MISMATCH DISLOCATIONS CAUSED BY PREFERENTIAL SPUTTERING OF A PLATINUM NICKEL-ALLOY SURFACE

Preferential sputtering and recoil mixing of a Pt25Ni75(111) single crystal surface leads to platinum enrichment in the upper monolayers, thereby increasing the lattice constant in these layers. This results in sub-surface lattice mismatch dislocations, which have been studied by scanning tunneling microscopy. While the sub-surface dislocations are only visible as shallow ditches in STM topographs, the Burgers vectors of the dislocation system can be determined by means of atomically resolved images of dislocations reaching the surface. A comparison with simulations of lattice relaxation using embedded-atom potentials shows good agreement with STM data and further allows the determination of the thickness of the Pt enrichment. We have estimated the Pt concentration in these layers from the dislocation density and studied the annealing behaviour of the surface.