First-principles study of stability and electronic structure of N2H4 adsorption on NiFe(111) alloy surface
First-principles study of stability and electronic structure of N2H4 adsorption on NiFe(111) alloy surface
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DOI：
10.7498/aps.64.203101
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发表时间：
2015-10-20
影响因子：
1
通讯作者：
Wu Hai-Shun
中科院分区：
文献类型：
--
作者：
He Yan-Bin;Jia Jian-Feng;Wu Hai-Shun
采用密度泛函理论（DFT）研究了肼（N2H4）吸附在Ni8Fe8/Ni（111）合金表面的稳定性和电子结构。介绍了该结构在Ni8Fe8合金表面的几何形状和吸附特性。结果表明，N2H4桥接在两个铁原子之间的吸附作用最强，吸附能为-1.578 eV/N2H4。顶模为局部最小值，吸附能分别为-1.346 eV/N2H4 （Fe原子上顶位）和-1.061 eV/N2H4 （Ni原子上顶位）。结果表明，在NiFe合金表面，桥接模式比顶部模式更有利，覆盖面积为1/16 ML， Fe原子比Ni原子提供更强的吸附位点。范德华贡献显著，约为0.4 eV/N2H4。同时，在Fe原子上吸附的范德瓦尔斯贡献大于Ni原子，桥接模式的吸附比顶模式的吸附大。我们还发现N2H4在NiFe合金表面上的反分子结构，而不是间式分子的结构，被结合在Fe原子的顶部位置，覆盖率为1/16 ML，这表明在低覆盖率的表面上，排斥性吸附-吸附相互作用较弱。表面原子与吸附质的强相互作用导致N2H4的孤对电子被Fe原子吸引。此外，对于N2H4在Ni8Fe8/Ni（111）合金表面的5种吸附结构，我们分析了吸附分子在合金表面Fe-N或Ni- n键上的投影电子态密度（DOS）、诱导电荷密度和电子局域函数（ELF）切片。结果表明，电子DOS表现为N2H4的HOMO与表面原子d轨道的混合，对应于底物与吸附物之间的电荷转移。电荷主要从N2H4转移到表面原子，桥接模式和感应电荷密度中存在的顶部模式的电荷转移程度不同。此外，在极低频片中可以发现N2H4的N原子与表面的Fe或Ni原子之间的吸附的局部区域，这为N-Fe或N-Ni相互作用的配位键提供了清晰的视图。
We use the density functional theory (DFT) with dispersion correction to investigate the stability and electronic structure of hydrazine (N2H4) adsorpted on Ni8Fe8/Ni (111) alloy surface. The geometries and adsorption characteristics of the structure on the Ni8Fe8 alloy surface are presented. Results show that N2H4 bridging between two iron atoms gives the strongest adsorption with an adsorption energy of -1.578 eV/N2H4. Top modes turn out to be the local minima with adsorption energies of -1.346 eV/N2H4 (for the top site on a Fe atom) and -1.061 eV/N2H4 (for the top site on a Ni atom). It is demonstrated that the bridging mode is more favorable than the top mode on the NiFe alloy surface with a coverage of 1/16 ML, and Fe atom can provide stronger adsorption site than Ni atom. The van der Waals contribution is significant with a value of about 0.4 eV/N2H4. Meanwhile, the van der Waals contribution is larger for adsorption on Fe atom than on Ni atom, and for adsorption of the bridging mode than of the top mode. We also find that the structure of N2H4 in the anti molecule, rather than the gauche molecule, is bound on the top site of Fe atom on the NiFe alloy surface with a coverage of 1/16 ML, which demonstrates that the repulsive adsorbate-adsorbate interaction is weak on the surface with low coverage. The strong interaction between the surface atom and the adsorbate contributes to the result that the lone pair electrons of N2H4 in gauche conformer are attracted by the Fe atom. In addition, for the five adsorption structures of N2H4 on Ni8Fe8/Ni(111) alloy surface, we analyze the projected electronic density of states (DOS), induced charge density and electron localisation function (ELF) slices through the Fe-N or Ni-N bonds of the adsorbed molecule on the alloy surface. It shows that the electronic DOS presents the mixture between HOMO of N2H4 and the d orbital of the surface atom, which corresponds to charge transfer between the substrate and the adsorbate. The charges are transferred mainly from N2H4 to the surface atoms, and the extents of charge transfer are different for the bridging mode and the top one which is present in the induced charge density. Furthermore, the region of localisation in the ELF slices can be found for the adsorptions between the N atom of N2H4 and the Fe or Ni atom of surface, which gives a clear view of the coordination bonds for the interactions of N-Fe or N-Ni.