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Single-Crystal Nanostructure Arrays Forming Epitaxially through Thermomechanical Nanomolding

  • Guannan Liu
    Guannan Liu
    Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States
    More by Guannan Liu
    Orcidhttps://orcid.org/0000-0002-7976-1739
  • , 
  • Sungwoo Sohn
    Sungwoo Sohn
    Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States
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  • , 
  • Naijia Liu
    Naijia Liu
    Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States
    More by Naijia Liu
  • , 
  • Arindam Raj
    Arindam Raj
    Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States
    More by Arindam Raj
    Orcidhttps://orcid.org/0000-0001-7277-6770
  • , 
  • Udo D. Schwarz
    Udo D. Schwarz
    Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States
    Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06511, United States
    More by Udo D. Schwarz
    Orcidhttps://orcid.org/0000-0002-5361-0342
  • , and 
  • Jan Schroers*
    Jan Schroers
    Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States
    *Email: [email protected]
    More by Jan Schroers
Cite this: Nano Lett. 2021, 21, 23, 10054–10061
Publication Date (Web):November 22, 2021
https://doi.org/10.1021/acs.nanolett.1c03744

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Abstract

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For nanostructures in advanced electronic and plasmonic systems, a single-crystal structure with controlled orientation is essential. However, the fabrication of such devices has remained challenging, as current nanofabrication methods often suffer from either polycrystalline growth or the difficulty of integrating single crystals with substrates in desired orientations and locations to create functional devices. Here we report a thermomechanical method for the controlled growth of single-crystal nanowire arrays, which enables the simultaneous synthesis, alignment, and patterning of nanowires. Within such diffusion-based thermomechanical nanomolding (TMNM), the substrate material diffuses into nanosized cavities under an applied pressure gradient at a molding temperature of ∼0.4 times the material’s melting temperature. Vertically grown face-centered cubic (fcc) nanowires with the [110] direction in an epitaxial relationship with the (110) substrate are demonstrated. The ability to control the crystal structure through the substrate takes TMNM a major step further, potentially allowing all fcc and body-centered cubic (bcc) materials to be integrated as single crystals into devices.

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High-quality single-crystal nanostructures of controlled orientation are critical for realizing desirable electronic and optical properties in nanomaterials and devices, as grain boundaries are often detrimental to these properties. In electronics, single-crystal nanostructures exhibit higher electrical conductivity than polycrystalline structures, (1) which suffer from grain boundary scattering. (2,3) In plasmonics, metallic nanostructures exhibit a multitude of optical resonances associated with localized surface plasmon excitations, (4) which enable a negative refractive index, (5) subwavelength resolution imaging, (6) nanolasing, (7) and field manipulation. (8) However, grain boundaries and surface roughness in plasmonic nanostructures can cause plasmon damping, which significantly increases losses in device performance. (9,10) Crystal orientation and imperfections can also affect the mechanical, (11,12) electrochemical, (13) and thermal properties. (14)
Today’s nanofabrication methods have been exploring the fabrication of single-crystal nanostructures, in response to the high demand for such structures. (15−19) Despite recent advances, these methods are still limited in critical aspects (Figure 1). For example, widely used physical vapor deposition (PVD) methods form polycrystalline structures (Figure 1b), typically with a high defect concentration. (20,21) Chemical vapor deposition (CVD) methods are limited in the choice of precursors as feedstock and often require specific catalysts and substrates for anisotropic crystal growth to form 1D nanostructures. (22,23) Another well-established nanofabrication method, solution-based chemical synthesis, suffers from impurities, a limited selection of precursor compounds, and the challenge of preventing synthesized nanocrystals from aggregation and agglomeration in liquids. (24,25) It is also challenging to integrate solution-grown nanostructures (Figure 1a) onto substrates to build 3D-functional devices. (21) In fact, today’s scalable nanofabrication methods are incapable of producing nanostructures attached to a substrate of the same material and orientation. This is in contrast with nanolithography techniques such as electron beam lithography (EBL) (26) and focused ion beam (FIB), (27) which allow the fabrication of nanowire arrays that are identically oriented and attached to a substrate (Figure 1c) but cannot be scaled to be used for practical nanofabrication. In addition, the surface layers of FIB-created structures may have implanted gallium or argon atoms that would be detrimental to device operation. (28) In summary, the presently existing approaches to nanofabrication remain deficient in the large-scale production of single-crystal nanostructures that are in an epitaxial relation to their substrates, even though such capability is crucial for realizing the advances in plasmonics and nanoelectronics envisioned above.

Figure 1

Figure 1. Current nanofabrication methods and atomic arrangement (in 2D illustration) of the nanostructures they can produce. (a) Schematic illustration of solution-based chemical synthesis and the resulting detached single-crystal nanowire. (b) Physical vapor deposition (PVD) method and the resulting nanostructure containing grain boundaries and often polycrystals. (c) Using a focused ion beam (FIB) inside a scanning electron microscope (SEM) allows the fabrication of single-crystal nanostructures integrated in the crystal of the substrate but lacks scalability.

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We have recently developed a controlled and scalable nanofabrication method called thermomechanical nanomolding (TMNM) (29−32) that holds promise for obtaining single-crystal nanostructures. TMNM exhibits high control over the size and aspect ratio of the nanowires. Nanowire arrays with aspect ratios of up to 1000 (see Figure S1, Supporting Information) and diameters down to 5 nm have been formed for a wide range of materials and structures. The nanowires’ length and diameter are limited practically by the mold dimensions, but there is no fundamental limit to these features. We have demonstrated that TMNM can be applied to a wide range of materials, including metals, alloys, and ordered phases. (29,31−33) The underlying mechanism of TMNM is based on diffusion, specifically on interface diffusion (see Figure S2 Supporting Information) for temperatures above ∼0.4TM, where TM is the melting temperature of the material. Notably, functional nanostructures fabricated by TMNM include superconductors, topological insulators, semiconductors, and phase change materials. (29) Nanowires synthesized through TMNM are almost entirely single crystals; (31) however, thus far, they have always exhibited a change in orientation and the associated multiple grains and grain boundaries in the area between the substrate material and the nanowire. The mechanisms for the observed growth direction and grain boundary formation in the nanowires are still unclear. As previously discussed, these associated grain boundaries deteriorate the performance in device applications. (2,3,9,10)
In this work, we introduce a fabrication method based on TMNM that prevents crystal reorientation and the formation of grain boundaries, resulting in the epitaxial growth of single-crystal nanowire arrays on substrates. Hence, we can form single-crystal nanostructures in a highly controllable manner that all exhibit the same crystal structure and orientation as the substrate.

Results and Discussion

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The fabrication of epitaxially grown nanowires on a substrate uses pressure and temperature (Figure 2a). TMNM involves pressing a substrate material against a mold with nanometer cavity sizes under an applied pressure p of typically p ≈ 10 to 500 MPa at a temperature of ∼0.4TM. After this molding step, the nanostructures are released by etching the mold. Representative Ag nanowire arrays that are vertically grown through TMNM are shown in Figure 2b,c, with nanowire diameters of 120 and 40 nm.

Figure 2

Figure 2. Overview of thermomechanical nanomolding (TMNM). (a) Schematic illustration of the process flow of TMNM performed in this study. A nanosized mold, for example, anodic aluminum oxide, and a flat feedstock substrate are depicted. (b,c) Morphology of the resulting vertically grown Ag nanowire arrays with nanowire diameters of 120 and 40 nm, respectively, revealed by SEM imaging at a 30° tilted angle. Nanowires with a small aspect ratio are free-standing and precisely aligned and located as shown in panel b, and nanowires with a large aspect ratio may agglomerate due to surface tension, as shown in panel c.

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Required for the epitaxial formation of nanowires is the use of a single crystal with a specific orientation as feedstock material. We observed that if this is not the case, for example, when using randomly oriented polycrystals as substrates (Figure 3a), then grains typically reorient, leading to grain boundary formation at the root of the nanowires (Figure 3b). Furthermore, a single crystal, which grows along a specific orientation, ultimately forms at a nanocavity depth that approximately coincides with the nanocavity diameter (Figure 3b). For face-centered cubic (fcc) materials, such orientation is [110]. Surprisingly, such [110] single-crystal growth is independent of the crystal orientation of the adjacent crystal in the substrate. This finding of the tendency for fcc nanowires to grow along [110] sets the requirement to use a (110) single-crystal substrate to avoid grain reorientation and associated grain boundary formation. However, because crystals tend to reorient themselves during plastic deformation under sufficient uniaxial pressure, we carried out experiments to determine under which conditions the single crystal changes its orientation and potentially forms polycrystals (Figure 3c,d and Figure 4a,b).

Figure 3

Figure 3. Orientation of nanowires with grain boundaries fabricated by TMNM. (a–d) Schematics of TMNM using polycrystalline and single-crystal substrates and the resulting microstructure and crystal orientation of the nanowires. (110) directions are denoted with red arrows. (a) Polycrystalline substrate for TMNM. (b) Crystal structure and grain orientation of a representative nanowire and its adjacent substrate area after processing in panel a. The nanowire grows along the (110) direction but forms grain boundaries at the root. (c) (110) single-crystal substrate exposed to a “high”-pressure ph during TMNM, where “high” means that ph is larger than the reorientation pressure of the crystal orientation. (d) Crystal structure and grain orientation of a representative nanowire and its adjacent substrate area after processing in panel c. Because of the acting “high” pressure ph, the (110) substrate reorients to (111). Because the growth direction deeper within the nanocavity is along (110), grain boundaries are forming at the root of the nanowire. (e) Transmission electron microscopy (TEM) image of a 40 nm nanowire with the polycrystalline root region. (f) TEM image from the area marked by the dashed red rectangle in panel e revealing the grain boundaries and multiple grains with different crystallographic orientations at the root of the nanowire. (See the original TEM image in Figure S3, Supporting Information.) (g) High-resolution TEM image from the area indicated in panel f by the yellow square showing lattice fringes with the (110) orientation along the growth direction. (h) Selected area electron diffraction (SAED) pattern obtained within the region enclosed by the dashed white circle in panel e, revealing that the nanowire root is polycrystalline. (i,j) High-magnification TEM images covering the regions within the blue and orange squares in panel f showing well-developed grain boundaries at the root of the nanowire. (See the original and additional TEM images in Figure S3, Supporting Information.)

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Figure 4

Figure 4. TEM characterization of single-crystal nanostructures fabricated by TMNM. (a,b) Schematics of TMNM using a single-crystal substrate and the resulting structure of nanowires. The [110] direction is denoted with a red arrow. (a) (110) single-crystal substrate under “low” pressure pl during TMNM. (b) Crystal structure and grain orientation of a representative nanowire and its adjacent substrate area after processing. If pl is below the reorientation threshold, then nanowires of the same [110] orientation grow from the (110) single-crystal substrate in an epitaxial relationship. (c) TEM image of a 40 nm single-crystal nanowire. (d) TEM image from the selected region in yellow in panel c revealing an absence of polycrystals and grain boundaries at the root of the nanowire. (e–h) SAED patterns from four sections of the nanowire in panel c, revealing that the sample is a face-centered cubic (fcc) single crystal. (See Figure S5 in the Supporting Information for the indexing.) Scale bar: 10 1/nm. (i–l) High-resolution TEM images from the regions marked in panel d in blue and orange (i,k) and further magnifications into the areas highlighted with the white dashed square (j,l), showing lattice fringes with (110) orientation along the growth direction of the nanowire.

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Crystallographic characterization via transmission electron microscopy (TEM) was used to reveal the structure of the nanowires. When using a (110) single-crystal substrate at high pressure (e.g., 500 MPa), we observed that grain reorientation takes place in both the substrate material and the nanowire. Consequently, an undesired polycrystalline structure at the nanowire’s root forms (Figure 3e–j). We propose that observed polycrystal formation at the root of the nanocavity originates from a pressure-induced reorientation of the substrate material adjacent to the nanocavity from [110] to [111]. Because the material in the nanocavity prefers to grow along the [110] direction, reorientation is required. The reorientation is accomplished by the formation of multiple grains, which gradually change their orientation such that their [110] direction, indicated by the red arrow, is eventually lined up with the nanocavity. Because the reorientation of the substrate toward [111] is pressure-induced, the use of a pressure below the material’s reorientation pressure is required to prevent reorientation. Using such a “low” pressure of ∼80 MPa, nanowires of the same [110] orientation as the (110) single-crystal substrate grow in an epitaxial manner and relationship (Figure 4c,d). Selected area electron diffraction (SAED) patterns (Figure 4e,h) from four different locations of the nanowire reveal the same [110] patterns and orientations, confirming that the nanowire is an fcc single crystal. High-resolution TEM images (Figure 4i–l) of the Ag nanowire body show clear lattice fringes representing (110) planes along the nanowire’s length. The spacing between fringes is 0.289 nm (±5% error), which precisely matches the expected spacing between (110) planes in the fcc Ag lattice. Additional high-resolution TEM images of the nanowire root and the indexed SAED patterns can be found in Figures S4 and S5 of the Supporting Information.
We explain the preferred [110] growth direction of Ag nanowires by a lower surface energy γ of the nanowire when growing along [110] (Figure 5b). Because nanowires have a large surface-to-volume ratio, the surface energy plays an important role. (34) Surface energies for different crystallographic planes vary on an fcc crystal structure, and for its three low-index surfaces (100), (111), and (110), its relative strengths are γ(111) < γ(100) < γ(110). (35,36) For example, for Ag, the surface energies are 0.713 J/m2 for {111} planes, 0.752 J/m2 for {100} planes, and 0.833 J/m2 for {110} planes. (35) Thereby, {111}-type planes have the lowest surface energy among all existing planes in an fcc crystal due to their close-packed atomic arrangement. Hence, to reduce the surface energy, an fcc nanowire prefers to orient itself so that as much of its surface area as possible represents {111} planes, which requires growth along a ⟨110⟩ direction, the close-packed direction on {111} planes. Note that to form a “prism”-like overall shape (Figure 5e), at least two of the terminating surfaces need to be of {100} type, which is the surface with the second-lowest surface energy in an fcc crystal. During TMNM, however, the nanowires are more likely trying to grow as cylinders to adopt to the largely spherical shape of the mold. To reduce the surface energy, the nanowire can then form alternating {111} and {100} surfaces as side walls to achieve the appearance of a “round” cross-section (Figure 5f). In contrast, nanowires formed with (100)- or (111)-terminated feedstock substrates would need to have, at least partially, walls with higher Miller indices and thus higher surface energies. Another advantage of terminating as much of the nanowire’s surface with {111}-type planes as possible is that they have the lowest activation energy barrier of single adatom hopping among different surface facets of fcc materials, (37) which better facilitates interface diffusion as compared with any other surface termination and consequently promotes nanowire growth during TMNM. To realize such orientation of the nanowire surfaces formed through TMNM, crystal reorientation and hence grain boundary formation are required unless the substrate is already of {110} type. To estimate when the formation of a grain boundary to enable the reorientation of the nanowire toward [110] is energetically favored, we calculate the energy of a nanowire–substrate system with the nanowire growing along a random non-⟨110⟩ direction (Figure 5a), which gives
(1)
where γav is the average surface energy that the many different (hkl) planes that must form the nanowire’s round walls would feature (with γav > γ(111)), r is the nanowire radius, and L is the nanowire length. We compare this energy to the energy of a system where the nanowire grows along a ⟨110⟩ direction, including a grain boundary (Figure 5b), to consider the required change of orientation
(2)
Here γ(111) is the surface energy of the (111) plane, and γGB is the grain boundary energy. Note that this calculation will slightly underestimate the nanowire’s surface energy, as some {100}-type surfaces will also be present. However, this underestimation is not too significant, as {100} planes feature the second lowest surface energies of all surface terminations possible in an fcc crystal, with γ(100) being only 5.5% larger than γ(111) for Ag. Consequently, the overall deviation of E2 from the actual value can be estimated to be <2.75%. An energetic preference for the [110] growth direction requires E2 < E1. This is the case when L > Lc, where Lc is the critical length. We can obtain Lc from eq 1 = eq 2
(3)
Going forward, we now use values for γ(111) of 0.713 J/m2, γ(100) of 0.752 J/m2, γ(210) of 0.87 J/m2, and γGB of 0.21 J/m2. (35,38) (See Table S1, Supporting Information.) If the nanowire does not already grow in a ⟨110⟩ direction, then γav cannot be lower than γ(100). Identifying γav with γ(100), we get Lc ≈ 4.4r. It is, however, more likely that γav will be higher than that, so choosing γav = γ(210) as a more realistic value causes Lc to already drop to 0.3r. This comparison of energies explains the polycrystalline structure at the nanowire roots as a consequence of the nanowire’s tendency to adjust its original crystal orientation, given by the crystal orientation in the substrate to the energetically preferred ⟨110⟩ growth direction. Therefore, for the formation of ⟨110⟩ single-crystal nanowires epitaxially grown from the substrate, it is imperative that the substrate also exhibits a ⟨110⟩ orientation to avoid polycrystallinity and associated grain boundary formation.

Figure 5

Figure 5. Mechanisms of grain reorientation in the substrate and in the nanowire. (a) Schematics of two unknown crystallographic orientations in the feedstock substrate and the nanowire of a typical nanowire-substrate system under uniaxial pressure. (b) Surface energy comparison among three different substrate–nanowire systems: randomly oriented substrate and nanowire along a random growth direction, randomly oriented substrate and nanowire along the [110] growth direction including a grain boundary, and (110) substrate and nanowire along the [110] growth direction. Surface I refers to a termination with a combination of various mostly non-{111} and non-{100} (hkl) planes, and surface II refers to a termination by a combination of {111} and {100} planes. (c) Rotation of a (110) plane under compression, which results in a polycrystalline substrate with {111} planes as the dominant orientation. (d) X-ray diffraction characterization of the Ag substrate before and after TMNM (experimental conditions: p = 1.3 GPa, T = 0.6TM, t = 30 s), revealing a structural change from a (110) single-crystal to a (111)-dominant polycrystal. (e) Perspective representation of a hexagonal prism-shaped fcc single-crystal nanowire that grows along the [110] direction with {111} and {100} surfaces as the side walls. (f) Schematic illustration of the atomic arrangement on the cross-section of a cylinder-shaped fcc (110) single-crystal nanowire. Zoom on the outer surface of the nanowire shows alternating {111}/{100} surfaces as side walls to achieve the appearance of a “round” shape.

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It is also important to consider that in general, a single-crystal substrate is prone to become polycrystalline with grains of different orientations during the application of a uniaxial pressure (Figure 5c). This behavior originates from plastic deformation owing to dislocation slip, grain boundary formation, and grain rotation. (39,40) This phenomenon has been confirmed by X-ray diffraction (XRD) measurements (Figure 5d) on the Ag substrate material before and after TMNM, revealing the structural change from a (110) single-crystal to a polycrystal with {111} planes as the dominant crystallographic orientation. This preferred orientation may also originate from lowering of the surface energy. For the experimental conditions under which TMNM is carried out, reorientation in the substrate is kinetically enabled by the combination of pressure and temperature providing the energy required for atoms to rearrange in significant numbers toward a more low-energy state, and hence lowering the processing pressure can prevent such reorientation from occurring. Therefore, to enable the epitaxial growth of a nanowire on the substrate, the processing pressure must be below the reorientation pressure to prevent crystal reorientation toward {111} crystals in the substrate. (See Figure S6 in the Supporting Information for the XRD characterization on (110) Ag substrate before and after TMNM under “low” pressure.) We identified the reorientation pressure to be approximately three times the yield stress in the case of Ag nanowires.
Within this work, we have focused on epitaxially grown single-crystal Ag nanostructures on a single-crystal Ag substrate. We choose Ag because it is a representative fcc material. Because our mechanistic descriptions only use information about the atomic structure, the same behavior should manifest for other fcc materials. As a result, we expect that the technique can be applied to the nanofabrication of all fcc materials.
Finally, a similar mechanism should be present for body-centered cubic (bcc) materials. (See Figure S7, Supporting Information.) In a bcc structure, {110} planes have the lowest surface energy. (41) Therefore, to reduce the surface energy of the system, a bcc nanowire orients itself so that its surfaces are {110} surfaces. This requires the nanowire to grow along a ⟨111⟩ direction, the close-packed direction on {110} planes. Therefore, epitaxial growth of any bcc single-crystal nanowire array via TMNM can be expected when a pressure below the reorientation pressure and a (111) substrate are used.

Conclusions

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The controlled fabrication of vertically aligned single-crystal nanowire arrays epitaxially grown on the substrate material is demonstrated via diffusion-based TMNM. The requirement for the epitaxial growth of single-crystal nanowires on a substrate is that the crystal orientations in the substrate and wire are identical. The crystal orientation in fcc nanowires prefers to be along the [110] direction, which is motivated by achieving the lowest possible surface energy of the associated side walls, which for [110] is {111} with some {100} in between to achieve an overall round shape of the wire. As a consequence, the formation of an fcc single crystal that continues from the substrate into the nanowire requires the use of a (110)-oriented single-crystal substrate, but because (110) single-crystal substrates tend to reorient toward the {111}-type under high pressure, the pressure exerted during formation must be limited to below the reorientation pressure to avoid reorientation and grain boundary formation. Because the formation motifs and orientation selections only depend on crystallographic-specific symmetries, we expect the method to be applicable to any fcc material. Our estimations also predict vertically aligned single-crystal bcc nanowire arrays along [111] epitaxially grown on a (111) substrate material. This suggests that most materials can be fabricated through this method as single-crystal nanowire arrays including technologically interesting materials such as magnetic materials, heterosystems, and a wide range of quantum materials. This very practical and self-regulating technique provides new insights and a new route for the nanofabrication of single-crystal structures and holds promise for the large-scale fabrication of high-performance nanoelectronic and plasmonic devices.

Methods

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Sample Preparation

Polycrystalline and single-crystal Ag samples were prepared for nanomolding. High-purity polycrystal Ag (99.99+% in purity, from Alfa Aesar) and (110) single-crystal Ag substrates (99.999% in purity, one side optical polished <30 Å, from MTI Corporation) were cut into 2.5 mm × 2.5 mm × 0.5 mm rectangular plates. The samples were then finely polished as needed.

Thermomechanical Nanomolding

Prepared feedstock samples were pressed against anodic aluminum oxide (AAO) molds (from InRedox) at a certain pressure and processing temperature using an Instron universal testing system equipped with heating plates. The load was applied over a period of 10 min and then held for a fixed period of time. After molding, AAO molds can be etched away in 20 wt % KOH or 10 wt % phosphoric acid at room temperature for 10 h to obtain free-standing nanowire arrays.

Characterization

The length and morphology of vertically grown Ag nanowire arrays were characterized by scanning electron microscopy (SEM) using a Hitachi SU-70 analytical field emission SEM at a voltage of 10 kV. TEM was performed using an FEI Tecnai Osiris 200 kV TEM to characterize the structure of Ag nanowires. Before TEM characterization, a portion of the sample (including the substrate material, nanowires, and mold) was lifted out using a Helios G4 UX DualBeam FIB/SEM system secured on a copper-based TEM grid. The sample was thinned to ∼50 nm. The crystal orientation of the Ag substrates before and after TMNM was evaluated by X-ray diffraction with a Rigaku SmartLab X-ray diffractometer using Bragg–Brentano focusing, Cu Kα radiation, and a 2 mm beam mask.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.1c03744.

  • Supplementary Text Sections 1−3: Diffusion Mechanisms of TMNM, Preferred Growth Direction Calculation for bcc Materials, and Reorientation Mechanism of the Substrate. Supplementary Figures S1–S7. Supplementary Table S1. Supplementary References (PDF)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Author
    • Jan Schroers - Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States;  Email: [email protected]
  • Authors
    • Guannan Liu - Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States;  Orcidhttps://orcid.org/0000-0002-7976-1739
    • Sungwoo Sohn - Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States
    • Naijia Liu - Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States
    • Arindam Raj - Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States;  Orcidhttps://orcid.org/0000-0001-7277-6770
    • Udo D. Schwarz - Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States;  Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06511, United States;  Orcidhttps://orcid.org/0000-0002-5361-0342
  • Author Contributions

    J.S. and G.L. conceived the project. G.L. designed and conducted the experiments. G.L. conducted the SEM, XRD, and FIB characterization. S.S. and G.L. performed the TEM characterization. All authors contributed to the discussion of the results and the writing of the manuscript. All authors have given approval to the final version of the manuscript.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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We thank Dr. Min Li and Dr. Yujun Xie for their help with the FIB. This work was supported by the National Science Foundation through the Advanced Manufacturing Program (CMMI 1901613).

References

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    Applied Physics Letters (2006), 89 (11), 114102/1-114102/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    The elec. cond. and temp. coeff. of resistance of polycryst. Pt nanofilms were investigated exptl. and theor. These elec. properties were greatly reduced mainly by grain boundary scattering. By applying the theory of Mayadas and co-workers [Appl. Phys. Lett. 14, 345 (1969); Phys. Rev. B 1, 1382 (1970)] to predict the elec. cond. and temp. coeff. of resistance with the same reflection coeff., however, obvious discrepancies have been found. These discrepancies indicate that Drude's relation for bulk metals cannot be applied directly in the nanosized grain interior of polycryst. metallic films.
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  3. 3
    Sciacca, B.; van de Groep, J.; Polman, A.; Garnett, E. C. Solution-Grown Silver Nanowire Ordered Arrays as Transparent Electrodes. Adv. Mater. 2016, 28, 905– 909,  DOI: 10.1002/adma.201504045
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    3
    Solution-Grown Silver Nanowire Ordered Arrays as Transparent Electrodes
    Sciacca, Beniamino; van de Groep, Jorik; Polman, Albert; Garnett, Erik C.
    Advanced Materials (Weinheim, Germany) (2016), 28 (5), 905-909CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The authors high-quality silver nanowire networks fabricated by a combination of soft-imprint lithog. and soft-soln. processing (Tollens' reaction). This relatively simple method yields ordered metal nanowire grids as transparent electrodes, without the need for energy intensive vacuum metal evapn. processes. The soln. process, combined with a short RTA treatment, yields superior performance compared to the thermally evapd. networks. This important result shows that soln.-based methods can lead to material quality comparable or even superior to vacuum based deposition methods, in contrast with common assumptions. The the lower material resistance is due to the larger av. grain size, which decreases electron scattering from grain boundaries. The simplicity of this soln. approach can be extended to other types of template-assisted metal nanowire network transparent electrodes, thus providing a general pathway for further improvement of transparent conductor performance at low cost.
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  4. 4
    Henzie, J.; Lee, J.; Lee, M. H.; Hasan, W.; Odom, T. W. Nanofabrication of Plasmonic Structures. Annu. Rev. Phys. Chem. 2009, 60, 147– 165,  DOI: 10.1146/annurev.physchem.040808.090352
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    Nanofabrication of plasmonic structures
    Henzie, Joel; Lee, Jeunghoon; Lee, Min Hyung; Hasan, Warefta; Odom, Teri W.
    Annual Review of Physical Chemistry (2009), 60 (), 147-165CODEN: ARPLAP; ISSN:0066-426X. (Annual Reviews Inc.)
    This review focuses on nanofabrication tools, based on soft lithog., which can generate a wide range of noble-metal structures with exceptional optical properties. These techniques offer a scalable and practical approach for producing arrays of complementary plasmonic structures (nanoholes and nanoparticles) and, in addn., expand the possible architectures of plasminic materials because the metal building blocks can be organized over multiple length scales. We describe the prepn. and characterization of five different systems: subwavelength nanohole arrays, finite arrays of nanoholes, microscale arrays of nanoholes, multiscale arrays of nanoparticles, and pyramidal particles. We also discuss how the surface plasmon resonances of these structures can be tuned across visible and near-IR wavelengths by varying different parameters. Applications and future prospects of these nanostructured metals are addressed.
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  5. 5
    Liu, N.; Guo, H. C.; Fu, L. W.; Kaiser, S.; Schweizer, H.; Giessen, H. Three-dimensional photonic metamaterials at optical frequencies. Nat. Mater. 2008, 7, 31– 37,  DOI: 10.1038/nmat2072
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    Three-dimensional photonic metamaterials at optical frequencies
    Liu, Na; Guo, Hongcang; Fu, Liwei; Kaiser, Stefan; Schweizer, Heinz; Giessen, Harald
    Nature Materials (2008), 7 (1), 31-37CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    Metamaterials are artificially structured media with unit cells much smaller than the wavelength of light. They proved to possess novel electromagnetic properties, such as neg. magnetic permeability and neg. refractive index. This enables applications such as neg. refraction, superlensing and invisibility cloaking. Although the phys. properties can already be demonstrated in 2-dimensional (2D) metamaterials, the practical applications require 3-dimensional bulk-like structures. This prerequisite was achieved in the gigahertz range for microwave applications owing to the ease of fabrication by simply stacking printed circuit boards. In the optical domain, such an elegant method was the missing building block towards the realization of 3-dimensional metamaterials. Here, the authors present a general method to manuf. 3-dimensional optical (IR) metamaterials using a layer-by-layer technique. Specifically, the authors introduce a fabrication process involving planarization, lateral alignment and stacking. The authors demonstrate stacked metamaterials, study the interaction between adjacent stacked layers and analyze the optical properties of stacked metamaterials with respect to an increasing no. of layers.
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    Zhang, X.; Liu, Z. W. Superlenses to overcome the diffraction limit. Nat. Mater. 2008, 7, 435– 441,  DOI: 10.1038/nmat2141
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    6
    Superlenses to overcome the diffraction limit
    Zhang, Xiang; Liu, Zhaowei
    Nature Materials (2008), 7 (6), 435-441CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    A review. The imaging resoln. of conventional lenses is limited by diffraction. Artificially engineered metamaterials now offer the possibility of building a superlens that overcomes this limit. The authors review the physics of such superlenses and the theor. and exptl. progress in this rapidly developing field. Superlenses have great potential in applications such as biomedical imaging, optical lithog. and data storage. The resoln. of conventional optical instruments is limited to length scales of roughly the wavelength of the light used. Nanoscale superlenses offer a soln. for achieving much higher resolns. that may find appllications in many imaging areas.
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  7. 7
    Zhou, W.; Dridi, M.; Suh, J. Y.; Kim, C. H.; Co, D. T.; Wasielewski, M. R.; Schatz, G. C.; Odom, T. W. Lasing action in strongly coupled plasmonic nanocavity arrays. Nat. Nanotechnol. 2013, 8, 506– 511,  DOI: 10.1038/nnano.2013.99
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    Lasing action in strongly coupled plasmonic nanocavity arrays
    Zhou, Wei; Dridi, Montacer; Suh, Jae Yong; Kim, Chul Hoon; Co, Dick T.; Wasielewski, Michael R.; Schatz, George C.; Odom, Teri W.
    Nature Nanotechnology (2013), 8 (7), 506-511CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
    Periodic dielec. structures are typically integrated with a planar waveguide to create photonic band-edge modes for feedback in one-dimensional distributed feedback lasers and two-dimensional photonic-crystal lasers. Although photonic band-edge lasers are widely used in optics and biol. applications, drawbacks include low modulation speeds and diffraction-limited mode confinement. In contrast, plasmonic nanolasers can support ultrafast dynamics and ultrasmall mode vols. However, because of the large momentum mismatch between their nanolocalized lasing fields and free-space light, they suffer from large radiative losses and lack beam directionality. Here, we report lasing action from band-edge lattice plasmons in arrays of plasmonic nanocavities in a homogeneous dielec. environment. We find that optically pumped, two-dimensional arrays of plasmonic Au or Ag nanoparticles surrounded by an org. gain medium show directional beam emission (divergence angle <1.5° and linewidth <1.3 nm) characteristic of lasing action in the far-field, and behave as arrays of nanoscale light sources in the near-field. Using a semi-quantum electromagnetic approach to simulate the active optical responses, we show that lasing is achieved through stimulated energy transfer from the gain to the band-edge lattice plasmons in the deep subwavelength vicinity of the individual nanoparticles. Using femtosecond-transient absorption spectroscopy, we verified that lattice plasmons in plasmonic nanoparticle arrays could reach a 200-fold enhancement of the spontaneous emission rate of the dye because of their large local d. of optical states.
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    Pendry, J. B.; Schurig, D.; Smith, D. R. Controlling electromagnetic fields. Science 2006, 312, 1780– 1782,  DOI: 10.1126/science.1125907
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    Controlling Electromagnetic Fields
    Pendry, J. B.; Schurig, D.; Smith, D. R.
    Science (Washington, DC, United States) (2006), 312 (5781), 1780-1782CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Using the freedom of design that metamaterials provide, we show how electromagnetic fields can be redirected at will and propose a design strategy. The conserved fields-elec. displacement field D, magnetic induction field B, and Poynting vector B-are all displaced in a consistent manner. A simple illustration is given of the cloaking of a proscribed vol. of space to exclude completely all electromagnetic fields. Our work has relevance to exotic lens design and to the cloaking of objects from electromagnetic fields.
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  9. 9
    Bosman, M.; Zhang, L.; Duan, H. G.; Tan, S. F.; Nijhuis, C. A.; Qiu, C. W.; Yang, J. K. W. Encapsulated Annealing: Enhancing the Plasmon Quality Factor in Lithographically-Defined Nanostructures. Sci. Rep. 2015, 4, 1– 6,  DOI: 10.1038/srep05537
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    There is no corresponding record for this reference.
  10. 10
    Park, J. H.; Ambwani, P.; Manno, M.; Lindquist, N. C.; Nagpal, P.; Oh, S. H.; Leighton, C.; Norris, D. J. Single-Crystalline Silver Films for Plasmonics. Adv. Mater. 2012, 24, 3988– 3992,  DOI: 10.1002/adma.201200812
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    Single-Crystalline Silver Films for Plasmonics
    Park, Jong Hyuk; Ambwani, Palak; Manno, Michael; Lindquist, Nathan C.; Nagpal, Prashant; Oh, Sang-Hyun; Leighton, Chris; Norris, David J.
    Advanced Materials (Weinheim, Germany) (2012), 24 (29), 3988-3992, S3988/1-S3988/13CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Epitaxially grown Ag films can provide several key benefits for plasmonics. Using a std. d.c. magnetron sputtering system, single-cryst. films can be easily obtained that are extremely flat over large areas. Because this flatness occurs on both sides, these films have previously been shown to be useful for devices that use long-range plasmonic waveguides or extraordinary optical transmission. The metallic films also exhibit an improved dielec. function with higher cond. and lower optical absorption compared to polycryst. films. This can increases the surface plasmon polariton propagation length. Also, when the epitaxial films are patterned via FIB milling, precise single-cryst. nanostructures can be obtained. The resulting films can therefore allow the fabrication of plasmonic devices with enhanced performance.
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  11. 11
    Cao, A.; Wei, Y.; Ma, E. Grain boundary effects on plastic deformation and fracture mechanisms in Cu nanowires: Molecular dynamics simulations. Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 77, 195429,  DOI: 10.1103/PhysRevB.77.195429
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    11
    Grain boundary effects on plastic deformation and fracture mechanisms in Cu nanowires: Molecular dynamics simulations
    Cao, Ajing; Wei, Yueguang; Ma, En
    Physical Review B: Condensed Matter and Materials Physics (2008), 77 (19), 195429/1-195429/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    Metal nanowires often contain grain boundaries which are expected to affect mech. properties significantly. According to mol. dynamics simulations, polycryst. Cu nanowires exhibit a tensile deformation behavior distinctly different from that of their single-crystal counterparts. A significantly lowered yield strength was obsd. as a result of dislocation emission from grain boundaries rather than from free surfaces, despite of the high surface to vol. ratio. Necking starts from the grain boundary followed by fracture, which results in decreased tensile ductility. The high stresses found in the grain boundary region clearly play a dominant role in controlling both inelastic deformation and fracture processes in nanowires. These findings have implications for designing stronger and more ductile structures and devices on a nanoscale.
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  12. 12
    Greer, J. R.; Jang, D.; Gu, X. W. Exploring deformation mechanisms in nanostructured materials. JOM 2012, 64, 1241– 1252,  DOI: 10.1007/s11837-012-0438-6
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    12
    Exploring deformation mechanisms in nanostructured materials
    Greer, Julia R.; Jang, Dongchan; Gu, X. Wendy
    JOM (2012), 64 (10), 1241-1252CODEN: JOMMER; ISSN:1047-4838. (Springer)
    A review. Useful properties of structural materials generally depend on their bulk microstructure. For centuries, improvements in structural materials relied heavily on processing, which in turn detd. the resulting microstructure and properties. Materials sciences are entering an era in which specific properties of a material are obtained not only from its processing but also by controlling of the architecture of its constituents, often with sub-micron dimensions. To utilize this newly achievable nanoscale engineering precision in structural applications, it is imperative to quantify the deformation processes at each relevant scale, with special attention focusing on the importance of internal and external heterogeneities, for example grain boundaries, bi-material interfaces, phase boundaries, etc., on mech. loading. It was shown for single crystals that yield (and fracture) strengths increase with power-law dependence on sample size redn. when the micron scale is reached, and therefore, can no longer be inferred from bulk response or from the literature. Although these studies provide a powerful foundation for fundamental deformation processes operating at small scales, they are far from representing real materials used in structural applications, whose microstructure is often complex, contg. boundaries and interfaces. Both homogeneous (i.e. grain and twin boundaries) and heterogeneous (i.e. phase and ppt.-matrix boundaries) interfaces in size-limited features are crucial aspects of the structural reliability of most modern materials. They are also of particular importance to damage initiation. This article provides a comprehensive overview of the state-of-the-art exptl. and computational methods used to investigate mech. behavior and microstructural evolution in small-scale metallic systems, deformation of which depends on intricate interactions of defects with internal interfaces and with free surfaces. Attention is focused on the effects of multiple grain boundaries spanning the sample vol. (nanocryst. and polycryst. metals). This overview sheds light on the relative importance of intrinsic vs. extrinsic length scale limitations on deformation mechanisms in nanostructured metals, which has significant implications for the development of new materials with tunable mech. properties.
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  13. 13
    Borkowska, Z.; Tymosiak-Zielinska, A.; Shul, G. Electrooxidation of methanol on polycrystalline and single crystal gold electrodes. Electrochim. Acta 2004, 49, 1209– 1220,  DOI: 10.1016/j.electacta.2003.09.046
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    13
    Electrooxidation of methanol on polycrystalline and single crystal gold electrodes
    Borkowska, Z.; Tymosiak-Zielinska, A.; Shul, G.
    Electrochimica Acta (2004), 49 (8), 1209-1220CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Science B.V.)
    Oxidn. of methanol has been investigated on polycryst. and single crystal gold electrodes: Au(poly), Au(111) and Au(210), in acidic, neutral and alk. solns. As expected, catalytic activity of gold towards methanol oxidn. increases with increasing pH of the soln. It has been found that in all studied solns. methanol is oxidized in two potential regions, prior to gold surface oxide monolayer formation and in more pos. potentials, on gold surface oxide after so called "turn over". Surface structure of the electrode has little influence on the oxidn. current, however potentials at which oxidn. is obsd. depends on the crystallog. orientation. The mechanism of electro-oxidn. of methanol on gold is discussed.
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  14. 14
    Zhang, Q. G.; Cao, B. Y.; Zhang, X.; Fujii, M.; Takahashi, K. Influence of grain boundary scattering on the electrical and thermal conductivities of polycrystalline gold nanofilms. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 74, 134109,  DOI: 10.1103/PhysRevB.74.134109
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    14
    Influence of grain boundary scattering on the electrical and thermal conductivities of polycrystalline gold nanofilms
    Zhang, Q. G.; Cao, B. Y.; Zhang, X.; Fujii, M.; Takahashi, K.
    Physical Review B: Condensed Matter and Materials Physics (2006), 74 (13), 134109/1-134109/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    The elec. and thermal conductivities of polycryst. Au nanofilms were measured simultaneously by a d.c. heating method, and the measured results are compared with the Mayadas and Shatzkes theory. The reduced elec. and thermal conductivities of Au nanofilms are strongly dominated by grain boundary scattering. The reflection coeff. of electrons striking the grain boundaries for charge transport is 0.7, which agrees well with a previous scanning tunneling potentiometry study. The reflection coeff. for thermal transport, however, is only 0.25. The Lorenz nos. for the polycryst. Au nanofilms, which are calcd. from the measured elec. and thermal conductivities, are much greater than the value predicted by the Wiedemann-Franz law for the bulk material. The electron scatterings on the grain boundaries impose different influences on the charge and heat transport in the polycryst. Au nanofilms. A model of effective d. of conduction electrons was utilized to interpret the violation of the Wiedemann-Franz law in polycryst. Au nanofilms.
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  15. 15
    Butburee, T.; Bai, Y.; Wang, H. J.; Chen, H. J.; Wang, Z. L.; Liu, G.; Zou, J.; Khemthong, P.; Lu, G. Q. M.; Wang, L. Z. 2D Porous TiO2 Single-Crystalline Nanostructure Demonstrating High Photo-Electrochemical Water Splitting Performance. Adv. Mater. 2018, 30, 1705666,  DOI: 10.1002/adma.201705666
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    There is no corresponding record for this reference.
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    Choi, S. H.; Kim, H. J.; Song, B.; Kim, Y. I.; Han, G.; Nguyen, H. T. T.; Ko, H.; Boandoh, S.; Choi, J. H.; Oh, C. S.; Cho, H. J.; Jin, J. W.; Won, Y. S.; Lee, B. H.; Yun, S. J.; Shin, B. G.; Jeong, H. Y.; Kim, Y. M.; Han, Y. K.; Lee, Y. H.; Kim, S. M.; Kim, K. K. Epitaxial Single-Crystal Growth of Transition Metal Dichalcogenide Monolayers via the Atomic Sawtooth Au Surface. Adv. Mater. 2021, 33, 2006601,  DOI: 10.1002/adma.202006601
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    16
    Epitaxial Single-Crystal Growth of Transition Metal Dichalcogenide Monolayers via the Atomic Sawtooth Au Surface
    Choi, Soo Ho; Kim, Hyung-Jin; Song, Bumsub; Kim, Yong In; Han, Gyeongtak; Nguyen, Huong Thi Thanh; Ko, Hayoung; Boandoh, Stephen; Choi, Ji Hoon; Oh, Chang Seok; Cho, Hyun Je; Jin, Jeong Won; Won, Yo Seob; Lee, Byung Hoon; Yun, Seok Joon; Shin, Bong Gyu; Jeong, Hu Young; Kim, Young-Min; Han, Young-Kyu; Lee, Young Hee; Kim, Soo Min; Kim, Ki Kang
    Advanced Materials (Weinheim, Germany) (2021), 33 (15), 2006601CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Growth of 2D van der Waals layered single-crystal (SC) films is highly desired not only to manifest the intrinsic phys. and chem. properties of materials, but also to enable the development of unprecedented devices for industrial applications. The SC growth of TMdC monolayers on a cm scale via the at. sawtooth Au surface as a universal growth template is reported. The at. tooth-gullet surface is constructed by the 1-step solidification of liq. Au, evidenced by TEM. The anisotropic adsorption energy of the TMdC cluster, confirmed by d. functional calcns., prevails at the periodic at.-step edge to yield unidirectional epitaxial growth of triangular TMdC grains, eventually forming the SC film, regardless of the Miller indexes. Growth using the at. sawtooth Au surface as a universal growth template is demonstrated for several transition metal dichalcogenide (TMdC) monolayer films, including WS2, WSe2, MoS2, the MoSe2/WSe2 heterostructure, and W1-xMoxS2 alloys. This strategy provides a general avenue for the SC growth of diat. van der Waals heterostructures on a wafer scale, to further facilitate the applications of TMdCs in post-Si technol.
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    Xie, D. G.; Nie, Z. Y.; Shinzato, S.; Yang, Y. Q.; Liu, F. X.; Ogata, S.; Li, J.; Ma, E.; Shan, Z. W. Controlled growth of single-crystalline metal nanowires via thermomigration across a nanoscale junction. Nat. Commun. 2019, 10, 1– 8,  DOI: 10.1038/s41467-019-12416-x
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    17
    DNA origami cryptography for secure communication
    Zhang, Yinan; Wang, Fei; Chao, Jie; Xie, Mo; Liu, Huajie; Pan, Muchen; Kopperger, Enzo; Liu, Xiaoguo; Li, Qian; Shi, Jiye; Wang, Lihua; Hu, Jun; Wang, Lianhui; Simmel, Friedrich C.; Fan, Chunhai
    Nature Communications (2019), 10 (1), 1-8CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
    Biomol. cryptog. exploiting specific biomol. interactions for data encryption represents a unique approach for information security. However, constructing protocols based on biomol. reactions to guarantee confidentiality, integrity and availability (CIA) of information remains a challenge. Here we develop DNA origami cryptog. (DOC) that exploits folding of a M13 viral scaffold into nanometer-scale self-assembled braille-like patterns for secure communication, which can create a key with a size of over 700 bits. The intrinsic nanoscale addressability of DNA origami addnl. allows for protein binding-based steganog., which further protects message confidentiality in DOC. The integrity of a transmitted message can be ensured by establishing specific linkages between several DNA origamis carrying parts of the message. The versatility of DOC is further demonstrated by transmitting various data formats including text, musical notes and images, supporting its great potential for meeting the rapidly increasing CIA demands of next-generation cryptog.
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    Xiong, Y. J.; Xia, Y. N. Shape-controlled synthesis of metal nanostructures: The case of palladium. Adv. Mater. 2007, 19, 3385– 3391,  DOI: 10.1002/adma.200701301
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    18
    Shape-controlled synthesis of metal nanostructures: the case of palladium
    Xiong, Yujie; Xia, Younan
    Advanced Materials (Weinheim, Germany) (2007), 19 (20), 3385-3391CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The shape-controlled synthesis of Pd nanostructures was investigated. A no. of useful parameters can be tuned to control the formation of Pd nanostructures with a specific shape in the soln.-phase synthesis. As the seed grows into a nanocrystal, the growth rates of the different facets can be altered with capping agents to control the final shape. The ability to control the shape provides an opportunity to evaluate elec., plasmonic, and catalytic properties as well as explore applications of Pd nanostructures.
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    Zhu, Y. C.; Bando, Y.; Xue, D. F.; Golberg, D. Oriented assemblies of ZnS one-dimensional nanostructures. Adv. Mater. 2004, 16, 831– 834,  DOI: 10.1002/adma.200305486
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    Oriented assemblies of ZnS one-dimensional nanostructures
    Zhu, Ying-Chun; Bando, Yoshio; Xue, Dong-Feng; Golberg, Dmitri
    Advanced Materials (Weinheim, Germany) (2004), 16 (9-10), 831-834CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Oriented ZnS nanobelt arrays and ZnS multicore microcables consisting of an oriented nanowire bundle with a sheath were synthesized via a controlled thermal process. The ZnS nanowires are single crystals grown along the [001] axis. Blue, green, and orange luminescence was obtained from different doped products. The formation mechanism is a catalyzed sublimation process. The special structures of the oriented assemblies of ZnS one-dimensional nanostructures may have potential applications in nanoelectronics and photonics.
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    Grayli, S. V.; Zhang, X.; MacNab, F. C.; Kamal, S.; Star, D.; Leach, G. W. Scalable, Green Fabrication of Single-Crystal Noble Metal Films and Nanostructures for Low-Loss Nanotechnology Applications. ACS Nano 2020, 14, 7581– 7592,  DOI: 10.1021/acsnano.0c03466
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    Zhang, H. Y.; Kinnear, C.; Mulvaney, P. Fabrication of Single-Nanocrystal Arrays. Adv. Mater. 2020, 32, 1904551,  DOI: 10.1002/adma.201904551
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    21
    Fabrication of Single-Nanocrystal Arrays
    Zhang, Heyou; Kinnear, Calum; Mulvaney, Paul
    Advanced Materials (Weinheim, Germany) (2020), 32 (18), 1904551CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. To realize the full potential of nanocrystals in nanotechnol., it is necessary to integrate single nanocrystals into addressable structures; for example, arrays and periodic lattices. The current methods for achieving this are reviewed. It is shown that a combination of top-down lithog. techniques with directed assembly offers a platform for attaining this goal. The most promising of these directed assembly methods are reviewed: capillary force assembly, electrostatic assembly, optical printing, DNA-based assembly, and electrophoretic deposition. The last of these appears to offer a generic approach to fabrication of single-nanocrystal arrays.
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    Chou, Y. C.; Hillerich, K.; Tersoff, J.; Reuter, M. C.; Dick, K. A.; Ross, F. M. Atomic-Scale Variability and Control of III-V Nanowire Growth Kinetics. Science 2014, 343, 281– 284,  DOI: 10.1126/science.1244623
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    Atomic-Scale Variability and Control of III-V Nanowire Growth Kinetics
    Chou, Y.-C.; Hillerich, K.; Tersoff, J.; Reuter, M. C.; Dick, K. A.; Ross, F. M.
    Science (Washington, DC, United States) (2014), 343 (6168), 281-284CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    In the growth of nanoscale device structures, the ultimate goal is at.-level precision. By growing III-V nanowires in a transmission electron microscope, the authors measured the local kinetics in situ as each at. plane was added at the catalyst-nanowire growth interface by the vapor-liq.-solid process. During growth of gallium phosphide nanowires at typical V/III ratios, the authors found surprising fluctuations in growth rate, even under steady growth conditions. The authors correlated these fluctuations with the formation of twin defects in the nanowire, and found that these variations can be suppressed by switching to growth conditions with a low V/III ratio. The authors derive a growth model showing that this unexpected variation in local growth kinetics reflects the very different supply pathways of the V and III species. The model explains under which conditions the growth rate can be controlled precisely at the at. level.
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    Jacobsson, D.; Panciera, F.; Tersoff, J.; Reuter, M. C.; Lehmann, S.; Hofmann, S.; Dick, K. A.; Ross, F. M. Interface dynamics and crystal phase switching in GaAs nanowires. Nature 2016, 531, 317– 322,  DOI: 10.1038/nature17148
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    Interface dynamics and crystal phase switching in GaAs nanowires
    Jacobsson, Daniel; Panciera, Federico; Tersoff, Jerry; Reuter, Mark C.; Lehmann, Sebastian; Hofmann, Stephan; Dick, Kimberly A.; Ross, Frances M.
    Nature (London, United Kingdom) (2016), 531 (7594), 317-322CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    Controlled formation of non-equil. crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) nanowires during growth as they switch between phases as a result of varying growth conditions. We find clear differences between the growth dynamics of the phases, including differences in interface morphol., step flow and catalyst geometry. We explain these differences, and the phase selection, using a model that relates the catalyst vol., the contact angle at the trijunction (the point at which solid, liq. and vapor meet) and the nucleation site of each new layer of GaAs. This model allows us to predict the conditions under which each phase should be obsd., and use these predictions to design GaAs heterostructures. These results could apply to phase selection in other nanowire systems.
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    Ditlbacher, H.; Hohenau, A.; Wagner, D.; Kreibig, U.; Rogers, M.; Hofer, F.; Aussenegg, F. R.; Krenn, J. R. Silver nanowires as surface plasmon resonators. Phys. Rev. Lett. 2005, 95, 257403,  DOI: 10.1103/PhysRevLett.95.257403
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    Silver Nanowires as Surface Plasmon Resonators
    Ditlbacher, Harald; Hohenau, Andreas; Wagner, Dieter; Kreibig, Uwe; Rogers, Michael; Hofer, Ferdinand; Aussenegg, Franz R.; Krenn, Joachim R.
    Physical Review Letters (2005), 95 (25), 257403/1-257403/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    The authors report on chem. prepd. Ag nanowires (diams. around 100 nm) sustaining surface plasmon modes with wavelengths shortened to about half the value of the exciting light. As the authors find by scattered light spectroscopy and near-field optical microscopy, the nonradiating character of these modes together with minimized damping due to the well developed wire crystal structure gives rise to large values of surface plasmon propagation length and nanowire end face reflectivity of ∼10 μm and 25%, resp. These properties allow one to apply the nanowires as efficient surface plasmon Fabry-Perot resonators.
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    Kim, F.; Sohn, K.; Wu, J. S.; Huang, J. X. Chemical Synthesis of Gold Nanowires in Acidic Solutions. J. Am. Chem. Soc. 2008, 130, 14442– 14443,  DOI: 10.1021/ja806759v
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    Chemical Synthesis of Gold Nanowires in Acidic Solutions
    Kim, Franklin; Sohn, Kwonnam; Wu, Jinsong; Huang, Jiaxing
    Journal of the American Chemical Society (2008), 130 (44), 14442-14443CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    High aspect ratio gold nanowires with single cryst. surface have long been a missing piece in the toolbox of plasmonics metal nanostructures. Such wires are now made with a room temp., surfactant assisted chem. synthesis in acidic aq. soln. The diams. and lengths of the multiply twinned gold nanowires can be tuned by varying the amt. of seed particles and acid in the growth soln. Nanowires with diams. around 35 nm and lengths up to 10 μm were made with a low seed concn. in pH ∼1 soln.
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    Hicks, E. M.; Zou, S. L.; Schatz, G. C.; Spears, K. G.; Van Duyne, R. P.; Gunnarsson, L.; Rindzevicius, T.; Kasemo, B.; Kall, M. Controlling plasmon line shapes through diffractive coupling in linear arrays of cylindrical nanoparticles fabricated by electron beam lithography. Nano Lett. 2005, 5, 1065– 1070,  DOI: 10.1021/nl0505492
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    Controlling Plasmon Line Shapes through Diffractive Coupling in Linear Arrays of Cylindrical Nanoparticles Fabricated by Electron Beam Lithography
    Hicks, Erin M.; Zou, Shengli; Schatz, George C.; Spears, Kenneth G.; Van Duyne, Richard P.; Gunnarsson, Linda; Rindzevicius, Tomas; Kasemo, Bengt; Kaell, Mikael
    Nano Letters (2005), 5 (6), 1065-1070CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    The effect of diffractive coupling on the collective plasmon line shape of linear arrays of Ag nanoparticles fabricated by electron beam lithog. was studied using Rayleigh scattering spectroscopy. The array spectra exhibit an intricate multi-peak structure, including a narrow mode that gains strength for interparticle distances that are close to the single particle resonance wavelength. A version of the discrete dipole approxn. method provides an excellent qual. description of the obsd. behavior.
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    Tseng, A. A. Recent developments in nanofabrication using focused ion beams. Small 2005, 1, 924– 939,  DOI: 10.1002/smll.200500113
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    Recent developments in nanofabrication using focused ion beams
    Tseng, Ampere A.
    Small (2005), 1 (10), 924-939CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Focused ion beam (FIB) technol. is becoming an increasingly popular technique for fabrication on the nanoscale. In this review, four areas of FIB technol. are examd.: milling, implantation, ion-induced deposition and ion-assisted etching. Together, these techniques are likely to be at the forefront in future nanotechnol. design (the picture shows a scanning ion microscopy (SIM) image of microbellows constructed using FIB-induced deposition (FIBID)).
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    Rubanov, S.; Munroe, P. R. FIB-induced damage in silicon. J. Microsc. 2004, 214, 213– 221,  DOI: 10.1111/j.0022-2720.2004.01327.x
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    FIB-induced damage in silicon
    Rubanov, S.; Munroe, P. R.
    Journal of Microscopy (Oxford, United Kingdom) (2004), 214 (3), 213-221CODEN: JMICAR; ISSN:0022-2720. (Blackwell Publishing Ltd.)
    The damage created in Si transmission electron microscope specimens prepd. using a focused ion beam miller is assessed using cross sections of trenches milled under different beam conditions. Side-wall damage consists of an amorphous layer formed by direct interaction with the energetic Ga ion beam; a small amt. of implanted Ga is also detected. By contrast, bottom-wall damage layers are more complex and contain both amorphous films and cryst. regions that are richer in implanted Ga. More complex milling sequences show that redeposition of milled material, enriched in Ga, can occur depending on the geometry of the mill employed. The thickness of the damage layers depends strongly on beam energy, but is independent of beam current. Monte Carlo modeling of the damage formed indicates that recoil Si atoms contribute significantly to the damaged formed in the specimen.
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    Liu, N. J.; Xie, Y. J.; Liu, G. N.; Sohn, S.; Raj, A.; Han, G. X.; Wu, B. Z.; Cha, J. J.; Liu, Z.; Schroers, J. General Nanomolding of Ordered Phases. Phys. Rev. Lett. 2020, 124, 036102  DOI: 10.1103/PhysRevLett.124.036102
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    General Nanomolding of Ordered Phases
    Liu, Naijia; Xie, Yujun; Liu, Guannan; Sohn, Sungwoo; Raj, Arindam; Han, Guoxing; Wu, Bozhao; Cha, Judy J.; Liu, Ze; Schroers, Jan
    Physical Review Letters (2020), 124 (3), 036102CODEN: PRLTAO; ISSN:1079-7114. (American Physical Society)
    Large-scale, controlled fabrication of ordered phases is challenging at the nanoscale, yet highly demanded as their well-ordered structure and chem. is the key for advanced functionality. Here, we demonstrate a general nanomolding process of ordered phases based on at. diffusion. Resulting nanowires are single crystals and maintain their compn. and structure throughout their length, which we explain by a self-ordering process originating from their narrow Gibbs free energy. The versatility, control, and precision of this thermomech. nanomolding method of ordered phases provides new insights into single crystal growth and suggest itself as a technol. to enable wide spread usage for nanoscale and quantum devices.
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    Liu, Z. One-step fabrication of crystalline metal nanostructures by direct nanoimprinting below melting temperatures. Nat. Commun. 2017, 8, 1– 7,  DOI: 10.1038/ncomms14910
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    In vivo cation exchange in quantum dots for tumor-specific imaging
    Liu, Xiangyou; Braun, Gary B.; Qin, Mingde; Ruoslahti, Erkki; Sugahara, Kazuki N.
    Nature Communications (2017), 8 (1), 1-13CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
    In vivo tumor imaging with nanoprobes suffers from poor tumor specificity. Here, we introduce a nanosystem, which allows selective background quenching to gain exceptionally tumor-specific signals. The system uses near-IR quantum dots and a membrane-impermeable etchant, which serves as a cation donor. The etchant rapidly quenches the quantum dots through cation exchange (ionic etching), and facilitates renal clearance of metal ions released from the quantum dots. The quantum dots are i.v. delivered into orthotopic breast and pancreas tumors in mice by using the tumor-penetrating iRGD peptide. Subsequent etching quenches excess quantum dots, leaving a highly tumor-specific signal provided by the intact quantum dots remaining in the extravascular tumor cells and fibroblasts. No toxicity is noted. The system also facilitates the detection of peritoneal tumors with high specificity upon i.p. tumor targeting and selective etching of excess untargeted quantum dots. In vivo cation exchange may be a promising strategy to enhance specificity of tumor imaging.
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    Liu, Z.; Han, G. X.; Sohn, S.; Liu, N. J.; Schroers, J. Nanomolding of Crystalline Metals: The Smaller the Easier. Phys. Rev. Lett. 2019, 122, 036101  DOI: 10.1103/PhysRevLett.122.036101
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    Nanomolding of Crystalline Metals: The Smaller the Easier
    Liu, Ze; Han, Guoxing; Sohn, Sungwoo; Liu, Naijia; Schroers, Jan
    Physical Review Letters (2019), 122 (3), 036101CODEN: PRLTAO; ISSN:1079-7114. (American Physical Society)
    We report on a thermomech. nanomolding method for cryst. metals. Quantified by the aspect ratio, this process becomes easier with decreasing mold diam. As the responsible underlying diffusion mechanism is present in all metals and alloys, the discovered nanomolding process provides a toolbox to shape essentially any metal and alloy into a nanofeature. Technol., this highly versatile and practical thermomech. nanomolding technique offers a method to fabricate high-surface-area metallic nanostructures which are impactful in diverse fields of applications including catalysts, sensors, photovoltaics, microelectronics, and plasmonics.
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    Liu, N.; Liu, G.; Raj, A.; Sohn, S.; Morales, M.; Liu, J.; Schroers, J. Unleashing Nanofabrication through Thermomechanical Nanomolding. Science Advances 2021, 7, eabi8795
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    Raj, A.; Liu, N.; Liu, G.; Sohn, S.; Xiang, J.; Liu, Z.; Schroers, J. Nanomolding of Gold and Gold-Silicon Heterostructures at Room Temperature. ACS Nano 2021, 15, 14275– 14284,  DOI: 10.1021/acsnano.1c02636
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    Nanomolding of Gold and Gold-Silicon Heterostructures at Room Temperature
    Raj, Arindam; Liu, Naijia; Liu, Guannan; Sohn, Sungwoo; Xiang, Junxiang; Liu, Ze; Schroers, Jan
    ACS Nano (2021), 15 (9), 14275-14284CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Nanofabrication techniques are limited by at least one of the required characteristics such as choice of material, control over geometry, fabrication requirements, yield, cost, and scalability. Our previously developed method of thermomech. nanomolding fulfills these requirements, although it requires high processing temps. Here, we demonstrate low-temp. molding where we utilize the enhanced diffusivity on "eutectic interfaces". Gold nanorods are molded at room temp. using Au-Si alloy as feedstock. Instead of using alloy feedstock, these "eutectic interfaces" can also be established through a feedstock-mold combination. We demonstrate this by using pure Au as feedstock, which is molded into Si molds at room temp., and also the reverse, Si feedstock is molded into Au molds forming high aspect ratio Au-Si core-shell nanorods. We discuss the mechanism of this low-temp. nanomolding in terms of lower homologous temp. at the eutectic interface. This technique, based on enhanced eutectic interface diffusion, provides a practical nanofabrication method that eliminates the previous high-temp. requirements, thereby expanding the range of the materials that can be practically nanofabricated.
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    Li, S.; Ding, X.; Li, J.; Ren, X.; Sun, J.; Ma, E. High-efficiency mechanical energy storage and retrieval using interfaces in nanowires. Nano Lett. 2010, 10, 1774– 1779,  DOI: 10.1021/nl100263p
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    High-efficiency mechanical energy storage and retrieval using interfaces in nanowires
    Li, Suzhi; Ding, Xiangdong; Li, Ju; Ren, Xiaobing; Sun, Jun; Ma, Evan
    Nano Letters (2010), 10 (5), 1774-1779CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    According to mol. dynamics simulations, a concept for mech. energy storage and retrieval using surface energy as a reservoir in bcc. tungsten nanowires achieved a combination of unique features such as high and const. actuation stress of >3 GPa, exceptionally high actuation strain of >30% and energy d., and >98% energy storage efficiency. The underlying mechanism is a shear-dominant diffusionless transformation akin to a martensitic transformation, but driven by surface rather than bulk free energies, and enabled by the motion of coherent twin boundaries, whose migration has been shown to possess ultralow friction in bcc. metals. Aside from energy storage, such surface-energy driven displacive transformations are important for phase transformation and energy-matter control on a nanoscale.
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    Wen, Y. N.; Zhang, H. M. Surface energy calculation of the fcc metals by using the MAEAM. Solid State Commun. 2007, 144, 163– 167,  DOI: 10.1016/j.ssc.2007.07.012
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    Surface energy calculation of the fcc metals by using the MAEAM
    Wen, Yan-Ni; Zhang, Jian-Min
    Solid State Communications (2007), 144 (3-4), 163-167CODEN: SSCOA4; ISSN:0038-1098. (Elsevier Ltd.)
    The surface energies of 40 surfaces for fcc. metals Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au and Al were calcd. by using the MAEAM. For all fcc. metals, the surface energies of (110) are higher than that of the (100) and (111) surfaces, the order of 3 low-index surface energies is Es(111) < Es(100) < Es(110). In all the (hkl) planes of fcc. metals, the lowest surface energy corresponds to the (111) surface and the highest surface energy corresponds to the (210) surface except that, for Rh it is a (320) surface. So from surface energy minimization, the (111) texture should be favorable in the fcc. films. The surface energy corresponding to the other surface increases linearly with increasing angle between the (hkl) planes and (111) plane by and large. This can be used to est. the relative values of the surface energies.
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    Hoefelmeyer, J. D.; Niesz, K.; Somorjai, G. A.; Tilley, T. D. Radial anisotropic growth of rhodium nanoparticles. Nano Lett. 2005, 5, 435– 438,  DOI: 10.1021/nl048100g
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    Radial Anisotropic Growth of Rhodium Nanoparticles
    Hoefelmeyer, James D.; Niesz, Krisztian; Somorjai, Gabor A.; Tilley, T. Don
    Nano Letters (2005), 5 (3), 435-438CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    In this contribution, we report the synthesis of rhodium multipods that result from a homogeneous seeded growth mechanism. Small Rh nanocrystal seeds were synthesized by the redn. of RhCl3 in ethylene glycol in the presence of PVP. These seed particles could be subsequently used, without isolation, to form larger rhodium nanoparticles. A reaction temp. of 190 °C led to isotropic cubic Rh particles. Lowering the reaction temp. resulted in more anisotropic growth, which gave Rh cubes with horns at 140 °C, and Rh multipods at 90 °C. The anisotropic growth occurred in the (111) direction, as detd. by high-resoln. TEM (HRTEM). Anisotropic growth proceeds via a seeded growth mechanism, and not by oriented attachment.
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    Sun, J.; He, L. B.; Lo, Y. C.; Xu, T.; Bi, H. C.; Sun, L. T.; Zhang, Z.; Mao, S. X.; Li, J. Liquid-like pseudoelasticity of sub-10-nm crystalline silver particles. Nat. Mater. 2014, 13, 1007– 1012,  DOI: 10.1038/nmat4105
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    Liquid-like pseudoelasticity of sub-10-nm crystalline silver particles
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    Nature Materials (2014), 13 (11), 1007-1012CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    In nanotechnol., small-vol. metals with large surface area are used as electrodes, catalysts, interconnects and antennae. Their shape stability at room temp. has, however, been questioned. Using in situ high-resoln. transmission electron microscopy, we find that Ag nanoparticles can be deformed like a liq. droplet but remain highly cryst. in the interior, with no sign of dislocation activity during deformation. Surface-diffusion-mediated pseudoelastic deformation is evident at room temp., which can be driven by either an external force or capillary-energy minimization. Atomistic simulations confirm that such highly unusual Coble pseudoelasticity can indeed happen for sub-10-nm Ag particles at room temp. and at timescales from seconds to months.
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    Barg, A. I.; Rabkin, E.; Gust, W. Faceting Transformation and Energy of a Sigma-3 Grain-Boundary in Silver. Acta Metall. Mater. 1995, 43, 4067– 4074,  DOI: 10.1016/0956-7151(95)00094-C
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    Faceting transformation and energy of a Σ3 grain boundary in silver
    Barg, A. I.; Rabkin, E.; Gust, W.
    Acta Metallurgica et Materialia (1995), 43 (11), 4067-74CODEN: AMATEB; ISSN:0956-7151. (Elsevier)
    Grain boundary facets forming at the intersection between a grain boundary and the free surface in diffusion bonded Σ3<011>Ag bicrystals during prolonged annealing were characterized crystallog. by metallog. methods. The obsd. faceting has qual. the same character as that in Σ3<011> grain boundaries in Cu. The energy of an incoherent Σ3 grain boundary in Ag (210 mJ/m2) is detd. from the dihedral angle of the thermal groove and the extrapolated literature data on the surface tension of Ag. The facet geometry is discussed with respect to computer simulation data on the inclination dependence of the energy of Σ3 grain boundaries in Cu. The geometrical stability of a grain boundary near the free surface is considered.
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    Deformation of single crystals, polycrystalline materials, and thin films: a review
    Yang, Guijun; Park, Soo-Jin
    Materials (2019), 12 (12), 2003CODEN: MATEG9; ISSN:1996-1944. (MDPI AG)
    With the rapid development of nano-prepn. processes, nanocryst. materials have beenwidelydevelopedinthefieldsofmechanics, electricity, optics, andthermalphysics. Comparedto the case of coarse-grained or amorphous materials, plastic deformation in nanomaterials is limited by the redn. in feature size, so that they generally have high strength, but the toughness is relatively high. The "reciprocal relationship" between the strength and toughness of nanomaterials limits the large-scale application and development of nanomaterials. Therefore, the maintenance of high toughness while improving the strength of nanomaterials is an urgent problem to be solved. So far, although the relevant mechanism affecting the deformation of nanocryst. materials has made a big breakthrough, it is still not very clear. Therefore, this paper introduces the basic deformation type, mechanism, and model of single crystals, polycryst. materials, and thin films, and aims to provide literature support for future research.
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    Wang, L.; Teng, J.; Liu, P.; Hirata, A.; Ma, E.; Zhang, Z.; Chen, M.; Han, X. Grain rotation mediated by grain boundary dislocations in nanocrystalline platinum. Nat. Commun. 2014, 5, 1– 7,  DOI: 10.1038/ncomms5402
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    Wen, Y. N.; Zhang, J. M. Surface energy calculation of the bcc metals by using the MAEAM. Comput. Mater. Sci. 2008, 42, 281– 285,  DOI: 10.1016/j.commatsci.2007.07.016
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    Surface energy calculation of the bcc metals by using the MAEAM
    Wen, Yan-Ni; Zhang, Jian-Min
    Computational Materials Science (2008), 42 (2), 281-285CODEN: CMMSEM; ISSN:0927-0256. (Elsevier B.V.)
    The surface energies of 24 surfaces both for the bcc alkali metals Li, Na, K, Rb, Cs and for the bcc transition metals Fe, W, Mo, Cr, Ta, Nb and V have been calcd. by using the modified anal. embedded-atom method (MAEAM). The surface energy of each (h k l) plane in alkali metals is much lower than that in transition metals. For all bcc metals, the order of three low-index surface energies E ( 1 1 0 ) s < E ( 1 0 0 ) s < E ( 1 1 1 ) s is in agreement with exptl. results, E ( 1 1 0 ) s is the lowest and E ( 1 1 1 ) s except that in the case of Nb is the highest surface energy for various surfaces. So that from surface energy minimization, the (1 1 0) texture should be favorable in the bcc films which is also consistent with exptl. results. The surface energy corresponding to the other surface increases linearly with increasing angle between the (h k l) planes and (1 1 0) plane. Therefore, a deviation of a surface orientation from (1 1 0) can be used to est. the relative values of the surface energies.
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This article is cited by 4 publications.

  1. Bozhao Wu, Yupeng Wu, Yangyang Pan, Ze Liu. Nanoscale deformation of crystalline metals: Experiments and simulations. International Journal of Plasticity 2023, 161 , 103501. https://doi.org/10.1016/j.ijplas.2022.103501
  2. Jun-Xiang Xiang, Ze Liu. Observation of enhanced nanoscale creep flow of crystalline metals enabled by controlling surface wettability. Nature Communications 2022, 13 (1) https://doi.org/10.1038/s41467-022-35703-6
  3. Mehrdad T. Kiani, Judy J. Cha. Nanomolding of topological nanowires. APL Materials 2022, 10 (8) , 080904. https://doi.org/10.1063/5.0096400
  4. Ze Liu, Naijia Liu, Jan Schroers. Nanofabrication through molding. Progress in Materials Science 2022, 125 , 100891. https://doi.org/10.1016/j.pmatsci.2021.100891
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  • Abstract

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    Figure 1

    Figure 1. Current nanofabrication methods and atomic arrangement (in 2D illustration) of the nanostructures they can produce. (a) Schematic illustration of solution-based chemical synthesis and the resulting detached single-crystal nanowire. (b) Physical vapor deposition (PVD) method and the resulting nanostructure containing grain boundaries and often polycrystals. (c) Using a focused ion beam (FIB) inside a scanning electron microscope (SEM) allows the fabrication of single-crystal nanostructures integrated in the crystal of the substrate but lacks scalability.

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    Figure 2. Overview of thermomechanical nanomolding (TMNM). (a) Schematic illustration of the process flow of TMNM performed in this study. A nanosized mold, for example, anodic aluminum oxide, and a flat feedstock substrate are depicted. (b,c) Morphology of the resulting vertically grown Ag nanowire arrays with nanowire diameters of 120 and 40 nm, respectively, revealed by SEM imaging at a 30° tilted angle. Nanowires with a small aspect ratio are free-standing and precisely aligned and located as shown in panel b, and nanowires with a large aspect ratio may agglomerate due to surface tension, as shown in panel c.

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    Figure 3. Orientation of nanowires with grain boundaries fabricated by TMNM. (a–d) Schematics of TMNM using polycrystalline and single-crystal substrates and the resulting microstructure and crystal orientation of the nanowires. (110) directions are denoted with red arrows. (a) Polycrystalline substrate for TMNM. (b) Crystal structure and grain orientation of a representative nanowire and its adjacent substrate area after processing in panel a. The nanowire grows along the (110) direction but forms grain boundaries at the root. (c) (110) single-crystal substrate exposed to a “high”-pressure ph during TMNM, where “high” means that ph is larger than the reorientation pressure of the crystal orientation. (d) Crystal structure and grain orientation of a representative nanowire and its adjacent substrate area after processing in panel c. Because of the acting “high” pressure ph, the (110) substrate reorients to (111). Because the growth direction deeper within the nanocavity is along (110), grain boundaries are forming at the root of the nanowire. (e) Transmission electron microscopy (TEM) image of a 40 nm nanowire with the polycrystalline root region. (f) TEM image from the area marked by the dashed red rectangle in panel e revealing the grain boundaries and multiple grains with different crystallographic orientations at the root of the nanowire. (See the original TEM image in Figure S3, Supporting Information.) (g) High-resolution TEM image from the area indicated in panel f by the yellow square showing lattice fringes with the (110) orientation along the growth direction. (h) Selected area electron diffraction (SAED) pattern obtained within the region enclosed by the dashed white circle in panel e, revealing that the nanowire root is polycrystalline. (i,j) High-magnification TEM images covering the regions within the blue and orange squares in panel f showing well-developed grain boundaries at the root of the nanowire. (See the original and additional TEM images in Figure S3, Supporting Information.)

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    Figure 4

    Figure 4. TEM characterization of single-crystal nanostructures fabricated by TMNM. (a,b) Schematics of TMNM using a single-crystal substrate and the resulting structure of nanowires. The [110] direction is denoted with a red arrow. (a) (110) single-crystal substrate under “low” pressure pl during TMNM. (b) Crystal structure and grain orientation of a representative nanowire and its adjacent substrate area after processing. If pl is below the reorientation threshold, then nanowires of the same [110] orientation grow from the (110) single-crystal substrate in an epitaxial relationship. (c) TEM image of a 40 nm single-crystal nanowire. (d) TEM image from the selected region in yellow in panel c revealing an absence of polycrystals and grain boundaries at the root of the nanowire. (e–h) SAED patterns from four sections of the nanowire in panel c, revealing that the sample is a face-centered cubic (fcc) single crystal. (See Figure S5 in the Supporting Information for the indexing.) Scale bar: 10 1/nm. (i–l) High-resolution TEM images from the regions marked in panel d in blue and orange (i,k) and further magnifications into the areas highlighted with the white dashed square (j,l), showing lattice fringes with (110) orientation along the growth direction of the nanowire.

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    Figure 5. Mechanisms of grain reorientation in the substrate and in the nanowire. (a) Schematics of two unknown crystallographic orientations in the feedstock substrate and the nanowire of a typical nanowire-substrate system under uniaxial pressure. (b) Surface energy comparison among three different substrate–nanowire systems: randomly oriented substrate and nanowire along a random growth direction, randomly oriented substrate and nanowire along the [110] growth direction including a grain boundary, and (110) substrate and nanowire along the [110] growth direction. Surface I refers to a termination with a combination of various mostly non-{111} and non-{100} (hkl) planes, and surface II refers to a termination by a combination of {111} and {100} planes. (c) Rotation of a (110) plane under compression, which results in a polycrystalline substrate with {111} planes as the dominant orientation. (d) X-ray diffraction characterization of the Ag substrate before and after TMNM (experimental conditions: p = 1.3 GPa, T = 0.6TM, t = 30 s), revealing a structural change from a (110) single-crystal to a (111)-dominant polycrystal. (e) Perspective representation of a hexagonal prism-shaped fcc single-crystal nanowire that grows along the [110] direction with {111} and {100} surfaces as the side walls. (f) Schematic illustration of the atomic arrangement on the cross-section of a cylinder-shaped fcc (110) single-crystal nanowire. Zoom on the outer surface of the nanowire shows alternating {111}/{100} surfaces as side walls to achieve the appearance of a “round” shape.

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      Influence of grain boundary scattering on the electrical and thermal conductivities of polycrystalline gold nanofilms
      Zhang, Q. G.; Cao, B. Y.; Zhang, X.; Fujii, M.; Takahashi, K.
      Physical Review B: Condensed Matter and Materials Physics (2006), 74 (13), 134109/1-134109/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      The elec. and thermal conductivities of polycryst. Au nanofilms were measured simultaneously by a d.c. heating method, and the measured results are compared with the Mayadas and Shatzkes theory. The reduced elec. and thermal conductivities of Au nanofilms are strongly dominated by grain boundary scattering. The reflection coeff. of electrons striking the grain boundaries for charge transport is 0.7, which agrees well with a previous scanning tunneling potentiometry study. The reflection coeff. for thermal transport, however, is only 0.25. The Lorenz nos. for the polycryst. Au nanofilms, which are calcd. from the measured elec. and thermal conductivities, are much greater than the value predicted by the Wiedemann-Franz law for the bulk material. The electron scatterings on the grain boundaries impose different influences on the charge and heat transport in the polycryst. Au nanofilms. A model of effective d. of conduction electrons was utilized to interpret the violation of the Wiedemann-Franz law in polycryst. Au nanofilms.
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    15. 15
      Butburee, T.; Bai, Y.; Wang, H. J.; Chen, H. J.; Wang, Z. L.; Liu, G.; Zou, J.; Khemthong, P.; Lu, G. Q. M.; Wang, L. Z. 2D Porous TiO2 Single-Crystalline Nanostructure Demonstrating High Photo-Electrochemical Water Splitting Performance. Adv. Mater. 2018, 30, 1705666,  DOI: 10.1002/adma.201705666
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    16. 16
      Choi, S. H.; Kim, H. J.; Song, B.; Kim, Y. I.; Han, G.; Nguyen, H. T. T.; Ko, H.; Boandoh, S.; Choi, J. H.; Oh, C. S.; Cho, H. J.; Jin, J. W.; Won, Y. S.; Lee, B. H.; Yun, S. J.; Shin, B. G.; Jeong, H. Y.; Kim, Y. M.; Han, Y. K.; Lee, Y. H.; Kim, S. M.; Kim, K. K. Epitaxial Single-Crystal Growth of Transition Metal Dichalcogenide Monolayers via the Atomic Sawtooth Au Surface. Adv. Mater. 2021, 33, 2006601,  DOI: 10.1002/adma.202006601
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      16
      Epitaxial Single-Crystal Growth of Transition Metal Dichalcogenide Monolayers via the Atomic Sawtooth Au Surface
      Choi, Soo Ho; Kim, Hyung-Jin; Song, Bumsub; Kim, Yong In; Han, Gyeongtak; Nguyen, Huong Thi Thanh; Ko, Hayoung; Boandoh, Stephen; Choi, Ji Hoon; Oh, Chang Seok; Cho, Hyun Je; Jin, Jeong Won; Won, Yo Seob; Lee, Byung Hoon; Yun, Seok Joon; Shin, Bong Gyu; Jeong, Hu Young; Kim, Young-Min; Han, Young-Kyu; Lee, Young Hee; Kim, Soo Min; Kim, Ki Kang
      Advanced Materials (Weinheim, Germany) (2021), 33 (15), 2006601CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Growth of 2D van der Waals layered single-crystal (SC) films is highly desired not only to manifest the intrinsic phys. and chem. properties of materials, but also to enable the development of unprecedented devices for industrial applications. The SC growth of TMdC monolayers on a cm scale via the at. sawtooth Au surface as a universal growth template is reported. The at. tooth-gullet surface is constructed by the 1-step solidification of liq. Au, evidenced by TEM. The anisotropic adsorption energy of the TMdC cluster, confirmed by d. functional calcns., prevails at the periodic at.-step edge to yield unidirectional epitaxial growth of triangular TMdC grains, eventually forming the SC film, regardless of the Miller indexes. Growth using the at. sawtooth Au surface as a universal growth template is demonstrated for several transition metal dichalcogenide (TMdC) monolayer films, including WS2, WSe2, MoS2, the MoSe2/WSe2 heterostructure, and W1-xMoxS2 alloys. This strategy provides a general avenue for the SC growth of diat. van der Waals heterostructures on a wafer scale, to further facilitate the applications of TMdCs in post-Si technol.
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    17. 17
      Xie, D. G.; Nie, Z. Y.; Shinzato, S.; Yang, Y. Q.; Liu, F. X.; Ogata, S.; Li, J.; Ma, E.; Shan, Z. W. Controlled growth of single-crystalline metal nanowires via thermomigration across a nanoscale junction. Nat. Commun. 2019, 10, 1– 8,  DOI: 10.1038/s41467-019-12416-x
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      17
      DNA origami cryptography for secure communication
      Zhang, Yinan; Wang, Fei; Chao, Jie; Xie, Mo; Liu, Huajie; Pan, Muchen; Kopperger, Enzo; Liu, Xiaoguo; Li, Qian; Shi, Jiye; Wang, Lihua; Hu, Jun; Wang, Lianhui; Simmel, Friedrich C.; Fan, Chunhai
      Nature Communications (2019), 10 (1), 1-8CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
      Biomol. cryptog. exploiting specific biomol. interactions for data encryption represents a unique approach for information security. However, constructing protocols based on biomol. reactions to guarantee confidentiality, integrity and availability (CIA) of information remains a challenge. Here we develop DNA origami cryptog. (DOC) that exploits folding of a M13 viral scaffold into nanometer-scale self-assembled braille-like patterns for secure communication, which can create a key with a size of over 700 bits. The intrinsic nanoscale addressability of DNA origami addnl. allows for protein binding-based steganog., which further protects message confidentiality in DOC. The integrity of a transmitted message can be ensured by establishing specific linkages between several DNA origamis carrying parts of the message. The versatility of DOC is further demonstrated by transmitting various data formats including text, musical notes and images, supporting its great potential for meeting the rapidly increasing CIA demands of next-generation cryptog.
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    18. 18
      Xiong, Y. J.; Xia, Y. N. Shape-controlled synthesis of metal nanostructures: The case of palladium. Adv. Mater. 2007, 19, 3385– 3391,  DOI: 10.1002/adma.200701301
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      18
      Shape-controlled synthesis of metal nanostructures: the case of palladium
      Xiong, Yujie; Xia, Younan
      Advanced Materials (Weinheim, Germany) (2007), 19 (20), 3385-3391CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The shape-controlled synthesis of Pd nanostructures was investigated. A no. of useful parameters can be tuned to control the formation of Pd nanostructures with a specific shape in the soln.-phase synthesis. As the seed grows into a nanocrystal, the growth rates of the different facets can be altered with capping agents to control the final shape. The ability to control the shape provides an opportunity to evaluate elec., plasmonic, and catalytic properties as well as explore applications of Pd nanostructures.
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    19. 19
      Zhu, Y. C.; Bando, Y.; Xue, D. F.; Golberg, D. Oriented assemblies of ZnS one-dimensional nanostructures. Adv. Mater. 2004, 16, 831– 834,  DOI: 10.1002/adma.200305486
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      19
      Oriented assemblies of ZnS one-dimensional nanostructures
      Zhu, Ying-Chun; Bando, Yoshio; Xue, Dong-Feng; Golberg, Dmitri
      Advanced Materials (Weinheim, Germany) (2004), 16 (9-10), 831-834CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Oriented ZnS nanobelt arrays and ZnS multicore microcables consisting of an oriented nanowire bundle with a sheath were synthesized via a controlled thermal process. The ZnS nanowires are single crystals grown along the [001] axis. Blue, green, and orange luminescence was obtained from different doped products. The formation mechanism is a catalyzed sublimation process. The special structures of the oriented assemblies of ZnS one-dimensional nanostructures may have potential applications in nanoelectronics and photonics.
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    20. 20
      Grayli, S. V.; Zhang, X.; MacNab, F. C.; Kamal, S.; Star, D.; Leach, G. W. Scalable, Green Fabrication of Single-Crystal Noble Metal Films and Nanostructures for Low-Loss Nanotechnology Applications. ACS Nano 2020, 14, 7581– 7592,  DOI: 10.1021/acsnano.0c03466
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      Zhang, H. Y.; Kinnear, C.; Mulvaney, P. Fabrication of Single-Nanocrystal Arrays. Adv. Mater. 2020, 32, 1904551,  DOI: 10.1002/adma.201904551
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      21
      Fabrication of Single-Nanocrystal Arrays
      Zhang, Heyou; Kinnear, Calum; Mulvaney, Paul
      Advanced Materials (Weinheim, Germany) (2020), 32 (18), 1904551CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. To realize the full potential of nanocrystals in nanotechnol., it is necessary to integrate single nanocrystals into addressable structures; for example, arrays and periodic lattices. The current methods for achieving this are reviewed. It is shown that a combination of top-down lithog. techniques with directed assembly offers a platform for attaining this goal. The most promising of these directed assembly methods are reviewed: capillary force assembly, electrostatic assembly, optical printing, DNA-based assembly, and electrophoretic deposition. The last of these appears to offer a generic approach to fabrication of single-nanocrystal arrays.
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    22. 22
      Chou, Y. C.; Hillerich, K.; Tersoff, J.; Reuter, M. C.; Dick, K. A.; Ross, F. M. Atomic-Scale Variability and Control of III-V Nanowire Growth Kinetics. Science 2014, 343, 281– 284,  DOI: 10.1126/science.1244623
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      22
      Atomic-Scale Variability and Control of III-V Nanowire Growth Kinetics
      Chou, Y.-C.; Hillerich, K.; Tersoff, J.; Reuter, M. C.; Dick, K. A.; Ross, F. M.
      Science (Washington, DC, United States) (2014), 343 (6168), 281-284CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      In the growth of nanoscale device structures, the ultimate goal is at.-level precision. By growing III-V nanowires in a transmission electron microscope, the authors measured the local kinetics in situ as each at. plane was added at the catalyst-nanowire growth interface by the vapor-liq.-solid process. During growth of gallium phosphide nanowires at typical V/III ratios, the authors found surprising fluctuations in growth rate, even under steady growth conditions. The authors correlated these fluctuations with the formation of twin defects in the nanowire, and found that these variations can be suppressed by switching to growth conditions with a low V/III ratio. The authors derive a growth model showing that this unexpected variation in local growth kinetics reflects the very different supply pathways of the V and III species. The model explains under which conditions the growth rate can be controlled precisely at the at. level.
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    23. 23
      Jacobsson, D.; Panciera, F.; Tersoff, J.; Reuter, M. C.; Lehmann, S.; Hofmann, S.; Dick, K. A.; Ross, F. M. Interface dynamics and crystal phase switching in GaAs nanowires. Nature 2016, 531, 317– 322,  DOI: 10.1038/nature17148
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      23
      Interface dynamics and crystal phase switching in GaAs nanowires
      Jacobsson, Daniel; Panciera, Federico; Tersoff, Jerry; Reuter, Mark C.; Lehmann, Sebastian; Hofmann, Stephan; Dick, Kimberly A.; Ross, Frances M.
      Nature (London, United Kingdom) (2016), 531 (7594), 317-322CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Controlled formation of non-equil. crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) nanowires during growth as they switch between phases as a result of varying growth conditions. We find clear differences between the growth dynamics of the phases, including differences in interface morphol., step flow and catalyst geometry. We explain these differences, and the phase selection, using a model that relates the catalyst vol., the contact angle at the trijunction (the point at which solid, liq. and vapor meet) and the nucleation site of each new layer of GaAs. This model allows us to predict the conditions under which each phase should be obsd., and use these predictions to design GaAs heterostructures. These results could apply to phase selection in other nanowire systems.
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    24. 24
      Ditlbacher, H.; Hohenau, A.; Wagner, D.; Kreibig, U.; Rogers, M.; Hofer, F.; Aussenegg, F. R.; Krenn, J. R. Silver nanowires as surface plasmon resonators. Phys. Rev. Lett. 2005, 95, 257403,  DOI: 10.1103/PhysRevLett.95.257403
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      Silver Nanowires as Surface Plasmon Resonators
      Ditlbacher, Harald; Hohenau, Andreas; Wagner, Dieter; Kreibig, Uwe; Rogers, Michael; Hofer, Ferdinand; Aussenegg, Franz R.; Krenn, Joachim R.
      Physical Review Letters (2005), 95 (25), 257403/1-257403/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      The authors report on chem. prepd. Ag nanowires (diams. around 100 nm) sustaining surface plasmon modes with wavelengths shortened to about half the value of the exciting light. As the authors find by scattered light spectroscopy and near-field optical microscopy, the nonradiating character of these modes together with minimized damping due to the well developed wire crystal structure gives rise to large values of surface plasmon propagation length and nanowire end face reflectivity of ∼10 μm and 25%, resp. These properties allow one to apply the nanowires as efficient surface plasmon Fabry-Perot resonators.
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    25. 25
      Kim, F.; Sohn, K.; Wu, J. S.; Huang, J. X. Chemical Synthesis of Gold Nanowires in Acidic Solutions. J. Am. Chem. Soc. 2008, 130, 14442– 14443,  DOI: 10.1021/ja806759v
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      25
      Chemical Synthesis of Gold Nanowires in Acidic Solutions
      Kim, Franklin; Sohn, Kwonnam; Wu, Jinsong; Huang, Jiaxing
      Journal of the American Chemical Society (2008), 130 (44), 14442-14443CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      High aspect ratio gold nanowires with single cryst. surface have long been a missing piece in the toolbox of plasmonics metal nanostructures. Such wires are now made with a room temp., surfactant assisted chem. synthesis in acidic aq. soln. The diams. and lengths of the multiply twinned gold nanowires can be tuned by varying the amt. of seed particles and acid in the growth soln. Nanowires with diams. around 35 nm and lengths up to 10 μm were made with a low seed concn. in pH ∼1 soln.
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    26. 26
      Hicks, E. M.; Zou, S. L.; Schatz, G. C.; Spears, K. G.; Van Duyne, R. P.; Gunnarsson, L.; Rindzevicius, T.; Kasemo, B.; Kall, M. Controlling plasmon line shapes through diffractive coupling in linear arrays of cylindrical nanoparticles fabricated by electron beam lithography. Nano Lett. 2005, 5, 1065– 1070,  DOI: 10.1021/nl0505492
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      Controlling Plasmon Line Shapes through Diffractive Coupling in Linear Arrays of Cylindrical Nanoparticles Fabricated by Electron Beam Lithography
      Hicks, Erin M.; Zou, Shengli; Schatz, George C.; Spears, Kenneth G.; Van Duyne, Richard P.; Gunnarsson, Linda; Rindzevicius, Tomas; Kasemo, Bengt; Kaell, Mikael
      Nano Letters (2005), 5 (6), 1065-1070CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      The effect of diffractive coupling on the collective plasmon line shape of linear arrays of Ag nanoparticles fabricated by electron beam lithog. was studied using Rayleigh scattering spectroscopy. The array spectra exhibit an intricate multi-peak structure, including a narrow mode that gains strength for interparticle distances that are close to the single particle resonance wavelength. A version of the discrete dipole approxn. method provides an excellent qual. description of the obsd. behavior.
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      Tseng, A. A. Recent developments in nanofabrication using focused ion beams. Small 2005, 1, 924– 939,  DOI: 10.1002/smll.200500113
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      Recent developments in nanofabrication using focused ion beams
      Tseng, Ampere A.
      Small (2005), 1 (10), 924-939CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Focused ion beam (FIB) technol. is becoming an increasingly popular technique for fabrication on the nanoscale. In this review, four areas of FIB technol. are examd.: milling, implantation, ion-induced deposition and ion-assisted etching. Together, these techniques are likely to be at the forefront in future nanotechnol. design (the picture shows a scanning ion microscopy (SIM) image of microbellows constructed using FIB-induced deposition (FIBID)).
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      Rubanov, S.; Munroe, P. R. FIB-induced damage in silicon. J. Microsc. 2004, 214, 213– 221,  DOI: 10.1111/j.0022-2720.2004.01327.x
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      FIB-induced damage in silicon
      Rubanov, S.; Munroe, P. R.
      Journal of Microscopy (Oxford, United Kingdom) (2004), 214 (3), 213-221CODEN: JMICAR; ISSN:0022-2720. (Blackwell Publishing Ltd.)
      The damage created in Si transmission electron microscope specimens prepd. using a focused ion beam miller is assessed using cross sections of trenches milled under different beam conditions. Side-wall damage consists of an amorphous layer formed by direct interaction with the energetic Ga ion beam; a small amt. of implanted Ga is also detected. By contrast, bottom-wall damage layers are more complex and contain both amorphous films and cryst. regions that are richer in implanted Ga. More complex milling sequences show that redeposition of milled material, enriched in Ga, can occur depending on the geometry of the mill employed. The thickness of the damage layers depends strongly on beam energy, but is independent of beam current. Monte Carlo modeling of the damage formed indicates that recoil Si atoms contribute significantly to the damaged formed in the specimen.
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    29. 29
      Liu, N. J.; Xie, Y. J.; Liu, G. N.; Sohn, S.; Raj, A.; Han, G. X.; Wu, B. Z.; Cha, J. J.; Liu, Z.; Schroers, J. General Nanomolding of Ordered Phases. Phys. Rev. Lett. 2020, 124, 036102  DOI: 10.1103/PhysRevLett.124.036102
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      General Nanomolding of Ordered Phases
      Liu, Naijia; Xie, Yujun; Liu, Guannan; Sohn, Sungwoo; Raj, Arindam; Han, Guoxing; Wu, Bozhao; Cha, Judy J.; Liu, Ze; Schroers, Jan
      Physical Review Letters (2020), 124 (3), 036102CODEN: PRLTAO; ISSN:1079-7114. (American Physical Society)
      Large-scale, controlled fabrication of ordered phases is challenging at the nanoscale, yet highly demanded as their well-ordered structure and chem. is the key for advanced functionality. Here, we demonstrate a general nanomolding process of ordered phases based on at. diffusion. Resulting nanowires are single crystals and maintain their compn. and structure throughout their length, which we explain by a self-ordering process originating from their narrow Gibbs free energy. The versatility, control, and precision of this thermomech. nanomolding method of ordered phases provides new insights into single crystal growth and suggest itself as a technol. to enable wide spread usage for nanoscale and quantum devices.
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      Liu, Z. One-step fabrication of crystalline metal nanostructures by direct nanoimprinting below melting temperatures. Nat. Commun. 2017, 8, 1– 7,  DOI: 10.1038/ncomms14910
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      In vivo cation exchange in quantum dots for tumor-specific imaging
      Liu, Xiangyou; Braun, Gary B.; Qin, Mingde; Ruoslahti, Erkki; Sugahara, Kazuki N.
      Nature Communications (2017), 8 (1), 1-13CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
      In vivo tumor imaging with nanoprobes suffers from poor tumor specificity. Here, we introduce a nanosystem, which allows selective background quenching to gain exceptionally tumor-specific signals. The system uses near-IR quantum dots and a membrane-impermeable etchant, which serves as a cation donor. The etchant rapidly quenches the quantum dots through cation exchange (ionic etching), and facilitates renal clearance of metal ions released from the quantum dots. The quantum dots are i.v. delivered into orthotopic breast and pancreas tumors in mice by using the tumor-penetrating iRGD peptide. Subsequent etching quenches excess quantum dots, leaving a highly tumor-specific signal provided by the intact quantum dots remaining in the extravascular tumor cells and fibroblasts. No toxicity is noted. The system also facilitates the detection of peritoneal tumors with high specificity upon i.p. tumor targeting and selective etching of excess untargeted quantum dots. In vivo cation exchange may be a promising strategy to enhance specificity of tumor imaging.
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      Liu, Z.; Han, G. X.; Sohn, S.; Liu, N. J.; Schroers, J. Nanomolding of Crystalline Metals: The Smaller the Easier. Phys. Rev. Lett. 2019, 122, 036101  DOI: 10.1103/PhysRevLett.122.036101
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      Nanomolding of Crystalline Metals: The Smaller the Easier
      Liu, Ze; Han, Guoxing; Sohn, Sungwoo; Liu, Naijia; Schroers, Jan
      Physical Review Letters (2019), 122 (3), 036101CODEN: PRLTAO; ISSN:1079-7114. (American Physical Society)
      We report on a thermomech. nanomolding method for cryst. metals. Quantified by the aspect ratio, this process becomes easier with decreasing mold diam. As the responsible underlying diffusion mechanism is present in all metals and alloys, the discovered nanomolding process provides a toolbox to shape essentially any metal and alloy into a nanofeature. Technol., this highly versatile and practical thermomech. nanomolding technique offers a method to fabricate high-surface-area metallic nanostructures which are impactful in diverse fields of applications including catalysts, sensors, photovoltaics, microelectronics, and plasmonics.
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      Liu, N.; Liu, G.; Raj, A.; Sohn, S.; Morales, M.; Liu, J.; Schroers, J. Unleashing Nanofabrication through Thermomechanical Nanomolding. Science Advances 2021, 7, eabi8795
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      Raj, A.; Liu, N.; Liu, G.; Sohn, S.; Xiang, J.; Liu, Z.; Schroers, J. Nanomolding of Gold and Gold-Silicon Heterostructures at Room Temperature. ACS Nano 2021, 15, 14275– 14284,  DOI: 10.1021/acsnano.1c02636
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      Nanomolding of Gold and Gold-Silicon Heterostructures at Room Temperature
      Raj, Arindam; Liu, Naijia; Liu, Guannan; Sohn, Sungwoo; Xiang, Junxiang; Liu, Ze; Schroers, Jan
      ACS Nano (2021), 15 (9), 14275-14284CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Nanofabrication techniques are limited by at least one of the required characteristics such as choice of material, control over geometry, fabrication requirements, yield, cost, and scalability. Our previously developed method of thermomech. nanomolding fulfills these requirements, although it requires high processing temps. Here, we demonstrate low-temp. molding where we utilize the enhanced diffusivity on "eutectic interfaces". Gold nanorods are molded at room temp. using Au-Si alloy as feedstock. Instead of using alloy feedstock, these "eutectic interfaces" can also be established through a feedstock-mold combination. We demonstrate this by using pure Au as feedstock, which is molded into Si molds at room temp., and also the reverse, Si feedstock is molded into Au molds forming high aspect ratio Au-Si core-shell nanorods. We discuss the mechanism of this low-temp. nanomolding in terms of lower homologous temp. at the eutectic interface. This technique, based on enhanced eutectic interface diffusion, provides a practical nanofabrication method that eliminates the previous high-temp. requirements, thereby expanding the range of the materials that can be practically nanofabricated.
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      Li, S.; Ding, X.; Li, J.; Ren, X.; Sun, J.; Ma, E. High-efficiency mechanical energy storage and retrieval using interfaces in nanowires. Nano Lett. 2010, 10, 1774– 1779,  DOI: 10.1021/nl100263p
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      High-efficiency mechanical energy storage and retrieval using interfaces in nanowires
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    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.1c03744.

    • Supplementary Text Sections 1−3: Diffusion Mechanisms of TMNM, Preferred Growth Direction Calculation for bcc Materials, and Reorientation Mechanism of the Substrate. Supplementary Figures S1–S7. Supplementary Table S1. Supplementary References (PDF)


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