Growth Rate Of Nanowires Research Articles

A Monte Carlo simulation study on growth mechanism of horizontal nanowires on crystal surface

With the kinetic Monte Carlo simulation of smooth (001) surface of symmetry-broken simple cubic crystal in fluid with low supersatuaration rate, the mechanism of nanowire growth based on crystal nuclei on the surface is discovered and the morphology of nanowire is obtained. The dependences of nanowire morphology on thermal roughness in the longitudinal and latitudinal direction and growth time on the anisotropic surface of the crystal are further discussed. The relations of nanowire growth rate with thermal roughness, supersaturation rate, surface size and diffusion rate on the surface are then systematically studied.

Heterogeneous catalysis model of growth mechanisms of carbon nanotubes, graphene and silicon nanowires

The catalytic chemical vapour deposition of carbon nanotubes on transition metal catalysts from hydrocarbons is analysed in terms of concepts of heterogeneous catalysis, which leads to a ‘volcano plot’ of the catalyst efficiency vs. the metal d orbital energy. In this plot, noble metals are inefficient because they dissociate the feedstock poorly, the early transition metals are inefficient because their surface sites become blocked by absorbed carbon and they do not release the nanotube, while the optimum catalyst dissociates the feedstock readily and releases the nanotube. The model is extended to explain why graphene CVD works best with non-optimum catalysts. For silicon nanowires, the rather high stability of metal silicides limits the nanowire growth rates and may explain why there are few alternatives to gold as a catalyst.

Influence of growth temperature on growth of InGaAs nanowires in selective-area metal–organic vapor-phase epitaxy

Indium-rich InGaAs nanowires were grown on an InP (111)B substrate by catalyst-free selective-area metal–organic vapor phase epitaxy, and the growth-temperature dependence of growth rate and composition was studied. In particular, nanowire growth rate rapidly decreases as growth temperature increases. This tendency is opposite (for a similar temperature range) to that found in a previous study on selective-area growth of gallium-rich InGaAs nanowires. This difference between indium-rich and gallium-rich nanowires suggests that the influence of growth temperature on the growth of InGaAs nanowires is dependent on the group-III supply ratio. On the basis of previous experimental observations in InAs and GaAs nanowires, temperature dependence of nanowire growth rate and its dependence on group-III supply ratio are predicted. A guideline to determine the optimum growth conditions of InGaAs nanowires is also discussed.

Germanium nanowire synthesis using a localized heat source and a comparison to synthesis in a uniform temperature environment

Abstract

Minimizing the Gibbs–Thomson effect in the low-temperature plasma synthesis of thin Sinanowires

An advanced combination of numerical models, including plasma sheath, ion- andradical-induced species creation and plasma heating effects on the surface and within a Aucatalyst nanoparticle, is used to describe the catalyzed growth of Si nanowires inthe sheath of a low-temperature and low-pressure plasma. These models havebeen used to explain the higher nanowire growth rates, low-energy barriers, muchthinner Si nanowire nucleation and the less effective Gibbs–Thomson effect inreactive plasma processes, compared with those of neutral gas thermal processes.The effects of variation in the plasma sheath parameters and substrate potentialon Si nanowire nucleation and growth have also been investigated. It is shownthat increasing the plasma-related effects leads to decreases in the nucleationenergy barrier and the critical nanoparticle radius, with the Gibbs–Thomson effectdiminished, even at low temperatures. The results obtained are consistent with availableexperimental results and open a path toward the energy- and matter-efficientnucleation and growth of a broad range of one-dimensional quantum structures.

The influence of asymmetric electrodeposition voltage on the microstructure and magnetic properties of Fe xCo 1− x nanowire arrays

FeCo alloy nanowires were synthesized by both the symmetric and asymmetric ac electrodepositions into highly ordered porous anodic aluminum oxide membrane. The effect of deposition frequency (100, 500, 1000, 1500 and 2500 Hz), alloy composition (Fe 0.1Co 0.9 to Fe 0.9Co 0.1) and asymmetric potential (18/18, 18/16, 18/14 and 18/12 V, reductive–oxidative voltages) on the magnetic properties and microstructure of FeCo nanowires were investigated. It was found that lower frequency regions are more sensitive to the Fe and Co ion concentrations. A body-centered cubic structure with a 〈1 1 0〉 preferential orientation was observed for all nanowire arrays. The growth rate of nanowires was enhanced with an increase in the difference between reductive–oxidative voltages. The coercivity of as-deposited samples was increased from 2160 to 2850 Oe after annealing at 570 °C in Ar–H 2 atmosphere.

Selective lateral ZnO nanowire growth by surface diffusion on nanometer scale–patterned alumina on silicon

Abstract

Anisotropic Wet Etched Silicon Substrates for Reoriented and Selective Growth of ZnO Nanowires and Enhanced Hydrophobicity

Herein we report the fabrication of ZnO nanowires on anisotropic wet etched silicon substrates by selective hydrothermal growth. <100> oriented silicon wafers were first patterned by anisotropic wet etch with a KOH solution, resulting in V-shaped stripes of different periods. Then, a thin layer of gold was deposited and annealed to promote the hydrothermal growth of ZnO nanowires. It was found that the growth rate of ZnO nanowires on <111> surfaces was much higher than that on <100> surfaces. As a first application of such micro- and nanostructured surfaces, we show enhanced wetting properties by measuring the contact angle of water droplets on the samples obtained under different patterning and growth conditions. Our results also demonstrated the possibility of tuning the contact angle of the sample in the range between 115° and 155°, by changing either the pattern of the silicon template or the hydrothermal growth conditions.

基于气液固模式生长的无缺陷闪锌矿结构GaAs/AlGaAs轴向异质纳米线

Pure zinc blende structure GaAs/AlGaAs axial heterostructure nanowires (NWs) are grown by metal organic chemical vapor deposition on GaAs(111) B substrates using Au-catalyzed vapor-liquid-solid mechanism. Al adatom enhances the influence of diameters on NWs growth rate. NWs are grown mainly through the contributions from the direct impingement of the precursors onto the alloy droplets and not so much from adatom diffusion. The results indicate that the droplet acts as a catalyst rather than an adatom collector.

Growth of Ge Nanowires from Au−Cu Alloy Nanoparticle Catalysts Synthesized from Aqueous Solution

Elemental metal nanoparticles are widely used to catalyze semiconductor nanowire growth, but size-controlled alloy nanoparticles have not been explored in this context. We present a simple aqueous synthesis of Au−Cu2O core−shell nanoparticles to produce Au−Cu alloy nanoparticles of controlled size and composition by vacuum annealing. Colloidal Au nanoparticles were used as size-controlled seeds, and fine control of the Cu2O shell thickness enabled tuning of the average Au−Cu alloy composition. The alloy nanoparticles were found to catalyze Ge nanowire growth in a low-pressure chemical vapor deposition environment. The nanowire growth rate for Au−Cu nanoparticles was intermediate to that of Cu (slowest) and Au (fastest) nanoparticles under identical conditions, suggesting a vapor−solid−solid growth process. These catalysts provide a useful platform to explore the influence of catalyst phase and chemistry on nanowire growth mechanisms that determine important variables including the doping rate and junction...

Self‐Organized Ce1‐xGdxO2‐y Nanowire Networks with Very Fast Coarsening Driven by Attractive Elastic Interactions

Assembling arrays of ordered nanowires is a key objective for many of their potential applications. However, a lack of understanding and control of the nanowires' growth mechanisms limits their thorough development. In this work, an appealing new path towards self-organized epitaxial nanowire networks produced by high-throughput solution methods is reported. Two requisites are identified to generate the nanowires: a thermodynamic driving force for an unrestricted elongated equilibrium island shape, and a very fast effective coarsening rate. These requirements are met in anisotropically strained Ce(1-x)Gd(x)O(2-y) nanowires with the (011) orientation grown on the (001) surface of LaAlO(3) substrates. Nanowires with aspect ratios above ≈100 oriented along two mutually orthogonal axes are obtained leading to labyrinthine networks. A very fast effective nanowire growth rate (≈60 nm min(-1)) for ex-situ thermally annealed nanostructures derives from simultaneous kinetic processes occurring in a branched network. Ostwald ripening and anisotropic dynamic coalescence, both promoted by strain-driven attractive nanowire interaction, and rapid recrystallization, enabled by fast atomic diffusion associated with a high concentration of oxygen vacancies, contribute to such an effective growth rate. This bottom-up approach to self-organized nanowire growth has a wide potential for many materials and functionalities.

Different growth rates for catalyst-induced and self-induced GaN nanowires

The catalyst- and self-induced pathways of GaN nanowire growth by molecular beam epitaxy are compared. The catalyst-induced nanowires elongate faster than the self-induced ones and their growth rate is fully determined by the impinging N rate. The self-induced nanowire growth rate is identical on both Si(111) and Si(001) and approaches the impinging N rate only for the few longest nanowires. This difference is attributed to the presence of the Ni-catalyst which enhances the incorporation of Ga at the nanowire tip while for the self-induced nanowires, growth is limited by the different incorporation rates on the nanowire tip and sidewall facets.

Position controlled self-catalyzed growth of GaAs nanowires by molecular beamepitaxy

GaAs nanowires are grown by molecular beam epitaxy using a self-catalyzed,Ga-assisted growth technique. Position control is achieved by nano-patterning aSiO2 layer with arrays of holes with a hole diameter of 85 nm and a hole pitch varying between 200 nm and 2 µm.Gallium droplets form preferentially at the etched holes acting as catalyst for the nanowire growth.The nanowires have hexagonal cross-sections with {110} side facets and crystallize predominantlyin zincblende. The interdistance dependence of the nanowire growth rate indicates a change of theIII/V ratio towards As-rich conditions for large hole distances inhibiting NW growth.

Direct Observation of Nanoscale Size Effects in Ge Semiconductor Nanowire Growth

Progress in the synthesis of semiconductor nanowires (NWs) has prompted intensive inquiry into understanding the science of their growth mechanisms and ultimately the technological applications they promise. We present new results for the size-dependent growth kinetics of Ge NWs and correlate the results with a direct experimental measurement of the Gibbs-Thomson effect, a measured increase in the Ge solute concentration in liquid Au-Ge droplets with decreasing diameter. This nanoscale-dependent effect emerges in vapor-liquid-solid Ge NW growth and leads to a decrease in the NW growth rate for smaller diameter NWs under a wide range of growth conditions with a cutoff in growth at sufficiently small sizes. These effects are described quantitatively by an analytical model based on the Gibbs-Thomson effect. A comprehensive treatment is provided and shown to be consistent with experiment for the effect of NW growth time, temperature, pressure, and doping on the supersaturation of Ge in Au, which determines the growth rate and critical cutoff diameter for NW growth. These results support the universal applicability of the Gibbs-Thomson effect to sub-100 nm diameter semiconductor NW growth.

Subeutectic synthesis of epitaxial Si-NWs with diverse catalysts using a novel Si precursor.

The applicability of a novel silicon precursor with respect to reasonable nanowire (NW) growth rates, feasibility of epitaxial NW growth and versatility with respect to diverse catalysts was investigated. Epitaxial growth of Si-NWs was achieved using octochlorotrisilane (OCTS) as Si precursor and Au as catalyst. In contrast to the synthesis approach with SiCl4 as precursor, OCTS provides Si without the addition of H2. By optimizing the growth conditions, effective NW synthesis is shown for alternative catalysts, in particular, Cu, Ag, Ni, and Pt with the latter two being compatible to complementary metal-oxide-semiconductor technology. As for these catalysts, the growth temperatures are lower than the lowest liquid eutectic; we suggest that the catalyst particle is in the solid state during NW growth and that a solid-phase diffusion process, either in the bulk, on the surface, or both, must be responsible for NW nucleation.

Measurement of Local Si‐Nanowire Growth Kinetics Using In situ Transmission Electron Microscopy of Heated Cantilevers

A technique to study nanowire growth processes on locally heated microcantilevers in situ in a transmission electron microscope has been developed. The in situ observations allow the characterization of the nucleation process of silicon wires, as well as the measurement of growth rates of individual nanowires and the ability to observe the formation of nanowire bridges between separate cantilevers to form a complete nanowire device. How well the nanowires can be nucleated controllably on typical cantilever sidewalls is examined, and the measurements of nanowire growth rates are used to calibrate the cantilever-heater parameters used in finite-element models of cantilever heating profiles, useful for optimization of the design of devices requiring local growth.

Growth mechanism of GaN nanowires: preferred nucleation site and effect ofhydrogen

The growth mechanism of epitaxial GaN nanowires grown using particle-mediated chemicalvapour deposition was investigated. By examining the diameter-dependent growth rate ofGaN nanowires, we show that the kinetic reaction-limited growth of GaN nanowiresoriginates from the combination of mono-nuclear and poly-nuclear growth rather than theGibbs–Thompson effect. We present a generalized nucleation-mediated growth model todescribe the diameter dependence of the nanowire growth rate and show that thenucleation of sources occurs at the vapour/liquid/solid three-phase boundary. Fromthe same model, we demonstrate that increased hydrogen concentration in thecarrier gas reduces the supersaturation, leading to a reduced GaN nanowire growthrate. Our approach can be applied to other nanowire materials systems, and itallows the determination of the preferred nucleation site during nanowire growth.

Fabrication of Co/Cu Multilayered Nanowires Using a Pulsed Current Deposition Technique

Co/Cu multilayered nanowires with 40 nm in diameter were fabricated using a pulsed current deposition technique into a nanoporous template with numerous nanochannels. To determine the optimum electrodeposition condition of Cu and Co into the template, cathodic polarization behavior was examined at a wide range of cathode potential. Time-dependence of deposition current was monitored to determine the growth rate of Co and Cu nanowires. Co layer and Cu layer thicknesses were adjusted to several tens nanometers, by controlling the deposition times. With decreasing the each layer thickness, the coercive force of Co/Cu multilayered nanowires was decreased and the soft magnetic property was improved.

Temperature dependence and activation energy of ZnO nanowires grown on amorphous carbon

ZnO nanowires have been self-assembled on amorphous carbon using the thermal chemical vapor transport and condensation without any metal catalysts. The temperature dependence of the growth rate of ZnO nanowires is characterized, and the growth activation energy is estimated to be 234 kJ/mol based on the experimental data. It is found that the growth rate of the thin ZnO nanowire is smaller than that of the thick one. A size-dependent kinetic model is proposed to address the unusual growth behaviors of ZnO nanowires. The theoretical predictions are consistent with experiments.

Growth and characterization of germanium nanowires by electron beam evaporation

Germanium nanowires were grown on Au coated Si substrates at 380 °C in a high vacuum (5 × 10 − 5 Torr) by e-beam evaporation of Germanium (Ge). The morphology observation by a field emission scanning electron microscope (FESEM) shows that the grown nanowires are randomly oriented with an average length and diameter of 600 nm and 120 nm respectively for a deposition time of 60 min. The nanowire growth rate was measured to be ∼ 10 nm/min. Transmission electron microscope (TEM) studies revealed that the Ge nanowires were single crystalline in nature and further energy dispersive X-ray analysis (EDAX) has shown that the tip of the grown nanowires was capped with Au nanoparticles, this shows that the growth of the Ge nanowires occurs by the vapour liquid solid (VLS) mechanism. HRTEM studies on the grown Ge nanowire show that they are single crystalline in nature and the growth direction was identified to be along [110].