Atomic replacement and vacancy formation and annihilation on iridium surfaces

Abstract

THE formation of nanometre-scale surface structures for quantum electronic devices, and the possibility of using the scanning tunnelling microscope and related instruments for atomic-scale surface modification^1–6, make necessary a detailed understanding of surface atomic processes. It has been observed previously^{7– 11} that surface diffusion of an atom can take place by a series of exchanges with atoms in the surface layer. Here we use the field ion microscope to observe surface atomic processes when the chemical nature of the adatom differs from that of the surface atoms. On the iridium {001} surface, an adsorbed rhenium atom will displace an iridium atom from the substrate to form a Re–Ir–vacancy bound complex at about 230 K. On heating the sample to about 300 K, we find that this complex dissociates and the rhenium atom becomes incorporated into the surface—a kind of atomic-scale surface alloying. Alternatively, the Re–Ir cluster can be removed by field evaporation to leave a lattice vacancy, into which another adatom can subsequently diffuse.