碳化硅表面氢气吸附机理研究

在CVD沉积SiC过程中，载气体H2与沉积SiC基体表面的反应影响沉积速率和沉积产物品质，因此研究这些微观反应机理具有十分重要的科学意义和工程价值。本文基于第一性原理研究了H2在3C-SiC(111)（硅原子暴露面）和3C-SiC(-1-1-1)（碳原子暴露面）面的吸附位置、吸附能、电子结构和覆盖率等吸附情况。发现H2倾向于吸附在3C-SiC(111)面，H原子的最稳定吸附位为OT位（顶位）且属于化学吸附。H2在吸附时会自发解离为两个H原子，以双顶位形式吸附在两个相邻的Si原子上。该过程中基体表面Si原子的电子向H偏移，此时两者的主要相互作用源于Si原子的p轨道和H的s轨道的重叠杂化。通过计算氢气在表面的覆盖率，发现吸附能随着覆盖率的增大而增大，在低H覆盖率(θH≤4/9 ML)下，H原子之间存在着较强的吸引力，随着H覆盖率的增加(θH＞4/9 ML)，H原子之间排斥力逐渐增大，吸附能增加趋缓，整体结构更加稳定。

Study on the adsorption mechanism of hydrogen molecules on the surface of silicon carbide

In the process of CVD deposition of SiC, the reaction of carrier gas H2 with the surface of the deposited SiC matrix affects the deposition rate and the quality of the deposited products, so it is of great theoretical and practical significance to study these microscopic reaction mechanisms.The adsorption locations, adsorption energies, electronic structures and coverages of H2 on 3C-SiC(111) (above it is the surface of a silicon atom) and 3C-SiC(-1-1-1) (above it is the surface of the carbon atom) planes were studied using the first principles based on density functional theory. The results show that the most stable adsorption position of H atom is the OT position (on top) and belongs to chemical adsorption. Upon adsorption H2 spontaneously dissociates into two H atoms which are adsorbed on two adjacent Si atoms in the form of a double top position, thus the electrons of the Si atoms on the surface of the matrix are shifted to H, where the main interaction between the two stems from the overlapping hybridization of the p-orbital of the Si atom and the s-orbital of H. By calculating the coverage of hydrogen on the surface, it is found that the adsorption energy increases with the increase of the coverage, under the low H coverage rate (θH≤4/9 ML), there is a strong attraction between H atoms, with the increase of H coverage (θH>4/9 ML), the repulsion force between H atoms gradually increases, the adsorption energy increases slowly, and the overall structure tends to be more stable.