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Compositional control over vapor–liquid–solid III–V ternary nanowires based on group V intermix (VLS IIIVxV1−x NWs) is complicated by the presence of a catalyst droplet with extremely low and hence undetectable concentrations of group V atoms. The liquid–solid and vapor–solid distributions of IIIVxV1−x NWs at a given temperature are influenced by the kinetic parameters (supersaturation and diffusion coefficients in liquid, V/III flux ratio in vapor), temperature and thermodynamic constants. We analyze the interplay of the kinetic and thermodynamic factors influencing the compositions of VLS IIIVxV1−x NWs and derive a new vapor–solid distribution that contains only one parameter of liquid, the ratio of the diffusion coefficients of dissimilar group V atoms. The unknown concentrations of group V atoms in liquid have no influence on the NW composition at high enough levels of supersaturation in liquid. The simple analytic shape of this vapor–solid distribution is regulated by the total V/III flux ratio in vapor. Calculating the temperature-dependent desorption rates, we show that the purely kinetic regime of the liquid–solid growth occurs for VLS IIIVxV1−x NWs in a wide range of conditions. The model fits the data well on the vapor–solid distributions of VLS InPxAs1−x and GaPxAs1−x NWs and can be used for understanding and controlling the compositions of any VLS IIIVxV1−x NWs, as well as modeling the compositional profiles across NW heterostructures in different material systems. [ABSTRACT FROM AUTHOR]

Due to the very efficient relaxation of elastic stress on strain-free sidewalls, III–V nanowires offer almost unlimited possibilities for bandgap engineering in nanowire heterostructures by using material combinations that are attainable in epilayers. However, axial nanowire heterostructures grown using the vapor–liquid–solid method often suffer from the reservoir effect in a catalyst droplet. Control over the interfacial abruptness in nanowire heterostructures based on the group V interchange is more difficult than for group-III-based materials, because the low concentrations of highly volatile group V atoms cannot be measured after or during growth. Here, we develop a self-consistent model for calculations of the coordinate-dependent compositional profiles in the solid and liquid phases during the vapor–liquid–solid growth of the axial nanowire heterostructure  A x 0 B 1 − x 0 C / A x 1 B 1 − x 1 C  with any stationary compositions  x 0  and  x 1 . The only assumption of the model is that the growth rates of both binaries AC and BC are proportional to the concentrations of group V atoms A and B in a catalyst droplet, requiring high enough supersaturations in liquid phase. The model contains a minimum number of parameters and fits quite well the data on the interfacial abruptness across double heterostructures in GaP/GaAsxP1−x/GaP nanowires. It can be used for any axial III–V nanowire heterostructures obtained through the vapor–liquid–solid method. It forms a basis for further developments in modeling the complex growth process and suppression of the interfacial broadening caused by the reservoir effect. [ABSTRACT FROM AUTHOR]

Control over the composition of III–V ternary nanowires grown by the vapor–liquid–solid (VLS) method is essential for bandgap engineering in such nanomaterials and for the fabrication of functional nanowire heterostructures for a variety of applications. From the fundamental viewpoint, III–V ternary nanowires based on group V intermix (InSbxAs1−x, InPxAs1−x, GaPxAs1−x and many others) present the most difficult case, because the concentrations of highly volatile group V atoms in a catalyst droplet are beyond the detection limit of any characterization technique and therefore principally unknown. Here, we present a model for the vapor–solid distribution of such nanowires, which fully circumvents the uncertainties that remained in the theory so far, and we link the nanowire composition to the well-controlled parameters of vapor. The unknown concentrations of group V atoms in the droplet do not enter the distribution, despite the fact that a growing solid is surrounded by the liquid phase. The model fits satisfactorily the available data on the vapor–solid distributions of VLS InSbxAs1−x, InPxAs1−x and GaPxAs1−x nanowires grown using different catalysts. Even more importantly, it provides a basis for the compositional control of III–V ternary nanowires based on group V intermix, and it can be extended over other material systems where two highly volatile elements enter a ternary solid alloy through a liquid phase. [ABSTRACT FROM AUTHOR]

Compositional control over vapor–liquid–solid III–V ternary nanowires based on group V intermix (VLS IIIVxV1−x NWs) is complicated by the presence of a catalyst droplet with extremely low and hence undetectable concentrations of group V atoms. The liquid–solid and vapor–solid distributions of IIIVxV1−x NWs at a given temperature are influenced by the kinetic parameters (supersaturation and diffusion coefficients in liquid, V/III flux ratio in vapor), temperature and thermodynamic constants. We analyze the interplay of the kinetic and thermodynamic factors influencing the compositions of VLS IIIVxV1−x NWs and derive a new vapor–solid distribution that contains only one parameter of liquid, the ratio of the diffusion coefficients of dissimilar group V atoms. The unknown concentrations of group V atoms in liquid have no influence on the NW composition at high enough levels of supersaturation in liquid. The simple analytic shape of this vapor–solid distribution is regulated by the total V/III flux ratio in vapor. Calculating the temperature-dependent desorption rates, we show that the purely kinetic regime of the liquid–solid growth occurs for VLS IIIVxV1−x NWs in a wide range of conditions. The model fits the data well on the vapor–solid distributions of VLS InPxAs1−x and GaPxAs1−x NWs and can be used for understanding and controlling the compositions of any VLS IIIVxV1−x NWs, as well as modeling the compositional profiles across NW heterostructures in different material systems.

Due to the very efficient relaxation of elastic stress on strain-free sidewalls, III–V nanowires offer almost unlimited possibilities for bandgap engineering in nanowire heterostructures by using material combinations that are attainable in epilayers. However, axial nanowire heterostructures grown using the vapor–liquid–solid method often suffer from the reservoir effect in a catalyst droplet. Control over the interfacial abruptness in nanowire heterostructures based on the group V interchange is more difficult than for group-III-based materials, because the low concentrations of highly volatile group V atoms cannot be measured after or during growth. Here, we develop a self-consistent model for calculations of the coordinate-dependent compositional profiles in the solid and liquid phases during the vapor–liquid–solid growth of the axial nanowire heterostructure Ax0B1−x0C/Ax1B1−x1C with any stationary compositions x0 and x1. The only assumption of the model is that the growth rates of both binaries AC and BC are proportional to the concentrations of group V atoms A and B in a catalyst droplet, requiring high enough supersaturations in liquid phase. The model contains a minimum number of parameters and fits quite well the data on the interfacial abruptness across double heterostructures in GaP/GaAsxP1−x/GaP nanowires. It can be used for any axial III–V nanowire heterostructures obtained through the vapor–liquid–solid method. It forms a basis for further developments in modeling the complex growth process and suppression of the interfacial broadening caused by the reservoir effect.

Controlling the morphology and composition of semiconductor nano- and micro-structures is crucial for fundamental studies and applications. Here, Si-Ge semiconductor nanostructures were fabricated using photolithographically defined micro-crucibles on Si substrates. Interestingly, the nanostructure morphology and composition of these structures are strongly dependent on the size of the liquid–vapour interface (i.e., the opening of the micro-crucible) in the CVD deposition step of Ge. In particular, Ge crystallites nucleate in micro-crucibles with larger opening sizes (3.74–4.73 μm2), while no such crystallites are found in micro-crucibles with smaller openings of 1.15 μm2. This interface area tuning also results in the formation of unique semiconductor nanostructures: lateral nano-trees (for smaller openings) and nano-rods (for larger openings). Further TEM imaging reveals that these nanostructures have an epitaxial relationship with the underlying Si substrate. This geometrical dependence on the micro-scale vapour–liquid–solid (VLS) nucleation and growth is explained within a dedicated model, where the incubation time for the VLS Ge nucleation is inversely proportional to the opening size. The geometric effect on the VLS nucleation can be used for the fine tuning of the morphology and composition of different lateral nano- and micro-structures by simply changing the area of the liquid–vapour interface. [ABSTRACT FROM AUTHOR]

Control over the composition of III–V ternary nanowires grown by the vapor–liquid–solid (VLS) method is essential for bandgap engineering in such nanomaterials and for the fabrication of functional nanowire heterostructures for a variety of applications. From the fundamental viewpoint, III–V ternary nanowires based on group V intermix (InSbxAs1−x, InPxAs1−x, GaPxAs1−x and many others) present the most difficult case, because the concentrations of highly volatile group V atoms in a catalyst droplet are beyond the detection limit of any characterization technique and therefore principally unknown. Here, we present a model for the vapor–solid distribution of such nanowires, which fully circumvents the uncertainties that remained in the theory so far, and we link the nanowire composition to the well-controlled parameters of vapor. The unknown concentrations of group V atoms in the droplet do not enter the distribution, despite the fact that a growing solid is surrounded by the liquid phase. The model fits satisfactorily the available data on the vapor–solid distributions of VLS InSbxAs1−x, InPxAs1−x and GaPxAs1−x nanowires grown using different catalysts. Even more importantly, it provides a basis for the compositional control of III–V ternary nanowires based on group V intermix, and it can be extended over other material systems where two highly volatile elements enter a ternary solid alloy through a liquid phase.

The synthesis of alloy nanocatalysts with controllable sizes and shapes is a critical prerequisite for vapor–liquid–solid (VLS) growth of one-dimensional nanostructures. In this work, we comprehensively examined surface reactions between evaporated In atoms and a Bi thin film on a Si(111) surface at ambient temperature. InBi 2 liquid nanodroplets nucleate and grow during initial vapor–solid (VS) reaction between the In vapor and surface Bi atoms, and the reaction proceeds until a saturation point is reached, following which InBi 2 begins to catalyze subsequent VLS growth of various nanocrystals under persistent In-beam flux. The scaled size distribution of individual InBi 2 nanodroplets could be explained adequately using the classical capillary nucleation theory, which suggests that the simultaneous homogeneous nucleation of InBi 2 nanodroplets occurs during the vapor–solid (VS) reaction of In and Bi. [Display omitted] • Amorphous InBi 2 alloy nanodroplets are prepared by unique In–Bi surface reactions. • The InBi 2 nanodroplets catalyze subsequent VLS growth of In–Bi nanocrystals. • The size distribution of InBi 2 droplets conforms to the capillary nucleation theory. [ABSTRACT FROM AUTHOR]

A method for fabricating flexible free-standing ZnO/Zn composite films from the vapor phase using a regular array of silicon microwhiskers as a substrate is presented. The structural and morphological peculiarities, as well as luminescent properties of the films, were studied. The films have a hybrid structure consisting of two main microlayers. The first layer is formed directly on the tops of Si whiskers and has a thickness up to 10 µm. This layer features a polycrystalline structure and well-developed surface morphology. The second layer, which makes up the front side of the films, is up to 100 µm thick and consists of large microcrystals. The films show good bending strength—in particular, resistance to repeated bending and twisting—which is provided by a zinc metallic part constituting the flexible carrier of the films. ZnO photoluminescence was observed from both surfaces of the films but with conspicuous spectral differences. In particular, a significant weakening of ZnO green luminescence (more than 10 times) at an almost constant intensity of UV near-band edge emission was found for the polycrystalline side of the films as compared to the microcrystalline side. A high degree of homogeneity of the luminescent properties of the films over their area was demonstrated. The results obtained emphasize the relevance of further studies of such ZnO structures—in particular, for application in flexible devices, sensors, photocatalysis and light generation. [ABSTRACT FROM AUTHOR]

Group‐IV monochalcogenides have emerged with immense potential to be used as ferroelectric materials in recent times. However, in most of them, ferroelectricity is limited by the presence of inversion symmetry in their natural crystal structure. Here, an experimental observation of ferroelectric order at room temperature by introducing Eshelby twist in Germanium sulfide (GeS) nanowires is reported. The twisted nanowires are synthesized by low‐pressure chemical vapor deposition. The existence of room temperature ferroelectricity in a single nanowire is confirmed by electrical measurements, piezoelectric force microscopy, and second harmonic generation spectroscopy. Density functional theory calculations reveal that the twist in the GeS nanowires breaks the inversion symmetry where the inversion symmetry breaking phonon modes get hardened giving rise to ferroelectricity. These results are expected to be useful in making non‐volatile memory devices, flexible electronics, electronic sensors, and neuromorphic computing. [ABSTRACT FROM AUTHOR]

Controlling the morphology and composition of semiconductor nano- and micro-structures is crucial for fundamental studies and applications. Here, Si-Ge semiconductor nanostructures were fabricated using photolithographically defined micro-crucibles on Si substrates. Interestingly, the nanostructure morphology and composition of these structures are strongly dependent on the size of the liquid–vapour interface (i.e., the opening of the micro-crucible) in the CVD deposition step of Ge. In particular, Ge crystallites nucleate in micro-crucibles with larger opening sizes (3.74–4.73 μm2), while no such crystallites are found in micro-crucibles with smaller openings of 1.15 μm2. This interface area tuning also results in the formation of unique semiconductor nanostructures: lateral nano-trees (for smaller openings) and nano-rods (for larger openings). Further TEM imaging reveals that these nanostructures have an epitaxial relationship with the underlying Si substrate. This geometrical dependence on the micro-scale vapour–liquid–solid (VLS) nucleation and growth is explained within a dedicated model, where the incubation time for the VLS Ge nucleation is inversely proportional to the opening size. The geometric effect on the VLS nucleation can be used for the fine tuning of the morphology and composition of different lateral nano- and micro-structures by simply changing the area of the liquid–vapour interface.

A method for fabricating flexible free-standing ZnO/Zn composite films from the vapor phase using a regular array of silicon microwhiskers as a substrate is presented. The structural and morphological peculiarities, as well as luminescent properties of the films, were studied. The films have a hybrid structure consisting of two main microlayers. The first layer is formed directly on the tops of Si whiskers and has a thickness up to 10 µm. This layer features a polycrystalline structure and well-developed surface morphology. The second layer, which makes up the front side of the films, is up to 100 µm thick and consists of large microcrystals. The films show good bending strength—in particular, resistance to repeated bending and twisting—which is provided by a zinc metallic part constituting the flexible carrier of the films. ZnO photoluminescence was observed from both surfaces of the films but with conspicuous spectral differences. In particular, a significant weakening of ZnO green luminescence (more than 10 times) at an almost constant intensity of UV near-band edge emission was found for the polycrystalline side of the films as compared to the microcrystalline side. A high degree of homogeneity of the luminescent properties of the films over their area was demonstrated. The results obtained emphasize the relevance of further studies of such ZnO structures—in particular, for application in flexible devices, sensors, photocatalysis and light generation.

Electromagnetic absorbents with peculiarities of light-weight, beneficial structure, broadband, adequate corrosion resistance, and facile synthesis route are always highly practical in the telecom and stealth fields. In this regard, a new type hybird material (SiC/Fe)@C nanowires (NWs) has been effectively synthesized through an in-situ vapor-liquid-solid growth confined at arc-plasma region. A (SiC/Fe)@C NW is composed of a dielectric SiC NW with a magnetic Fe nanoparticle at it tip, both tightly encapsulated by conductive graphene-like carbon nanolayers at the surfaces. Such carbon-coated NWs form a randomly interconnected network, endowing a proper impedance matching to microwave and an anti-corrosion ability. It is found that the composite of (SiC/Fe)@C NWs and paraffin with a 25 wt% loading has shown the lowest reflection loss (RL) of −63.44 dB at 12.4 GHz, with a wide effective absorption band (RL ≤ −10 dB) of 7 GHz in thickness of 1.95 mm. This superb RL is attributed to the synergic outcomes from the balanced dielectric/magnetic losses with an appropriate impedance matching, resulted from the intrinsic physical properties and special structures of the (SiC/Fe)@C NWs. Pseudo percolation threshold, near 30 wt% loading of (SiC/Fe)@C NWs in the electromagnetically transparent matrix, implies the significant efficacy of concentration/distribution of absorbent on RL performances. Image 1 • (SiC/Fe)@C NWs have been fabricated by arc-discharge plasma; formation mechanism well explained by VLS growth. • (SiC/Fe)@C NWs found oxidation resistant up to ∼500 °C, allowing the microwave absorber adaptive in an atrocious condition. • 1D geometry of (SiC/Fe)@C NW synergistically contribute to microwave absorption. • The (SiC/Fe)@C NWs/paraffin composite reveals RL min. of -63.44 dB at 12.4 GHz in 1.95 mm thickness, and EAB of 7 GHz. [ABSTRACT FROM AUTHOR]

One of the promising nonvolatile memories of the next generation is resistive random-access memory (ReRAM). It has vast benefits in comparison to other emerging nonvolatile memories. Among different materials, dielectric films have been extensively studied by the scientific research community as a nonvolatile switching material over several decades and have reported many advantages and downsides. However, less attention has been given to low-dimensional materials for resistive memory compared to dielectric films. Particularly, β-Ga2O3 is one of the promising materials for high-power electronics and exhibits the resistive switching phenomenon. However, low-dimensional β-Ga2O3 nanowires have not been explored in resistive memory applications, which hinders further developments. In this article, we studied the resistance switching phenomenon using controlled electron flow in the 1D nanowires and proposed possible resistive switching and electron conduction mechanisms. High-density β-Ga2O3 1D-nanowires on Si (100) substrates were produced via the VLS growth technique using Au nanoparticles as a catalyst. Structural characteristics were analyzed via SEM, TEM, and XRD. Besides, EDS, CL, and XPS binding feature analyses confirmed the composition of individual elements, the possible intermediate absorption sites in the bandgap, and the bonding characteristics, along with the presence of various oxygen species, which is crucial for the ReRAM performances. The forming-free bipolar resistance switching of a single β-Ga2O3 nanowire ReRAM device and performance are discussed in detail. The switching mechanism based on the formation and annihilation of conductive filaments through the oxygen vacancies is proposed, and the possible electron conduction mechanisms in HRS and LRS states are discussed.

Two-dimensional transition metal nitrides offer intriguing possibilities for achieving novel electronic and mechanical functionality owing to their distinctive and tunable bonding characteristics compared to other 2D materials. We demonstrate here the enabling effects of strong bonding on the morphology and functionality of 2D tungsten nitrides. The employed bottom-up synthesis experienced a unique substrate stabilization effect beyond van-der-Waals epitaxy that favored W 5 N 6 over lower metal nitrides. Comprehensive structural and electronic characterization reveals that monolayer W 5 N 6 can be synthesized at large scale and shows semimetallic behavior with an intriguing indirect band structure. Moreover, the material exhibits exceptional resilience against mechanical damage and chemical reactions. Leveraging these electronic properties and robustness, we demonstrate the application of W 5 N 6 as atomic-scale dry etch stops that allow the integration of high-performance 2D materials contacts. These findings highlight the potential of 2D transition metal nitrides for realizing advanced electronic devices and functional interfaces.

Copper doped zinc oxide (Cu:ZnO) nanonails with uniformly distributed Cu ions through the nail structure were synthesized via a vapor-liquid-solid technique using seed Cu:ZnO nanoparticles. The seed nanoparticles were prepared with a simple precipitation method. The structure and morphology of nanonails and the distribution of Cu ions were investigated using X-ray diffraction, electron energy loss spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and elemental mapping analysis. The defect states in the Cu:ZnO nanonails were characterized by room temperature photoluminescence (PL) spectra. The obtained Cu:ZnO nanonails have single phase wurtzite structure of ZnO and incorporated copper ions are in the Cu2+ oxidation state. SEM and TEM micrographs revealed that nanostructures with well-defined nail morphology composed of a hexagonal cap (~350 nm in diameter) and a prismatic shaft (~550 nm in diameter) connected with cylindrical neck (~250 nm in diameter). Both SEM and TEM elemental mapping analysis proved that the usage of Cu:ZnO seed nanoparticles resulted in highly homogeneous distribution of Cu ions into ZnO nanonails. High crystallinity of the Cu:ZnO nanonails was revealed with PL spectra composed of predominant second order diffraction peak and near band edge of UV emission peak and also weak defect related deep level green and violent emission peaks. Image 1 [ABSTRACT FROM AUTHOR]

We studied the electrical transport properties of Au-seeded germanium nanowires with radii ranging from 11 to 80 nm at ambient conditions. We found a non-trivial dependence of the electrical conductivity, mobility and carrier density on the radius size. In particular, two regimes were identified for large (lightly doped) and small (stronger doped) nanowires in which the charge-carrier drift is dominated by electron-phonon and ionized-impurity scattering, respectively. This goes in hand with the finding that the electrostatic properties for radii below ca. 37 nm have quasi one-dimensional character as reflected by the extracted screening lengths.

The possibility to expand the range of material combinations in defect-free heterostructures is one of the main motivations for the great interest in semiconductor nanowires. However, most axial nanowire heterostructures suffer from interface compositional gradients and kink formation, as a consequence of nanoparticle-nanowire interactions during the metal-assisted growth. Understanding such interactions and how they affect the growth mode is fundamental to achieve a full control over the morphology and the properties of nanowire heterostructures for device applications. Here we demonstrate that the sole parameter affecting the growth mode (straight or kinked) of InP segments on InAs nanowire stems by the Au-assisted method is the nanoparticle composition. Indeed, straight InAs-InP nanowire heterostructures are obtained only when the In/Au ratio in the nanoparticles is low, typically smaller than 1.5. For higher In content, the InP segments tend to kink. Tailoring the In/Au ratio by the precursor fluxes at a fixed growth temperature enables us to obtain straight and radius-uniform InAs-InP nanowire heterostructures (single and double) with atomically sharp interfaces. We present a model that is capable of describing all the experimentally observed phenomena: straight growth versus kinking, the stationary nanoparticle compositions in pure InAs and InAs-InP nanowires, the crystal phase trends, and the interfacial abruptness. By taking into account different nanowire/nanoparticle interfacial configurations (forming wetting or nonwetting monolayers in vertical or tapered geometry), our generalized model provides the conditions of nanoparticle stability and abrupt heterointerfaces for a rich variety of growth scenarios. Therefore, our results provide a powerful tool for obtaining high quality InAs-InP nanowire heterostructures with well-controlled properties and can be extended to other material combinations based on the group V interchange. [ABSTRACT FROM AUTHOR]

In the present study, a C/SiFeN(O)-based ceramic paper with in situ generated hierarchical micro/nano-morphology was prepared upon thermal treatment of a cellulose-base paper surface-modified with a polymeric single-source precursor prepared from perhydropolysilazane (PHPS) and iron(II) acetylacetonate (Fe(acac) 2 ). The ammonolysis at 1000 °C of the paper/precursor hybrid materials leads to a C/SiFeN(O)-based ceramic paper which exhibits the same morphology as that of the cellulose paper. Subsequent annealing of the ceramic paper in nitrogen atmosphere at temperatures from 1200 to 1400 °C results in the in-situ generation of ultra-long silicon nitride nanowires with aspect ratios in the range of 10 3 on the surface and in the macropores of the ceramic paper. The nanowires exhibit round Fe 3 Si tips at the end, indicating that the growth occurred via iron-catalyzed VLS (vapor-liquid-solid) mechanism. The combination of single-source precursor, porous template and in situ VLS growth of 1D nanostructures provides a convenient one-pot synthesis approach to produce ceramic nanocomposites with hierarchical morphologies. [ABSTRACT FROM AUTHOR]

Nanowires with inhomogeneous heterostructures such as polytypes and periodic twin boundaries are interesting due to their potential use as components for optical, electrical, and thermophysical applications. Additionally, the incorporation of metal impurities in semiconductor nanowires could substantially alter their electronic and optical properties. In this highlight article, we review our recent progress and understanding in the deliberate induction of imperfections, in terms of both twin boundaries and additional impurities in germanium nanowires for new/enhanced functionalities. The role of catalysts and catalyst-nanowire interfaces for the growth of engineered nanowires via a three-phase paradigm is explored. Three-phase bottom-up growth is a feasible way to incorporate and engineer imperfections such as crystal defects and impurities in semiconductor nanowires via catalyst and/or interfacial manipulation. 'Epitaxial defect transfer' process and catalyst-nanowire interfacial engineering are employed to induce twin defects parallel and perpendicular to the nanowire growth axis. By inducing and manipulating twin boundaries in the metal catalysts, twin formation and density are controlled in Ge nanowires. The formation of Ge polytypes is also observed in nanowires for the growth of highly dense lateral twin boundaries. Additionally, metal impurity in the form of Sn is injected and engineered via third-party metal catalysts resulting in above-equilibrium incorporation of Sn adatoms in Ge nanowires. Sn impurities are precipitated into Ge bi-layers during Ge nanowire growth, where the impurity Sn atoms become trapped with the deposition of successive layers, thus giving an extraordinary Sn content (>6 at.%) in Ge nanowires. A larger amount of Sn impingement (>9 at.%) is further encouraged by utilizing the eutectic solubility of Sn in Ge along with impurity trapping. [ABSTRACT FROM AUTHOR]

Growth experiments of monoclinic gallium oxide ( β -Ga 2 O 3 ) nanostructures were performed by the atmospheric-pressure CVD using metal gallium (Ga) beads and water (H 2 O) as source materials and a Au film as a catalyst in terms of substrate materials, Au film thickness, growth temperature and growth time. Local structure analysis based on transmission electron microscope (TEM) observations and selective area electron diffraction (SAED) measurements revealed the successful growth of single crystalline β -Ga 2 O 3 nanowires (NWs) through vapor-liquid-solid (VLS) growth mechanism. The average diameter of the NWs was changed in the range from ~ 60 to ~ 1500 nm under the growth conditions picked up in this paper. The critical temperature for the VLS growth using the 30 nm-thick Au catalytic film was experimentally estimated to be ~ 789 °C. The diversity of shapes of nanostructures was probably due to the temperature evolution of Au catalytic particle size, the film growth on the NW sides by vapor-solid (VS) growth mechanism, and the epitaxial relation between the substrate and the individual NW. The photoluminescence intensity of the blue band emission at ~ 490 nm relative to that of the ultraviolet band emission at ~ 360 nm became larger with increasing average diameter, suggesting the increase in the native defects formed near the surface region. [ABSTRACT FROM AUTHOR]

Au-catalyzed III-V nanowire heterostructures based on the group III interchange usually grow straight only in one of the two growth sequences, whereas the other sequence produces kinked geometries; thus, the realization of double heterostructures remains challenging. Here, we investigate the growth of Au-assisted InAs-GaAs and GaAs-InAs axial nanowire heterostructures. A detailed study of the heterostructure morphology as a function of growth parameters and chemical composition of the catalyst nanoparticle is performed by means of scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray analysis. Our results clearly demonstrate that the nanoparticle composition, rather than other growth parameters, as postulated so far, controls the growth mode and the resulting nanowire morphology. Although GaAs easily grows straight on InAs, straight growth of InAs on GaAs is achieved only if the nanoparticle composition is properly tuned. We find that straight InAs segments on GaAs require high group III-to-Au ratios in the nanoparticle (greater than 0.8); otherwise, the droplet wets the sidewalls and the nanowire kinks. We discuss the observed behavior within a theoretical model that relates the nanoparticle stability to the group III-to-Au ratio. Based on this finding, we demonstrate the growth of straight nanowire heterostructures for both sequences. The proposed strategy can be extended to other III-V nanowire heterostructures based on the group III interchange, allowing for straight morphology regardless of the growth sequence, and ultimately for designing nanowire heterostructures with the required properties for different applications. [ABSTRACT FROM AUTHOR]

Nanometer sized silicon (Si) needles (nanowires) offer a vehicle for varieties of applications at nanoscale. We grow Si nanoneedles (SiNNs) using very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method with distinct gold (Au) nanostructures (NSs) as catalyst. Au NSs in the form of nanoparticles (NPs) and continuous thin film are prepared on Si(1 0 0) substrates via radio frequency magnetron sputtering. Au catalyst size dependent surface morphology and structural features of these SiNNs are determined. Samples are characterized via imaging and spectroscopic measurements. Controlled growth of such SiNNs structure with reproducibility that is achieved via Au NPs size tunability is attributed to the vapor–liquid–solid (VLS) growth mechanism. SiNNs with diameters between 20 and 120 nm and length up to 5 μm are acquired. SiNNs diameter is found to increase with the increase of Au NPs size. Processing parameters optimization is demonstrated to play a critical role in nucleating Au NPs and thereby achieving high density SiNNs morphology. X-ray diffraction patterns authenticated an enhanced SiNNs crystallinity with increasing catalyst size. Raman spectra of SiNNs revealed a red-shift (∼8.26 cm −1 ) in the first-order transversal band as the average diameter of NNs are decrease from 69 to 57 nm. Our systematic method for synthesis and characterization may contribute toward the development of SiNNs based optoelectronics. [ABSTRACT FROM AUTHOR]

Although the various effects of strain on silicon are subject of intensive research since the 1950s the physical background of anomalous piezoresistive effects in Si nanowires (NWs) is still under debate. Recent investigations concur in that due to the high surface-to-volume ratio extrinsic surface related effects superimpose the intrinsic piezoresistive properties of nanostructures. To clarify this interplay of piezoresistive effects and stress related surface potential modifications, we explored a particular tensile straining device (TSD) with a monolithic embedded vapor-liquid-solid (VLS) grown Si NW. Integrating the suspended NW in a gate all around (GAA) field effect transistor (FET) configuration with a transparent gate stack enables optical and field modulated electrical characterization under high uniaxial tensile strain applied along the ?111? Si NW growth direction. A model based on stress-induced carrier mobility change and surface charge modulation is proposed to interpret the actual piezoresistive behavior of Si NWs. By controlling the nature and density of surface states via passivation the "true" piezoresistance of the NWs is found to be comparable with that of bulk Si. This demonstrates the indispensability of application-specific NW surface conditioning and the modulation capability of Si NWs properties for sensor applications. [ABSTRACT FROM AUTHOR]

High-density growth of single-crystalline BiSeTe nanowires was achieved via the vapour-liquid-solid process. The stoichiometry of samples grown at various substrate temperatures is precisely determined based on energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy on individual nanowires. We discuss the growth mechanism and present insights into the catalyst-precursor interaction. [ABSTRACT FROM AUTHOR]

Ultralong GaAs nanowires were grown by molecular beam epitaxy using the vapor-liquid-solid method. In this ultralong regime we show the existence of two features concerning the growth kinetic and the structural properties. Firstly, we observed a non-classical growth mode, where the axial growth rate is attenuated. Secondly, we observed structural defects at the surface of Wurtzite segments located at the bottom part of the nanowires. We explain these two phenomena as arising from a particular pathway of the group V species, specific to ultralong nanowires. Finally, the optical properties of such ultralong nanowires are studied by photoluminescence experiments., (© 2022 IOP Publishing Ltd.)

Abstract: ZnO nanorods (NRs) are grown in different atmospheres (argon, air, oxygen and nitrogen) by using the vapor–liquid–solid (VLS) method. The influence of different growth atmospheres on the luminescence properties has been investigated by using the photoluminescence (PL), cathodoluminescence (CL) and electroluminescence (EL) spectra measurements at room temperature. The PL spectra investigations reveal that the air, the oxygen and the nitrogen growth atmospheres have strongly affected the oxygen interstitial (Oi) and oxygen vacancy (VO) related deep level emission (DLE) bands in ZnO and this fact is also found consistent with the cathodoluminescence (CL) and electroluminescence (EL) spectra investigations. The color rendering investigations reveal that the growth atmospheres have also influenced the color quality of the emitted light. These results indicate that the defects related emissions from the band gap of ZnO NRs can be tuned by using different growth atmospheres. These results can be useful for the development of white light emitting diodes (WLEDs). [Copyright &y& Elsevier]

Abstract: This works deals with the localized growth of SiC on monocrystalline (100) diamond surface. It describes an attempt of selective epitaxy using vapor–liquid–solid (VLS) transport. Patterns of Al–Si stacking were melted and fed by propane. Morphology, structure and doping type of the SiC deposit were evaluated. The deposit was found to be successfully selective but polycrystalline, with the 3C-SiC polytype. Study of the initial step of growth showed that SiC nucleation occurs without any propane addition but just through the interaction of liquid Al–Si and diamond via a dissolution/precipitation process. The VLS transport mainly assists the growth of these nuclei by providing a secondary carbon source. This explains the random nucleation and the polycrystalline growth. Despite this, the deposit was dense enough to perform some preliminary electrical measurements which show encouraging results. [Copyright &y& Elsevier]

Si nanowires are of interest for photovoltaics and sensors. We report about the growth of Si nanowires from SiH4 using a Au catalyzed vapor-liquid-solid (VLS) growth process in a tube furnace at atmospheric pressure. At elevated growth temperatures, single crystalline wires with clear facets are obtained. The influence of the furnace temperature and the Au layer thickness on the nanowire growth is investigated in detail. The orientation of the wires has been studied by EBSD. For electrical characterization, Pt metal contacts have been applied to individual wires using Pt deposition in a FIB microscope. The high values found for the conductivity indicate that Ga implantation occurs during the FIB process. Electrical characterization under illumination shows the presence of a significant photoconductivity. Further functionalization of the Si nanowires will be done by combining them with luminescent nanoparticles (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In this study, we investigated the thermal oxidation of silicon nanowires (SiNWs) grown via the vapor-liquid-solid (VLS) method with an Au catalyst. We systematically analyzed the oxidation mechanism of the SiNWs in both the radial and axial directions and mapped the behavior of the Au atoms on the sidewall and at top of the wire as a function of oxidation time. After thermal oxidation at a temperature of 900 °C, two kinds of oxidation behavior in SiNWs were observed: one was conventional radial oxidation and the other was axial oxidation. In particular, the axial oxidation rate at the Si/Au interface increased dramatically compared with the radial oxidation rate, which can be explained by the reaction between the Si atoms precipitated from the Au tip and the O gas injected in the area surrounding the Au tip. Additionally, we observed that the oxidation rate in the axial direction was inversely proportional to the wire diameter, which is related to the SiO surrounding the Si wire. Moreover, the Au shape changed with respect to the wire diameter, suggesting that both the stress in the Au-Si alloy and the SiO shell thickness of the wire critically affect the growth of SiO on Au. [InlineMediaObject not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: We report a study of low temperature gate stack on silicon nanowires compatible with Back-End-Of-Line (BEOL) integration. The same gate stack is deposited at low temperature on Si nanowires obtained thanks to either Chemical Vapor Deposition (CVD) or Selective Epitaxial Growth (SEG) in patterns. Gate stack characterization on CVD nanowires (NWs) shows low leakages and good agreement with simulated curves without interface states. A dramatic decrease of the capacitance in accumulation region and faster electron generation are observed and attributed to NW defects. In contrast, SEG devices reveals lower capacitance decrease with frequency but higher interface state density of about 1013 cm−2. [Copyright &y& Elsevier]

This paper discusses the electronic transport properties of nanowire field-effect transistors (NW-FETs). Four different device concepts are studied in detail: Schottky-barrier NW-FETs with metallic source and drain contacts, conventional-type NW-FETs with doped NW segments as source and drain electrodes, and, finally, two new concepts that enable steep turn-on characteristics, namely, NW impact ionization FETs and tunnel NW-FETs. As it turns out, NW-FETs are, to a large extent, determined by the device geometry, the dimensionality of the electronic transport, and the way of making contacts to the NW. Analytical as well as simulation results are compared with experimental data to explain the various factors impacting the electronic transport in NW-FETs. [ABSTRACT FROM AUTHOR]

Abstract: In order to improve a critical temperature (T c) of LaBa2Cu3O y (LaBCO) thin films for achieving a high irreversibility field, we investigated the vapor–liquid–solid (VLS) technique with various composition ratios of Ba/Cu in a liquid layer as growth solvent. As a result, we achieved the VLS-LaBCO thin films with excellent crystallinity and observed a spiral growth consisted of the wide terrace with a width of about 300nm. Moreover, the orthorhombicity and the T c onset of VLS-LaBCO thin films increased with increasing Ba/Cu ratio in the liquid layer. [Copyright &y& Elsevier]

A chemical route for synthesizing whiskers of refractory metal borides, carbides, and carbonitrides will be presented. Examples of whiskers are TiB2, B4C, TiC, TaC, NbC, and TixTa1-x(C,N). The synthesis technique used for the preparation is carbothermal reduction (CTR) of a starting oxide in combination with a vapor–liquid–solid growth mechanism (VLS) in the temperature range 1150–1800 °C in argon or nitrogen. Synthesis of e.g. TaC whiskers was made with Ta2O5 as a source for Ta. Carbon black was used to reduce the oxide, Ni to catalyse the whisker growth. NaCl was used as a source of Cl for vapor phase transportation of Ta-oxochlorides to the catalyst. The catalyst metal was recycled several times during the synthesis and was transported as NiCl2(g) according to thermodynamic calculations. The rate of whisker formation was found to depend on many parameters e.g. the synthesis temperature, the choice of catalyst, and the atmosphere. Many of the different whisker types were obtained in a yield of 70–90 vol.% with a diameter of 0.5–1 μm and a length of 10–30 μm. The intended use for the whiskers is as reinforcing materials in ceramic composites. Application areas are e.g. ceramic cutting tools. [Copyright &y& Elsevier]

A large number of Si wires on Si(111) can be fabricated selectively by the vapor–liquid–solid growth method with a high aspect ratio greater than 100. The diameter of the wire can be controlled from less than a micron to a few hundred microns. We propose a novel smart field electron emission device using silicon nano-wires fabricated by this vapor–liquid–solid growth method, and demonstrate field electron emission with a quite low operation voltage from a gated silicon nano-wire. The threshold voltage is about 13 V, and the value is similar to those for gated carbon-nanotube field emitters. The emission current reaches 10 nA at 15 V gate voltage. [Copyright &y& Elsevier]

High indium content III–V materials are one of the most promising candidates for beyond Si CMOS technologies. We present InAs planar nanowire (NW) MOSFETs grown directly on a semi-insulating GaAs (100) substrate by the selective lateral epitaxy (SLE) method via the metal-seeded planar vapor-liquid-solid mechanism. Despite a \sim 7 % lattice mismatch, in-plane and self-aligned single-crystal InAs NWs are grown epitaxially on GaAs. Such heterogeneous SLE provides a potential solution for the integration of different channel materials on one substrate. Gate-all-around MOSFET devices are fabricated by releasing the NW channel from the substrate through a combination of digital etching and selective etching processes. The device with a NW width of 30 nm and gate length of 350 nm shows an I_{\mathrm{{\scriptscriptstyle ON}}} / I_{\mathrm{{\scriptscriptstyle OFF}}} ratio of 10^4 and a peak transconductance of 220 mS/mm at V\mathrm {ds} = 0.5 V. [ABSTRACT FROM AUTHOR]

One of the promising nonvolatile memories of the next generation is resistive random-access memory (ReRAM). It has vast benefits in comparison to other emerging nonvolatile memories. Among different materials, dielectric films have been extensively studied by the scientific research community as a nonvolatile switching material over several decades and have reported many advantages and downsides. However, less attention has been given to low-dimensional materials for resistive memory compared to dielectric films. Particularly, β-Ga2O3 is one of the promising materials for high-power electronics and exhibits the resistive switching phenomenon. However, low-dimensional β-Ga2O3 nanowires have not been explored in resistive memory applications, which hinders further developments. In this article, we studied the resistance switching phenomenon using controlled electron flow in the 1D nanowires and proposed possible resistive switching and electron conduction mechanisms. High-density β-Ga2O3 1D-nanowires on Si (100) substrates were produced via the VLS growth technique using Au nanoparticles as a catalyst. Structural characteristics were analyzed via SEM, TEM, and XRD. Besides, EDS, CL, and XPS binding feature analyses confirmed the composition of individual elements, the possible intermediate absorption sites in the bandgap, and the bonding characteristics, along with the presence of various oxygen species, which is crucial for the ReRAM performances. The forming-free bipolar resistance switching of a single β-Ga2O3 nanowire ReRAM device and performance are discussed in detail. The switching mechanism based on the formation and annihilation of conductive filaments through the oxygen vacancies is proposed, and the possible electron conduction mechanisms in HRS and LRS states are discussed. [ABSTRACT FROM AUTHOR]