甲基、氨基和甲胺在清洁及C(N,O)改性的Mo(100)表面的吸附

采用广义梯度近似(GGA)的密度泛函理论(DFT), 并结合平板模型, 研究了甲基、氨基和甲胺在清洁及C(N, O)改性的Mo(100)面的吸附行为. 计算结果表明, 在较低覆盖度下(θ=1/6 ML(monolayer)), 吸附物种在不同表面上的稳定吸附位的吸附能变化不大; 而在较高覆盖度下(θ=1/4 ML), 其稳定的吸附位置可能发生变化, 且吸附能有了明显的区别. 它们在改性的Mo(100)表面吸附能较清洁表面小, 并且按C、N、O的顺序降低. 究其原因可归结为C、N、O性原子的存在使得金属表面的供电子能力减弱, 从而导致金属的d带中心的下移. 通过对金属Mo的d带性质的分析, 发现d带中心只能笼统地说明改性原子对于清洁表面的性质有一定的影响, 不能很好地体现C、N、O对于清洁表面性质影响的差异, 而dz2轨道的能量中心却能很好地反映出吸附物种在改性表面上的吸附能按C、N、O的顺序依次减小这一规律.

Adsorption of Methyl,Amido and Methylamine Species on the Clean and C(N,O)Modified Mo(100)Surfaces

The adsorption of the species(CH3, NH2, and CH3NH2) on clean and carbon(nitrogen or oxygen) modified Mo(100) surfaces has been investigated by the first-principles DFT-GGA calculations with the slab model. The calculated results showed that the adsorption energies of the adsorbed species(CH3, NH2 and CH3NH2) changed a little with the coverage of θ=1/6 ML (monolayer); but an obvious change could be observed at the relative higher coverage (θ=1/4 ML). In addition, it was found that the adsorption energies were lower on the modified Mo(100) surface as compared with the results on clean Mo(100) surface, and the activity of the Mo(100) surface decreased in the presence of the pre-adsorbed C(N, O) atoms with the order of C>N>O. It may be due to the reason that these electronegative atoms reduce the capability of electron donation of the metal, which results in the downshift of the surface metal atom d-band center. By the analysis of the density of state(DOS) projected onto Mo d-band, it can be found that d-band center only account for the diversification of the surface caused by the pre-adsorbed atoms, whereas the dz2-center can explain the changing trend of the adsorption energies more exactly.