Nb（110）表面氧原子覆盖度对氧分子解离的影响

摘要

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.%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 (H4d) 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. Overal , 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.