Continuum and Molecular Modeling of Chemical Vapor Deposition at Nano-Scale Fibrous Substrates

Himel Barua, A. Povitsky
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Abstract

Chemical vapor deposition (CVD) is a common industrial process that incorporates a complex combination of fluid flow, chemical reactions, and surface deposition. Understanding CVD processes requires rigorous and costly experimentation involving multiple spatial scales, from meters to nanometers. The numerical modeling of deposition over macro-scale substrates has been conducted in the literature and results show compliance with experimental data. For smaller-scale substrates, where the corresponding Knudsen number is larger than zero, continuum modeling does not provide accurate results, which calls for the implementation of molecular-level modeling techniques. In the current study, the finite-volume method (FVM) and Direct Simulation Monte Carlo (DSMC) method were combined to model the reactor-scale flow with CVD around micro- and nano-scale fibers. CVD at fibers with round cross-sections was modeled in the reactor, where fibers were oriented perpendicularly with respect to the feedstock gas flow. The DSMC method was applied to modeling flow around the matrix of nano-scale circular individual fibers. Results show that for smaller diameters of individual fibers with the same filling ratio, the residence time of gas particles inside the fibrous media reduces, and, consequently, the amount of material surface deposition decreases. The sticking coefficient on the fibers’ surface plays an important role; for instance, increasing the sticking coefficient from 20% to 80% will double the deposition rate.
纳米级纤维基底化学气相沉积的连续和分子建模
化学气相沉积(CVD)是一种常见的工业过程,它结合了流体流动、化学反应和表面沉积的复杂组合。了解CVD过程需要涉及多个空间尺度(从米到纳米)的严格且昂贵的实验。文献中已经进行了宏观衬底上沉积的数值模拟,结果与实验数据相符。对于较小规模的基片,其对应的Knudsen数大于零,连续体建模不能提供准确的结果,这需要实施分子水平的建模技术。本研究将有限体积法(FVM)和直接模拟蒙特卡罗(DSMC)相结合,模拟了反应器尺度的微纳米尺度纤维周围的CVD流动。在反应器中模拟了具有圆形截面的纤维的CVD,其中纤维相对于原料气流垂直定向。将DSMC方法应用于纳米尺度圆形单个纤维基体周围流动的模拟。结果表明,在填充率相同的情况下,单个纤维直径越小,气体颗粒在纤维介质中的停留时间越短,材料表面沉积量也随之减少。纤维表面的粘接系数起着重要的作用;例如,将粘附系数从20%增加到80%将使沉积速率增加一倍。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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