Center for Interdisciplinary Molecular Science, Department of Applied Chemistry, National Chiao Tung University , Hsinchu 300, Taiwan.
J Phys Chem A. 2013 Oct 24;117(42):10811-23. doi: 10.1021/jp407553a. Epub 2013 Oct 9.
The kinetics and mechanisms for SiH2 + Si2H6 and SiH3 + Si2H5 reactions and the related unimolecular decomposition of Si3H8 have been investigated by ab initio molecular orbital theory based on the QCISD(T)/CBS//QCISD/6-311++G(d,p) method in conjunction with quantum statistical variational Rice-Ramsperger-Kassel-Marcus (RRKM) calculations. For the barrierless radical association processes, their variational transition states have been characterized by the CASPT2//CASSCF method. The species involved in the study are known to coexist under CVD conditions. The results show that the association reaction of SiH2 and Si2H6 producing Si3H8 occurs by insertion via its lowest-energy path forming a loose hydrogen-bonding molecular complex with 8.3 kcal/mol binding energy; the reaction is exothermic by 55.0 kcal/mol. The chemically activated Si3H8 adduct can fragment by several paths, producing SiH4 + SiH3SiH (-0.7 kcal/mol), Si(SiH3)2 + H2 (-1.4 kcal/mol), and SiH3SiH2SiH + H2 (-1.4 kcal/mol). The predicted enthalpy changes as given agree well with available thermochemical data. Three other decomposition channels of Si3H8 occurring by Si-H or Si-Si breaking were found to be highly endothermic, and the reactions take place without a well-defined barrier. The heats of formation of Si3H8, SiH2SiH, Si2H4, i-Si3H7, n-Si3H7, Si(SiH3)2, and SiH3SiH2SiH have been predicted and found to be in close agreement with those available data in the literature. The product branching rate constants for SiH2 + Si2H6 and SiH3 + Si2H5 reactions and the thermal unimolecular decomposition of Si3H8 for all low-energy paths have been calculated with multichannel variational RRKM theory covering varying P,T conditions typically employed in PECVD and Cat-CVD processes for hydrogenated amorphous silicon (a-Si/H) film growth. The results were also found to be in good agreement with available kinetic data. Our kinetic results may be employed to model and control very large-area a-Si/H film growth for a new generation of solar cell applications.
通过基于 QCISD(T)/CBS//QCISD/6-311++G(d,p)方法的从头算分子轨道理论，并结合量子统计变分 Rice-Ramsperger-Kassel-Marcus（RRKM）计算，研究了 SiH2 + Si2H6 和 SiH3 + Si2H5 反应的动力学和机理以及相关的 Si3H8 单分子分解。对于无势垒自由基缔合过程，通过 CASPT2//CASSCF 方法对其变分过渡态进行了表征。研究中涉及的物种已知在 CVD 条件下共存。结果表明，SiH2 和 Si2H6 通过插入反应生成 Si3H8，通过其最低能量路径形成具有 8.3 kcal/mol 结合能的松散氢键分子络合物；反应放热 55.0 kcal/mol。化学活化的 Si3H8 加合物可以通过多条途径分解，生成 SiH4 + SiH3SiH（-0.7 kcal/mol）、Si（SiH3）2 + H2（-1.4 kcal/mol）和 SiH3SiH2SiH + H2（-1.4 kcal/mol）。预测的焓变与可用的热化学数据吻合较好。还发现了三个通过 Si-H 或 Si-Si 断裂发生的 Si3H8 其他分解通道，这些通道是高度吸热的，反应没有明确的势垒。Si3H8、SiH2SiH、Si2H4、i-Si3H7、n-Si3H7、Si（SiH3）2 和 SiH3SiH2SiH 的生成焓已被预测，并与文献中可用数据非常吻合。对于 SiH2 + Si2H6 和 SiH3 + Si2H5 反应以及 Si3H8 的热单分子分解的所有低能路径的产物分支速率常数，已使用多通道变分 RRKM 理论进行了计算，该理论涵盖了 PECVD 和 Cat-CVD 工艺中通常用于氢化非晶硅（a-Si/H）薄膜生长的变化 P、T 条件。结果也与可用的动力学数据吻合较好。我们的动力学结果可用于模拟和控制新一代太阳能电池应用的大面积 a-Si/H 薄膜生长。
