Equilibration of ring-cluster surface phases and suicide islands for Co adsorbed on Si(111)

We have used scanning photoemission microscopy (SPEM) and low energy electron microscopy (LEEM) to investigate the equilibration of the submonolayer surface phases and suicide islands formed in the reactive system Co-Si(111). Real-time LEEM images of the surface during annealing show an irreversible conversion of the close-packed, ordered (√7× √7) 'ring-cluster' phase, into a lower density, disordered '(1×1)' ring-cluster structure, which occurs surrounding the suicide islands. SPEM images and microscopically resolved photoemission spectra show directly that the islands are CoSi₂ and that they draw Co away from the nearby surface, resulting in the formation of the lower coverage phase. LEEM observations during extended annealing of the '(1×1)'-RC phase in the presence of these islands indicate a further depletion of the '(1×1)'-RC phase and the eventual formation of the (7×7) reconstruction.