An amorphous mixing layer (3.5–4.0 nm in thickness) containing silicon (Si), oxygen (O), molybdenum (Mo) atoms, named <i>α</i>-SiO_<i>x</i>(Mo), is usually formed by evaporating molybdenum trioxide (MoO₃) powder on an n-type Si substrate. In order to investigate the process of adsorption, diffusion and nucleation of MoO₃ in the evaporation process and ascertain the formation mechanism of <i>α</i>-SiO_<i>x</i>(Mo) on a atomic scale, the first principle calculation is used and all the results are obtained by using the Vienna <i>ab initio</i> simulation package. The possible adsorption model of MoO₃ on the Si (100) and the defect formation energy for substitutional defects and vacancy defects in <i>α</i>-SiO₂ and <i>α</i>-MoO₃ are calculated by the density functional theory. The results show that an amorphous layer is formed between MoO₃ film and Si (100) substrate according to <i>ab initio</i> molecular dynamics at 1500 K, which are in good agreement with experimental observations. The O and Mo atoms diffuse into Si substrate and form the bonds of Si—O or Si—O—Mo, and finally, form an <i>α</i>-SiO_<i>x</i>(Mo) layer. The adsorption site of MoO₃ on the reconstructed Si (100) surface, where the two oxygen atoms of MoO₃ bond with two silicon atoms of Si (100) surface, is the most stable and the adsorption energy is －5.36 eV, accompanied by the electrons transport from Si to O. After the adsorption of MoO₃ on the Si substrate, the structure of MoO₃ is changed. Two Mo—O bond lengths of MoO₃ are 1.95 Å and 1.94 Å, respectively, elongated by 0.22 Å and 0.21 Å compared with the those before the adsorption of MoO₃ on Si substrate, while the last bond length of MoO₃ is little changed. The defect formation energy value of neutral oxygen vacancy in <i>α</i>-SiO₂ is 5.11 eV and the defect formation energy values of neutral oxygen vacancy in <i>α</i>-MoO₃ are 0.96 eV, 1.96 eV and 3.19 eV, respectively. So it is easier to form oxygen vacancy in MoO₃ than in SiO₂, which implies that the oxygen atoms will migrate from MoO₃ to SiO₂ and forms a 3.5–4.0-nm-thick <i>α</i>-SiO_<i>x</i>(Mo) layer. As for the substitutional defects in MoO₃ and SiO₂, Mo substitutional defects are most likely to form in SiO₂ in a large range of Mo chemical potential. So based on our obtained results, the forming process of the amorphous mixing layer may be as follows: the O atoms from MoO₃ bond with Si atoms first and form the SiO_<i>x</i>. Then, part of Mo atoms are likely to replace Si atoms in SiO_<i>x</i>. Finally, the ultra-thin buffer layer containing Si, O, Mo atoms is formed at the interface of MoO₃/Si. This work simulates the reaction of MoO₃/Si interface and makes clear the interfacial geometry. It is good for us to further understand the process of adsorption and diffusion of atoms during evaporating, and it also provides a theoretical explanation for the experimental phenomenon and conduces to obtaining better interface passivation and high conversion efficiency of solar cell.

We calculate the atomic and electronic structure of β-SiC(001)-(2×1) using augmented plane wave and local orbital (APW+LO) method. The calculated results show that the atomic structure of β-SiC(001)-(2×1) surface can be described by symmetrical Si dimmer model, which is different from the asymmetrical Si dimmer model of Si(001)-(2×1) surface. The bond length of Si dimmer of β-SiC(001)-(2×1) surface is 0.269 nm, which is larger than that of Si(001)-(2×1) surface. The calculated results of electronic structure show that a prominent density of states exists at the Fermi level, so β-SiC(001)-(2×1) surface has the characteristics of metal. There are four surface state bands in the gap. Among them, two occupied surface state bands have been confirmed by valence band spectra of synchrotron radiation photoelectron spectroscopy.

TiO 2 作为一种重要过渡金属氧化物, 因其表面 的化学性质, 在许多领域都引起了人们的广泛关注, 如光催化、电化学、化学涂料、防腐蚀等 [9,10] . 随着 新能源的开发利用, TiO 2 在光催化分解水产氢方面具 有广阔的发展前景 [11] , 因此人们对水在 TiO 2 (110)表 面的吸附做了大量的实验与理论研究, 其中一个主 要的研究问题是关于水在 TiO 2 (110)表面的吸附模式. 大量实验研究结果表明, 水在无缺陷的 TiO 2 (110)清 洁表面是以分子吸附模式存在的 [1216] . 而理论计算 结果却存在较大差异, 一些工作表明分子吸附模式 比较稳定, 另外一些则表明解离吸附模式比较稳定. 因此, 有人认为理论计算结果与所选择的计算参数 有密切的关系, 尤其与水的吸附率、基底的厚度以及 泛函的选取等有关 [1726] . 而实际情况中, TiO 2 (110)表 面 一 般 都 会 存 在 缺 陷 . 实 验 结 果 [2732] 和 计 算 结