Quantum chemistry model of surface reactions and kinetic model of diamond growth: Effects of CH 3 radicals and C 2 H 2 molecules at low-temperatures CVD

The objective of this study is to explore conditions that facilitate a significant reduction in substrate temperature during diamond growth. The typical temperature for this process is around 1200 K; we aim to reduce it to a much lower level. To achieve this, we need to understand processes that limit the diamond growth at low temperatures. Therefore, we developed a detailed chemical kinetic model to analyze diamond growth on the (100) surface. This model accounts for variations in substrate temperature and gas composition. Using an ab initio quantum chemistry, we calculated the reaction rates of all major gas phase reactants with the diamond surface, totaling 91 elemental surface reactions. Based on this comprehensive model, we developed a reduced model consisting of 8 reactions. This reduction enabled us to derive an analytical equation that describes the rate of diamond growth across a broad range of temperatures involving CH 3, H, H 2, and C 2 H 2 reactants. Consistent with previous studies, the model identifies that CH 3 is a major precursor of diamond growth, and the contribution from C 2 H 2 to the growth is significantly smaller. However, C 2 H 2 can also contribute to forming a sp 2 -phase instead of a sp 3 -phase, and this process becomes dominant below a critical temperature. As a result, C 2 H 2 flux inhibits diamond growth at low temperatures. To quantify this deleterious process, we developed a new mechanism for sp 2 -phase nucleation on the (100) surface. Similar to the so-called HACA mechanism for soot formation it involves hydrogen abstraction and C 2 H 2 addition. Consequently, optimal low-temperature CVD growth could be realized in a reactor designed to maximize the CH 3 radical production, while minimizing the generation of C 2 H 2 and other sp. and sp 2 hydrocarbons.