Energetics and Rate Constants of Si2H6 and Ge2H6 Dissociative Adsorption on Dimers of SiGe(100)-2 × 1

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• 作者：Chia-Liang Cheng ; Dah-Shyang Tsai ; Jyh-Chiang Jiang
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：September 13, 2007
• 年：2007
• 卷：111
• 期：36
• 页码：13466 - 13472
• 全文大小：282K
• 年卷期：v.111,no.36(September 13, 2007)
• ISSN：1932-7455

文摘

Dissociative adsorption of Si₂H₆ and Ge₂H₆ on various buckled dimers of SiGe(100)-2 × 1 surface has beenstudied using density functional theory at the B3LYP level. Two paths, individually leading to (I) twochemisorbed SiH₃ or GeH₃ and (II) surface hydrides plus a gas-phase SiH₄ or GeH₄, are considered in theenergetics calculation. Contrary to the intuitive mechanism involving a four-center transition state (TS) thatyields two SiH₃(a) or GeH₃(a) in one step, the intermolecular bond scission on a dimer is accomplished intwo consecutive steps of three-center TS, in which the first step is rate-limiting. The calculated energy barrierof the first step in Si-Si bond scission is higher than that of the H-Si bond scission on Si*-Si dimer by 9kcal/mol. Therefore, in contrast to the conventional wisdom of favoring Si-Si bond cleavage over H-Si asthe first step in chemisorption on Si(100)-2 × 1, the calculation result supports Niwano and co-workers'experiments that concluded that Si₂H₆ adsorption without breaking the Si-Si bond was preferred. On theother hand, the Ge alloying on the surface reduces the barrier height difference between these two paths.Hence, the energy blockade between dehydrogenation and intermolecular bond scission decreases when Ge₂H₆is added in Si₂H₆ chemical vapor deposition. Rate constants are also calculated and the results are qualitativelyin line with the Ge₂H₆ reactivity on Si(100) measured by Lam et al.