Multiphysics, Multiphase Modeling of Carbon Nanotube Synthesis Process by Chemical Vapor Deposition

In the present paper, a comprehensive modeling framework is proposed to conduct multiphysics, multiphase modeling of carbon nanotube (CNT) fabrication process by chemical vapor deposition (CVD). The modeling is based on fluid dynamics, heat transfer, chemical reaction, as well as mass transport phenomena which have been fully coupled with each other. The inserted gasses are considered as methane (CH₄) as the main hydrocarbon gas and hydrogen (H₂) as the process enhancement gas. In the gas phase reaction section, a novel set of reactions for CH₄ hydrocarbon gas is proposed which is based on 71 different chemical reactions that take place near CVD inlet. Also, surface reactions are modeled by considering 19 set of reactions acting near substrate surface which lead to CNTs formation. The investigation is performed for different combination of gas flow rate quantities ranging from 500 to 1000 sccm (standard cubic centimeter per minute) for methane and 250 to 500 sccm for hydrogen gas. Also, the quartz tube temperature is considered to change from 700 to 1000 °C. Since the thermal specifications for each species are calculated individually, the gas flow inside the quartz tube is treated as nonisothermal flow. Numerous simulations are conducted and the results are compared with the fabricated CNT’s images taken by the SEM (scanning electron microscopy). Utilizing the obtained diagrams from modeling, the effects caused by gas mixture flow rate and temperature changes on the production rate of gas phase species such as H, CH₃, C₂H₂ and bulk carbon species (C and 2C) that produced by surface species TC and TC₂ are investigated. It is found that increasing the fabricated temperature causes a rise in species production rate. However, it is observed that the produced species respond differently to any change in hydrogen and hydrocarbon flow rates. The velocity, temperature profile as well as concentration distribution along the silicon substrate length have been also investigated. This study can lead to a controlled CNTs manufacturing process when combined with in-situ measurement systems.