Ru(0001) 表面BaO吸附层的原子结构和氮分子的吸附性质

采用密度泛函理论研究了Ru(0001) /BaO表面的原子层结构和氮分子的吸附性质. 研究结果表明, 在低覆盖度下氧化钡倾向于以相同的构型形成Ru(0001) 表面原子层. 在此构型中, 氧原子位于表面p(1× 1) 结构的hcp谷位, 而钡原子则位于同一p(1× 1) 结构的顶位附近. 钌氧键键长等于0.209 nm, 比EXAFS的实验值大0.018 nm. 在Ru(0001) /BaO表面氮分子倾向吸附于钡原子附近. 相应位置的氮分子吸附能位于0.70到0.87 eV之间, 大于氧原子附近的氮分子吸附能. 钡原子附近的钌原子对氮分子具有更强的活化性能. 相应位置的氮分子拉伸振动频率等于1946 cm^{- 1}, 比氧原子附近的最大分子振动频率小约130 cm^-1. Ru(0001) /BaO表面氮分子键强度介于清洁Ru(0001) 和Ru(0001) /Ba表面之间. Ru(0001)/BaO表面不同位置的氮分子吸附性质差异是由钡和氧原子化学性质不同造成的. 表面钡原子的作用能够减少吸附氮分子的σ^*轨道电子密度, 增加π^*轨道电子密度, 从而增强氮分子和钌原子间的轨道杂化作用, 弱化氮分子键.

Geometric structures and nitrogen adsorption properties of BaO adlayer on Ru(0001) surface

First principles calculations are performed to study the geometric structures and the nitrogen adsorption properties of BaO adlayer on Ru（0001） surface.It is suggested that BaO adlayer is more stable on Ru（0001） surface at low coverage.A configuration is observed in surface phase at low coverage.In this structure oxygen is adsorbed on the hcp site of one p（1×1） cell,and barium is adsorbed close to the top site of the same p（1×1） cell.Bond length of oxygen and ruthenium is calculated to be 0.209 nm,longer than the EXAFS experimental value about 0.018 nm.Nitrogen prefers to be adsorbed on the sites close to barium.Nitrogen adsorption energies at those sites are calculated to be in a range from 0.70 to 0.87 eV,which are bigger than those at the sites close to oxygen.Adsorption sites near barium atoms have more activities to weaken nitrogen.The lowest N-N stretching vibrational frequency on the sites is about 1946 cm"1,less than the highest frequency on sites around oxygen(about 130 cm^-1).Bond strengths of nitrogen on Ru（0001） /BaO surface are between those on clean Ru（0001） and Ru（0001） /Ba surface.The adsorption properties of sites around BaO layer are determined by chemical characteristic of barium and oxygen.Electron transfer from barium to ruthenium enhances the hybridization between ruthenium and nitrogen by reducing and increasing the occupation ofσ^* andπ^* orbitals respectively.