Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
J Chem Phys. 2010 Aug 21;133(7):074708. doi: 10.1063/1.3469978.
Even though the decomposition of disilane on silicon surfaces has been extensively studied, the molecular mechanism for its decomposition has not been fully resolved. The general view motivated partly by spectroscopic data is that decomposition occurs through silicon-silicon bond dissociation although there is evidence from kinetics that silicon-hydrogen bond dissociation is important, and perhaps even dominant. Thus, we reexamine the assignment of the experimental vibrational peaks observed in disilane and silane adsorption in order to assess the evidence for the silicon hydride species that are formed during decomposition. We calculate the vibrational density of states for a number of silicon hydride species on the Si(100)-(2x1) surface using Car-Parrinello molecular dynamics. We obtain the calculated vibrational frequency in the adiabatic limit by extrapolating to zero orbital mass, calibrating our method using the well-established monohydride peak. The calculated vibrational frequencies of the monohydride are in good agreement experimental data. Our results show that the spectroscopic data for silicon hydrides does not preclude the occurrence of Si(2)H(5) on the surface thus providing evidence for silicon-hydrogen bond dissociation during disilane adsorption. Specifically, we find that an experimentally observed vibrational peak at 2150 cm(-1) that has generally been attributed to the trihydride SiH(3) is more likely to be due to Si(2)H(5). Our results also clear up the assignment of two peaks for monohydride species adsorbed at the edge of a growing terrace, and a peak for the dihydride species adsorbed in the interdimer configuration.
尽管二硅烷在硅表面的分解已经得到了广泛的研究，但它的分解分子机制尚未完全解决。部分受光谱数据驱动的一般观点是，尽管动力学证据表明硅氢键的解离很重要，甚至可能占主导地位，但分解是通过硅硅键的解离发生的。因此，我们重新审查了在二硅烷和硅烷吸附中观察到的实验振动峰的分配，以评估在分解过程中形成的硅氢化物的证据。我们使用 Car-Parrinello 分子动力学计算了 Si(100)-(2x1)表面上许多硅氢化物的振动态密度。我们通过将轨道质量外推到零来获得绝热极限下的计算振动频率，使用已经确立的单氢化物峰来校准我们的方法。单氢化物的计算振动频率与实验数据非常吻合。我们的结果表明，硅氢化物的光谱数据不排除表面上 Si(2)H(5)的存在，从而为二硅烷吸附过程中硅氢键的解离提供了证据。具体来说，我们发现实验上观察到的 2150 cm(-1)处的振动峰通常归因于三氢化物 SiH(3)，更可能是由于 Si(2)H(5)。我们的结果还澄清了在生长平台边缘吸附的单氢化物物种的两个峰和在二聚体构型中吸附的二氢化物物种的一个峰的分配。
