Nb(110)表面氧原子覆盖度对氧分子解离的影响

用基于密度泛函理论的第一性原理方法研究了Nb(110)表面氧原子覆盖度分别为0.25、0.50、0.75 和1.00单层时对氧分子解离的影响. 结果表明, 在氧原子覆盖度不大于0.50单层时, 由于氧分子和表面铌原子的较强相互作用, 使它们能够自发解离. 然而在氧原子覆盖度为0.75单层时, 氧分子只能够在未占据的洞位附近解离, 同时发生严重的晶格畸变. 在形成一个氧原子单层后(1.00 单层), 氧分子只能弱吸附在Nb(100)表面上,此时氧原子向内扩散成为氧分子继续解离的速率决定步骤. 这些结果从理论上解释了在形成一个氧原子单层后, Nb(110)表面氧分子吸收速率迅速下降的原因.

Effects of O Coverage on the Dissociation of O2 Molecules on the Nb(110) Surface

The effects of oxygen atom coverage on the dissociation of O₂ molecules at the Nb(110) surface were investigated using density functional theory (DFT) methods. The dissociation of O₂ molecules is facile at low O coverages Θ≤0.50 monolayer (ML)] because of the strong electronic interaction between O₂ molecules and the Nb substrate. At a coverage of 0.75 ML, O₂ molecules next to unoccupied distorted four-fold (H_4d) sites only dissociate with severe lattice distortions. However, the inward diffusion of O atoms is the rate limiting step for the dissociation of O₂ molecules after adsorption of 1.00 ML O atoms. Overall, our theoretical study provides a rationale for the experimental result that the dissociation of O₂ molecules decreases markedly after rapid adsorption of 1.00 ML O atoms on the low index Nb surfaces.