Si(111)表面吸附氢会形成双氢化相吗?

用热脱附谱研究了原子氢在Si(111)表面的吸附,得到了两个吸附状态。从脱附谱特性同Si(100)/H系统的相似性,可以推测氢在Si(111)表面也存在单氢化相和双氢化相两种状态。单氢化相主要是顶位吸附所形成的,而双氢化相的形成则可以用McRae所提出的Si(111)(7×7)表面原子结构的三角形二聚物层错模型来解释。关键词：

A STUDY ABOUT THE EXISTENCE OF DIHYDRIDE PHASE ON HYDROGEN CHEMISORBED Si(111) SURFACE

The chemisorption states of atomic hydrogen on Si (111) surface have been studied by means of thermal desorption spectra. Two desorption peaks β₁ and β₂ were observed. At low hydrogen exposure only peak β₁ could be seen. The peak β₂ appeared at higher hydrogen exposure and could not exist if the sample was exposed to hydrogen at a temperature higher than 400℃ or was annealed above 380℃ after hydrogen exposure. The saturated coverage of β₂ was less than that of β₁ by a factor of 2. The peak β₁ is related to the top site adsorption of H on surface Si atoms as reported by previous works. The relatively high activation energy of desorption for β₂ implies that its adsorption state is likely to be a chemical, bonding state instead of a non-bonding state as postulated by Schulze and Hender. All the above desorption behaviors of β₁ and β₂ are quite similar to those of monohydride phase and dihydride phase of H on Si (100) surface. Therefore, it is reasonable to deduce that the β₁ and β₂ states correspond to the monohydride and dihydride phase on Si (111) respectively. A triangle dimer stacking fault model of Si (111) (7×7) reconstruction proposed by McRae could be used to give an exp-laination of forming surface silicon dimer bond and thus the dihydride phase on clean Si (111) surface.