OBSERVATION OF 2 DIFFUSION MODES OF A RE-IR DIMER-VACANCY COMPLEX ON THE IR(001) SURFACE AND THEIR DIFFUSION MECHANISMS

A Re-Ir dimer-vacancy complex can be formed on an Ir(001) surface when the surface is heated to approximately 240 K with a Re atom vapor deposited on it. Above approximately 210 K, the geometrical center of this complex can displace by one step of the substrate by an exchange displacement of its Ir atom with a substrate Ir atom. This mechanism confines the movement of the complex to four nearest-neighbor sites of the substrate lattice. Only above approximately 235 K can the complex move out of these four sites by a combined hopping-exchange mechanism. Above approximately 280 K, the Re-Ir dimer can dissociate. Upon dissociation, the Re atom will combine with the vacancy and self-diffusion of Ir will then occur.