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 dep osited on it. Above approximately 210 K, the geometrical center of thi s complex can displace by one step of the substrate by an exchange dis placement of its Ir atom with a substrate Ir atom. This mechanism conf ines the movement of the complex to four nearest-neighbor sites of the substrate lattice. Only above approximately 235 K can the complex mov e out of these four sites by a combined hopping-exchange mechanism. Ab ove approximately 280 K, the Re-Ir dimer can dissociate. Upon dissocia tion, the Re atom will combine with the vacancy and self-diffusion of Ir will then occur.