Xu Xin, Kang Song-Yun, Yamabe Tokio
State Key Laboratory for Physical Chemistry of Solid Surfaces, Department of Chemistry, Institute of Physical Chemistry, Xiamen University, Xiamen 361005, China.
Chemistry. 2002 Dec 2;8(23):5351-62. doi: 10.1002/1521-3765(20021202)8:23<5351::AID-CHEM5351>3.0.CO;2-K.
In this paper, we present a detailed mechanism for the complete decomposition of NH3 to NHx(a) (x = 0-2). Our calculations show that the initial decomposition of NH3 to NH2(a) and H(a) is facile, with a transition-state energy 7.4 kcal mol-1 below the vacuum level. Further decomposition to N(a) or recombination-desorption to NH3(g) is hindered by a large barrier of approximately 46 kcal mol-1. There are two plausible NH2 decomposition pathways: 1) NH2(a) insertion into the surface Si-Si dimer bond, and 2) NH2(a) insertion into the Si-Si backbond. We find that pathway (1) leads to the formation of a surface Si = N unit, similar to a terminal Si = Nt pair in silicon nitride, Si3N4, while pathway (2) leads to the formation of a near-planar, subsurface Si3N unit, in analogy to a central nitrogen atom (Nc) bounded to three silicon atoms in the Si3N4 environment. Based on these results, a plausible microscopic mechanism for the nitridation of the Si(100)-(2 x 1) surface by NH3 is proposed.
在本文中，我们提出了一个将NH₃完全分解为NHₓ(a)（x = 0 - 2）的详细机制。我们的计算表明，NH₃初始分解为NH₂(a)和H(a)很容易，过渡态能量比真空能级低7.4 kcal mol⁻¹。进一步分解为N(a)或通过复合解吸回到NH₃(g)受到约46 kcal mol⁻¹的大势垒阻碍。NH₂有两种可能的分解途径：1）NH₂(a)插入表面Si - Si二聚体键中，以及2）NH₂(a)插入Si - Si反馈键中。我们发现途径（1）导致形成表面Si = N单元，类似于氮化硅Si₃N₄中的末端Si = Nt对，而途径（2）导致形成近平面的次表面Si₃N单元，类似于在Si₃N₄环境中与三个硅原子键合的中心氮原子（Nc）。基于这些结果，提出了一个由NH₃对Si(100)-(2×1)表面进行氮化的合理微观机制。
