FeO/Pt(111)与FeO2/Pt(111)的几何、电子结构及表面氧活性的第一性原理研究

采用密度泛函理论系统研究了超薄氧化物膜/金属体系FeO/Pt和FeO₂/Pt及其表面不同区域(FCC,HCP和TOP)的几何结构、电子性质及氧的活性.研究发现,表面O-Fe高度差δ_z作为一个重要的特征结构参数直接影响局域表面静电势和表面氧的结合能: δ_z越大,静电势越大,氧的结合能越弱.计算发现,在FeO/Pt体系中,δ_z顺序为FCC > HCP > TOP,而FeO₂/Pt中是FCC > TOP > HCP.此外,在FeO/Pt中,电荷转移方向是从氧化物膜到衬底,Fe的表观价态为+2.36,表面功函较纯Pt(111)的变化可忽略; 而FeO₂/Pt中,电荷转移的方向是从衬底到氧化物,Fe的表观价态为+2.95,表面功函较纯Pt增加1.24 eV.进一步分析了电荷转移和表面偶极对电子性质的作用机制.这些研究结果对于认识超薄氧化物薄膜对表面几何结构、电子性质、表面氧活性的调制具有重要的启示意义.

A first-principles study of the structure,electronic properties,and oxygen binding of FeO/Pt(111) and FeO2/Pt(111)

The ultrathin oxide films of bilayer FeO and trilayer FeO₂ superstructures on Pt(111) with periodicity of (√84×√84)R10.9° are studied in detail by density functional theory, and the corresponding structural properties, electronic properties, and oxygen activities in different domains (FCC, HCP, and TOP) are calculated. It is found that for both superstructures, the in-plane lattice constants slightly increase in the order FCC < HCP < TOP. The calculated order of the surface corrugation (O-Fe rumpling) is FCC > HCP > TOP for FeO/Pt(111), and FCC > TOP > HCP for FeO₂/Pt(111). The surface electrostatic potentials and the binding energies of the surface oxygen atoms are found to follow the same order as the surface corrugation. There is net charge transfer from the supported FeO film to the Pt substrate for FeO/Pt(111), and the calculated oxidation state of iron is +2.36. In contrast, for FeO₂/Pt(111), there is charge transfer from the Pt substrate to the supported FeO₂ film, and the calculated oxidation state of iron is +2.95 (ferric state). Compared with Pt(111), the change of the surface work function of FeO/Pt(111) is negligible, while it is 1.24 eV for FeO₂/Pt(111). The role of the surface dipole of the supported oxide film and the charge transfer of the ultrathin oxide film are discussed.