Computational analysis on relation between iron surface condition and surface potential change

Igarashi, Takahiro  ; Komatsu, Atsushi ; Yamaguchi, Masatake   ; Ebihara, Kenichi   ; Ueno, Fumiyoshi  

Hydrogen embrittlement has become important because of demand for higher strength steel. To clarify the mechanism, it is one of the important issues to evaluate hydrogen distribution in steel. Recently, metal surface potential mapping has used to evaluate hydrogen distribution in metal using surface potential lowering by hydrogen adsorption on metal surface. However, the mechanism of that behavior has been unclear. To elucidate the surface potential lowering mechanism of iron by hydrogen atom, work function and electric dipole moment analysis by density functional theory (DFT) calculation method were carried out. In the study, Fe(100) clean surface and oxygen adsorbed surface were prepared. Hydrogen atoms were adsorbed on surface or penetrated into interior of iron slab in the model. There was a negative correlation between work function and electric dipole. In addition, the surface potential decreased due to hydrogen adsorption on oxygen adsorption surface. It is suggested that electronic state around surface was changed by hydrogen atom adsorption and then surface potential was lowered by the electric dipoles on the surface generated.