures using a single electron wave phase image, thereby eliminating the cumbersome acquisition of tomog. data. Using symmetry arguments, we have reconstructed the 3D magnetic field of a nickel nanowire as well as the 3D elec. field around a carbon nanotube field emitter, from one single projection. The accuracy of quant. values detd. here is shown to be a better fit to the physics at play than the value obtained by conventional anal. Moreover the 3D reconstructions can then directly be visualized and used in the design of functional 3D architectures built using 1D nanostructures.
- 24Beleggia, M.; Kasama, T.; Dunin-Borkowski, R. E.; Hofmann, S.; Pozzi, G. Direct measurement of the charge distribution along a biased carbon nanotube bundle using electron holography. Appl. Phys. Lett. 2011, 98, 243101, DOI: 10.1063/1.3598468Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXntlKgs7Y%253D&md5=380a7161981a1c021926ad1b0fe502a0Direct measurement of the charge distribution along a biased carbon nanotube bundle using electron holographyBeleggia, M.; Kasama, T.; Dunin-Borkowski, R. E.; Hofmann, S.; Pozzi, G.Applied Physics Letters (2011), 98 (24), 243101/1-243101/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Nanowires and nanotubes can be examd. in the transmission electron microscope under an applied bias. Here we introduce a model-independent method, which allows the charge distribution along a nanowire or nanotube to be measured directly from the Laplacian of an electron holog. phase image. We present results from a biased bundle of C nanotubes, in which we show that the charge d. increases linearly with distance from its base, reaching a value of ∼0.8 electrons/nm near its tip. (c) 2011 American Institute of Physics.
- 25Gatel, C.; Lubk, A.; Pozzi, G.; Snoeck, E.; Hÿtch, M. Counting elementary charges on nanoparticles by electron holography. Phys. Rev. Lett. 2013, 111, 025501, DOI: 10.1103/PhysRevLett.111.025501Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXht1SntbnM&md5=84682a3988db0b54a7bc96f650234b4cCounting elementary charges on nanoparticles by electron holographyGatel, C.; Lubk, A.; Pozzi, G.; Snoeck, E.; Hytch, M.Physical Review Letters (2013), 111 (2), 025501/1-025501/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)The distribution and movement of charge is fundamental to many phys. phenomena, particularly for applications involving nanoparticles, nanostructures, and electronic devices. However, there are very few ways of quantifying charge at the necessary length scale. Here, we show that aberration-cor. electron holog. is capable of counting the charge on individual nanoparticles to a precision of one elementary unit of charge. We present a method that measures charges within predefined contours by directly applying Gauss's law at the nanoscale. We perform a statistical anal. to reveal the relationship between the size of the contours and the precision of the charge measurement and present strategies to optimize the spatial and signal resoln. for the presented method.
- 26Gan, Z.; Gu, M.; Tang, J.; Wang, C.-Y.; He, Y.; Wang, K. L.; Wang, C.; Smith, D. J.; McCartney, M. R. Direct mapping of charge distribution during lithiation of Ge nanowires using off-axis electron holography. Nano Lett. 2016, 16, 3748– 3753, DOI: 10.1021/acs.nanolett.6b01099Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XotFKrtrg%253D&md5=35bee915db7cc0b6c87a234afc9b6846Direct Mapping of Charge Distribution during Lithiation of Ge Nanowires Using Off-Axis Electron HolographyGan, Zhaofeng; Gu, Meng; Tang, Jianshi; Wang, Chiu-Yen; He, Yang; Wang, Kang L.; Wang, Chongmin; Smith, David J.; McCartney, Martha R.Nano Letters (2016), 16 (6), 3748-3753CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The successful operation of rechargeable batteries relies on reliable insertion/extn. of ions into/from the electrodes. The battery performance and the response of the electrodes to such ion insertion and extn. are directly related to the spatial distribution of the charge and its dynamic evolution. However, it remains unclear how charge is distributed in the electrodes during normal battery operation. In this work, we have used off-axis electron holog. to measure charge distribution during lithium ion insertion into a Ge nanowire (NW) under dynamic operating conditions. We discovered that the surface region of the Ge core is neg. charged during the core-shell lithiation of the Ge NW, which is counterbalanced by pos. charge on the inner surface of the lithiated LixGe shell. The remainder of the lithiated LixGe shell is free from net charge, consistent with its metallic characteristics. The present work provides a vivid picture of charge distribution and dynamic evolution during Ge NW lithiation and should form the basis for tackling the response of these and related materials under real electrochem. conditions.
- 27Vicarelli, L.; Migunov, V.; Malladi, S.; Zandbergen, H. W.; Dunin-Borkowski, R. E. Single electron precision in the measurement of charge distributions on electrically biased graphene nanotips using electron holography. Nano Lett. 2019, 19, 4091– 4096, DOI: 10.1021/acs.nanolett.9b01487Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXpvFKmur4%253D&md5=9c04f80261311fdbc33508aace185551Single Electron Precision in the Measurement of Charge Distributions on Electrically Biased Graphene Nanotips Using Electron HolographyVicarelli, Leonardo; Migunov, Vadim; Malladi, Sairam K.; Zandbergen, Henny W.; Dunin-Borkowski, Rafal E.Nano Letters (2019), 19 (6), 4091-4096CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)We use off-axis electron holog. to measure the electrostatic charge d. distributions on graphene-based nanogap devices that have thicknesses of between 1 and 10 monolayers and sepns. of between 8 and 58 nm with a precision of better than a single unit charge. Our exptl. measurements, which are compared with finite element simulations, show that wider graphene tips, which have thicknesses of a single monolayer at their ends, exhibit charge accumulation along their edges. The results are relevant for both fundamental research on graphene electrostatics and applications of graphene nanogaps to single nucleotide detection in DNA sequencing, single mol. electronics, plasmonic antennae, and cold field emission sources.
- 28Zheng, F.; Caron, J.; Migunov, V.; Beleggia, M.; Pozzi, G.; Dunin-Borkowski, R. E. Measurement of charge density in nanoscale materials using off-axis electron holography. J. Electron Spectrosc. Relat. Phenom. 2020, 241, 146881, DOI: 10.1016/j.elspec.2019.07.002Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVyls7jO&md5=feb1c34a84ccd9f69f4a070382b09d38Measurement of charge density in nanoscale materials using off-axis electron holographyZheng, Fengshan; Caron, Jan; Migunov, Vadim; Beleggia, Marco; Pozzi, Giulio; Dunin-Borkowski, Rafal E.Journal of Electron Spectroscopy and Related Phenomena (2020), 241 (), 146881CODEN: JESRAW; ISSN:0368-2048. (Elsevier B.V.)Three approaches for the measurement of charge d. distributions in nanoscale materials from electron optical phase images recorded using off-axis electron holog. are illustrated through the study of an elec. biased needle-shaped sample. We highlight the advantages of using a model-based iterative algorithm, which allows a priori information, such as the shape of the object and the influence of charges that are located outside the field of view, to be taken into account. The recovered charge d. can be used to infer the elec. field and electrostatic potential.
- 29Lai, G.; Hirayama, T.; Ishizuka, K.; Tanji, T.; Tonomura, A. Three-dimensional reconstruction of electric-potential distribution in electron-holographic interferometry. Appl. Opt. 1994, 33, 829– 833, DOI: 10.1364/AO.33.000829Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3cfktlSlsw%253D%253D&md5=5fc2faa27a7d7ed945fd33d55d2467dcThree-dimensional reconstruction of electric-potential distribution in electron-holographic interferometryLai G; Hirayama T; Ishizuka K; Tanji T; Tonomura AApplied optics (1994), 33 (5), 829-33 ISSN:1559-128X.A method of reconstructing the three-dimensional electric-potential distribution of a microscopic object with electron-holographic interferometry is presented. A sequence of processing techniques is developed to obtain the projected phase proportional to the potential distribution. A modified backprojection algorithm is used to reconstruct a three-dimensional potential distribution from the projected potentials obtained at different projection directions. In an experiment this method is applied to reconstruct three-dimensional latex particles.
- 30Simon, P.; Wolf, D.; Wang, C.; Levin, A. A.; Lubk, A.; Sturm, S.; Lichte, H.; Fecher, G. H.; Felser, C. Synthesis and three-dimensional magnetic field mapping of Co2FeGa Heusler nanowires at 5 nm resolution. Nano Lett. 2016, 16, 114– 120, DOI: 10.1021/acs.nanolett.5b03102Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVejtb7M&md5=dcd6d273feefc31e9cd382df08308731Synthesis and Three-Dimensional Magnetic Field Mapping of Co2FeGa Heusler Nanowires at 5 nm ResolutionSimon, Paul; Wolf, Daniel; Wang, Changhai; Levin, Aleksandr A.; Lubk, Axel; Sturm, Sebastian; Lichte, Hannes; Fecher, Gerhard H.; Felser, ClaudiaNano Letters (2016), 16 (1), 114-120CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)We present the synthesis of Co2FeGa Heusler nanowires and the results of our investigations on their three-dimensional (3D) elec. and magnetic internal and external fields mapped by electron holog. tomog. (EHT). These fields will be of great importance in next-generation nanomagnets integrated in spintronics and memory devices. The Co2FeGa nanowires with a L21 ordered structure are prepd. by a SBA-15 silica-assisted method. The magnetic dipole-like stray fields of several Co2FeGa nanowires are revealed by holog. reconstructed phase images. Based on the measured magnetic phase shifts of an individual nanowire and its 3D reconstruction using EHT, we obtain an internal magnetic induction with a magnitude of 1.15 T and a nonmagnetic surface layer of 10 nm thickness. Furthermore, we also reconstruct the 3D distribution of the electrostatic potential of the same nanowire.
- 31Wolf, D.; Rodriguez, L. A.; Beche, A.; Javon, E.; Serrano, L.; Magen, C.; Gatel, C.; Lubk, A.; Lichte, H.; Bals, S.; Van Tendeloo, G.; Fernandez-Pacheco, A.; De Teresa, J. M.; Snoeck, E. 3D magnetic induction maps of nanoscale materials revealed by electron holographic tomography. Chem. Mater. 2015, 27, 6771– 6778, DOI: 10.1021/acs.chemmater.5b02723Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVKls77J&md5=1503b9410307882f3aa437c6693776373D Magnetic Induction Maps of Nanoscale Materials Revealed by Electron Holographic TomographyWolf, Daniel; Rodriguez, Luis A.; Beche, Armand; Javon, Elsa; Serrano, Luis; Magen, Cesar; Gatel, Christophe; Lubk, Axel; Lichte, Hannes; Bals, Sara; Van Tendeloo, Gustaaf; Fernandez-Pacheco, Amalio; De Teresa, Jose M.; Snoeck, EtienneChemistry of Materials (2015), 27 (19), 6771-6778CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The study of three-dimensional (3D) ferromagnetic nanoscale materials constitutes one of the key research areas of the current magnetism roadmap and carries great potential to impact areas such as data storage, sensing, and biomagnetism. The properties of such nanostructures are closely connected with their 3-dimensional magnetic nanostructure, making their detn. highly valuable. Quant. 3-dimensional maps providing both the internal magnetic and elec. configuration of the same specimen with high spatial resoln. are missing. Here, the authors demonstrate the quant. 3-dimensional reconstruction of the dominant axial component of the magnetic induction and electrostatic potential within a Co nanowire (NW) of 100 nm in diam. with spatial resoln. <10 nm by applying electron holog. tomog. The tomogram was obtained using a dedicated TEM sample holder for acquisition, in combination with advanced alignment and tomog. reconstruction routines. The powerful approach presented here is widely applicable to a broad range of 3-dimensional magnetic nanostructures and may trigger the progress of novel spintronic nonplanar nanodevices.
- 32Wu, M.; Tafel, A.; Hommelhoff, P.; Spiecker, E. Determination of 3D electrostatic field at an electron nano-emitter. Appl. Phys. Lett. 2019, 114, 013101, DOI: 10.1063/1.5055227Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXivFyltA%253D%253D&md5=3a88af34fe14d5542fbba7aeee76d433Determination of 3D electrostatic field at an electron nano-emitterWu, Mingjian; Tafel, Alexander; Hommelhoff, Peter; Spiecker, ErdmannApplied Physics Letters (2019), 114 (1), 013101/1-013101/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Differential phase contrast in scanning transmission electron microscopy has been applied to image nanoscale electrostatic fields of a sharp tungsten electron emitter with an apex radius of about 20 nm and under field emission conditions. Assuming axial symmetry of the nano-emitter, we derived a method based on the inverse Abel transform to quant. reconstruct an axial slice of the 3D electrostatic field from a single projection measurement. The highest field strength of 2.92 V/nm is measured at the nano-emitter apex under the condition of a bias voltage of -140 V with respect to the grounded counter electrode located at about 650 nm from the apex, resulting in an emission current of more than 2 μA. The exptl. results are compared with simulations based on a finite element numerical Maxwell equation solver. Quant. agreement between expt. and simulation has been achieved. (c) 2019 American Institute of Physics.
- 33Lade, S. J.; Paganin, D.; Morgan, M. J. Electron tomography of electromagnetic fields, potentials and sources. Opt. Commun. 2005, 253, 392– 400, DOI: 10.1016/j.optcom.2005.04.071Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXpsF2lsrc%253D&md5=8e12e3e89d77d8715489ad7a0f0e7b3cElectron tomography of electromagnetic fields, potentials and sourcesLade, S. J.; Paganin, D.; Morgan, M. J.Optics Communications (2005), 253 (4-6), 392-400CODEN: OPCOB8; ISSN:0030-4018. (Elsevier B.V.)The exit phase of an electron moving through electromagnetic potentials can, as is well known, be written as line integrals of the potentials. The use of vector tomog. to reconstruct electromagnetic potentials from such phase measurements in a transmission electron microscope is proposed. Electromagnetic fields and source distributions can similarly be reconstructed from phase gradients and Laplacians, resp. The method can recover elec. and magnetic fields independently, and requires only that the fields be magnetostatic, that the projection approxn. applies and that there not be excessive inelastic scattering. Propagation-based phase retrieval is considered as the method of measuring electron phase, giving as a useful special case the reconstruction of current densities directly from defocused electron micrographs.
- 34Mohan, K. A.; Prabhat, K.; Phatak, C.; De Graef, M.; Bouman, C. A. Iterative reconstruction of the magnetization and charge density using vector field electron tomography. Microsc. Microanal. 2016, 22, 1686– 1687, DOI: 10.1017/S1431927616009272Google ScholarThere is no corresponding record for this reference.
- 35Matteucci, G.; Missiroli, G.; Muccini, M.; Pozzi, G. Electron holography in the study of the electrostatic fields: the case of charged microtips. Ultramicroscopy 1992, 45, 77– 83, DOI: 10.1016/0304-3991(92)90039-MGoogle ScholarThere is no corresponding record for this reference.
- 36Caron, J. Model-based reconstruction of magnetisation distributions in nanostructures from electron optical phase images. Ph.D. Thesis, RWTH Aachen University, 2017.Google ScholarThere is no corresponding record for this reference.
- 37Oikawa, T.; Kim, J. J.; Tomita, T.; Park, H. S.; Shindo, D. Measurement of electric potential distributions around FEG-emitters by electron holography. Journal of Electron Microscopy 2007, 56, 171– 175, DOI: 10.1093/jmicro/dfm022Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD2sjlsVeqtg%253D%253D&md5=08cc9ceb197283c48efe8c0428e390b4Measurement of electric potential distributions around FEG-emitters by electron holographyOikawa Tetsuo; Kim Joong Jung; Tomita Takeshi; Park Hyun Soon; Shindo DaisukeJournal of electron microscopy (2007), 56 (5), 171-5 ISSN:.An evaluation technique for field emission guns (FEG-emitters) was established by using electron holography. For performing electron holography under an applied voltage, a specimen holder with the capabilities of three-directional motion as well as voltage application was developed. An unused Schottky emitter and a used emitter that had failed after operating for about 10,000 h were selected for this study. By visualizing the electric potential distributions around the emitters, it was clarified that a change in the edge shape of the emitter led to the change in the strength of the electric field. The observations revealed that electron holography can be applied to evaluate the performances of the various emitters.
- 38Mandal, S.; Pradeep, K. G.; Zaefferer, S.; Raabe, D. A novel approach to measure grain boundary segregation in bulk polycrystalline materials in dependence of the boundaries’ five rotational degrees of freedom. Scripta Materialia 2014, 81, 16– 19, DOI: 10.1016/j.scriptamat.2014.02.016Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXkslegtbs%253D&md5=ad70f1f6309d36bf14550120beef8a55A novel approach to measure grain boundary segregation in bulk polycrystalline materials in dependence of the boundaries' five rotational degrees of freedomMandal, S.; Pradeep, K. G.; Zaefferer, S.; Raabe, D.Scripta Materialia (2014), 81 (), 16-19CODEN: SCMAF7; ISSN:1359-6462. (Elsevier Ltd.)We demonstrate a simplified nondestructive 3-D electron backscatter diffraction (EBSD) methodol. that enables the measurement of all five degrees of freedom of grain boundaries (GBs) combined with segregation anal. using atom probe tomog. (APT). The approach is based on two 2-D EBSD measurements on orthogonal surfaces at a sharp edge of the specimen followed by site-specific GB compn. anal. using APT. An example of an asym. Σ9 boundary exhibiting GB segregation emphasizes the need for complete GB characterization in this context.
- 39Volkov, V.; Han, M.; Zhu, Y. Double-resolution electron holography with simple Fourier transform of fringe-shifted holograms. Ultramicroscopy 2013, 134, 175– 184, DOI: 10.1016/j.ultramic.2013.06.018Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtF2mt73L&md5=f5d75cd6d58ca4701da1db22e44db875Double-resolution electron holography with simple Fourier transform of fringe-shifted hologramsVolkov, V. V.; Han, M. G.; Zhu, Y.Ultramicroscopy (2013), 134 (), 175-184CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)The authors propose a fringe-shifting holog. method with an appropriate image wave recovery algorithm leading to exact soln. of holog. equations. With this new method the complex object image wave recovered from holograms appears to have much less traditional artifacts caused by the autocorrelation band present practically in all Fourier transformed holograms. The new anal. solns. make possible a double-resoln. electron holog. free from autocorrelation band artifacts and thus push the limits for phase resoln. The new image wave recovery algorithm uses a popular Fourier soln. of the side band-pass filter technique, while the fringe-shifting holog. method is simple to implement in practice.
- 40Ru, Q.; Lai, G.; Aoyama, K.; Endo, J.; Tonomura, A. Principle and application of phase-shifting electron holography. Ultramicroscopy 1994, 55, 209– 220, DOI: 10.1016/0304-3991(94)90171-6Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXhvVKgsbs%253D&md5=30151f95b8614f1208fc74ec98838691Principle and application of phase-shifting electron holographyRu, Q.; Lai, G.; Aoyama, K.; Endo, J.; Tonomura, A.Ultramicroscopy (1994), 55 (2), 209-20CODEN: ULTRD6; ISSN:0304-3991.Electron holog. using an improved phase-shifting (fringe-scanning) interferometric technique is described. The improvements it makes in phase measurement, in spatial resoln. of reconstructed images and in hologram formation are clarified and demonstrated with three expts.: (1) quant. detection of at. surface steps on molybdenite crystal film, (2) topog. measurement of gold platelets epitaxially grown on a molybdenite substrate, and (3) sensitive observation of a bacterial flagellum filament.
- 41van Aarle, W.; Palenstijn, W. J.; De Beenhouwer, J.; Altantzis, T.; Bals, S.; Batenburg, K. J.; Sijbers, J. The ASTRA Toolbox: A platform for advanced algorithm development in electron tomography. Ultramicroscopy 2015, 157, 35– 47, DOI: 10.1016/j.ultramic.2015.05.002Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXotVKhsLs%253D&md5=3712da2f93e931cb64ef3c7e65dee01eThe ASTRA Toolbox: A platform for advanced algorithm development in electron tomographyvan Aarle, Wim; Palenstijn, Willem Jan; De Beenhouwer, Jan; Altantzis, Thomas; Bals, Sara; Batenburg, K. Joost; Sijbers, JanUltramicroscopy (2015), 157 (), 35-47CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)We present the ASTRA Toolbox as an open platform for 3D image reconstruction in tomog. Most of the software tools that are currently used in electron tomog. offer limited flexibility with respect to the geometrical parameters of the acquisition model and the algorithms used for reconstruction. The ASTRA Toolbox provides an extensive set of fast and flexible building blocks that can be used to develop advanced reconstruction algorithms, effectively removing these limitations. We demonstrate this flexibility, the resulting reconstruction quality, and the computational efficiency of this toolbox by a series of expts., based on exptl. dual-axis tilt series.
- 42Jackson, J. Classical Electrodynamics; Wiley: 1998.Google ScholarThere is no corresponding record for this reference.
- 43Tsong, T. Field penetration and band bending near semiconductor surfaces in high electric fields. Surf. Sci. 1979, 81, 28– 42, DOI: 10.1016/0039-6028(79)90503-XGoogle Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE1MXhsVCqsrw%253D&md5=951c54df431f09fdb980dab6db8a24cdField penetration and band bending near semiconductor surfaces in high electric fieldsTsong, T. T.Surface Science (1979), 81 (1), 28-42CODEN: SUSCAS; ISSN:0039-6028.The existing theory of band bending in the surface space charge region of semiconductors is adapted to problems in field emission, field ionization and field evapn. The surface field in the space charge layers of semiconductors appropriate for these phenomena ranges from ∼10-2 V/Å to a few 10-1 V/Å, similar to those encountered in many interface phenomena involving semiconductors. The surface potential resulting from band bending may amt. to a few eV. The field penetrates ∼10 Å into the semiconductor surface for intrinsic cases, and ∼200 Å for an n-type semiconductor in a pos. field, or for a p-type semiconductor in a neg. field. Both the surface potential and the field penetration will affect significantly the electronic properties of the near surface layers. In particular, the photon adsorption edge will be shifted toward the red by the field penetration effect.
- 44Zheng, F.; Pozzi, G.; Migunov, V.; Pirker, L.; Remkar, M.; Beleggia, M.; Dunin-Borkowski, R. E. Quantitative measurement of charge accumulation along a quasi-one-dimensional W5O14 nanowire during electron field emission. Nanoscale 2020, 12, 10559– 10564, DOI: 10.1039/D0NR00739KGoogle Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXktl2qsr4%253D&md5=1145c1841085c15942eb7cf574d37f5fQuantitative measurement of charge accumulation along a quasi-one-dimensional W5O14 nanowire during electron field emissionZheng, Fengshan; Pozzi, Giulio; Migunov, Vadim; Pirker, Luka; Remskar, Maja; Beleggia, Marco; Dunin-Borkowski, Rafal E.Nanoscale (2020), 12 (19), 10559-10564CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)We use an electron holog. method to det. the charge distribution along a quasi-one-dimensional W5O14 nanowire during in situ field emission in a transmission electron microscope. The results show that the continuous charge distribution along the nanowire is not linear, but that there is an addnl. accumulation of charge at its apex. An anal. expression for this addnl. contribution to the charge distribution is proposed and its effect on the field enhancement factor and emission current is discussed.
- 45Du, S.; Burgess, T.; Tjing Loi, S.; Gault, B.; Gao, Q.; Bao, P.; Li, L.; Cui, X.; Kong Yeoh, W.; Hoe Tan, H.; Jagadish, C.; Ringer, S. P.; Zheng, R. Full tip imaging in atom probe tomography. Ultramicroscopy 2013, 124, 96– 101, DOI: 10.1016/j.ultramic.2012.08.014Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslKgu7jJ&md5=e8a68c6b474b9d077c2ca5fc05ca6cbbFull tip imaging in atom probe tomographyDu, Sichao; Burgess, Timothy; Loi, Shyeh Tjing; Gault, Baptiste; Gao, Qiang; Bao, Peite; Li, Li; Cui, Xiangyuan; Yeoh, Wai Kong; Tan, Hark Hoe; Jagadish, Chennupati; Ringer, Simon P.; Zheng, RongkunUltramicroscopy (2013), 124 (), 96-101CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)Atom probe tomog. (APT) is capable of simultaneously revealing the chem. identities and three dimensional positions of individual atoms within a needle-shaped specimen, but suffers from a limited field-of-view (FOV), i.e., only the core of the specimen is effectively detected. Therefore, the capacity to analyze the full tip is crucial and much desired in cases that the shell of the specimen is also the region of interest. In this paper, we demonstrate that in the anal. of III-V nanowires epitaxially grown from a substrate, the presence of the flat substrate positioned only micrometers away from the analyzed tip apex alters the field distribution and ion trajectories, which provides extra image compression that allows for the anal. of the entire specimen. An array of exptl. results, including field desorption maps, elemental distributions, and crystallog. features clearly demonstrate the fact that the whole tip has been imaged, which is confirmed by electrostatic simulations.
- 46Loi, S. T.; Gault, B.; Ringer, S. P.; Larson, D. J.; Geiser, B. P. Electrostatic simulations of a local electrode atom probe: The dependence of tomographic reconstruction parameters on specimen and microscope geometry. Ultramicroscopy 2013, 132, 107– 113, DOI: 10.1016/j.ultramic.2012.12.012Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXktlOntQ%253D%253D&md5=b15d80e2ef91bbea3b19997d5e45df33Electrostatic simulations of a local electrode atom probe: The dependence of tomographic reconstruction parameters on specimen and microscope geometryLoi, Shyeh Tjing; Gault, Baptiste; Ringer, Simon P.; Larson, David J.; Geiser, Brian P.Ultramicroscopy (2013), 132 (), 107-113CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)We electrostatically model a local electrode atom probe microscope using the com. software IES LORENTZ 2D v9.0 to investigate factors affecting the reconstruction parameters. We find strong dependences on the specimen geometry and voltage, and moderate dependences on the tip-aperture sepn., which confirm that the current approach to atom probe reconstruction overlooks too many factors. Based on our data, which are in excellent agreement with known trends and exptl. results, we derive a set of empirical relations which predict the values of the reconstruction parameters. These may be used to advance current reconstruction protocols by enabling the parameters to be adjusted as the specimen geometry changes.
- 47Morgan, P. Carbon Fibers and Their Composites; CRC Press: 2005.Google ScholarThere is no corresponding record for this reference.
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Abstract
Figure 1
Figure 1. (a) Low-magnification bright-field TEM image showing the experimental setup for electrical biasing of a C fiber needle in the TEM. (b) Higher magnification image of the end of the needle. (c) Electron holographic phase difference image with +40 V applied between the needle and the counter electrode at a 0° sample tilt angle. The mean inner potential contribution to the phase has been removed by subtracting an aligned phase image recorded without a bias applied to the needle. Equiphase contour lines (black) are superimposed. The phase contour spacing is 2π radians. A TEM image of the C fiber needle is overlaid to guide the eye.
Figure 2
Figure 2. Visualization of 3D charge density in a C fiber needle reconstructed using electron holographic tomography and the MBIR approach. The needle is biased at +40 V with a distance of 4.5 μm from a Au counter electrode. (a) Side view of the 3D charge density. (b, c) 2D slices of charge density in the (b) xy and (c) yz planes, extracted from the 3D reconstructed charge density shown in (a). (d–f) Three representative slices of charge density in the xz plane extracted from the 3D reconstructed charge density shown in (a). The positions of the planes are marked by white arrows and numbers in (b). The white dashed lines mark the outline of the needle. See text for details.
Figure 3
Figure 3. Line profiles of charge density extracted from the 3D charge density shown in Figure 2a along the axis of the needle (y) in the central xy plane (marked by a red arrow in Figure 2b) and (b, c) along z and x in three different xz planes (1: red; 2: green; 3: blue) marked in Figure 2b. (d) Cumulative charge profile along the length of the needle.
Figure 4
Figure 4. 3D electric field determined from the reconstructed 3D charge density shown in Figure 2 for the electrically biased C fiber needle. (a) Magnitude of the electric field plotted on a logarithmic scale. (b, c) Magnitude of the electric field in the central xy and yz planes, respectively. The black dashed line shows the outline of the needle.
Figure 5
Figure 5. Combination of a streamline plot of the electric field and a plot of the electrostatic potential in the central xy plane of the reconstructed volume of the C fiber needle. The interior of the needle is marked in blue. The scale bar is 50 nm.
References
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- 3Zhang, H.; Tang, J.; Yuan, J.; Yamauchi, Y.; Suzuki, T. T.; Shinya, N.; Nakajima, K.; Qin, L.-C. An ultrabright and monochromatic electron point source made of a LaB6 nanowire. Nat. Nanotechnol. 2016, 11, 273, DOI: 10.1038/nnano.2015.2763https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFemsb3L&md5=9119110fcf7b516095f76bc41855210bAn ultrabright and monochromatic electron point source made of a LaB6 nanowireZhang, Han; Tang, Jie; Yuan, Jinshi; Yamauchi, Yasushi; Suzuki, Taku T.; Shinya, Norio; Nakajima, Kiyomi; Qin, Lu-ChangNature Nanotechnology (2016), 11 (3), 273-279CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Electron sources as 1-dimensional nanotubes and nanowires are an essential tool for studies in a variety of fields, such as x-ray computed tomog., flexible displays, chem. sensors and electron optics applications. However, field emission instability and the need to work under high-vacuum or high-temp. conditions have imposed stringent requirements that are currently limiting the range of application of electron sources. Here the authors report the fabrication of a LaB6 nanowire with only a few La atoms bonded on the tip that emits collimated electrons from a single point with high monochromaticity. The nanostructured tip has a low work function of 2.07 eV (lower than that of Cs) while remaining chem. inert, two properties usually regarded as mutually exclusive. Installed in a scanning electron microscope (SEM) field emission gun, the authors' tip shows a c.d. gain that is ∼1,000 times greater than that achievable with W(310) tips, and no emission decay for tens of hours of operation. Using this new SEM, the authors acquired very low-noise, high-resoln. images together with rapid chem. compositional mapping using a tip operated at room temp. and at 10-times higher residual gas pressure than that required for W tips.
- 4Zhou, Y.; Liang, Y.; Fu, J.; Liu, K.; Chen, Q.; Wang, X.; Li, H.; Zhu, L.; Hu, J.; Pan, H.; Miyauchi, M.; Jiang, L.; Cortés, E.; Liu, M. Vertical Cu nanoneedle arrays enhance the local electric field promoting C2 Hydrocarbons in the CO2 electroreduction. Nano Lett. 2022, 22, 1963– 1970, DOI: 10.1021/acs.nanolett.1c046534https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XjsFSkur4%253D&md5=2c4a2879e044b69c4bfb1ec1247670d6Vertical Cu Nanoneedle Arrays Enhance the Local Electric Field Promoting C2 Hydrocarbons in the CO2 ElectroreductionZhou, Yajiao; Liang, Yanqing; Fu, Junwei; Liu, Kang; Chen, Qin; Wang, Xiqing; Li, Hongmei; Zhu, Li; Hu, Junhua; Pan, Hao; Miyauchi, Masahiro; Jiang, Liangxing; Cortes, Emiliano; Liu, MinNano Letters (2022), 22 (5), 1963-1970CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Electrocatalytic redn. of CO2 to multicarbon products is a potential strategy to solve the energy crisis while achieving C neutrality. To improve the efficiency of multicarbon products in Cu-based catalysts, optimizing the *CO adsorption and reducing the energy barrier for C-C (C-C) coupling are essential features. A strong local elec. field was obtained by regulating the arrangement of Cu nanoneedle arrays (CuNNAs). CO2 redn. performance tests indicate that an ordered nanoneedle array reaches a 59% Faraday efficiency for multicarbon products (FEC2) at -1.2 V (vs. RHE), compared to a FEC2 of 20% for a disordered nanoneedle array (CuNNs). As such, the very high and local elec. fields achieved by an ordered Cu nanoneedle array leads to the accumulation of K+ ions, which benefit both *CO adsorption and C-C coupling. The authors' results contribute to the design of highly efficient catalysts for multicarbon products.
- 5Gault, B.; Chiaramonti, A.; Cojocaru-Mirédin, O.; Stender, P.; Dubosq, R.; Freysoldt, C.; Makineni, S. K.; Li, T.; Moody, M.; Cairney, J. M. Atom probe tomography. Nature Reviews Methods Primers 2021, 1, 51, DOI: 10.1038/s43586-021-00047-w5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XjsVGnsL0%253D&md5=ac7361639febed57f478c11b293c3819Atom probe tomographyGault, Baptiste; Chiaramonti, Ann; Cojocaru-Miredin, Oana; Stender, Patrick; Dubosq, Renelle; Freysoldt, Christoph; Makineni, Surendra Kumar; Li, Tong; Moody, Michael; Cairney, Julie M.Nature Reviews Methods Primers (2021), 1 (1), 51CODEN: NRMPAT; ISSN:2662-8449. (Nature Portfolio)A review. Atom probe tomog. (APT) provides three-dimensional compositional mapping with sub-nanometer resoln. The sensitivity of APT is in the range of ppm for all elements, including light elements such as hydrogen, carbon or lithium, enabling unique insights into the compn. of performance-enhancing or lifetime-limiting microstructural features and making APT ideally suited to complement electron-based or X-ray-based microscopies and spectroscopies. Here, we provide an introductory overview of APT ranging from its inception as an evolution of field ion microscopy to the most recent developments in specimen prepn., including for nanomaterials. We touch on data reconstruction, anal. and various applications, including in the geosciences and the burgeoning biol. sciences. We review the underpinnings of APT performance and discuss both strengths and limitations of APT, including how the community can improve on current shortcomings. Finally, we look forwards to true at.-scale tomog. with the ability to measure the isotopic identity and spatial coordinates of every atom in an ever wider range of materials through new specimen prepn. routes, novel laser pulsing and detector technologies, and full interoperability with complementary microscopy techniques.
- 6Vurpillot, F.; Oberdorfer, C. Modeling atom probe tomography: A review. Ultramicroscopy 2015, 159, 202– 216, DOI: 10.1016/j.ultramic.2014.12.0136https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVWisw%253D%253D&md5=c4ef728fed985c769409192c1108ba71Modeling Atom Probe Tomography: A reviewVurpillot, F.; Oberdorfer, C.Ultramicroscopy (2015), 159 (Part_2), 202-216CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)A review. Improving both the precision and the accuracy of Atom Probe Tomog. reconstruction requires a correct understanding of the imaging process. In this aim, numerical modeling approaches were developed for 15 years. The injected ingredients of these modeling tools are related to the basic physic of the field evapn. mechanism. The interplay between the sample nature and structure of the analyzed sample and the reconstructed image artifacts have pushed to gradually improve and make the model more and more sophisticated. This paper reviews the evolution of the modeling approach in Atom Probe Tomog. and presents some future potential directions to improve the method.
- 7Su, Y.; Liu, C.; Brittman, S.; Tang, J.; Fu, A.; Kornienko, N.; Kong, Q.; Yang, P. Single-nanowire photoelectrochemistry. Nat. Nanotechnol. 2016, 11, 609, DOI: 10.1038/nnano.2016.307https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XkvFGisrw%253D&md5=6734e926aad989ba71a1f2727759303aSingle-nanowire photoelectrochemistrySu, Yude; Liu, Chong; Brittman, Sarah; Tang, Jinyao; Fu, Anthony; Kornienko, Nikolay; Kong, Qiao; Yang, PeidongNature Nanotechnology (2016), 11 (7), 609-612CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Photoelectrochem. is one of several promising approaches for the realization of efficient solar-to-fuel conversion. Recent work has shown that photoelectrodes made of semiconductor nano-/microwire arrays can have better photoelectrochem. performance than their planar counterparts because of their unique properties, such as high surface area. Although considerable research effort has focused on studying wire arrays, the inhomogeneity in the geometry, doping, defects and catalyst loading present in such arrays can obscure the link between these properties and the photoelectrochem. performance of the wires, and correlating performance with the specific properties of individual wires is difficult because of ensemble averaging. Here, we show that a single-nanowire-based photoelectrode platform can be used to reliably probe the current-voltage (I-V) characteristics of individual nanowires. We find that the photovoltage output of ensemble array samples can be limited by poorly performing individual wires, which highlights the importance of improving nanowire homogeneity within an array. Furthermore, the platform allows the flux of photogenerated electrons to be quantified as a function of the lengths and diams. of individual nanowires, and we find that the flux over the entire nanowire surface (7-30 electrons/nm2 s) is significantly reduced as compared with that of a planar analog (∼1,200 electrons /nm2 s). Such characterization of the photogenerated carrier flux at the semiconductor/electrolyte interface is essential for designing nanowire photoelectrodes that match the activity of their loaded electrocatalysts.
- 8Liu, M. Enhanced electrocatalytic CO2 reduction via field-induced reagent concentration. Nature 2016, 537, 382, DOI: 10.1038/nature190608https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1yqsbzO&md5=11d8dcf8010b105587ba93d7035bc657Enhanced electrocatalytic CO2 reduction via field-induced reagent concentrationLiu, Min; Pang, Yuanjie; Zhang, Bo; De Luna, Phil; Voznyy, Oleksandr; Xu, Jixian; Zheng, Xueli; Dinh, Cao Thang; Fan, Fengjia; Cao, Changhong; Garcia de Arquer, F. Pelayo; Safaei, Tina Saberi; Mepham, Adam; Klinkova, Anna; Kumacheva, Eugenia; Filleter, Tobin; Sinton, David; Kelley, Shana O.; Sargent, Edward H.Nature (London, United Kingdom) (2016), 537 (7620), 382-386CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Electrochem. redn. of CO2 (CO2) to CO (CO) is the 1st step in the synthesis of more complex C-based fuels and feedstocks using renewable electricity. Unfortunately, the reaction suffers from slow kinetics owing to the low local concn. of CO2 surrounding typical CO2 redn. reaction catalysts. Alkali metal cations are known to overcome this limitation through noncovalent interactions with adsorbed reagent species, but the effect is restricted by the soly. of relevant salts. Large applied electrode potentials can also enhance CO2 adsorption, but this comes at the cost of increased H (H2) evolution. Here we report that nanostructured electrodes produce, at low applied overpotentials, local high elec. fields that conc. electrolyte cations, which in turn leads to a high local concn. of CO2 close to the active CO2 redn. reaction surface. Simulations reveal 10-fold higher elec. fields assocd. with metallic nm-sized tips compared to quasi-planar electrode regions, and measurements using Au nanoneedles confirm a field-induced reagent concn. that enables the CO2 redn. reaction to proceed with a geometric c.d. for CO of 22 mA per square centimeter at -0.35 V (overpotential of 0.24 V). This performance surpasses by an order of magnitude the performance of the best Au nanorods, nanoparticles and oxide-derived noble metal catalysts. Similarly designed Pd nanoneedle electrocatalysts produce formate with a faradaic efficiency of >90 per cent and an unprecedented geometric c.d. for formate of 10 mA per square centimeter at -0.2 V, demonstrating the wider applicability of the field-induced reagent concn. concept.
- 9Lichte, H.; Lehmann, M. Electron holography–basics and applications. Rep. Prog. Phys. 2008, 71, 016102, DOI: 10.1088/0034-4885/71/1/0161029https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXitVSjt78%253D&md5=17f9da9c25d61f7328fc135530831e79Electron holography-basics and applicationsLichte, Hannes; Lehmann, MichaelReports on Progress in Physics (2008), 71 (1), 016102/1-016102/46CODEN: RPPHAG; ISSN:0034-4885. (Institute of Physics Publishing)A review. Despite the huge progress achieved recently by means of the corrector for aberrations, allowing now a true at. resoln. of 0.1 nm, hence making it an unrivalled tool for nanoscience, transmission electron microscopy (TEM) suffers from a severe drawback: in a conventional electron micrograph only a poor phase contrast can be achieved, i.e. phase structures are virtually invisible. Therefore, conventional TEM is nearly blind for elec. and magnetic fields, which are pure phase objects. Since such fields provoked by the at. structure, e.g. of semiconductors and ferroelecs., largely det. the solid state properties, hence the importance for high technol. applications, substantial object information is missing. Electron holog. in TEM offers the soln.: by superposition with a coherent ref. wave, a hologram is recorded, from which the image wave can be completely reconstructed by amplitude and phase. Now the object is displayed quant. in two sep. images: one representing the amplitude, the other the phase. From the phase image, elec. and magnetic fields can be detd. quant. in the range from micrometre down to at. dimensions by all wave optical methods that one can think of, both in real space and in Fourier space. Electron holog. is pure wave optics. Therefore, we discuss the basics of coherence and interference, the implementation into a TEM, the path of rays for recording holograms as well as the limits in lateral and signal resoln. We outline the methods of reconstructing the wave by numerical image processing and procedures for extg. the object properties of interest. Furthermore, we present a broad spectrum of applications both at mesoscopic and at. dimensions. This paper gives an overview of the state of the art pointing at the needs for further development. It is also meant as encouragement for those who refrain from holog., thinking that it can only be performed by specialists in highly specialized labs. In fact, a modern TEM built for at. resoln. and equipped with a field emitter or a Schottky emitter, well aligned by a skilled operator, can deliver good holograms. Running com. available image processing software and mathematics programs on a laptop-computer is sufficient for reconstruction of the amplitude and phase images and extg. desirable object information.
- 10Twitchett, A.; Dunin-Borkowski, R.; Midgley, P. Quantitative electron holography of biased semiconductor devices. Phys. Rev. Lett. 2002, 88, 238302, DOI: 10.1103/PhysRevLett.88.23830210https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XktFGktb4%253D&md5=cc051b3903a6d33e3c09f3637a9fea4bQuantitative Electron Holography of Biased Semiconductor DevicesTwitchett, A. C.; Dunin-Borkowski, R. E.; Midgley, P. A.Physical Review Letters (2002), 88 (23), 238302/1-238302/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Electron holog. is used to measure electrostatic potential profiles across reverse-biased Si p-n junctions in situ in the transmission electron microscope. A novel sample geometry based on focused ion-beam milling is developed, and results are obtained for a range of sample thicknesses and bias voltages to allow the holog. contrast to be interpreted. The phys. and elec. nature of the sample surface, which is affected by sample prepn. and electron beam irradn., is discussed.
- 11Twitchett-Harrison, A. C.; Yates, T. J.; Newcomb, S. B.; Dunin-Borkowski, R. E.; Midgley, P. A. High-resolution three-dimensional mapping of semiconductor dopant potentials. Nano Lett. 2007, 7, 2020– 2023, DOI: 10.1021/nl070858n11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXmt12isbs%253D&md5=d57c0420e8a188bc2c229e634ea3c891High-resolution 3-dimensional mapping of semiconductor dopant potentialsTwitchett-Harrison, Alison C.; Yates, Timothy J. V.; Newcomb, Simon B.; Dunin-Borkowski, Rafal E.; Midgley, Paul A.Nano Letters (2007), 7 (7), 2020-2023CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Semiconductor device structures are becoming increasingly 3D at the nanometer scale. A key issue that must be addressed to enable future device development is the 3D mapping of dopant distributions, ideally under working conditions. Here we demonstrate how a combination of electron holog. and electron tomog. can be used to det. quant. the 3D electrostatic potential in an elec. biased semiconductor device with nanometer spatial resoln.
- 12Wolf, D.; Lichte, H.; Pozzi, G.; Prete, P.; Lovergine, N. Electron holographic tomography for mapping the three-dimensional distribution of electrostatic potential in III-V semiconductor nanowires. Appl. Phys. Lett. 2011, 98, 264103, DOI: 10.1063/1.360479312https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotV2hurk%253D&md5=fb1569935b9fc404b77e2b27156740d8Electron holographic tomography for mapping the three-dimensional distribution of electrostatic potential in III-V semiconductor nanowiresWolf, D.; Lichte, H.; Pozzi, G.; Prete, P.; Lovergine, N.Applied Physics Letters (2011), 98 (26), 264103/1-264103/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Electron holog. tomog. (EHT), the combination of off-axis electron holog. with electron tomog., is a technique, which can be applied to the quant. 3D mapping of electrostatic potential at the nanoscale. Here, we show the results obtained in the EHT investigation of GaAs and GaAs-AlGaAs core-shell nanowires grown by Au-catalyzed metalorg. vapor phase epitaxy. The unique ability of EHT of disentangling the materials mean inner potential (MIP) from the specimen projected thickness allows reconstruction of the nanowire 3D morphol. and inner compositional structure as well as the measurement of the MIP. (c) 2011 American Institute of Physics.
- 13Li, L.; Smith, D. J.; Dailey, E.; Madras, P.; Drucker, J.; McCartney, M. R. Observation of hole accumulation in Ge/Si core/shell nanowires using off-axis electron holography. Nano Lett. 2011, 11, 493– 497, DOI: 10.1021/nl103310713https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXmslCitg%253D%253D&md5=30537c2b68e304e6066258ff003d78e2Observation of hole accumulation in Ge/Si core/shell nanowires using off-axis electron holographyLi, Luying; Smith, David J.; Dailey, Eric; Madras, Prashanth; Drucker, Jeff; McCartney, Martha R.Nano Letters (2011), 11 (2), 493-497CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Hole accumulation in Ge/Si core/shell nanowires (NWs) was obsd. and quantified using off-axis electron holog. and other electron microscopy techniques. The epitaxial (110)-oriented Ge/Si core/shell NWs were grown on Si (111) substrates by chem. vapor deposition through the vapor-liq.-solid growth mechanism. High-angle annular-dark-field scanning transmission electron microscopy images and off-axis electron holograms were obtained from specific NWs. The excess phase shifts measured by electron holog. across the NWs indicated the presence of holes inside the Ge cores. Calcns. based on a simplified coaxial cylindrical model gave hole densities of (0.4 ± 0.2) /nm3 in the core regions.
- 14Wolf, D.; Lubk, A.; Lenk, A.; Sturm, S.; Lichte, H. Tomographic investigation of fermi level pinning at focused ion beam milled semiconductor surfaces. Appl. Phys. Lett. 2013, 103, 264104, DOI: 10.1063/1.485895714https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXitVWntL3K&md5=0a7759535556fc7e15994446951241e0Tomographic investigation of fermi level pinning at focused ion beam milled semiconductor surfacesWolf, D.; Lubk, A.; Lenk, A.; Sturm, S.; Lichte, H.Applied Physics Letters (2013), 103 (26), 264104/1-264104/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Electron holog. in the transmission electron microscope (TEM) offers the spatial and signal resoln. for studying effects like Fermi level pinning or dopant concn. variations important for the design of modern electronic devices. To overcome the loss of information along the projection direction, surface effects, and surface damage due to TEM specimen prepn., we apply electron holog. tomog. to analyze the 3D potential distribution of semiconductor samples prepd. by focused-ion-beam. We observe mid-band gap pinning of the Fermi level at Si surfaces but valence band pinning at Ge surfaces. The pinning extends over tens of nanometers into the bulk. (c) 2013 American Institute of Physics.
- 15Wolf, D.; Lubk, A.; Prete, P.; Lovergine, N.; Lichte, H. 3D mapping of nanoscale electric potentials in semiconductor structures using electron-holographic tomography. J. Phys. D: Appl. Phys. 2016, 49, 364004, DOI: 10.1088/0022-3727/49/36/36400415https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFOqs7zJ&md5=40af8f3387e5a15b33acf7145e1d4e393D mapping of nanoscale electric potentials in semiconductor structures using electron-holographic tomographyWolf, Daniel; Lubk, Axel; Prete, Paola; Lovergine, Nico; Lichte, HannesJournal of Physics D: Applied Physics (2016), 49 (36), 364004/1-364004/9CODEN: JPAPBE; ISSN:0022-3727. (IOP Publishing Ltd.)Off-axis electron holog. (EH) is a powerful method for mapping projected elec. potentials, such as built-in potentials in semiconductor devices, in two dimensions (2D) at nanometer resoln. However, not well-defined thickness profiles, surface effects, and compn. changes of the sample under investigation complicate the interpretation of the projected potentials. Here, we demonstrate how these problems can be overcome by combining EH with tomog. techniques, i.e., electron holog. tomog. (EHT), reconstructing elec. potentials in 3D. We present EHT reconstructions of an n-type MOSFET including its dopant-related built-in potentials inside the device, as well as of a GaAs/AlGaAs core-multishell nanowire contg. a 5 nm thick quantum well tube.
- 16Gan, Z.; Perea, D.; Yoo, J.; He, Y.; Colby, R.; Barker, J.; Gu, M.; Mao, S.; Wang, C.; Picraux, S.; Smith, D.; McCartney, M. Characterization of electrical properties in axial Si-Ge nanowire heterojunctions using off-axis electron holography and atom-probe tomography. J. Appl. Phys. 2016, 120, 104301, DOI: 10.1063/1.496238016https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFWnurfL&md5=062fa88688fc755e18dd2f99c55ef8fbCharacterization of electrical properties in axial Si-Ge nanowire heterojunctions using off-axis electron holography and atom-probe tomographyGan, Zhaofeng; Perea, Daniel E.; Yoo, Jinkyoung; He, Yang; Colby, Robert J.; Barker, Josh E.; Gu, Meng; Mao, Scott X.; Wang, Chongmin; Picraux, S. T.; Smith, David J.; McCartney, Martha R.Journal of Applied Physics (Melville, NY, United States) (2016), 120 (10), 104301/1-104301/8CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)Nanowires (NWs) consisting of P-doped Si/B-doped Ge axial heterojunctions were grown via vapor-liq.-solid synthesis using a combination of Au and AuGa catalyst particles. Off-axis electron holog. (EH) was used to measure the electrostatic potential profile across the junction resulting from elec. active dopants, and atom-probe tomog. (APT) was used to map total dopant concn. profiles. A comparison of the electrostatic potential profile measured from EH with simulations that were based on the APT results indicates that Ga atoms unintentionally introduced during AuGa catalyst growth were mostly electronically inactive. This finding was also corroborated by in situ electron-holog. biasing expts. Electronic band structure simulations guided by the exptl. results helped to provide a much better explanation of the NW elec. behavior. Overall, this work demonstrates that the combination of EH, APT, in situ biasing, and simulations allows a more complete understanding of NW elec. properties to be developed. (c) 2016 American Institute of Physics.
- 17Chalasani, R.; Pekin, A.; Rabkin, A.; Abutbul, R. E.; Diéguez, O.; Kauffmann, Y.; Golan, Y.; Kohn, A. Mapping charge distribution in single PbS core-CdS arm nano-multipod heterostructures by off-axis electron holography. Nano Lett. 2017, 17, 2778– 2787, DOI: 10.1021/acs.nanolett.6b0495717https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlslCjtr8%253D&md5=1277f0eba081351a9b16dec68cd1a964Mapping Charge Distribution in Single PbS Core - CdS Arm Nano-Multipod Heterostructures by Off-Axis Electron HolographyChalasani, Rajesh; Pekin, Alexander; Rabkin, Alexander; Abutbul, Ran E.; Dieguez, Oswaldo; Kauffmann, Yaron; Golan, Yuval; Kohn, AmitNano Letters (2017), 17 (5), 2778-2787CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The authors synthesized PbS core-CdS arm nanomultipod heterostructures (NMHs) that exhibit PbS{111}/CdS{0002} epitaxial relations. The PbS-CdS interface is chem. sharp as detd. by aberration cor. TEM and compared to d. functional theory (DFT) calcns. Ensemble fluorescence measurements show quenching of the optical signal from the CdS arms indicating charge sepn. due to the heterojunction with PbS. A finite-element three-dimensional (3D) calcn. of the Poisson equation shows a type-I heterojunction, which would prevent recombination in the CdS arm after optical excitation. To examine charge redistribution, the authors used off-axis electron holog. (OAEH) in the TEM to map the electrostatic potential across an individual heterojunction. Indeed, a built-in potential of 500 mV is estd. across the junction, though as opposed to the thermal equil. calcns. significant accumulation of pos. charge at the CdS side of the interface is detected. The NMH multipod geometry prevents efficient removal of generated charge carriers by the high energy electrons of the TEM. Simulations of generated electron-hole pairs in the insulated CdS arm of the NMH indeed show charge accumulation in agreement with the exptl. measurements. Thus, OAEH can be used as a complementary methodol. to ensemble measurements by mapping the charge distribution in single NMHs with complex geometries.
- 18Li, L.; Cheng, Y.; Liu, Z.; Yan, S.; Li, L.; Wang, J.; Zhang, L.; Gao, Y. Study of structure-property relationship of semiconductor nanomaterials by off-axis electron holography. Journal of Semiconductors 2022, 43, 041103, DOI: 10.1088/1674-4926/43/4/041103There is no corresponding record for this reference.
- 19Cumings, J.; Zettl, A.; McCartney, M.; Spence, J. Electron holography of field-emitting carbon nanotubes. Phys. Rev. Lett. 2002, 88, 056804, DOI: 10.1103/PhysRevLett.88.05680419https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XnsF2nsQ%253D%253D&md5=d446e4c240cc05504f9c407316acc09eElectron holography of field-emitting carbon nanotubesCumings, John; Zettl, A.; McCartney, M. R.; Spence, J. C. H.Physical Review Letters (2002), 88 (5), 056804/1-056804/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Electron holog. performed in situ inside a high resoln. transmission electron microscope was used to det. the magnitude and spatial distribution of the elec. field surrounding individual field-emitting C nanotubes. The elec. field (and hence the assocd. field emission current) is concd. precisely at the tips of the nanotubes and not at other nanotube defects such as sidewall imperfections. The elec. field magnitude and distribution are stable in time, even in cases where the nanotube field emission current exhibits extensive temporal fluctuations.
- 20Lubk, A.; Wolf, D.; Simon, P.; Wang, C.; Sturm, S.; Felser, C. Nanoscale three-dimensional reconstruction of electric and magnetic stray fields around nanowires. Appl. Phys. Lett. 2014, 105, 173110, DOI: 10.1063/1.490082620https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvVertrjF&md5=d7f41ebe44b5dcbbb635757db94482f1Nanoscale three-dimensional reconstruction of electric and magnetic stray fields around nanowiresLubk, A.; Wolf, D.; Simon, P.; Wang, C.; Sturm, S.; Felser, C.Applied Physics Letters (2014), 105 (17), 173110/1-173110/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Static electromagnetic stray fields around nanowires (NWs) are characteristic for a no. of important phys. effects such as field emission or magnetic force microscopy. Consequently, an accurate characterization of these fields is of high interest and electron holog. tomog. (EHT) is unique in providing tomog. 3D reconstructions at nm spatial resoln. However, several limitations of the exptl. setup and the specimen itself are influencing EHT. Here, we show how a deliberate restriction of the tomog. reconstruction to the exterior of the NWs can be used to mitigate these limitations facilitating a quant. 3D tomog. reconstruction of static electromagnetic stray fields at the nanoscale. As an example, we reconstruct the electrostatic stray field around a GaAs-AlGaAs core shell NW and the magnetic stray field around a Co2FeGa Heusler compd. NW. (c) 2014 American Institute of Physics.
- 21Beleggia, M.; Kasama, T.; Larson, D.; Kelly, T.; Dunin-Borkowski, R.; Pozzi, G. Towards quantitative off-axis electron holographic mapping of the electric field around the tip of a sharp biased metallic needle. J. Appl. Phys. 2014, 116, 024305, DOI: 10.1063/1.488744821https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFeqs7bM&md5=9a790b971d1a9d94d573dd4656d3b928Towards quantitative off-axis electron holographic mapping of the electric field around the tip of a sharp biased metallic needleBeleggia, M.; Kasama, T.; Larson, D. J.; Kelly, T. F.; Dunin-Borkowski, R. E.; Pozzi, G.Journal of Applied Physics (Melville, NY, United States) (2014), 116 (2), 024305/1-024305/9CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)We apply off-axis electron holog. and Lorentz microscopy in the transmission electron microscope to map the elec. field generated by a sharp biased metallic tip. A combination of exptl. data and modeling provides quant. information about the potential and the field around the tip. Close to the tip apex, we measure a max. field intensity of 82 MV/m, corresponding to a field k factor of 2.5, in excellent agreement with theory. In order to verify the validity of the measurements, we use the inferred charge d. distribution in the tip region to generate simulated phase maps and Fresnel (out-of-focus) images for comparison with exptl. measurements. While the overall agreement is excellent, the simulations also highlight the presence of an unexpected astigmatic contribution to the intensity in a highly defocused Fresnel image, which is thought to result from the geometry of the applied field. (c) 2014 American Institute of Physics.
- 22Migunov, V.; London, A.; Farle, M.; Dunin-Borkowski, R. Model-independent measurement of the charge density distribution along an Fe atom probe needle using off-axis electron holography without mean inner potential effects. J. Appl. Phys. 2015, 117, 134301, DOI: 10.1063/1.491660922https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlslCnurs%253D&md5=2da3dc2a8aee9b40892c7346624b519eModel-independent measurement of the charge density distribution along an Fe atom probe needle using off-axis electron holography without mean inner potential effectsMigunov, V.; London, A.; Farle, M.; Dunin-Borkowski, R. E.Journal of Applied Physics (Melville, NY, United States) (2015), 117 (13), 134301/1-134301/8CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)The one-dimensional charge d. distribution along an elec. biased Fe atom probe needle is measured using a model-independent approach based on off-axis electron holog. in the transmission electron microscope. Both the mean inner potential and the magnetic contribution to the phase shift are subtracted by taking differences between electron-optical phase images recorded with different voltages applied to the needle. The measured one-dimensional charge d. distribution along the needle is compared with a similar result obtained using model-based fitting of the phase shift surrounding the needle. On the assumption of cylindrical symmetry, it is then used to infer the three-dimensional elec. field and electrostatic potential around the needle with ∼10 nm spatial resoln., without needing to consider either the influence of the perturbed ref. wave or the extension of the projected potential outside the field of view of the electron hologram. The present study illustrates how a model-independent approach can be used to measure local variations in charge d. in a material using electron holog. in the presence of addnl. contributions to the phase, such as those arising from changes in mean inner potential and specimen thickness. (c) 2015 American Institute of Physics.
- 23Phatak, C.; De Knoop, L.; Houdellier, F.; Gatel, C.; Hÿtch, M.; Masseboeuf, A. Quantitative 3D electromagnetic field determination of 1D nanostructures from single projection. Ultramicroscopy 2016, 164, 24– 30, DOI: 10.1016/j.ultramic.2016.03.00523https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlsFSkt78%253D&md5=9edcf6f872fc66b35bf6a10c93e21858Quantitative 3D electromagnetic field determination of 1D nanostructures from single projectionPhatak, C.; de Knoop, L.; Houdellier, F.; Gatel, C.; Hytch, M. J.; Masseboeuf, A.Ultramicroscopy (2016), 164 (), 24-30CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)One-dimensional (1D) nanostructures have been regarded as the most promising building blocks for nanoelectronics and nanocomposite material systems as well as for alternative energy applications. Although they result in confinement of a material, their properties and interactions with other nanostructures are still very much three-dimensional (3D) in nature. In this work, we present a novel method for quant. detn. of the 3D electromagnetic fields in and around 1D nanostructures using a single electron wave phase image, thereby eliminating the cumbersome acquisition of tomog. data. Using symmetry arguments, we have reconstructed the 3D magnetic field of a nickel nanowire as well as the 3D elec. field around a carbon nanotube field emitter, from one single projection. The accuracy of quant. values detd. here is shown to be a better fit to the physics at play than the value obtained by conventional anal. Moreover the 3D reconstructions can then directly be visualized and used in the design of functional 3D architectures built using 1D nanostructures.
- 24Beleggia, M.; Kasama, T.; Dunin-Borkowski, R. E.; Hofmann, S.; Pozzi, G. Direct measurement of the charge distribution along a biased carbon nanotube bundle using electron holography. Appl. Phys. Lett. 2011, 98, 243101, DOI: 10.1063/1.359846824https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXntlKgs7Y%253D&md5=380a7161981a1c021926ad1b0fe502a0Direct measurement of the charge distribution along a biased carbon nanotube bundle using electron holographyBeleggia, M.; Kasama, T.; Dunin-Borkowski, R. E.; Hofmann, S.; Pozzi, G.Applied Physics Letters (2011), 98 (24), 243101/1-243101/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Nanowires and nanotubes can be examd. in the transmission electron microscope under an applied bias. Here we introduce a model-independent method, which allows the charge distribution along a nanowire or nanotube to be measured directly from the Laplacian of an electron holog. phase image. We present results from a biased bundle of C nanotubes, in which we show that the charge d. increases linearly with distance from its base, reaching a value of ∼0.8 electrons/nm near its tip. (c) 2011 American Institute of Physics.
- 25Gatel, C.; Lubk, A.; Pozzi, G.; Snoeck, E.; Hÿtch, M. Counting elementary charges on nanoparticles by electron holography. Phys. Rev. Lett. 2013, 111, 025501, DOI: 10.1103/PhysRevLett.111.02550125https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXht1SntbnM&md5=84682a3988db0b54a7bc96f650234b4cCounting elementary charges on nanoparticles by electron holographyGatel, C.; Lubk, A.; Pozzi, G.; Snoeck, E.; Hytch, M.Physical Review Letters (2013), 111 (2), 025501/1-025501/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)The distribution and movement of charge is fundamental to many phys. phenomena, particularly for applications involving nanoparticles, nanostructures, and electronic devices. However, there are very few ways of quantifying charge at the necessary length scale. Here, we show that aberration-cor. electron holog. is capable of counting the charge on individual nanoparticles to a precision of one elementary unit of charge. We present a method that measures charges within predefined contours by directly applying Gauss's law at the nanoscale. We perform a statistical anal. to reveal the relationship between the size of the contours and the precision of the charge measurement and present strategies to optimize the spatial and signal resoln. for the presented method.
- 26Gan, Z.; Gu, M.; Tang, J.; Wang, C.-Y.; He, Y.; Wang, K. L.; Wang, C.; Smith, D. J.; McCartney, M. R. Direct mapping of charge distribution during lithiation of Ge nanowires using off-axis electron holography. Nano Lett. 2016, 16, 3748– 3753, DOI: 10.1021/acs.nanolett.6b0109926https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XotFKrtrg%253D&md5=35bee915db7cc0b6c87a234afc9b6846Direct Mapping of Charge Distribution during Lithiation of Ge Nanowires Using Off-Axis Electron HolographyGan, Zhaofeng; Gu, Meng; Tang, Jianshi; Wang, Chiu-Yen; He, Yang; Wang, Kang L.; Wang, Chongmin; Smith, David J.; McCartney, Martha R.Nano Letters (2016), 16 (6), 3748-3753CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The successful operation of rechargeable batteries relies on reliable insertion/extn. of ions into/from the electrodes. The battery performance and the response of the electrodes to such ion insertion and extn. are directly related to the spatial distribution of the charge and its dynamic evolution. However, it remains unclear how charge is distributed in the electrodes during normal battery operation. In this work, we have used off-axis electron holog. to measure charge distribution during lithium ion insertion into a Ge nanowire (NW) under dynamic operating conditions. We discovered that the surface region of the Ge core is neg. charged during the core-shell lithiation of the Ge NW, which is counterbalanced by pos. charge on the inner surface of the lithiated LixGe shell. The remainder of the lithiated LixGe shell is free from net charge, consistent with its metallic characteristics. The present work provides a vivid picture of charge distribution and dynamic evolution during Ge NW lithiation and should form the basis for tackling the response of these and related materials under real electrochem. conditions.
- 27Vicarelli, L.; Migunov, V.; Malladi, S.; Zandbergen, H. W.; Dunin-Borkowski, R. E. Single electron precision in the measurement of charge distributions on electrically biased graphene nanotips using electron holography. Nano Lett. 2019, 19, 4091– 4096, DOI: 10.1021/acs.nanolett.9b0148727https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXpvFKmur4%253D&md5=9c04f80261311fdbc33508aace185551Single Electron Precision in the Measurement of Charge Distributions on Electrically Biased Graphene Nanotips Using Electron HolographyVicarelli, Leonardo; Migunov, Vadim; Malladi, Sairam K.; Zandbergen, Henny W.; Dunin-Borkowski, Rafal E.Nano Letters (2019), 19 (6), 4091-4096CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)We use off-axis electron holog. to measure the electrostatic charge d. distributions on graphene-based nanogap devices that have thicknesses of between 1 and 10 monolayers and sepns. of between 8 and 58 nm with a precision of better than a single unit charge. Our exptl. measurements, which are compared with finite element simulations, show that wider graphene tips, which have thicknesses of a single monolayer at their ends, exhibit charge accumulation along their edges. The results are relevant for both fundamental research on graphene electrostatics and applications of graphene nanogaps to single nucleotide detection in DNA sequencing, single mol. electronics, plasmonic antennae, and cold field emission sources.
- 28Zheng, F.; Caron, J.; Migunov, V.; Beleggia, M.; Pozzi, G.; Dunin-Borkowski, R. E. Measurement of charge density in nanoscale materials using off-axis electron holography. J. Electron Spectrosc. Relat. Phenom. 2020, 241, 146881, DOI: 10.1016/j.elspec.2019.07.00228https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVyls7jO&md5=feb1c34a84ccd9f69f4a070382b09d38Measurement of charge density in nanoscale materials using off-axis electron holographyZheng, Fengshan; Caron, Jan; Migunov, Vadim; Beleggia, Marco; Pozzi, Giulio; Dunin-Borkowski, Rafal E.Journal of Electron Spectroscopy and Related Phenomena (2020), 241 (), 146881CODEN: JESRAW; ISSN:0368-2048. (Elsevier B.V.)Three approaches for the measurement of charge d. distributions in nanoscale materials from electron optical phase images recorded using off-axis electron holog. are illustrated through the study of an elec. biased needle-shaped sample. We highlight the advantages of using a model-based iterative algorithm, which allows a priori information, such as the shape of the object and the influence of charges that are located outside the field of view, to be taken into account. The recovered charge d. can be used to infer the elec. field and electrostatic potential.
- 29Lai, G.; Hirayama, T.; Ishizuka, K.; Tanji, T.; Tonomura, A. Three-dimensional reconstruction of electric-potential distribution in electron-holographic interferometry. Appl. Opt. 1994, 33, 829– 833, DOI: 10.1364/AO.33.00082929https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3cfktlSlsw%253D%253D&md5=5fc2faa27a7d7ed945fd33d55d2467dcThree-dimensional reconstruction of electric-potential distribution in electron-holographic interferometryLai G; Hirayama T; Ishizuka K; Tanji T; Tonomura AApplied optics (1994), 33 (5), 829-33 ISSN:1559-128X.A method of reconstructing the three-dimensional electric-potential distribution of a microscopic object with electron-holographic interferometry is presented. A sequence of processing techniques is developed to obtain the projected phase proportional to the potential distribution. A modified backprojection algorithm is used to reconstruct a three-dimensional potential distribution from the projected potentials obtained at different projection directions. In an experiment this method is applied to reconstruct three-dimensional latex particles.
- 30Simon, P.; Wolf, D.; Wang, C.; Levin, A. A.; Lubk, A.; Sturm, S.; Lichte, H.; Fecher, G. H.; Felser, C. Synthesis and three-dimensional magnetic field mapping of Co2FeGa Heusler nanowires at 5 nm resolution. Nano Lett. 2016, 16, 114– 120, DOI: 10.1021/acs.nanolett.5b0310230https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVejtb7M&md5=dcd6d273feefc31e9cd382df08308731Synthesis and Three-Dimensional Magnetic Field Mapping of Co2FeGa Heusler Nanowires at 5 nm ResolutionSimon, Paul; Wolf, Daniel; Wang, Changhai; Levin, Aleksandr A.; Lubk, Axel; Sturm, Sebastian; Lichte, Hannes; Fecher, Gerhard H.; Felser, ClaudiaNano Letters (2016), 16 (1), 114-120CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)We present the synthesis of Co2FeGa Heusler nanowires and the results of our investigations on their three-dimensional (3D) elec. and magnetic internal and external fields mapped by electron holog. tomog. (EHT). These fields will be of great importance in next-generation nanomagnets integrated in spintronics and memory devices. The Co2FeGa nanowires with a L21 ordered structure are prepd. by a SBA-15 silica-assisted method. The magnetic dipole-like stray fields of several Co2FeGa nanowires are revealed by holog. reconstructed phase images. Based on the measured magnetic phase shifts of an individual nanowire and its 3D reconstruction using EHT, we obtain an internal magnetic induction with a magnitude of 1.15 T and a nonmagnetic surface layer of 10 nm thickness. Furthermore, we also reconstruct the 3D distribution of the electrostatic potential of the same nanowire.
- 31Wolf, D.; Rodriguez, L. A.; Beche, A.; Javon, E.; Serrano, L.; Magen, C.; Gatel, C.; Lubk, A.; Lichte, H.; Bals, S.; Van Tendeloo, G.; Fernandez-Pacheco, A.; De Teresa, J. M.; Snoeck, E. 3D magnetic induction maps of nanoscale materials revealed by electron holographic tomography. Chem. Mater. 2015, 27, 6771– 6778, DOI: 10.1021/acs.chemmater.5b0272331https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVKls77J&md5=1503b9410307882f3aa437c6693776373D Magnetic Induction Maps of Nanoscale Materials Revealed by Electron Holographic TomographyWolf, Daniel; Rodriguez, Luis A.; Beche, Armand; Javon, Elsa; Serrano, Luis; Magen, Cesar; Gatel, Christophe; Lubk, Axel; Lichte, Hannes; Bals, Sara; Van Tendeloo, Gustaaf; Fernandez-Pacheco, Amalio; De Teresa, Jose M.; Snoeck, EtienneChemistry of Materials (2015), 27 (19), 6771-6778CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The study of three-dimensional (3D) ferromagnetic nanoscale materials constitutes one of the key research areas of the current magnetism roadmap and carries great potential to impact areas such as data storage, sensing, and biomagnetism. The properties of such nanostructures are closely connected with their 3-dimensional magnetic nanostructure, making their detn. highly valuable. Quant. 3-dimensional maps providing both the internal magnetic and elec. configuration of the same specimen with high spatial resoln. are missing. Here, the authors demonstrate the quant. 3-dimensional reconstruction of the dominant axial component of the magnetic induction and electrostatic potential within a Co nanowire (NW) of 100 nm in diam. with spatial resoln. <10 nm by applying electron holog. tomog. The tomogram was obtained using a dedicated TEM sample holder for acquisition, in combination with advanced alignment and tomog. reconstruction routines. The powerful approach presented here is widely applicable to a broad range of 3-dimensional magnetic nanostructures and may trigger the progress of novel spintronic nonplanar nanodevices.
- 32Wu, M.; Tafel, A.; Hommelhoff, P.; Spiecker, E. Determination of 3D electrostatic field at an electron nano-emitter. Appl. Phys. Lett. 2019, 114, 013101, DOI: 10.1063/1.505522732https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXivFyltA%253D%253D&md5=3a88af34fe14d5542fbba7aeee76d433Determination of 3D electrostatic field at an electron nano-emitterWu, Mingjian; Tafel, Alexander; Hommelhoff, Peter; Spiecker, ErdmannApplied Physics Letters (2019), 114 (1), 013101/1-013101/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Differential phase contrast in scanning transmission electron microscopy has been applied to image nanoscale electrostatic fields of a sharp tungsten electron emitter with an apex radius of about 20 nm and under field emission conditions. Assuming axial symmetry of the nano-emitter, we derived a method based on the inverse Abel transform to quant. reconstruct an axial slice of the 3D electrostatic field from a single projection measurement. The highest field strength of 2.92 V/nm is measured at the nano-emitter apex under the condition of a bias voltage of -140 V with respect to the grounded counter electrode located at about 650 nm from the apex, resulting in an emission current of more than 2 μA. The exptl. results are compared with simulations based on a finite element numerical Maxwell equation solver. Quant. agreement between expt. and simulation has been achieved. (c) 2019 American Institute of Physics.
- 33Lade, S. J.; Paganin, D.; Morgan, M. J. Electron tomography of electromagnetic fields, potentials and sources. Opt. Commun. 2005, 253, 392– 400, DOI: 10.1016/j.optcom.2005.04.07133https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXpsF2lsrc%253D&md5=8e12e3e89d77d8715489ad7a0f0e7b3cElectron tomography of electromagnetic fields, potentials and sourcesLade, S. J.; Paganin, D.; Morgan, M. J.Optics Communications (2005), 253 (4-6), 392-400CODEN: OPCOB8; ISSN:0030-4018. (Elsevier B.V.)The exit phase of an electron moving through electromagnetic potentials can, as is well known, be written as line integrals of the potentials. The use of vector tomog. to reconstruct electromagnetic potentials from such phase measurements in a transmission electron microscope is proposed. Electromagnetic fields and source distributions can similarly be reconstructed from phase gradients and Laplacians, resp. The method can recover elec. and magnetic fields independently, and requires only that the fields be magnetostatic, that the projection approxn. applies and that there not be excessive inelastic scattering. Propagation-based phase retrieval is considered as the method of measuring electron phase, giving as a useful special case the reconstruction of current densities directly from defocused electron micrographs.
- 34Mohan, K. A.; Prabhat, K.; Phatak, C.; De Graef, M.; Bouman, C. A. Iterative reconstruction of the magnetization and charge density using vector field electron tomography. Microsc. Microanal. 2016, 22, 1686– 1687, DOI: 10.1017/S1431927616009272There is no corresponding record for this reference.
- 35Matteucci, G.; Missiroli, G.; Muccini, M.; Pozzi, G. Electron holography in the study of the electrostatic fields: the case of charged microtips. Ultramicroscopy 1992, 45, 77– 83, DOI: 10.1016/0304-3991(92)90039-MThere is no corresponding record for this reference.
- 36Caron, J. Model-based reconstruction of magnetisation distributions in nanostructures from electron optical phase images. Ph.D. Thesis, RWTH Aachen University, 2017.There is no corresponding record for this reference.
- 37Oikawa, T.; Kim, J. J.; Tomita, T.; Park, H. S.; Shindo, D. Measurement of electric potential distributions around FEG-emitters by electron holography. Journal of Electron Microscopy 2007, 56, 171– 175, DOI: 10.1093/jmicro/dfm02237https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD2sjlsVeqtg%253D%253D&md5=08cc9ceb197283c48efe8c0428e390b4Measurement of electric potential distributions around FEG-emitters by electron holographyOikawa Tetsuo; Kim Joong Jung; Tomita Takeshi; Park Hyun Soon; Shindo DaisukeJournal of electron microscopy (2007), 56 (5), 171-5 ISSN:.An evaluation technique for field emission guns (FEG-emitters) was established by using electron holography. For performing electron holography under an applied voltage, a specimen holder with the capabilities of three-directional motion as well as voltage application was developed. An unused Schottky emitter and a used emitter that had failed after operating for about 10,000 h were selected for this study. By visualizing the electric potential distributions around the emitters, it was clarified that a change in the edge shape of the emitter led to the change in the strength of the electric field. The observations revealed that electron holography can be applied to evaluate the performances of the various emitters.
- 38Mandal, S.; Pradeep, K. G.; Zaefferer, S.; Raabe, D. A novel approach to measure grain boundary segregation in bulk polycrystalline materials in dependence of the boundaries’ five rotational degrees of freedom. Scripta Materialia 2014, 81, 16– 19, DOI: 10.1016/j.scriptamat.2014.02.01638https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXkslegtbs%253D&md5=ad70f1f6309d36bf14550120beef8a55A novel approach to measure grain boundary segregation in bulk polycrystalline materials in dependence of the boundaries' five rotational degrees of freedomMandal, S.; Pradeep, K. G.; Zaefferer, S.; Raabe, D.Scripta Materialia (2014), 81 (), 16-19CODEN: SCMAF7; ISSN:1359-6462. (Elsevier Ltd.)We demonstrate a simplified nondestructive 3-D electron backscatter diffraction (EBSD) methodol. that enables the measurement of all five degrees of freedom of grain boundaries (GBs) combined with segregation anal. using atom probe tomog. (APT). The approach is based on two 2-D EBSD measurements on orthogonal surfaces at a sharp edge of the specimen followed by site-specific GB compn. anal. using APT. An example of an asym. Σ9 boundary exhibiting GB segregation emphasizes the need for complete GB characterization in this context.
- 39Volkov, V.; Han, M.; Zhu, Y. Double-resolution electron holography with simple Fourier transform of fringe-shifted holograms. Ultramicroscopy 2013, 134, 175– 184, DOI: 10.1016/j.ultramic.2013.06.01839https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtF2mt73L&md5=f5d75cd6d58ca4701da1db22e44db875Double-resolution electron holography with simple Fourier transform of fringe-shifted hologramsVolkov, V. V.; Han, M. G.; Zhu, Y.Ultramicroscopy (2013), 134 (), 175-184CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)The authors propose a fringe-shifting holog. method with an appropriate image wave recovery algorithm leading to exact soln. of holog. equations. With this new method the complex object image wave recovered from holograms appears to have much less traditional artifacts caused by the autocorrelation band present practically in all Fourier transformed holograms. The new anal. solns. make possible a double-resoln. electron holog. free from autocorrelation band artifacts and thus push the limits for phase resoln. The new image wave recovery algorithm uses a popular Fourier soln. of the side band-pass filter technique, while the fringe-shifting holog. method is simple to implement in practice.
- 40Ru, Q.; Lai, G.; Aoyama, K.; Endo, J.; Tonomura, A. Principle and application of phase-shifting electron holography. Ultramicroscopy 1994, 55, 209– 220, DOI: 10.1016/0304-3991(94)90171-640https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXhvVKgsbs%253D&md5=30151f95b8614f1208fc74ec98838691Principle and application of phase-shifting electron holographyRu, Q.; Lai, G.; Aoyama, K.; Endo, J.; Tonomura, A.Ultramicroscopy (1994), 55 (2), 209-20CODEN: ULTRD6; ISSN:0304-3991.Electron holog. using an improved phase-shifting (fringe-scanning) interferometric technique is described. The improvements it makes in phase measurement, in spatial resoln. of reconstructed images and in hologram formation are clarified and demonstrated with three expts.: (1) quant. detection of at. surface steps on molybdenite crystal film, (2) topog. measurement of gold platelets epitaxially grown on a molybdenite substrate, and (3) sensitive observation of a bacterial flagellum filament.
- 41van Aarle, W.; Palenstijn, W. J.; De Beenhouwer, J.; Altantzis, T.; Bals, S.; Batenburg, K. J.; Sijbers, J. The ASTRA Toolbox: A platform for advanced algorithm development in electron tomography. Ultramicroscopy 2015, 157, 35– 47, DOI: 10.1016/j.ultramic.2015.05.00241https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXotVKhsLs%253D&md5=3712da2f93e931cb64ef3c7e65dee01eThe ASTRA Toolbox: A platform for advanced algorithm development in electron tomographyvan Aarle, Wim; Palenstijn, Willem Jan; De Beenhouwer, Jan; Altantzis, Thomas; Bals, Sara; Batenburg, K. Joost; Sijbers, JanUltramicroscopy (2015), 157 (), 35-47CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)We present the ASTRA Toolbox as an open platform for 3D image reconstruction in tomog. Most of the software tools that are currently used in electron tomog. offer limited flexibility with respect to the geometrical parameters of the acquisition model and the algorithms used for reconstruction. The ASTRA Toolbox provides an extensive set of fast and flexible building blocks that can be used to develop advanced reconstruction algorithms, effectively removing these limitations. We demonstrate this flexibility, the resulting reconstruction quality, and the computational efficiency of this toolbox by a series of expts., based on exptl. dual-axis tilt series.
- 42Jackson, J. Classical Electrodynamics; Wiley: 1998.There is no corresponding record for this reference.
- 43Tsong, T. Field penetration and band bending near semiconductor surfaces in high electric fields. Surf. Sci. 1979, 81, 28– 42, DOI: 10.1016/0039-6028(79)90503-X43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE1MXhsVCqsrw%253D&md5=951c54df431f09fdb980dab6db8a24cdField penetration and band bending near semiconductor surfaces in high electric fieldsTsong, T. T.Surface Science (1979), 81 (1), 28-42CODEN: SUSCAS; ISSN:0039-6028.The existing theory of band bending in the surface space charge region of semiconductors is adapted to problems in field emission, field ionization and field evapn. The surface field in the space charge layers of semiconductors appropriate for these phenomena ranges from ∼10-2 V/Å to a few 10-1 V/Å, similar to those encountered in many interface phenomena involving semiconductors. The surface potential resulting from band bending may amt. to a few eV. The field penetrates ∼10 Å into the semiconductor surface for intrinsic cases, and ∼200 Å for an n-type semiconductor in a pos. field, or for a p-type semiconductor in a neg. field. Both the surface potential and the field penetration will affect significantly the electronic properties of the near surface layers. In particular, the photon adsorption edge will be shifted toward the red by the field penetration effect.
- 44Zheng, F.; Pozzi, G.; Migunov, V.; Pirker, L.; Remkar, M.; Beleggia, M.; Dunin-Borkowski, R. E. Quantitative measurement of charge accumulation along a quasi-one-dimensional W5O14 nanowire during electron field emission. Nanoscale 2020, 12, 10559– 10564, DOI: 10.1039/D0NR00739K44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXktl2qsr4%253D&md5=1145c1841085c15942eb7cf574d37f5fQuantitative measurement of charge accumulation along a quasi-one-dimensional W5O14 nanowire during electron field emissionZheng, Fengshan; Pozzi, Giulio; Migunov, Vadim; Pirker, Luka; Remskar, Maja; Beleggia, Marco; Dunin-Borkowski, Rafal E.Nanoscale (2020), 12 (19), 10559-10564CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)We use an electron holog. method to det. the charge distribution along a quasi-one-dimensional W5O14 nanowire during in situ field emission in a transmission electron microscope. The results show that the continuous charge distribution along the nanowire is not linear, but that there is an addnl. accumulation of charge at its apex. An anal. expression for this addnl. contribution to the charge distribution is proposed and its effect on the field enhancement factor and emission current is discussed.
- 45Du, S.; Burgess, T.; Tjing Loi, S.; Gault, B.; Gao, Q.; Bao, P.; Li, L.; Cui, X.; Kong Yeoh, W.; Hoe Tan, H.; Jagadish, C.; Ringer, S. P.; Zheng, R. Full tip imaging in atom probe tomography. Ultramicroscopy 2013, 124, 96– 101, DOI: 10.1016/j.ultramic.2012.08.01445https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslKgu7jJ&md5=e8a68c6b474b9d077c2ca5fc05ca6cbbFull tip imaging in atom probe tomographyDu, Sichao; Burgess, Timothy; Loi, Shyeh Tjing; Gault, Baptiste; Gao, Qiang; Bao, Peite; Li, Li; Cui, Xiangyuan; Yeoh, Wai Kong; Tan, Hark Hoe; Jagadish, Chennupati; Ringer, Simon P.; Zheng, RongkunUltramicroscopy (2013), 124 (), 96-101CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)Atom probe tomog. (APT) is capable of simultaneously revealing the chem. identities and three dimensional positions of individual atoms within a needle-shaped specimen, but suffers from a limited field-of-view (FOV), i.e., only the core of the specimen is effectively detected. Therefore, the capacity to analyze the full tip is crucial and much desired in cases that the shell of the specimen is also the region of interest. In this paper, we demonstrate that in the anal. of III-V nanowires epitaxially grown from a substrate, the presence of the flat substrate positioned only micrometers away from the analyzed tip apex alters the field distribution and ion trajectories, which provides extra image compression that allows for the anal. of the entire specimen. An array of exptl. results, including field desorption maps, elemental distributions, and crystallog. features clearly demonstrate the fact that the whole tip has been imaged, which is confirmed by electrostatic simulations.
- 46Loi, S. T.; Gault, B.; Ringer, S. P.; Larson, D. J.; Geiser, B. P. Electrostatic simulations of a local electrode atom probe: The dependence of tomographic reconstruction parameters on specimen and microscope geometry. Ultramicroscopy 2013, 132, 107– 113, DOI: 10.1016/j.ultramic.2012.12.01246https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXktlOntQ%253D%253D&md5=b15d80e2ef91bbea3b19997d5e45df33Electrostatic simulations of a local electrode atom probe: The dependence of tomographic reconstruction parameters on specimen and microscope geometryLoi, Shyeh Tjing; Gault, Baptiste; Ringer, Simon P.; Larson, David J.; Geiser, Brian P.Ultramicroscopy (2013), 132 (), 107-113CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)We electrostatically model a local electrode atom probe microscope using the com. software IES LORENTZ 2D v9.0 to investigate factors affecting the reconstruction parameters. We find strong dependences on the specimen geometry and voltage, and moderate dependences on the tip-aperture sepn., which confirm that the current approach to atom probe reconstruction overlooks too many factors. Based on our data, which are in excellent agreement with known trends and exptl. results, we derive a set of empirical relations which predict the values of the reconstruction parameters. These may be used to advance current reconstruction protocols by enabling the parameters to be adjusted as the specimen geometry changes.
- 47Morgan, P. Carbon Fibers and Their Composites; CRC Press: 2005.There is no corresponding record for this reference.
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.2c03879.
Representative off-axis electron hologram, reconstructed phase images, phase contour maps, reconstructed 3D shape of the needle and parameters used for model-based iterative reconstruction (PDF)
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