Search

(In, Ga) alloy droplets are used to catalyse the growth of (In, Ga)As nanowires by molecular beam epitaxy on Si(111) substrates. The composition, morphology and optical properties of these nanowires can be tuned by the employed elemental fluxes. To incorporate more than 10% of In, a high In/(In+Ga) flux ratio above 0.7 is required. We report a maximum In content of almost 30% in bulk (In, Ga)As nanowires for an In/(In+Ga) flux ratio of 0.8. However, with increasing In/(In+Ga) flux ratio, the nanowire length and diameter are notably reduced. Using photoluminescence and cathodoluminescence spectroscopy on nanowires covered by a passivating (In, Al)As shell, two luminescence bands are observed. A significant segment of the nanowires shows homogeneous emission, with a wavelength corresponding to the In content in this segment, while the consumption of the catalyst droplet leads to a spectrally-shifted emission band at the top of the nanowires. The (In,Ga)As nanowires studied in this work provide a new approach for the integration of infrared emitters on Si platforms. [ABSTRACT FROM AUTHOR]

Herein, the crystal phase switching between the cubic zinc‐blende and hexagonal wurtzite phases in self‐catalyzed GaAs nanowires (NWs) is theoretically studied, considering the dependence of the droplet contact angle on the position at the triple‐phase line. This dependence is calculated for the droplets resting on the NW top facet, which has the shape of truncated hexagon. The nucleation of c and h islands, corresponding to the cubic and hexagonal crystal phases, at the triple‐phase line and in the center of the catalyst–NW interface, is considered within the classical nucleation theory. As a result, the probability of h‐island nucleation as a function of the average contact angle is obtained. It is found that the maximum of this probability shifts to the region of large contact angles when the length of narrow edges of the NW top facet decreases. Also, it is shown that the GaAs island nucleation at the triple‐phase line occurs preferentially in the vicinity of the top facet corners. [ABSTRACT FROM AUTHOR]

Monolayer MoS2 is a two‐dimensional transition‐metal dichalcogenide (TMD), and its atomic‐level thickness makes it an appealing research target in beyond‐silicon devices. Future practical uses are intimately related to controllable synthesis of materials at present, and salt‐assisted chemical vapor deposition (SA‐CVD) offers a promising way. However, the specific growth mechanism of alkali metal salts on MoS2 crystal development and their influence on optoelectronic characteristics of the as‐grown MoS2 crystals is not fully identified. Here, based on large amount experiments, we present a vapor‐liquid‐solid (VLS) edge‐adsorbed growth model for synthesizing MoS2 nanoflakes, emphasizing the edge‐adsorbed phenomena of the alkali metal element Na in regulating MoS2 crystal shape. Through controlling flow rate of carrier gas, the MoS2 defective morphology can be effectively suppressed. This study contributes to a better understanding of the role of alkali metal halide salts in TMD development by providing experimental and theoretical evidence, which is critical for synthesizing high quality TMD by alkali metal halide salts catalyst. [ABSTRACT FROM AUTHOR]

Compositional control in III–V ternary nanowires grown by the vapor–liquid–solid method is essential for bandgap engineering and the design of functional nanowire nano-heterostructures. Herein, we present rather general theoretical considerations and derive explicit forms of the stationary vapor–solid and liquid–solid distributions of vapor–liquid–solid III–V ternary nanowires based on group-III intermix. It is shown that the vapor–solid distribution of such nanowires is kinetically controlled, while the liquid–solid distribution is in equilibrium or nucleation-limited. For a more technologically important vapor-solid distribution connecting nanowire composition with vapor composition, the kinetic suppression of miscibility gaps at a growth temperature is possible, while miscibility gaps (and generally strong non-linearity of the compositional curves) always remain in the equilibrium liquid–solid distribution. We analyze the available experimental data on the compositions of the vapor–liquid–solid AlxGa1−xAs, InxGa1−xAs, InxGa1−xP, and InxGa1−xN nanowires, which are very well described within the model. Overall, the developed approach circumvents uncertainty in choosing the relevant compositional model (close-to-equilibrium or kinetic), eliminates unknown parameters in the vapor–solid distribution of vapor–liquid–solid nanowires based on group-III intermix, and should be useful for the precise compositional tuning of such nanowires. [ABSTRACT FROM AUTHOR]

Performance of the group IV monochalcogenide GeSe in solar cells, electronic, and optoelectronic devices is expected to improve when high-quality single crystalline material is used rather than polycrystalline films. Crystalline flakes represent an attractive alternative to bulk single crystals as their synthesis may be developed to be scalable, faster, and with higher overall yield. However, large - and especially large and thin - single crystal flakes are notoriously hard to synthesize. Here it is demonstrated that vapor-liquid-solid growth combined with direct lateral vapor-solid incorporation produces high-quality single crystalline GeSe ribbons with tens of micrometers size and controllable thickness. Electron microscopy shows that the ribbons exhibit perfect equilibrium (AB) van der Waals stacking order without extended defects across the entire thickness, in contrast to the conventional case of substrate-supported flakes where material is added via layer-by-layer nucleation and growth on the basal plane. Electrical measurements show anisotropic transport and a high Hall mobility of 85 cm 2  V -1  s -1 , on par with the best single crystals to date. Growth from mixed GeSe and SnSe vapors, finally, yields ribbons with unchanged structure and composition but with jagged edges, promising for applications that rely on ample chemically active edge sites, such as catalysis or photocatalysis., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

Compositional control in III–V ternary nanowires grown by the vapor–liquid–solid method is essential for bandgap engineering and the design of functional nanowire nano-heterostructures. Herein, we present rather general theoretical considerations and derive explicit forms of the stationary vapor–solid and liquid–solid distributions of vapor–liquid–solid III–V ternary nanowires based on group-III intermix. It is shown that the vapor–solid distribution of such nanowires is kinetically controlled, while the liquid–solid distribution is in equilibrium or nucleation-limited. For a more technologically important vapor-solid distribution connecting nanowire composition with vapor composition, the kinetic suppression of miscibility gaps at a growth temperature is possible, while miscibility gaps (and generally strong non-linearity of the compositional curves) always remain in the equilibrium liquid–solid distribution. We analyze the available experimental data on the compositions of the vapor–liquid–solid AlxGa1−xAs, InxGa1−xAs, InxGa1−xP, and InxGa1−xN nanowires, which are very well described within the model. Overall, the developed approach circumvents uncertainty in choosing the relevant compositional model (close-to-equilibrium or kinetic), eliminates unknown parameters in the vapor–solid distribution of vapor–liquid–solid nanowires based on group-III intermix, and should be useful for the precise compositional tuning of such nanowires.

The vapor–liquid–solid growth of semiconductor nanowires proceeds via the sequential nucleation and extension of biatomic monolayers at the interface between the solid wire and a liquid catalyst nanodroplet. In the case of III–V compounds, this mother phase contains only a small concentration of the volatile group V atoms. The growth regime where there is not enough such atoms available in the liquid at nucleation to complete a whole monolayer is studied experimentally and theoretically. Each monolayer cycle then consists in the rapid formation of a partial monolayer, followed by a slower propagation stage and by a waiting time preceding the next nucleation. The propagation and waiting times of long sequences of monolayers are measured in situ in a transmission electron microscope at three growth temperatures, in a single GaAs nanowire. The process is modeled and the statistics of the characteristic times are computed numerically and analytically. At low temperature, the weakness of group V desorption from the liquid should lead to a constant total monolayer cycle time, despite the stochasticity of the nucleation events. The modeling of the experiments yields values of several crucial growth parameters and provides guidance for the growth of nanowires in a deterministic regime. [ABSTRACT FROM AUTHOR]

The control of domain sizes provides a powerful means to engineer the characteristics of monolayer (ML) MoS2 films for specific applications including catalysts for hydrogen evolution and thin-film transistors. Here, we report an efficient way to control domain structures of MoS2 by substrate-dependent growth mode control. Deterministic control of growth modes, associated with catalytic intermediates, is introduced by utilizing different growth substrates in metal-organic chemical vapor deposition (MOCVD) of ML MoS2. Na-Mo-O eutectic alloys formed by a soda lime (SL) substrate dominate the growth based on a vapor-liquid-solid (VLS) process, resulting in large-crystalline domains of MoS2 with a reduced density of liquid nuclei. On the other hand, MoO3-x seeds formed from an alkali aluminosilicate (AA) substrate accelerate nucleation via a vapor-solid-solid (VSS) process for nanocrystalline domains. ML MoS2 of nanocrystalline domains resulted in efficient hydrogen evolution reactions (HERs), while large-domain films showed better electron conductivity. [ABSTRACT FROM AUTHOR]

Self‐catalyzed GaAs nanowire (NW) growth via the vapor–liquid–solid mechanism is investigated by a theoretical model including the kinetics of material transport inside the catalyst droplet. The proposed model allows the description of nucleation and growth of 2D islands on the top facet of GaAs NWs. Analytical expressions for the growth rate of the disk‐shaped GaAs island due to the volume diffusion of species in the droplet and for the attachment rate of GaAs pairs to the critical island are derived. As a result, the duration of the droplet refilling stage and the island growth stage at typical growth conditions of self‐catalyzed GaAs NWs are obtained by a self‐consistent calculation. Also, the time evolution of the droplet composition and the island radius are found. The derived equations for the island growth rate can be applied for modeling of catalyst‐assisted growth of other III–V compounds. The results of the modeling are in good agreement with the experimental data on self‐catalyzed GaAs NW growth via molecular beam epitaxy and can be used for the optimization of the NW growth conditions. [ABSTRACT FROM AUTHOR]

Abstract III–V nanowires (NWs) possess great potential for use in future semiconductor technology. Alloying with dilute amounts of nitrogen provides further flexibility in tuning their material properties. In this study, we report on successful in situ nitrogen incorporation into GaP(N) NWs during growth via the Au-catalyzed vapor-liquid-solid (VLS) mechanism. The impact of the nitrogen precursur unsymmetrical dimethyl hydrazine (UDMH) on morphology was found to be overall beneficial as it strongly reduces tapering. Analysis of the crystal structure of NWs with and without N reveals zinc blende structure with an intermediate amount of stacking faults (SF). Interestingly, N incorporation leads to segments completely free of SFs, which are related to dislocations transverse to the growth direction.

It is well known that chemical potential driving the vapor–liquid–solid growth of nanowires oscillates in synchronization with the monolayer growth. In III–V nanowires, this occurs due to depletion of group V atoms in a catalyst droplet. The amphoteric behavior of silicon doping, which often changes from n‐type in planar GaAs layers to p‐type in nanowires, is attributed to low arsenic concentrations. Herein, we present an analytical model which quantifies the doping oscillations over the monolayer formation cycle, and its impact on the electron‐to‐hole ratio for the silicon doping of GaAs nanowires. It is shown that arsenic depletion can easily double the amphoteric effect and strongly favor the tendency for p‐type doping. On a more general ground, the nanowire doping process appears highly sensitive to the chemical potential oscillations related to a restricted amount of material in a nanoscale catalyst. [ABSTRACT FROM AUTHOR]

<100>‐oriented hafnium carbide (HfC) nanowires are synthesized on the graphite substrate by chemical vapor deposition. The dependence of temperature, HfCl4 content, and flow rate of CH4 gas on the morphology of nanowires is investigated herein. The results indicate that the HfC nanowire often kinks to another growth direction at a high HfCl4 content or a low temperature due to the destabilization of the catalyst droplet induced by either a faster growth rate or slower thermal activation. Reduced nanowire density and length are observed at the sample synthesized at a lower CH4 flow rate. Based on the experimental results, high‐crystallinity nanowires with high aspect ratios and high densities are prepared at a lower HfCl4 content, higher temperature, and high CH4 flow rate. The field‐emission properties of a single HfC nanowire are also characterized by assembling a single HfC nanowire emitter. An extremely high field enhancement factor of 5.57 × 106 m−1 is obtained herein. [ABSTRACT FROM AUTHOR]

Scanning transmission electron microscopy (STEM) was successfully applied to the analysis of silicon nanowires (SiNWs) that were self-assembled during an inductively coupled plasma (ICP) process. The ICP-synthesized SiNWs were found to present a Si–SiO2 core–shell structure and length varying from ≈100 nm to 2–3 μm. The shorter SiNWs (maximum length ≈300 nm) were generally found to possess a nanoparticle at their tip. STEM energy dispersive X-ray (EDX) spectroscopy combined with electron tomography performed on these nanostructures revealed that they contain iron, clearly demonstrating that the short ICP-synthesized SiNWs grew via an iron-catalyzed vapor–liquid–solid (VLS) mechanism within the plasma reactor. Both the STEM tomography and STEM-EDX analysis contributed to gain further insight into the self-assembly process. In the long-term, this approach might be used to optimize the synthesis of VLS-grown SiNWs via ICP as a competitive technique to the well-established bottom-up approaches used for the production of thin SiNWs.

The vapor–liquid–solid growth of III-V nanowires proceeds via the mononuclear regime, where only one island nucleates in each nanowire monolayer. The expansion of the monolayer is governed by the surface energetics depending on the monolayer size. Here, we study theoretically the role of surface energy in determining the monolayer morphology at a given coverage. The optimal monolayer configuration is obtained by minimizing the surface energy at different coverages for a set of energetic constants relevant for GaAs nanowires. In contrast to what has been assumed so far in the growth modeling of III-V nanowires, we find that the monolayer expansion may not be a continuous process. Rather, some portions of the already formed monolayer may dissolve on one of its sides, with simultaneous growth proceeding on the other side. These results are important for fundamental understanding of vapor–liquid–solid growth at the atomic level and have potential impacts on the statistics within the nanowire ensembles, crystal phase, and doping properties of III-V nanowires.

We have previously demonstrated that we can grow p-type GaAs nanowires using Zn doping during gold catalyzed growth with aerotaxy. In this investigation, we show how to calculate the hole concentrations in such nanowires. We base the calculations on the Zhang–Northrup defect formation energy. Using density functional theory, we calculate the energy of the defect, a Zn atom on a Ga site, using a supercell approach. The chemical potentials of Zn and Ga in the liquid catalyst particle are calculated from a thermodynamically assessed database including Au, Zn, Ga, and As. These quantities together with the chemical potential of the carriers enable us to calculate the hole concentration in the nanowires self-consistently. We validate our theoretical results against aerotaxy grown GaAs nanowires where we have varied the hole concentration by varying the Zn/Ga ratio in the aerotaxy growth.

III–V nanowires grown by the vapor–liquid–solid method often show self-regulated oscillations of group V concentration in a catalyst droplet over the monolayer growth cycle. We investigate theoretically how this effect influences the electron-to-hole ratio in Si-doped GaAs nanowires. Several factors influencing the As depletion in the vapor–liquid–solid nanowire growth are considered, including the time-scale separation between the steps of island growth and refill, the “stopping effect” at very low As concentrations, and the maximum As concentration at nucleation and desorption. It is shown that the As depletion effect is stronger for slower nanowire elongation rates and faster for island growth relative to refill. Larger concentration oscillations suppress the electron-to-hole ratio and substantially enhance the tendency for the p-type Si doping of GaAs nanowires, which is a typical picture in molecular beam epitaxy. The oscillations become weaker and may finally disappear in vapor deposition techniques such as hydride vapor phase epitaxy, where the n-type Si doping of GaAs nanowires is more easily achievable.

Position‐controlled vapor‐liquid‐solid (VLS) growth of nanowires (NWs) is investigated using GaAs substrates with SiN‐patterned masks and Au catalysts for the realization of axial GaAsSb/InAs heterostructures. Rod‐like InAs NWs are obtained by the introduction of a small amount of HCl gas. The InAs NW diameter depends on the Au catalyst size and pitch of NWs, which can be explained by the VLS growth accompanied by lateral growth. A peculiar change in NW shapes for additive HCl gas is also revealed. Moreover, the formation of axial GaAsSb/InAs heterostructure NWs, by controlling the growth temperature of GaAsSb segments is demonstrated. These results indicate that this growth method is promising for the development of NWs suitable for vertical nano‐scale devices with Sb‐containing heterostructures. [ABSTRACT FROM AUTHOR]

Engineering interfacial interactions like adhesion and strain during the growth of two-dimensional (2D) materials is of absolute importance for their properties manipulation and applications. Here, a self-relaxation vapor-liquid-solid (SRVLS) growth of 2D transition metal dichalcogenides (TMDs) is proposed and investigated through molten-precursor-mediated chemical vapor deposition (CVD) method. The liquid droplets can coordinate and balance both processes of precipitation of metal oxides and capture of chalcogens, leading the growth fronts of 2D TMDs and thus forming a contact angle between the resulted solid TMD edges and the growth substrate. On this basis, a loose interface adhesion and in-plane relaxation of strains are revealed in the as-grown TMD layers. The average work of adhesion energy of 33.7 mJ/m2 for SRVLS-grown MoS 2 on SiO 2 is determined according to Young–Dupré equation, which is approximately three times reduction compared to traditional vapor-solid (VS) growth. Moreover, these SRVSL growth features can be utilized for implement of curl-free delamination and reverse transfer of TMD layers onto target substrates for applications through water-dissolving the solidified droplets by only using water. [Display omitted] • Insights into molten-salt-mediated vapor-liquid-solid growth mechanisms. • Engineering loose interface of CVD TMDs with relaxed adhesion and strains. • The average work of adhesion energy of 33.7 mJ/m2 is determined for SRVLS MoS 2 on SiO 2. • Loose interface facilitates the water delamination and transfer of TMDs for HER. [ABSTRACT FROM AUTHOR]

The large-scale synthesis of high-quality boron nitride nanotubes (BNNTs) has attracted considerable interests due to their applications in nanocomposites, thermal management, and so on. Despite decades of development, efficient preparation of high-quality BNNTs, which relies on the effective design of precursors and catalysts and deep insights into the catalytic mechanisms, is still urgently needed. Here, a self-catalytic process is designed to grow high-quality BNNTs using ternary W-B-Li compounds. W-B-Li compounds provide boron source and catalyst for BNNTs growth. High-quality BNNTs are successfully obtained via this approach. Density functional theory-based molecular dynamics (DFT-MD) simulations demonstrate that the Li intercalation into the lattice of W 2 B 5 promotes the formation of W-B-Li liquid and facilitates the compound evaporation for efficient BNNTs growth. This work demonstrates a high-efficient self-catalytic growth of high-quality BNNTs via ternary W-B-Li compounds, providing a new understanding of high-quality BNNTs growth., (© 2023 Wiley-VCH GmbH.)

Vapor-liquid-solid (VLS) growth process of single crystalline metal oxide nanowires has proven the excellent ability to tailor the nanostructures. However, the VLS process of metal oxides in general requires relatively high growth temperatures, which essentially limits the application range. Here we propose a rational concept to reduce the growth temperature in VLS growth process of various metal oxide nanowires. Molecular dynamics (MD) simulation theoretically predicts that it is possible to reduce the growth temperature in VLS process of metal oxide nanowires by precisely controlling the vapor flux. This concept is based on the temperature dependent "material flux window" that the appropriate vapor flux for VLS process of nanowire growth decreases with decreasing the growth temperature. Experimentally, we found the applicability of this concept for reducing the growth temperature of VLS processes for various metal oxides including MgO, SnO2, and ZnO. In addition, we show the successful applications of this concept to VLS nanowire growths of metal oxides onto tin-doped indium oxide (ITO) glass and polyimide (PI) substrates, which require relatively low growth temperatures. [ABSTRACT FROM AUTHOR]

Tin sulfide films were synthesized on different metal (Ag, Au) buffer layers by the deposition method of thermal evaporation. X-ray studies indicated an orthorhombic phase of SnS and Sn 2 S 3 and hexagonal phase of SnS 2 for all specimens. Microscopic investigations showed sheet morphologies with high density and uniform distribution across the surface of the specimens. It was also observed that Ag-buffer layer nanosheet films had the smallest thickness. The elemental analysis indicated the desired element on the surface of the films. Optical investigations confirmed that the SnS films on the buffer layer had strong emission bands which were red and near infrared (NIR) regions. Furthermore, Raman studies presented five Raman bands, and a shift to lower value of the wavenumber was observed by using buffer layers. The I–V and Mott–Schottky plots confirmed the p-type conductivity of nanosheet films. The solar cell devices fabricated from the films of SnS nanosheets exhibited a higher efficiency and power efficiency conversion (PEC) for the specimens that had buffer layers. The results of photosensitivity also demonstrated higher photosensitivity in red and NIR regions. And finally, photocurrent results displayed a higher photocurrent and lower raise and fall times for the films with buffer layers compared to the free-buffer layer film. [ABSTRACT FROM AUTHOR]

Kinking, a common anomaly in nanowire (NW) vapor-liquid-solid (VLS) growth, represents a sudden change of the wire's axial growth orientation. This study focuses on defect-free kinking during germanium NW VLS growth, after nucleation on a Ge (111) single crystal substrate, using Au-Ge catalyst liquid droplets of defined size. Statistical analysis of the fraction of kinked NWs reveals the dependence of kinking probability on the wire diameter and the growth temperature. The morphologies of kinked Ge NWs studied by electron microscopy show two distinct, defect-free, kinking modes, whose underlying mechanisms are explained with the help of 3D multiphase field simulations. Type I kinking, in which the growth axis changes from vertical [111] to (110), was observed in Ge NWs with a nominal diameter of ~20 nm. This size coincides with a critical diameter at which a spontaneous transition from (111) to (110) growth occurs in the phase field simulations. Larger diameter NWs only exhibit Type II kinking, in which the growth axis changes from vertical [111] directly to an inclined (111) axis during the initial stages of wire growth. This is caused by an error in sidewall facet development, which produces a shrinkage in the area of the (111) growth facet with increasing NW length, causing an instability of the Au-Ge liquid droplet at the tip of the NW. [ABSTRACT FROM AUTHOR]

The article discusses study on surface-directed nanocrystal epitaxy on a surface with an irregular lattice constant. Topics discussed include use of zinc oxide (ZnO) and gallium nitride (GaN) along with surface-directed vapor-liquid-solid (SVLS), high-resolution transmission electron microscopy (HRTEM) and cathodoluminescence (CL) microscopy to reveal impact of miniature surface alteration on nanocrystals and reduction in the lattice match to block the epitaxy.

Abstract: To investigate structure–property correlations, high-coercivity Mn x Ga nanoparticles were synthesized by the method of sequential deposition of Ga and Mn fluxes using molecular beam epitaxy. Spontaneous nanostructuring was assisted by the use of an Au precursor and thermal annealing, and the growth properties, structure and magnetic properties were characterized. Atomic force microscopy revealed average particle dimensions of 100nm and X-ray diffraction revealed a dominant tetragonal D022 crystal structure. Magnetic characterization at room temperature identified the presence of two magnetic phases, dominated by a high-coercivity (2.3T) component in addition to a low-coercivity component. [Copyright &y& Elsevier]

We present the fabrication of a vapor-liquid-solid grown silicon nanowire array solar cell with a radial heterojunction. Lithography defined Cu catalyst patterning is used to grow a periodic array of 300 nm diameter nanowires with a center-to-center distance of 800 nm. A conformal a-Si:H layer is deposited on the nanowire surface to create the heterojunction and passivate the nanowire surface. Transparent conductive oxide and Ni-Al metal grid are then deposited to complete the solar cell fabrication. With a nanowire height of 1.6 µm, the solar cell has an open-circuit voltage of 467 mV. This clear improvement of the open-circuit voltage compared to previous works may be due to the conformal deposition of a-Si:H and to the use of a Cu catalyst. The parameters limiting the solar cell performances are discussed and explained. This work opens up the possibility to fabricate silicon nanowire array solar cells on low-cost substrates. [ABSTRACT FROM AUTHOR]

Highlights: [•] HfC microcrystal chains were synthesized by a catalyst-assisted CVD. [•] The chains grow along a [001] direction and have a periodically changing diameter. [•] Single-crystal HfC core is sheathed by a thin carbon-rich shell. [•] A growth mechanism model is proposed to explain the growth of microcrystal chians. [•] This work achieves the controllable preparation of nanoscale HfC sharpening tips. [ABSTRACT FROM AUTHOR]

We study the effect of ZnO source and growth temperatures on morphology of the ZnO nanostructures. Nanostructures grown from ZnO nanopowder show the shape evolution from nanowires to nanoribbons and then to nanorods with variation in growth temperature and zinc vapor pressure. At 750°C, only vertically aligned nanowires have been observed and with increase in growth temperature nanowires transforms to nanoribbons and then finally to nanorods at 870°C. On the other hand, in case of ZnO bulk powder as a source material, only nanowires are produced at all temperatures. Raman scattering studies on the nanostructures show distinct $E_{2}^{{\rm high}}$ mode at ~ 437 cm-1, confirming the hexagonal wurtzite phase of the as grown nanostructures. Room temperature photoluminescence spectra exhibit bound exciton related strong UV emission at ~ 379 nm indicating high quality of the as-grown nanostructures. Possible mechanism of growth and shape evolution in ZnO nanostructures are explored through systematic studies of the effect of growth temperatures and zinc vapor pressure. [ABSTRACT FROM AUTHOR]

Abstract: We report here a technique for use in electrical interfaces between neurons and microelectronics, using vertically integrated silicon probe arrays with diameters of 2–3.5μm and lengths of 60–120μm. Silicon probe arrays can be fabricated by selective vapor–liquid–solid (VLS) growth. A doped n-type silicon probe with the resistance of 1kΩ has an electrical impedance of less than 10MΩ in physiological saline. After inserting the probe arrays into the retina of a carp (Cyrpinus carpio), we conducted electrical recording of neural signals, using the probes to measure light-evoked electrical neural signals. We determined that recorded signals represented local field potentials of the retina (electroretinogram (ERG)). The VLS-probe can provide minimally invasive neural recording/stimulation capabilities at high spatial resolution for fundamental studies of nervous systems. In addition, the probe arrays can be integrated with microelectronics; therefore, these probes make it possible to construct interfaces between neurons and microelectronics in advanced neuroscience applications. [Copyright &y& Elsevier]

Abstract: In this paper the synthesis of three-dimensional hierarchical nanostructures by pyrolysis of acetylene to grow carbon nanofibers (CNFs) on carbon microfibers (CMFs) and glass microfibers (GMFs) is reported. The morphology and structure of the as-prepared CNFs were studied by scanning electron microscopy and high-resolution transmission electron microscopy. CNFs grown on both substrates typically exhibited two types of morphology: the coil-like CNFs with frequent change in orientation and the relatively straight and long CNFs with parallel graphene sheets. The ethanol pretreatment was effective at improving the yield and distribution of the as-grown CNFs on CMFs, but showed an adverse effect to the CNF growth on GMFs. The influence of different substrates and growth temperatures on CNF morphology and the possible growth mechanism for the observed microstructures was discussed. [Copyright &y& Elsevier]

Abstract: In order to improve a critical current density (J c) under applied magnetic fields, an addition of BaMO3 (BMO; M=Zr, Sn) nanorods into REBa2Cu3O y (REBCO) films is actively discussed. Although superconducting properties of the REBCO films are dramatically enhanced by self-assembled BMO nanorods, the growth mechanisms of the BMO nanorods have not been clarified yet. In this study, in order to clarify the growth mechanisms of the BZrO3 (BZO) nanorods and to further improve the superconducting properties, we fabricated a BZO-doped Sm1+ x Ba2− x Cu3O y (Sm+BZO) film by using modified Vapor–Liquid–Solid (VLS) technique (VLS-Sm+BZO/i). The in-field J c of the VLS-Sm+BZO/i film showed 4.5 times higher than that of Sm+BZO film fabricated by conventional pulsed laser deposition method (PLD-Sm+BZO) at B =4T and the J c–B–θ curves of the VLS-Sm+BZO/i film was higher than that of the PLD-Sm+BZO film around the applied field angle of 40° against the c-axis of the SmBCO. From a TEM observation, we found that the BZO nanorods of VLS-Sm+BZO/i film grew discontinuously along the c-axis of the SmBCO. [Copyright &y& Elsevier]

We report studies defining the diameter-dependent location of electrically active dopants in silicon (Si) and germanium (Ge) nanowires (NWs) prepared by nanocluster catalyzed vapor-liquidsolid (VLS) growth without measurable competing homogeneous decomposition and surface overcoating. The location of active dopants was assessed from electrical transport measurements before and after removal of controlled thicknesses of material from NW surfaces by low-temperature chemical oxidation and etching. These measurements show a well-defined transition from bulk-like to surface doping as the diameter is decreased <22-25 nm for nand p-type Si NW5, although the surface dopant concentration is also enriched in the larger diameter Si NW5. Similar diameterdependent results were also observed for n-type Ge NW5, suggesting that surface dopant segregation may be general for small diameter NW5 synthesized by the VLS approach. Natural surface doping of small diameter semiconductor NW5 is distinct from many top-down fabricated NWs. explains enhanced transport properties of these NWs and could yield robust properties in ultrasmall devices often dominated by random dopant fluctuations. [ABSTRACT FROM AUTHOR]

Abstract: Silicon nanowires (SiNWs) with a single-crystalline Si core and a thermally oxidized shell (core-shell SiNWs) were synthesized by gold-catalyzed chemical vapor deposition followed by rapid thermal oxidation. To synthesize high-quality core-shell SiNWs, the relationship between the growth parameters and the crystallinity was studied. Furthermore, the formation process of the oxide shell was analyzed in detail by transmission electron microscopy. Using SiNWs as channels, back gate-type field effect transistors (FETs) were fabricated on p-type silicon wafers. FETs with core-shell SiNWs channels exhibited smaller hysteresis in the drain current (I d ) vs. gate voltage (V GS ) characteristics and higher on/off drain current ratio (ION/IOFF ) than those with bare SiNWs channels. [Copyright &y& Elsevier]

Abstract: On the α-Al2O3 (0001) surface low-dimensional nanostructure of β-Ga2O3 was synthesized on a large scale (1cm square) at relatively low substrate temperature (650°C) by thermal evaporation of Ga2O3 with presence or absence of Au catalyst. Whitish layer over the substrate surface consisted of rod-like or block-like β-Ga2O3 nanostructures with presence or absence of the catalyst, respectively. In growth with the catalyst, a nanosphere with diameter of 200–450nm placed at the top of each nanorod with diameter of 250–700nm and ∼4μm long. In growth without the catalyst, distorted pentagonal nanoblock with longer and shorter sides for a section of 1–1.7μm long and 300–400nm long, respectively, reached as long as 5.5μm. The shape and size of the nanostructure were affected by presence or absence of the catalyst in the deposition of Ga2O3. The vapor–liquid–solid growth using Au catalyst increased rather small rod-like nanostructure of β-Ga2O3 promising for nanodevice applications. [Copyright &y& Elsevier]

Abstract: A rich variety of nanostructures can be synthesized by varying pressure and temperature during vapor–liquid–solid (VLS) epitaxy on Si. The chemical vapor deposition (CVD) growth by VLS of epitaxial Ge nanowires and nanopillars seeded by metallic nanodots on (111) and (100) oriented Si is reported with an emphasis on analyses by ion backscattering and channeling in combination with scanning electron microscopy. The nanostructures are grown using digermane in an Ultra High Vacuum (UHV) system at pressures from 10−6 to 10−2 Torr and temperatures between 400 and 600°C. Au nanodots with diameters of 10–50nm are formed by vapor deposition on H-terminated Si surfaces. The Ge growth kinetics and morphology are observed to depend strongly on pressure. At lower pressures the Au seeds the growth of layered heteroepitaxial islands (referred to here as nanopillars) which grow both vertically and laterally. At higher pressures a transition to rapid 〈111〉 axial nanowire epitaxial growth occurs with a growth rate that scales linearly with pressure. We contrast quantitative measurements of the kinetics for VLS nanowire growth with that for uniform CVD layer growth. [Copyright &y& Elsevier]

Abstract: A simple and fast, controllable gas vaporization of alloy method for producing various micro- and nanostructures of ZnO in air atmosphere with a large yield was presented in this paper. The presence of Cu was proved to strongly affect the growth morphology of the synthesized ZnO through the control of the partial pressure of zinc, which could be fulfilled by changing the composition of Zn and Cu for the used reactants. Given the simplicity of the procedure, and the economic advantages, the method described here is likely to be of interest in industrial-scale applications. [Copyright &y& Elsevier]

A micro-Si wire probe array chip with on-chip circuits has been developed for the applications on multichannel electrodes of neuroelectronic interface systems. Selective Au–Si2H6 vapor–liquid–solid (VLS) growth method provides a successful Si probe array on Si(1 1 1) wafers in predetermined positions and probe sizes. Si probes with 160 μm in length and 3.5 μm in diameter at tip were grown for 2 h at 700 °C. Moreover, the circular cone type shape of the Si probes was controlled by changing the Si2H6 gas pressures in the VLS growth. After wiring process for on-chip circuits on Si(1 1 1) wafers, the Si probes were grown perpendicular to the wafer surface by the VLS growth process. Conductivity of Si probes was controlled by using phosphorous diffusion, resulting in a resistivity of 10−2 Ω · cm from 104 Ω · cm at a diffusion temperature of 1100 °C. In in vivo studies, penetrating micro-probe array with low impedance such as the VLS grown Si probes has been desired. Using the VLS grown Si probes, these electrical signals was detected successfully. [Copyright &y& Elsevier]

[Display omitted] • Random Ni@a.-SiO2 NWs are synthesized through an instantaneous VLS growth. • The energy state of working arc plasma are diagnosed by real-time OES. • Ni@NiO@a.-SiO2 NWs is obtained by controlling Ni to convert to Ni@NiO in air. • Optimal Ni@NiO@SiO2 a.-NWs exhibit better cycling stability and rate capability. Amorphous SiO2 (a.-SiO2) species is a promising anode material for lithium ion batteries (LIBs) due to its high theoretical capacity (1965 mAh g−1) and abundant resource. One-dimensional a.-SiO2 nanowires (NWs) can provide efficient pathways for charge transport/diffusion and fast strain release during reciprocating lithiation/delithiation. Herein, an instantaneous vapor–liquid-solid (VLS) growth of a.-SiO2 NWs was performed in a high-temperature DC arc plasma using metal Ni as the catalyst. The Ni@a.-SiO2 NWs contain a high content of Ni (26.68 wt%) at the tips of NWs, allowing the synthesis of two derived products of Ni@NiO@a.-SiO2 NWs and NiO@a.-SiO2 NWs via an oxidation treatment in flowing air. A real-time optical emission spectroscopy (OES) diagnosis was carried out on the working arc plasma. This indicates the electron temperature (T e) of 8088.3 K and electron density (n e) of 1.7 × 1014 cm−3 within the local-equilibrium plasma. Electrochemical properties of typical products show the optimization available by control of the core-shell structure attached at the tip of nanowire. In other words, the Ni@NiO@a.-SiO2 NWs exhibited a higher specific capacity of up to 996.8 mAh g−1 after 200 cycles with Coulombic efficiency of 99.5%, and a better rate capability at an intense current of 2.0 A·g−1. [ABSTRACT FROM AUTHOR]

The vapor–liquid–solid growth of III-V nanowires proceeds via the mononuclear regime, where only one island nucleates in each nanowire monolayer. The expansion of the monolayer is governed by the surface energetics depending on the monolayer size. Here, we study theoretically the role of surface energy in determining the monolayer morphology at a given coverage. The optimal monolayer configuration is obtained by minimizing the surface energy at different coverages for a set of energetic constants relevant for GaAs nanowires. In contrast to what has been assumed so far in the growth modeling of III-V nanowires, we find that the monolayer expansion may not be a continuous process. Rather, some portions of the already formed monolayer may dissolve on one of its sides, with simultaneous growth proceeding on the other side. These results are important for fundamental understanding of vapor–liquid–solid growth at the atomic level and have potential impacts on the statistics within the nanowire ensembles, crystal phase, and doping properties of III-V nanowires. [ABSTRACT FROM AUTHOR]