First-principles study of stability and electronic structure of N2H4 adsorption on NiFe(111) alloy surface

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.