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

We have used scanning photoemission microscopy (SPEM) and low energy electr on microscopy (LEEM) to investigate the equilibration of the submonolayer s urface phases and silicide islands formed in the reactive system Co-Si(lll) . Real-time LEEM images of the surface during annealing show an irreversibl e conversion of the close-packed, ordered (root 7 x root 7) 'ring-cluster' phase, into a lower density, disordered'(1 x 1)' ring-cluster structure, wh ich occurs surrounding the silicide islands. SPEM images and microscopicall y resolved photoemission spectra show directly that the islands are CoSi2 a nd that they draw Co away from the nearby surface, resulting in the formati on of the lower coverage phase. LEEM observations during extended annealing of the `(1 x 1)'-RC phase in the presence of these islands indicate a furt her depletion of the '(1 x 1)'-RC phase and the eventual formation of the ( 7 x 7) reconstruction. (C) 1999 Elsevier Science B.V. All rights reserved.