Preparation of SiC nanowires with fins by chemical vapor deposition

SiC nanowires with fins have been prepared by chemical vapor deposition in a vertical vacuum furnace by using a powder mixture of milled Si and SiO₂ and gaseous CH₄ as the raw materials. The products were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). These investigations confirm that the nanowires with fins are cubic β-SiC. The diameter of the fins is about 100–120 nm and the diameter of the inner core stems is about 60–70 nm. The formation process of the β-SiC nanowires with fins is analyzed and discussed briefly.     

Preparation of SiC nanowires with fins by chemical vapor deposition

SiC nanowires with fins have been prepared by chemical vapor deposition in a vertical vacuum furnace by using a powder mixture of milled Si and SiO₂ and gaseous CH₄ as the raw materials. The products were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). These investigations confirm that the nanowires with fins are cubic β-SiC. The diameter of the fins is about 100–120 nm and the diameter of the inner core stems is about 60–70 nm. The formation process of the β-SiC nanowires with fins is analyzed and discussed briefly.     

等离子体增强化学气相沉积法实现硅纳米线掺硼

用等离子体增强化学气相沉积(PECVD)方法成功实现硅纳米线的掺B.选用Si片作衬底，硅烷 （SiH4）作硅源，硼烷（B2H6）作掺杂气体， Au作催化剂，生长温度440℃.基于气-液-固(VLS)机制，探讨了掺B硅纳米线可能的生长机制.PECVD法化学成分配比更灵活，更容易实现纳米线掺杂，进一步有望生长硅纳米线pn结，为研制纳米量级器件提供技术基础. 关键词： 硅纳米线 化学气相沉积 纳米器件     

Aligned synthesis of multi-walled carbon nanotubes with high purity by aerosol assisted chemical vapor deposition: Effect of water vapor

Aligned multi-walled carbon nanotubes (MWCNTs) with high purity and bulk yield were achieved on a silicon substrate by an aerosol-assisted chemical vapor deposition. The introduction of specific amounts of water vapor played a key role in in situ controlling the purity and surface defects of the nanotubes. The morphology, surface quality and structure of MWCNTs were characterized by secondary and backscattered electron imaging in a field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). Crystallinity and defects of the MWCNTs’ were investigated by high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. In this work, water vapor was found to provide a weak oxidative environment, which enhanced and purified the MWCNTs’ growth. However, excessive water vapor would inhibit the MWCNTs growth with a poor surface quality. In addition, it has been found that the surface morphology of the CNTs can be modified intentionally through producing some surface defects by tuning the amount of the water vapor, which may offer more nucleation sites on the chemically inert CNT surface for various applications such as catalyst support.     

The fabrication of ReS2 flowers at controlled locations by chemical vapor deposition

Here we report a metal induced nucleation to realize the growth of ReS₂ flowers at controlled locations. The ordered arrays of ReS₂ flowers have been successfully prepared on SiO₂/Si substrate using Pt metal dots as nucleation sites and S, NH₄ReO₄ powders as precursors by a chemical vapor depostion method. The NH₄ReO₄ powders are used as the rhenium sources. The ReS₂ flowers are grown above the pre-patterned Pt dots, Raman and transmission electron microscopy measurements indicated that the prepared ReS₂ flowers have excellent crystalline quality.     

Thin strain-relaxed SiGe grown by ultrahigh vacuum chemical vapor deposition

Large-scale preparation of thin strain-relaxed SiGe is achieved by combining ion implantation and ultrahigh vacuum chemical vapor deposition. The resulting materials were analyzed by double crystal X-ray diffraction, micro-Raman spectroscopy, and tapping mode atomic force microscope. Results revealed that 100-nm-thick Si_0.7Ge_0.3 layers with the diameter of 125 mm and full strain relaxation are successfully prepared by pre-modifying the Si substrates using 50 keV Ar⁺ ions. The strain relaxation is also disclosed to change with both ion species and energy. However, post-modification of SiGe by ion implantation will cause serious damage to the crystal structures, and result in the formation of poly-crystal SiGe.     

Growth behavior of Bi2Te3 and Sb2Te3 thin films on graphene substrate grown by plasma‐enhanced chemical vapor deposition

A comparative study of the substrate effect on the growth mechanism of chalcogenide Bi₂Te₃ and Sb₂Te₃ thin films was carried out. Obvious microstructural discrepancy in both the as‐deposited Bi₂Te₃ and Sb₂Te₃ thin films was observed when grown on graphene or SiO₂/Si substrate. Bi₂Te₃ and Sb₂Te₃ thin films deposited on the graphene substrate were observed to be grown epitaxially along c‐axis and show very smooth surface compared to that on SiO₂/Si substrate. Based on the experimental results of this study, the initial adsorption sites on graphene substrate during deposition process, which had been discussed theoretically, could be demonstrated empirically.     

Catalyst-free growth of well-aligned arsenic-doped ZnO nanowires by chemical vapor deposition method

ZnO nanowires with different arsenic concentration were grown on Si (1 0 0) substrates by chemical vapor deposition method without using catalyst. Zn/GaAs mixed powders were used as Zn and As source, respectively. Oxygen was used as oxidant. The images of scanning electron microscope show that the arsenic-doped ZnO nanowires with preferred c-axial orientation were obtained, which is in well accordance with the X-ray diffraction analysis. The arsenic related acceptor emission was observed in the photoluminescence spectra at 11 K for all arsenic-doped ZnO samples. This method for the preparation of arsenic-doped ZnO nanowires may open the way to realize the ZnO nanowires based light-emitting diode and laser diode.     

Growth study of indium-catalyzed silicon nanowires by plasma enhanced chemical vapor deposition

Indium was used as a catalyst for the synthesis of silicon nanowires in a plasma enhanced chemical vapor deposition reactor. In order to foster the catalytic activity of indium, the indium droplets had to be exposed to a hydrogen plasma prior to nanowire growth in a silane plasma. The structure of the nanowires was investigated as a function of the growth conditions by electron microscopy and Raman spectroscopy. The nanowires were found to crystallize along the <111>, <112> or <001> growth direction. When growing on the <112> and <111> directions, they revealed a similar crystal quality and the presence of a high density of twins along the {111} planes. The high density and periodicity of these twins lead to the formation of hexagonal domains inside the cubic structure. The corresponding Raman signature was found to be a peak at 495 cm⁻¹, in agreement with previous studies. Finally, electron energy loss spectroscopy indicates an occasional migration of indium during growth.     

Growth kinetics of low temperature single-wall and few walled carbon nanotubes grown by plasma enhanced chemical vapor deposition

Single-wall, double walled or few walled nanotubes (FWNT) are grown by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) at temperature as low as 600 °C. Most of these structures are isolated and self-oriented perpendicular to the substrate. The growth mechanism observed for single-wall and few walled (less than seven walls) nanotubes is the “base-growth” mode. Their grow kinetics is investigated regarding two parameters namely the growth time and the synthesis temperature. It is shown that nucleation and growth rate is correlated with the number of walls into FWNT. It also provides an evidence of a critical temperature for FWNT synthesis.     

化学气相沉积SiC材料超光滑表面纳米加工

 利用传统光学加工方法，采用陶瓷磨盘和金刚石微粉对国产化学气相沉积(CVD) SiC进行了粗磨、细磨加工；然后，利用颗粒直径从4 μm到1 μm的金刚石研磨膏逐级进行抛光，发现SiC表面存在纳米级划痕；最后，改用颗粒直径为20 nm氧化铝纳米颗粒的碱性水溶液进行抛光，表面粗糙度达到0.6 nm(RMS)，表面纳米级划痕得到很好改善，获得了较高表面质量的超光滑表面。     

化学气相沉积SiC材料超光滑表面纳米加工

利用传统光学加工方法,采用陶瓷磨盘和金刚石微粉对国产化学气相沉积(CVD) SiC进行了粗磨、细磨加工;然后,利用颗粒直径从4 μm到1 μm的金刚石研磨膏逐级进行抛光,发现SiC表面存在纳米级划痕;最后,改用颗粒直径为20 nm氧化铝纳米颗粒的碱性水溶液进行抛光,表面粗糙度达到0.6 nm(RMS),表面纳米级划痕得到很好改善,获得了较高表面质量的超光滑表面。     

衬底对化学气相沉积法制备氧化硅纳米线的影响

通过化学气相沉积法在不同衬底上制备了大量的氧化硅纳米线.选用衬底为Si片、带有约100nm厚SiO2氧化层Si片和石英片.利用场发射扫描电子显微镜(SEM)和透射电镜(TEM，配备有能谱仪)对样品的表面形貌、结构和成分进行研究.结果表明：这些纳米线都为非晶态，但在不同衬底上生长的纳米线形貌、尺寸和化学成分不同.讨论了各种衬底对不同特征氧化硅纳米线生长的影响. 关键词： 化学气相沉积 纳米线 纳米颗粒     

Synthesis and characterization of GaN nanowires by a catalyst assisted chemical vapor deposition

GaN nanowires have been fabricated on Si(1 1 1) substrates by chemical vapor deposition (CVD) method with NiCl₂ as catalyst and their compositions, microstructures, morphologies and light emitting properties were characterized by X-ray diffraction (XRD), FT-IR spectrophotometer (FTIR), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), Raman spectroscopy and photoluminescence (PL). The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure and high crystalline quality, having the size of 20-50 nm in diameter and several tens of microns in length with some nano-droplets on their tips, which reveals that the growth mechanism of GaN nanowires agrees with vapor-liquid-solid (VLS) process. Five first-order Raman active phonon bands move to low shift and A₁(TO), E₁(TO), and E₂ (high) bands are overlapped and broaden, which is caused by uncertainty in the phonon wave vector. Five non-first-order active Raman phonons also appear, which is caused by the small dimension and high surface disorder degree. A blue-shift of the band-gap emission occurs due to quantum confinement effect.     

Relatively low temperature synthesis of graphene by radio frequency plasma enhanced chemical vapor deposition

We present a simple, low-cost and high-effective method for synthesizing high-quality, large-area graphene using radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) on SiO₂/Si substrate covered with Ni thin film at relatively low temperatures (650 °C). During deposition, the trace amount of carbon (CH₄ gas flow rate of 2 sccm) is introduced into PECVD chamber and the deposition time is only 30 s, in which the carbon atoms diffuse into the Ni film and then segregate on its surface, forming single-layer or few-layer graphene. After deposition, Ni is removed by wet etching, and the obtained single continuous graphene film can easily be transferred to other substrates. This investigation provides a large-area, low temperature and low-cost synthesis method for graphene as a practical electronic material.     

The formation mechanism of the coaxial carbon-metal nanowires in a chemical vapor deposition process

In the synthesis of carbon nanotubes from ethylene decomposition by a Fe/Mo/Al₂O₃ catalyst at 823 K, the long and continuous coaxial carbon-metal nanowires up to 540 nm is observed. And for the first time, it is observed that the coaxial carbon-metal nanowires can grow in tip and base growth mode simultaneously. A detailed formation mechanism is proposed, where the aggregation of metal particles, lift-up of nanotubes obeying different growth modes and the deformation of metal particles by nanotubes are considered as the necessary steps for the formation of the nanowires.     

化学气相沉积法制备Zn2GeO4纳米线及其发光性质的研究

利用化学气相沉积法（CVD）,气-液-固（VLS）生长法则在表面溅有金属Au催化剂层的1 cm×1 cm的Si片上制备三元Zn₂GeO₄纳米线。X射线衍射仪（XRD）测试结果表明,锌源与锗源质量比为8：1时可成功制备出Zn₂GeO₄纳米结构;扫描电子显微镜（SEM）测试结果表明,Zn₂GeO₄纳米线直径为100 nm,长度为10~11 μm;光致发光（PL）测试结果表明,Zn₂GeO₄纳米线在432和480 nm处具有两个发光峰,最后对其生长机理进行了分析。     

Dimensional evolution of silicon nanowires synthesized by Au–Si island-catalyzed chemical vapor deposition

This study explores the nucleation and morphological evolution of silicon nanowires (Si-NWs) on Si (0 0 1) and (1 1 1) substrates synthesized using nanoscale Au–Si island-catalyzed rapid thermal chemical vapor deposition. The Au–Si islands are formed by Au thin film (1.2–3.0 nm) deposition at room temperature followed by annealing at 700 °C, which are employed as a liquid-droplet catalysis during the growth of the Si-NWs. The Si-NWs are grown by exposing the substrates with Au–Si islands to a mixture of gasses SiH₄ and H₂. The growth temperatures and the pressures are 500–600 °C and 0.1–1.0 Torr, respectively. We found a critical thickness of the Au film for Si-NWs nucleation at a given growth condition. Also, we observed that the dimensional evolution of the NWs significantly depends on the growth pressure and temperature. The resulting NWs are 30–100 nm in diameter and 0.4–12.0 μm in length. For Si (0 0 1) substrates 80% of the NWs are aligned along the 1 1 1 direction which are 30° and 60° with respect to the substrate surface while for Si (1 1 1) most of the NWs are aligned vertically along the 1 1 1 direction. In particular, we observed that there appears to be two types of NWs; one with a straight and another with a tapered shape. The morphological and dimensional evolution of the Si-NWs is significantly related to atomic diffusion kinetics and energetics in the vapor–liquid–solid processes.     

Low pressure chemical vapor deposition of niobium coating on silicon carbide

Nb coatings were prepared on a SiC substrate by low pressure chemical vapor deposition using NbCl₅. Thermodynamic calculations were performed to study the effect of temperature and partial pressure of NbCl₅ on the final products. The as-deposited coatings were characterized by scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy. The Nb coatings are oriented and grow in the preferred (2 0 0) plane and (2 1 1) plane, at 1173 K and 1223-1423 K, respectively. At 1123-1273 K, the deposition is controlled by the surface kinetic processes. The activation energy is found to be 133 kJ/mol. At 1273-1373 K, the deposition is controlled by the mass transport processes. The activation energy is found to be 46 kJ/mol. The growth mechanism of the chemical vapor deposited Nb is also discussed based on the morphologies and the deposition rates.     

Axial periodical nanostructures of Sb-doped SnO2 grown by chemical vapor deposition

We report the synthesis and characterization Sb-doped SnO₂ nanowires by chemical vapor deposition (CVD) at 850 °C. The as-synthesized-doped nanowires showed unique periodical structures in contrast to the traditional nanowires with smooth surfaces. The fascinating structures lead to a much higher surface to volume ratio and greater changes of depletion layer volume after gas absorption, and the sensitivity of gas sensing devices may be improved by using axial periodical nanostructures, instead of ordinary one. The photoluminescence of the Sb-doped SnO₂ nanostructures were measured. The doping of Sb atoms brings two new emission peaks at 561 and 670 nm.