Cluster formation and atomic intermixing at the reactive V/Ge(111) interface

A detailed low-energy electron-diffraction, synchrotron-radiation, and resonance-lamp photoemission-spectroscopy study of the reactive V/Ge(111)2×{}1 interface is presented. High-resolution core-level and valence-band results indicate the formation of vanadium islands for coverages CTHETA less than {~}2 A{} (average radius {~}20 A{}, number density {~}10¹² cm^-2). Core-level decomposition makes it possible to then follow the growth and attenuation of each Ge species. In particular, disruption of the substrate occurs above {~}2 A{} and an intermixed V-Ge region forms. This reacted region is ultimately covered up for CTHETA{≥}20 A{}, but strong out-diffusion of Ge allows the formation of a more V-rich species up to {~}80 A{}. Beyond {~}80 A{}, Ge out-diffusion is significantly reduced and a pure vanadium overlayer forms. Evolution of the Schottky-barrier height variation was monitored through binding-energy changes for the Ge 3d core level and, although the Schottky-barrier height Φb was completely developed by {~}2 A{}, a slow increase of Φb was observed as a secondary effect of atomic intermixing ({~}0.05 eV after 10 A{}).