氢原子在Ru(0001)表面的化学吸附

用密度泛函理论研究了氢原子的污染对于Ru(0001)表面结构的影响. 通过PAW(projector-augmented wave)总能计算研究了p(1×1)、p(1×2)、(3^(1/2)×3^(1/2))R30°和p(2×2)等几种氢原子覆盖度下的吸附结构, 以及在上述结构下Ru(0001)面fcc(面心立方)格点和hcp(六方密堆)格点的氢原子吸附. 所得结果表明, 在p(1×1)-H、p(1×2)-H、(3^(1/2)×3^(1/2))R30°-H和p(2×2)-H几种H原子覆盖度下, 以p(1×1)-H结构单个氢原子吸附能为最大. 在p(1×1)-H吸附结构下,由于氢原子吸附导致的Ru(0001) 表面第一层Ru 原子收缩的理论计算数值分别为-1.11%(hcp 吸附)和-1.55%(fcc 吸附), 因此实际上最有可能的情况是两种吸附方式都有一定的几率. 而实验中观察到的“清洁”Ru(0001)表面实际上是有少量氢原子污染的表面. 不同覆盖度和氢分压下氢原子吸附的污染对Ru(0001)表面结构有极大的影响,其表面的各种特性都会随覆盖度的不同而产生相应的变化.

Hydrogen Chemisorption on the Ru(0001) Surface

The influence of hydrogen contamination on the atomic geometry of Ru(0001) surface was studied by using the density-functional theory and the projector-augmented wave (PAW) method. Based on the optimized structural parameters of hcp Ru from the PAWtotal energy calculation, the surface relaxation, surface energy, and work function of clean Ru(0001) surface were calculated in the same way. The adsorption geometries and total energies of several coverages of hydrogen on Ru(0001) surface including p(1×1), p(1×2), (3^(1/2)×3^(1/2))R30°, and p(2×2), were studied for the hcp and fcc site absorptions combined with the both sites occupation in p(1×1) structure. These results suggested that the Ru(0001) p(1×1)-H geometry had the largest energy gain among all these conformations, so under the condition of low coverage and low H2 pressure, the most possible conformation was p(1×1)-H adsorption. The shrink of Ru(0001) surface with H contamination was -3.7%fromavailable experiments and this work yields -1.11%for hcp and -1.55% for fcc adsorption geometries. It was deduced that the most possible adsorption configuration for a hydrogen contaminated Ru(0001) surface was a mixture of hcp and fcc adsorptions. For a clean Ru(0001) surface the surface contraction was calculated to be near -3.9%, while the experimental measurement predicted -1.9%. This observation implied that even for a“clean”Ru (0001) surface there was still about 13.6%of surface area covered with hydrogen adsorption. These results reflected that the hydrogen contamination could affect the Ru(0001) surface structure dramatically. Furthermore the present study could yield a conclusion naturally that the shrink of the Ru(0001) surface would be reduced with the increase of H atomadsorption below 1.0 ML (monolayer).