The aim of the present work is to develop a numerical model to understand and optimize the process parameters for the growth of carbon nanofibers (CNFs) inside the plasma enhanced chemical vapor deposition system containing acetylene, hydrogen, and argon gases. Two-dimensional axis-symmetrical inductive couple plasma module is implemented using COMSOL Multiphysics 5.2 simulation software to analyze the density profiles and temperatures of electrons, ions, and neutral species in the plasma at different gas pressures and input plasma powers. The outcomes of the COMSOL computational model show that the electron density in the plasma decreases with increase in gas pressure and increases with increase in plasma power. Other than the computational model, an analytical model is developed in the present paper that accounts the plasma sheath equations to study the fluxes and energies of the plasma species. The results obtained from the plasma sheath model at the catalyst-substrate surface boundary are fed as the input parameters to surface deposition model to investigate the growth characteristics of carbon nanofibers, i.e., poisoning of the catalyst nanoparticle, height, and diameter of carbon nanofiber at different gas pressures and input plasma powers. It is found that electron density decays at the faster rate when gas pressure is increased and decays at slower rate when input plasma power is raised. Moreover, it is also found that growth rate of CNFs increases with increase in gas pressure and plasma power. However, the significant drop in CNF growth rate is observed when the gas pressure is high enough (above and around 50 Torr). From the results obtained, it can be concluded that the CNFs having good growth characteristics can be obtained at some optimum pressure range, i.e., one order of the magnitude in the units of Torr. A good comparison between numerical simulation results and analytical results with each other and with existing experimental results confirms the adequacy of the computational and analytical approach.

中文翻译：

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PECVD 系统中等离子体特性和碳纳米纤维生长的参数研究：数值建模

本工作的目的是开发一个数值模型，以了解和优化碳纳米纤维 (CNF) 在包含乙炔、氢气和氩气的等离子体增强化学气相沉积系统内生长的工艺参数。二维轴对称电感耦合等离子体模块使用 COMSOL Multiphysics 5.2 仿真软件实现，以分析在不同气压和输入等离子体功率下等离子体中电子、离子和中性物质的密度分布和温度。COMSOL 计算模型的结果表明，等离子体中的电子密度随着气压的增加而降低，随着等离子体功率的增加而增加。除了计算模型，本论文开发了一个分析模型，该模型考虑了等离子体鞘层方程，以研究等离子体物质的通量和能量。从催化剂-基材表面边界处的等离子体鞘模型获得的结果作为输入参数提供给表面沉积模型，以研究碳纳米纤维的生长特性，即催化剂纳米颗粒的中毒、碳纳米纤维在不同的气体压力和输入等离子体功率。发现当气压增加时电子密度以较快的速率衰减，而当输入等离子体功率增加时以较慢的速率衰减。此外，还发现 CNF 的生长速率随着气压和等离子体功率的增加而增加。然而，当气压足够高（高于和大约 50 Torr）时，可以观察到 CNF 增长率的显着下降。从获得的结果可以得出结论，可以在某个最佳压力范围内获得具有良好生长特性的 CNF，即以 Torr 为单位的一个数量级。数值模拟结果和分析结果相互之间以及与现有实验结果之间的良好比较证实了计算和分析方法的充分性。