化学气相沉积法制备GaN纳米线及其形貌结构和生长机理研究

采用化学气相沉积(CVD)法,分别以Ni、Au为催化剂,氨化金属Ga制备出GaN纳米线。运用SEM,EDX,TEM等表征手段分析了GaN纳米线的形貌与结构。通过改变氨化温度、生长时间、催化剂、衬底以及Ga源和衬底间的距离等生长条件,研究了其对GaN纳米线形貌和结构的影响,通过分析探讨纳米线的生长过程与机制,得到了生长GaN纳米线的最佳工艺。     

GaN纳米棒的制备及机理研究

本文分别用三甲基镓和高纯蓝氨作为Ga源和N源,Ni(NO3)2作为催化剂,在Si(111)衬底上制得针尖状GaN纳米棒.测试结果表明制备的GaN纳米棒是沿<100>方向生长的纯六方相结构.通过对生长过程的分析,我们认为GaN纳米棒的生长过程不仅受到VLS机制的控制,而是多种生长方式共同作用的结果.在反应的初期,GaN纳米棒的生长遵从VLS机制;但是随着GaN纳米棒轴向和径向的生长,GaN纳米结构中纳米棒端部的Ni催化剂纳米球会被"挤"出顶部,在较大的气流流速下被吹落至衬底上,失去催化剂诱导作用的纳米棒随后自行外延生长;而吹落至衬底上的Ni催化剂纳米球成为第二次生长有利的形核位置,且再次生长出粗短的纳米棒.因此不同生长机制得到的GaN纳米棒交织在一起,形成了最终的GaN纳米结构.     

微波水热及氨化法制备GaN纳米棒

以Ga2O3为原料,用微波水热法和高温氨化两步法合成GaN纳米棒。采用XRD及SEM对其结晶形貌进行表征。研究得出,GaN纳米粉呈长径比约为5:1的棒状,该纳米棒是由沿(002)方向高度取向一致的GaN晶粒结晶而成。XRD分析显示,GaN纳米棒为六方纤锌矿结构且结晶良好。光致发光(PL)分析显示,合成纳米棒在367nm处存在GaN本征发光峰。中心位于468nm、493nm及534nm附近出现了宽而弱的发射带,这有助于GaN在光电领域的应用。     

冷壁装置化学气相沉积制备纳米碳管

采用冷壁装置化学气相沉积(CVD)制备纳米碳管,以乙炔(C2H2)为碳源气体,研究了2种催化剂(镍、铁)、3种基底、3种稀释气体、3种稀释气体和碳源气体流量比以及温度对CVD法生长纳米碳管的影响,用SEM和TEM分析了产物的形貌.结果表明,镍催化活性高于铁的催化活性.与石墨和纯铁基底相比,以单晶硅基底生长的纳米碳管纯度更高,管壁更干净.3种稀释气体和碳源气体流量比(2/1、10/1、19/1)中,以流量比为10/1时生长纳米碳管效果最好.3种稀释气体(氨气、氢气、氮气)中,以氨气最好.随着生长温度的升高,催化剂的活性提高,有利于碳的有序排列,但生长的碳纳米管直径增大.当基底为单晶硅、催化剂镍膜厚度为20nm、氨气气氛、生长温度为850℃时,得到了近似定向生长的纳米碳管.     

磁控溅射与氨化法催化合成GaN纳米棒

使用一种新奇的稀土元素作为GaN纳米棒生长的催化剂,通过氨化溅射在Si(111)衬底上的Ga2O3/Tb薄膜成功合成了大规模的GaN纳米棒.采用扫描电子显微镜,X射线衍射,透射电子显微镜,高分辨透射电子显微镜和傅立叶红外吸收光谱来检测样品的形态,结构和成分.研究结果表明,合成的样品为六方纤锌矿结构的单晶GaN纳米棒.最后讨论了GaN纳米棒的生长机理.     

GaN纳米线材料的特性和制备技术

GaN是一种具有优越热稳定性和化学性质的宽禁带半导体材料，这种材料及相关器件可以工作在高温、高辐射等恶劣环境中，并可用于大功率微波器件．最近几年，由于GaN蓝光二极管的成功研制，使GaN成为了化合物半导体领域中最热门的研究课题．简要介绍了GaN纳米线材料的制备技术；综述了GaN纳米线材料的制备结果和特性．用CVD法研制的GaN纳米线的直径已经达到5～12nm，长度达到几百个微米．纳米线具有GaN的六方纤锌矿结构，其PL谱具有宽的发射峰，谱峰中心在420nm．GaN纳米线已经在肖特基二极管的研制中得到应用．     

化学气相沉积制备纳米结构碳化钨薄膜

采用氟化钨(WF6)和甲烷(CH4)为前驱体,采用等离子体增强化学气相沉积(PECVD)方法制备具有纳米结构的碳化钨薄膜。采用SEM、XRD、EDS等方法表征了碳化钨薄膜的形貌、晶体结构和化学组成。通过表征,表明在前驱体混合气体中的甲烷与氟化钨气体的流量比(碳钨比)为20、基底温度为800℃的条件下得到的碳化钨薄膜是由直径为20～35nm的圆球状纳米晶构成。通过分析影响薄膜的晶体结构、化学组成的因素后,认为要得到具有纳米晶结构的碳化钨薄膜,主要应控制前驱体气体中的碳钨比以及基底温度。     

化学气相沉积法制备超纳米金刚石薄膜

采用微波等离子体化学气相沉积法,利用CH4、SiO2和Ar的混合气体在单晶硅片基底上制备出高质量的超纳米金刚石薄膜.表征结果显示,制备的薄膜致密而均匀,晶粒平均尺寸约7.47nm,表面粗糙度约15.72nm,并且其金刚石相的物相纯度相对较高,是质量优异的超纳米金刚石薄膜材料.     

火焰化学气相沉积法制备氮掺杂纳米TiO_2研究

用火焰化学气相沉积法,分别以氨气为氮源、TiCl4为TiO2前驱体,在丙烷-空气湍流火焰中氧化制备氮掺杂纳米TiO2颗粒,以及用TiCl4为TiO2前驱体,在丙烷-空气湍流火焰中氧化制备纳米TiO2颗粒,然后在管式炉中,在氨气的环境下高温煅烧制备氮掺杂纳米TiO2颗粒。利用X射线衍射仪、紫外可见光谱仪、透射电子显微镜、X射线光电子能谱等分析方法对两种方法所制备的样品进行表征。结果表明:在相同的氨气流量下,火焰化学气相沉积法直接制备的氮掺杂纳米TiO2颗粒在波长400～500 nm的可见光的吸收强度大,氮掺杂量多。     

超长单晶硅纳米丝的化学气相沉积法制备

采用化学气相沉积法在镀金硅片上制备出了大量直径均匀、长度大于100肿的单晶纳米硅丝。采用场发射扫描电镜（FESEM）、能谱分析（EDX）、透射电镜（TEM）和拉曼光谱（Rarnan）对样品进行了表征和分析，并对超长纳米硅丝的生长机理进行了讨论。     

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.     

GaN纳米棒的合成与表征

利用化学气相沉淀法（CVD）以Ga2O3和NH3为原料在沉积有乙酸镍的硅衬底上合成出了GaN纳米棒,纳米棒直径在50-200nm，长度在2-10μm，表面比较光滑,利用场发射扫描电镜（FESEM），X射线衍射仪（XRD），能量散射谱（EDS）对样品进行了成分和结构分析，表明GaN纳米棒是单晶的纤锌矿结构，同时对其生长机理进行了探讨。     

Synthesis of FePt nanorods and nanowires by a facile method

FePt nanorods and nanowires have been synthesized by the reduction of Pt(acac)(2) and the thermal decomposition of Fe(CO)(5) in the presence of solvents/surfactants by simply controlling the sequence of addition of surfactants. The as-synthesized FePt nanorods and nanowires have a face centered cubic structure with average diameter of 3?nm. Length of nanorods and nanowires can be adjusted in the range of 15-150?nm by varying reaction parameters. Nanocrystalline L1(0) FePt phase with coercivity up to 24?kOe was obtained after heat treatments.     

The growth of GaN films by alternate source gas supply hot-mesh CVD method

Gallium nitride (GaN) films and Aluminium nitride (AlN) layers were deposited on SiC/Si (111) substrates by an alternating source gas supply or an intermittent supply of a source gas such as ammonia (NH₃), trimethylgallium (TMG) or trimethylaluminum (TMA) in a hot-mesh chemical vapor deposition (CVD) apparatus. The AlN layer was deposited as a buffer layer using NH₃ and TMA on a SiC layer grown by carbonization on Si substrates using propane (C₃H₈). GaN films were grown on an AlN layer by a reaction between NH_x radicals generated on a ruthenium (Ru) coated tungsten (W)-mesh and TMG molecules. An alternating source gas supply or an intermittent supply of one of the source gases during the film growth are expected to be effective for the suppression of gas phase reactions and for the enhancement of precursor migration on the substrate surface. By the intermittent supply of alkylmetal gas only during the growth of the AlN layer, the defect generation in the GaN films was reduced. GaN film growth by intermittent supply on an AlN buffer layer, however, did not lead to the improvement of the film quality.     

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.     

CVD法制备纳米石墨棒

以甲烷为碳源，在865℃-930℃温度条件下，通过化学气相沉积法，在铁基催化剂上生长出纳米石墨棒。对产物进行X射线衍射分析，确认其为石墨结构，晶粒径估算为16．3nm，长度为200nm～800nm。用透射电子显微镜和激光拉曼光谱仪作进一步的分析，结果表明：产物为纯度较高的纳米石墨棒。     

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.     

Fabrication of GaN nanowires and nanorods catalyzed with tantalum

Single-crystalline GaN nanowires and nanorods have been fabricated through ammoniating Ga₂O₃ films catalyzed with tantalum (Ta) by RF magnetron sputtering, and microstructure, morphology and optical properties were investigated in particular. The results indicate that the nanowires have a hexagonal wurtzite structure with size about 50 nm in diameter and more than ten microns in length, however, the nanorods are rod-like structures with smooth surface and 100–300 nm in diameter. The growth direction of these nanostructures are perpendicular to the (100) crystal plane. The photoluminescence spectrum at room temperature exhibits a strong UV light emission band centered at 364 nm.     

Synthesis of ITO nanowires and nanorods with corundum structure by a co-precipitation-anneal method

Tin-doped indium oxide (ITO) nanowires and nanorods were synthesized by a co-precipitation-anneal process. Both the nanowires and the nanorods had nearly uniform diameter of ca. 60 nm. The nanowires had long and straight morphology with length up to several micrometers. Moreover, the products were the ITO with corundum structure.     

Growth of GaN on SiC/Si substrates using AlN buffer layer by hot-mesh CVD

GaN films were grown on SiC/Si (111) substrates by hot-mesh chemical vapor deposition (CVD) using ammonia (NH₃) and trimetylgallium (TMG) under low V/III source gas ratio (NH₃/TMG = 80). The SiC layer was grown by a carbonization process on the Si substrates using propane (C₃H₈). The AlN layer was deposited as a buffer layer using NH₃ and trimetylaluminum (TMA). GaN films were formed and grown by the reaction between NH_x radicals, generated on a tungsten hot mesh, and the TMG molecules. The GaN films with the AlN buffer layer showed better crystallinity and stronger near-band-edge emission compared to those without the AlN layer.