Ni(111)表面上N原子对C原子电子结构的影响

N是金刚石中的主要杂质之一, 为了研究金刚石生长过程中杂质N对C电子结构转化的影响, 用密度泛函理论研究了Ni(111)表面上C与N共吸附的三个不等价模型, 同时建立了三个C吸附模型作为比较. 计算结果表明, N原子的出现使得吸附体系相对不稳定, 吸附原子之间的相互作用不能忽略; 通过比较相互作用能可以看出, 相同的吸附位下C-C相互作用比C-N 相互作用强. 通过比较不同模型中C原子分波态密度可以看出, N-C相互作用一定程度上增加了Ni的催化活性, 但是与C-C自身的相互作用比较起来效果并不明显. 吸附几何结构和分波态密度还表明, 当吸附的原子过于紧密以致占有同一个Ni(111)-(1×1)晶胞表面时, 就会形成CN化合物或者类石墨杂质.

Electronic Effects of Atomic Nitrogen on Carbon on the Ni(111) Surface

Nitrogen is a common impurity found in diamonds. We used three nonequivalent models to study carbon and nitrogen coadsorption on Ni(111) surface. Density functional theory (DFT) calculations were performed to study the influence of nitrogen upon the transformation of carbon's electronic structure during diamond synthesis. Three carbon adsorption models were constructed for comparison. Results indicated that nitrogen atoms destabilize the adsorption system and that the interaction between adatoms could not be ignored. According to the calculated interaction energies, the C-C interaction was stronger than the C-N interaction. Differences in the partial density of states (PDOSs) among the models suggested that the N-C interaction also improved catalysis to some extent, but this effect was not evident in comparison to the C-C interaction. The obtained atomic geomeCy and PDOS also indicated formation of CN compounds or graphite-like impurities if the adatom distance was too short, because they would occupy the same Ni(111)-(1×1) unit cell.