Growth of silicon nanowires by electron beam evaporation using indium catalyst

For the first time silicon nanowires have been grown on indium (In) coated Si (100) substrates using e-beam evaporation at a low substrate temperature of 300 °C. Standard spectroscopic and microscopic techniques have been employed for the structural, morphological and compositional properties of as grown Si nanowires. The as grown Si nanowires have randomly oriented with an average length of 600 nm for a deposition time of 15 min. As grown Si nanowires have shown indium nanoparticle (capped) on top of it confirming the Vapor Liquid Solid (VLS) growth mechanism. Transmission Electron Microscope (TEM) measurements have revealed pure and single crystalline nature of Si nanowires. The obtained results have indicated good progress towards finding alternative catalyst to gold for the synthesis of Si nanowires.     

GaN nanowires: CVD synthesis and properties

The growth of GaN nanowires from Ga and NH₃ sources in the flow of Ar carrier gas using a chemical vapor deposition (CVD) system was systematically studied. The substrates used were Si(111) and Si(100). Fabricated nanowires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). We investigated the influence of growth temperature, catalyst used, Ga amount, and the ratio of Ar and NH₃ flow rates on the morphology and properties of GaN nanowires. We found that the best results were obtained for a growth temperature of 950 °C. Optimal catalysts were Au and metallic Ni, while the use of nickel nitrate was found to lead to formation of SiO_x nanowire bunches in addition to GaN nanowires. For the optimal temperature and catalyst used, the influence of the Ga to N ratio on the nanowire growth was studied. It was found that different types of nanostructures are observed in relatively Ga-rich and in relatively N-rich conditions. Growth mechanisms of different types of nanowires, including the stacked-cone nanowires and the microscale structures formed by lateral growth under N-rich conditions, are discussed.     

Gold nanocluster distribution on faceted and kinked Si nanowires

Si nanowires were grown on (111) substrates by ultra high vacuum chemical vapor deposition using the Au-catalyzed vapor-liquid-solid (VLS) technique. Depending on the growth temperature, the nanowires can be straight in the <111> direction or kinked towards <112>. We present a transmission electron microscopy investigation of the <112> Si nanowires. Results exhibit the relationship between the morphology of nanowires and the distribution of gold on sidewalls bounding the nanowires. The distribution of Au nanoclusters is used as a probe to investigate the growth mechanisms of the VLS process. Our observations are consistent with the model of nucleation and step flow related to the oscillatory behavior of the catalyst droplet.     

Ultra-sharp pointed tip Si nanowires produced by very high frequency plasma enhanced chemical vapor deposition via VLS mechanism

Needle-like silicon nanowires have been grown using gold colloid as the catalyst and silane (SiH₄) as the precursor by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Si nanowires produced by this method were unique with sharpness below 3 nm. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction technique (XRD) confirmed the single crystalline growth of the Si nanowires with (111) crystalline structure. Raman spectroscopy also has revealed the presence of crystalline Si in the grown Si nanowire body. In this research, presence of a gold nanoparticle on tip of the nanowires proved vapor–liquid–solid growth mechanism.     

Self-catalytic growth of silicon nanowires on stainless steel

Silicon nanowires were grown on a stainless steel substrate using a vapor-liquid-solid mechanism in self-catalytic mode. The multi-component Fe-Cr-Ni-Mn-Si catalyst that was formed from the substrate leads the growth of single-crystal Si nanowires with lengths of several micrometers and diameters ranging from 100 to 150 nm. A systematic investigation of the processing parameters revealed that the hydrogen flow rate is critical to the growth of the nanowires. At a high flow rate that exceeds 1000 sccm, the substrate is embrittled by H₂, and liquid droplets, which lead the growth of nanowires by the vapor-liquid-solid mechanism, are formed on the substrate. Electrical transport measurements indicated that the nanowires grown with the multi-component catalyst have electrical properties comparable to those grown by a single-component Ti catalyst.     

Epitaxial growth of silicon nanowires using an aluminium catalyst

Silicon nanowires have been identified as important components for future electronic and sensor nanodevices. So far gold has dominated as the catalyst for growing Si nanowires via the vapour-liquid-solid (VLS) mechanism. Unfortunately, gold traps electrons and holes in Si and poses a serious contamination problem for Si complementary metal oxide semiconductor (CMOS) processing. Although there are some reports on the use of non-gold catalysts for Si nanowire growth, either the growth requires high temperatures and/or the catalysts are not compatible with CMOS requirements. From a technological standpoint, a much more attractive catalyst material would be aluminium, as it is a standard metal in Si process lines. Here we report for the first time the epitaxial growth of Al-catalysed Si nanowires and suggest that growth proceeds via a vapour-solid-solid (VSS) rather than a VLS mechanism. It is also found that the tapering of the nanowires can be strongly reduced by lowering the growth temperature.     

Ultrafast growth of single-crystalline Si nanowires

Silicon nanowires (SiNWs) have been catalytically synthesized by heat treatment of Si nanopowder at 980 °C. The SiNWs comprise crystalline Si nanoparticles interconnected with metal catalyst. The formation mechanism of nanowires generally depends on the presence of Fe catalysts in the synthesis process of solid–liquid–solid (SLS). Although gas phase of vapor–liquid–solid (VLS) method can be used to produce various of different nanowire materials, growth model based on the SLS mechanism by heat treatment is more ascendant for providing ultrafast growth of single-crystalline Si nanowires and controlling the diameter of them easily. The growth of single-crystalline SiNWs and morphology were discussed.     

Synthesis and characterization of indium nitride nanowires by plasma-assisted chemical vapor deposition

High-quality indium nitride (InN) nanowires were synthesized in a high temperature furnace on Au-coated Si substrates through the reaction of indium metal vapor with highly reactive nitrogen radicals generated by N₂ plasma. Highly-reactive nitrogen radicals provided a wide process window for the synthesis of InN nanowires by lowering the process temperature to avoid the decomposition of InN. X-ray diffraction, transmission electron microscopy and Raman spectra further showed that the as-synthesized InN nanowires were perfect single crystallites of wurtzite structure with the growth direction along [110].     

Influence of reaction time on growth of GaN nanowires fabricated by CVD method

GaN nanowires have been fabricated successfully on Si (111) substrates coated with NiCl₂ thin films by chemical vapor deposition method using Ga₂O₃ as raw material. The growth of GaN nanowires was investigated as a function of reaction times so as to study the influence of different durations on the components, microstructure, morphologies and optical properties of GaN samples in particular by X-ray diffraction, FT-IR spectrophotometer, scanning electron microscope, and photoluminescence. The results show that the samples after reaction are single crystal GaN with hexagonal wurtzite structure and high-quality crystalline after reaction at 1,100 °C for 60 min, which have good optical properties as revealed by PL spectra. Reaction time greatly influences the growth of GaN nanowires, that is, with the increase in reaction time, the crystalline quality of GaN nanowires is improved accordingly. The growth of the GaN nanowires follows the vapor–liquid-solid mechanism and Ni plays an important role as catalyst, which forms nucleation point in the growth of GaN nanowires.     

Influence of Sb as a catalyst in the growth of ZnO nano wires and nano sheets using Nanoparticle Assisted Pulsed Laser Deposition (NAPLD)

The methodology on the synthesis of Sb-doped ZnO nanostructures by considering dopant as a catalyst is proposed and demonstrated. The nanostructures were synthesized using intrinsic ZnO as target and Sb-coated Si as substrate, where Sb simultaneously acts as dopant and the catalyst. The catalyst Sb is highly sensitive to temperature conditions resulted in two different nanostructures, the nanowires and the nanosheets. The surface, structural and optical characteristics of the nanowires and the nanosheets are comparatively investigated through SEM, EDX, XRD, Raman spectroscopy and photo luminescence (PL) spectroscopy. The nanowires showed a strong green emission in the PL spectrum and the presence of oxygen vacancies is confirmed thorough Raman peak shift at 556 cm⁻¹. In the case of nanosheets, the defect in oxygen vacancies is completely reduced, and improved UV emission is observed, which confirms the diffusion of Sb in the ZnO lattice.     

Study of the growth,and effects of filament to substrate distance on the structural and optical properties of Si/SiC core–shell nanowires synthesized by hot-wire chemical vapor deposition

Silicon/silicon carbide (Si/SiC) core–shell nanowires grown on quartz substrates by hot-wire chemical vapor deposition were studied. Nickel was used as a catalyst to induce the growth of these core–shell nanowires followed by the vapor–solid–solid growth mechanism. The nanowires were grown by varying substrate-to-filament distance; d_s-f from 1.9 to 3.1 cm with an interval of 0.4 cm. Lower d_s-f produced a high density of straight core–shell nanowires. A highly crystalline single crystal Si core of the nanowires was produced at lower d_s-f as well. Presence of Si and SiC nano-crystallites embedded within an amorphous matrix in the shell of the nanowires exhibited a high intensity of photoluminescence emission spectra from 600 to 1000 nm. The effects of the d_s-f on the structural and optical properties of the nanowires are discussed.     

Aluminium nitride nanowire array films for nanomanufacturing applications

The present paper presents a systematic investigation of both catalyst free and catalyst assisted AlN nanowire synthesis by chemical vapour deposition using Al and NH₃ as source materials. Growth runs have mostly been carried out at 1100°C under H₂ as carrier gas. While the catalyst free growth runs resulted in long (～40?μm) and dense AlN nanowire array films, the catalyst assisted growth resulted in short nanowires (3–5?μm). Growth mechanisms have been presented. Raman spectroscopy of the catalyst free grown nanowires has revealed very symmetric and strong phonon modes [e.g. strong E₂ (high)] indicating very good crystal quality of the grown AlN nanowires. In brief, catalyst free growth eliminates catalyst contamination and produces high quality and density of long nanowires, which is very valuable for scale-up manufacturing opportunities of the AlN nanostructures.     

Edge‐Epitaxial Growth of InSe Nanowires toward High‐Performance Photodetectors

Semiconducting nanowires offer many opportunities for electronic and optoelectronic device applications due to their unique geometries and physical properties. However, it is challenging to synthesize semiconducting nanowires directly on a SiO₂/Si substrate due to lattice mismatch. Here, a catalysis‐free approach is developed to achieve direct synthesis of long and straight InSe nanowires on SiO₂/Si substrates through edge‐homoepitaxial growth. Parallel InSe nanowires are achieved further on SiO₂/Si substrates through controlling growth conditions. The underlying growth mechanism is attributed to a selenium self‐driven vapor–liquid–solid process, which is distinct from the conventional metal‐catalytic vapor–liquid–solid method widely used for growing Si and III–V nanowires. Furthermore, it is demonstrated that the as‐grown InSe nanowire‐based visible light photodetector simultaneously possesses an extraordinary photoresponsivity of 271 A W^?1, ultrahigh detectivity of 1.57 × 10¹⁴ Jones, and a fast response speed of microsecond scale. The excellent performance of the photodetector indicates that as‐grown InSe nanowires are promising in future optoelectronic applications. More importantly, the proposed edge‐homoepitaxial approach may open up a novel avenue for direct synthesis of semiconducting nanowire arrays on SiO₂/Si substrates.     

Fabrication of needle-shaped GaN nanowires by ammoniating Ga2O3 films on MgO layers deposited on Si (111) substrates

Needle-shaped GaN nanowires have been synthesized on Si (111) substrate through ammoniating Ga₂O₃/MgO films under flowing ammonia atmosphere at the temperature of 950 °C. The as-synthesized GaN nanowires were characterized by X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM). The results demonstrate that these nanowires are hexagonal GaN and possess a smooth surface with an average diameter about 200 nm and a length ranging from 5 μm to 15 μm. In addition, the diameters of these nanowires diminish gradually. The growth mechanism of crystalline GaN nanowires is discussed briefly.     

Synthesis of GaN nanowires by CVD method: effect of reaction temperature

GaN nanowires are fabricated on Si substrates by ammoniating Ga₂O₃/NiCl₂ thin films using chemical vapour deposition method. The influence of reaction temperature on microstructure, morphology and optical properties of GaN nanowires is characterised by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectrophotometer, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and photoluminescence. The results demonstrate that the GaN nanowires are single crystalline and exhibit hexagonal wurtzite symmetry. The best crystalline quality was achieved for an reaction temperature of 1150°C for 15?min. The growth process follows vapour–liquid–solid mechanism and Ni plays an important role as the nucleation point and as a catalyst.     

Synthesis of single-crystal GaN nanowires on Si(111) substrate by ammonification technology

GaN nanowires have been synthesized on Si(111) substrate through ammoniating Ga₂O₃/BN films under flowing ammonia atmosphere at the temperature of 900 °C. The as-synthesized GaN nanowires were characterized by X-ray diffraction (XRD), selected-area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM). The results demonstrated that the nanowires are hexagonal wurtzite GaN and possess a smooth surface with diameters ranging from 40 to 100 nm and lengths up to several tens of micrometers. The growth mechanism of crystalline GaN nanowires is discussed briefly.     

Synthesis of aligned arrays of “Microropes” of silica nanowires by gas-jet electron beam plasma chemical vapor deposition method

For the first time, aligned arrays of bundles (“microropes”) of silica nanowires were synthesized from a monosilane-hydrogen mixture by gas-jet electron beam plasma chemical vapor deposition method. The synthesis was performed on single-crystal silicon substrates coated by micron-sized particles of stannic catalyst. A bundle (“microrope”) of silica nanowires each of which is about 15 nm in diameter grows from a catalyst particle. It seems that the synthesis proceeds by the vapor-liquid-solid mechanism, and several nanowires grow synchronously from the surface of one catalyst particle. The “microrope” growth rate was about 25 nm/s at a synthesis temperature of 400°C. A possible growth model was proposed to explain these results.     

Synthesis and properties of copper phthalocyanine nanowires

Copper phthalocyanine (CuPc) nanowires were fabricated by organic vapor deposition. The nanowires were studied by scanning electron microscopy, X-ray diffraction, and absorption spectroscopy. The effect of the nature of substrate (glass, Si, indium tin oxide, fluorine doped tin oxide) and its temperature on the morphology and properties of the fabricated nanowires was studied. Deposition of a thin CuPc film before the nanostructure growth ensured high yield of CuPc nanowires for all the substrates except Si. The nanowire size and crystal structure were mainly determined by the substrate temperature, with α-CuPc nanowires obtained at the lowest temperature (∼ 190 °C) and β-CuPc nanowires obtained at higher temperatures (above 200 °C).     

Self-catalytic formation and characterization of Zn2SnO4 nanowires

Mass production of transparent semiconducting ternary oxide Zn₂SnO₄ nanowires is successfully synthesized by the thermal evaporation method without any catalyst. The as-synthesized products are characterized with field-emission scanning electron microscope (FE-SEM), X-ray powder diffraction (XRD), energy-dispersive spectroscopy (EDS), high-resolution transmission electron microscope (HR-TEM) and selected area electron diffraction (SEAD). A formation of Zn₂SnO₄ nanowires based on a self-catalytic VLS growth mechanism is discussed. The photoluminescence spectrum (PL) of the nanowires shows a broad blue-green emission around the 300-600 nm wavelengths with a maximum center at 580 nm under room temperature.     

Silicon nanowire growth on glass substrates using hot wire chemical vapor deposition

We report here, the first observation of silicon nanowire growth via the VLS route at 400 °C using the HWCVD technique with gold (Au) as catalyst. The supersaturation of the alloy droplet, due to a large flux of atomic silicon generated due to efficient dissociation of the silane over the hot wire, leads to the precipitation of Si nanowires. The hot wire process plays a dual role in the entire nanowire growth. Firstly, the atomic hydrogen generated from the hot wire leads to the formation of the metal nanoclusters. Secondly, it offers a continuous supply of silicon atoms enabling efficient diffusion of Si into the Si-Au eutectic alloy leading to the growth of dense silicon nanowires as observed in the SEM. The Raman and TEM data show that the Si nanowires are amorphous in nature. Precise tuning of the hot wire CVD process parameters gives rise to a high density of silicon nanowires having diameters as small as 50 nm and lengths of about a few microns.