Sulfur is the most surface active segregant on the surface of Fe (100) and replaces other segregants. The mechanism of the replacement of segregant from oxygen to sulfur on the surface of Fe (100) was investigated by angle-resolved XPS.
It was observed that the bonding between iron and segregated oxygen was ionic, on the other hand, the bonding between iron and segregated sulfur was covalent. When only oxygen segregated, the binding energy of O 1 s was 529.8 eV. As sulfur segregated, the XPS spectrum of O 1 s had two peaks ; one of them was at 529.8 eV described above, the other was at about 531 eV. The peak at about 531 eV corresponded to oxygen of non-ionic bonding state and had the strongest intensity at the lowest exit angle. The binding energy of S 2 p was the same whether oxygen existed or not. It suggests that the binding state of sulfur to iron was not affected by the existence of oxygen. Therefore, the bond between oxygen and iron was broken by sulfur segregation and sulfur segregation caused the disappearance of oxygen from the surface.