Film precursors and growth mechanisms of carbon and silicon carbide deposition from gas phase

采用薄管CVD反应器，在1010℃、50 Torr条件下对热解碳进行化学气相沉积。为了考察气相络合反应生成的各种烃类的影响，对甲烷、乙烷、乙烯、乙炔、丙烷、丙烯、烯丙烯、正丁烷、苯等进行了沉积实验。得到热解碳样品，用微气相色谱仪分析产物气相组成。对丙烷制得的样品进行XPS测定，发现sp^3的C-C键分数约为70%，sp^2的C-C键很少。由丙烯制备的样品的sp^3分数为30%。丙烯样品的sp^3分数为15%。x射线衍射和拉曼散射测量显示，每个样品似乎都是非结晶的。然而，通过透射电镜观察到，苯、烯和丙烯制备的热解碳样品呈层状结构。产物气相分析表明，当丙烷进入反应器时，气相中烯丙烯的含量仍能达到5%左右。从丙烷制备的薄膜中观察到sp^2结构的来源被认为是气相形成的烯丙烯和烯丙烯。气相中的薄膜前体似乎决定了所得薄膜的结构。利用基本反应数据库对气相反应进行了数值模拟。提出了一种将由数百种基本反应组成的反应模型简化为可用于设计目的的化学反应工程模型的方法。在该方法中，首先通过比较实际气体组成的反应速率来筛选元素反应，然后从化学反应工程的角度进行模型还原。通过数值模拟和实验气体组成分析，从丙烷热解的651个基本反应中提取出26个重要反应。所推导的简化模型与实验结果吻合良好。少

Chemical vapor deposition of pyrolytic carbon was carried out by using a thin tubular CVD reactor at 1010℃ and 50 Torr. In order to investigate the effects of various hydrocarbons formed by complex reactions in the gas phase, deposition experiments from methane, ethane, ethylene, acetylene, propane, propylene, allene, allylene, n-butane, benzene, etc. were conducted. Pyrolytic carbon samples were obtained and the product gas composition was analyzed by micro gas chromatograph. XPS measurement of the sample prepared from propane showed that the sp^3 C-C bond fraction was ca. 70% and few sp^2 C-C bonds were detected. The sample prepared from propylene had a sp^3 fraction of 30%. The sample from allene had a sp^3 fraction of 15%. X-ray diffraction and Raman scattering measurements showed each sample seemed non-crystalline. However, a layered structure was observed by TEM in the pyrolytic carbon samples prepared from benzene, allene, and allylene. The product gas analysis showed the allene … More and allylene fraction in the gas phase was able to reach ca. 5% even when propane was fed to the reactor. The origin of the sp^2 structure observed in the film prepared from propane was thought to be allene and allylene formed in the gas phase. Film precursors in the gas phase seem to determine the structure of the resulting film. Numerical simulation of the gas phase reactions was also carried out by using an elementary reaction database. A procedure to reduce a reaction model consisting of hundreds of elementary reactions to a chemical reaction engineering model that can be used for design purpose was proposed. In the proposed procedure, elementary reactions were first screened by comparing the reaction rates for an actual gas composition, and then the model reduction was made from chemical reaction engineering point of view. From the results of the numerical simulation and gas composition analysis in the experiments, 26 important reactions were extracted from 651 elementary reactions concerning propane pyrolysis. The derived reduced model and the experimental results correlated well. Less