Surface segregation in alloys: LEED, Auger, and gas adsorption study of segregation of Au to the (111) surface of Ni

The (111) surface of Ni single crystals containing less than 1% Au was studied using Auger spectroscopy, LEED, and gas adsorption. The heat of segregation of gold to the Ni(111) surface, obtained from equilibrium measurements of the surface composition as a function of temperature, was found to be 12±2 kcal/mole. This result is not temperature, was found to be 12±2 kcal/mole. This result is not adequately described by existing theories of surface segregation. We also observed a variety of other complex phenomena. For gold surface concentrations above about 50%, an ordered overlayer of gold formed on the nickel substrate. Exposure of a partially gold covered surface to oxygen causes the disappearance of the gold. Small amounts of gold on the surface effectively poison it for adsorption of CO.