【作者】 庞巧莲；

【导师】 钱逸泰；

【作者基本信息】 山东大学 ， 无机化学， 2010， 硕士

【摘要】 SiC半导体材料是第三代宽带隙(WBP)半导体材料。由于具有宽带隙、高临界击穿电场、高热导率、高载流子饱和漂移速度等优异的性质,所以在高温、高频、大功率、光电子及抗辐射等方面具有巨大的应用前景。本论文在对碳化硅纳米材料的合成、应用等方面的发展现状进行充分调研的基础上,采用几种简单的方法(硅粉为硅源,金属单质为还原剂,卤代烃CHI3、CBr4、CHCl3及CH2Cl2和CCl4的混合物为碳源)制备了3C-SiC纳米线和微米级多面体,并对其物相、形貌、光学及热稳定性等进行了表征。主要内容概括如下：1.低温制备SiC纳米线和微米级多面体及其控制生长。以硅粉为硅源,CHI3为碳源,金属Na为还原剂在230℃条件下,于高压反应釜中成功制备出碳化硅纳米线；当反应物用量均加倍,在500℃条件下可以制得大量碳化硅多面体。粉末X-射线衍射(XRD)显示制得的碳化硅纳米线样品为面心立方结构(3C-SiC),计算所得晶格常数a=4.359A,与JCPDS卡片值(No.65-0360,a=4.358A)接近。透射电子显微镜(TEM)照片显示所得3C-SiC纳米线的直径主要分布在10-80 nm,长度有几微米,其生长方向为[111]。值得一提的是,所得的碳化硅纳米线中有约三分之一为弯曲纳米线。根据实验结果分析并结合相关的文献报道,该实验中SiC纳米线可能的形成机制为气-液-固(VLS)生长机理。XRD衍射花样证实多面体样品也是面心立方相的碳化硅(3C-SiC)。场发射扫描电镜显示多面体具有光滑的表面,直径为2-5μm。热重分析(TGA)显示立方碳化硅多面体样品在1100℃以下具有极好的热稳定性,即使在1200℃也只有很微量增重,这表明该样品有很强的抗氧化性；室温光致发光测试(PL)显示3C-SiC纳米线和微米级多面体样品分别在360和354nm处有强的发射峰。此外,以硅粉为硅源,CHI3为碳源,金属K为还原剂在140℃条件下,也成功制备出了立方相碳化硅纳米线(30%)和多面体(70%)；然而,若把还原剂换成金属镁粉,即使反应温度升高到600℃也不能合成出碳化硅。2.制备SiC支晶纳米线。300℃条件下以硅粉为硅源,CBr4为碳源,金属Na为还原剂,成功制备出了碳化硅支晶纳米线。X-射线粉末衍射(XRD)显示制得的样品为面心立方相的碳化硅,晶格常数a=4.355A,与JCPDS卡片值(No.65-0360,a=4.358 A)接近；透射电子显微镜(TEM)显示碳化硅纳米线存在支晶结构,其纳米线直径为20-50nm,长度有几微米,选区电子衍射(SAED)表明样品为单晶SiC；高分辨透射电镜(HRTEM)显示相邻的晶格条纹间距约为0.25 nm,与3C-SiC的(111)面间距相一致,其生长方向为[111]。光致发光测试(PL)显示样品在355 nm左右有一个强的发射峰。此外,当反应体系中的金属还原剂改为金属K时,也可以成功制备出面心立方相的碳化硅纳米线。3.溶剂热法制备碳化硅材料。通过溶剂热法以硅粉为硅源,CHCl3为碳源,金属Na为还原剂在高压反应釜中350℃条件下制得了碳化硅纳米线。粉末X-射线衍射(XRD)显示得到的样品为面心立方相的碳化硅(3C-SiC),晶格常数a=4.357A,与JCPDS卡片值(No.65-0360,a=4.358A)基本吻合；透射电子显微镜(TEM)照片显示所制得的碳化硅形貌主要是纳米线和六方块结构,纳米线的直径约为20-50 nm,长度为十几微米。高分辨透射电镜(HRTEM)显示相邻的晶格条纹间距约为0.25 nm,与3C-SiC的(111)面间距相一致。另外,以硅粉为硅源,CH2C12和CCl4的共同作为碳源,金属钠为还原剂在高压反应釜中300℃条件下成功制备出面心立方相碳化硅。场发射扫描电镜照片显示碳化硅主要有不规则的六角片堆积而成花状结构。室温光致发光测试(PL)显示样品在439 nm左右有一个强的发射峰。更多还原

【Abstract】 Silicon carbide is an important wide band gap semiconducting material, and has attracted extensively attention due to its excellent properties, including high breakdown electric field strength, high saturated drift velocity of electrons, wide gap, high thermal conductivity, high mechanical strength, high chemical stability, and low induced activity; therefore, SiC-based devices could be used at higher temperature and in harsh conditions as functional ceramic or as a high temperature semiconductor. On the basis of comprehensive and thorough investigation of literature concerning the synthesis and application developments of silicon carbide (SiC) nanomaterials, in this dissertation, cubic silicon carbide nanowires and micro-scaled polyhedra were synthesized by several simple methods (silicon powder as silicon source, metalic as the redrctant, halogenated hydrocarbons CHI3, CBr4, CH2Cl2, and CHCl3 as the carbon source), and the phase, morphology, optics and thermal ability of the as-obtained sample were characterized. The main contents can be summarized as follows:1. Preparation of SiC nanowires and micro-scaled polyhedra at low temperature and the control growth of themSilicon Carbide (3C-SiC) nanowires was successfully synthesized through a one-step route using CHI3, Si powder, and metallic Na as reactants in a stainless steel autoclave at 230℃. When the amounts of the reactants were doubled and in the mean time the target temperature was set at 500℃, large quantities of SiC polyhedra were produced. X-ray powder diffraction (XRD) pattern of the nanowires sample can be indexed as the cubic SiC with the lattice constant a= 4.359 (?) which is close to that of the reported value (JCPDS card no.65-0360, a= 4.358 (?)). Transmission electron microscopy images show that the product mainly composed of nanowires. These nanowires has diameters ranging from 10-80 nm and lengths up to several micrometers, which have a preferential grow along the [111] direction. It is worth mentioning that one thirds of these nanowires are bent. According to the experimental analysis results and the study of the related reports, vapor-liquid-solid (VLS) mechanism is the possible growth mechanism of SiC nanowires. X-ray diffraction patterns of the polyhedra sample also can be indexed as the cubic SiC. FESEM indicates that the polyhedra sample has smooth surface, its diameter in the range of 2-5μm. TGA curve reveals that the polyhedra sample has excellent thermal stability below 1100℃; The polyhedra sample has very small weight gain even at 1200℃, this demonstrate that it possess outstanding oxidation resistance. The room-temperature photoluminescence spectra of SiC nanowire and SiC polyhedra display strong ultraviolet emission peaks centered at 360 nm and 354 nm, respectively.In addition, Silicon Carbide (3C-SiC) nanowires (30%) and polyhedra (60%) were also successfully synthesized through a one-step route using CHI3, Si powder, and metallic K as reactants in a stainless steel autoclave at 140℃, whereas SiC product can not be produced when the metallic K as the reducing agent at 600℃.2. Synthesis of branched SiC nanowiresCubic branched SiC nanowires were successfully prepared by using silicon powder, CBr4 and metallic Na as reductant at 300℃. X-ray powder diffraction (XRD) pattern of the branched SiC nanowires sample can be indexed as the cubic SiC with the lattice constant a= 4.355 (?) which is close to that of the reported value (JCPDS card no. 65-0360, a= 4.358 (?)). Transmission electron microscopy images show that the product mainly composed of branched nanowires. These nanowires have diameters ranging from 20-50 nm and lengths up to several micrometers, selected area electron diffraction (SAED) pattern showed that the samples were crystal SiC; The HRTEM image of a part of the sample show that the inter-planar spacing of the two adjacent frings is about 0.25 nm, which is consist with the (111) lattice planes of 3C-SiC, and it indicates that the nanowire grow along the [111] direction. The room-temperature photoluminescence (PL) spectrum of the sample show a strong emission peak centered at 400 nm. Moreover, cubic SiC nanowires were also could be synthesized when metallic Na was replaced by K in this experimental system, while keeping other parameters unchanged. 3. Preparation of SiC materials by solvothermal routes3C-SiC nanowires were prepared starting from Si powder, CHCl3, and Na as reductant through a solvothermal route at 350℃. XRD patterns of the sample can be indexed to the cubic cell of SiC with the lattice constant a= 4.355 (?), which is in agreement with the reported value (JCPDS card no.65-0360, a= 4.358 (?)). Transmission electron microscopy images show that the product mainly consist of nanowires with diameters of 20-50 nm and lengths up to tens of micrometers; The HRTEM image of a part of SiC nanowires reveals that the inter-planar spacing of the two adjacent frings is about 0.25 nm, which is consistent with the (111) lattice planes of the crystalline SiC.In addition, cubic SiC were successfully synthesized by using Si, CH2Cl2, CCl4, and Na as reactants at 300℃. Field emission scanning electron microscopy images show that the SiC flower-like structures deposited by irregular hexagon. The room-temperature photoluminescence (PL) spectrum of the sample show a strong emission peak centered at 439 nm.更多还原