Annealing of CaF2 adlayers grown on Si(111): investigations of the morphology by atomic force microscopy

The successive annealing of CaF2 adlayers deposited at low temperature ( 40 0 degrees) on vicinal Si(111) has been studied in situ by ultra high vacuum atomic force microscopy (UHV-AFM. Monoatomic islands on top of closed CaF2 layers observed for the as-deposited adlayers vanish during the first anne aling steps (<600 degrees C). In addition notches of monoatomic height are formed at the previous straight adlayer steps of the CaF2 terraces. They ha ve triangular shape in agreement with the non-polar {111} facets of the B-o rientated CaF2 adlayer. For higher annealing temperatures the CaF2 is partl y dissociated so that Ca clusters are formed on top of the adlayer steps. T his extraordinary nucleation site is attributed to the partial lateral rela xation of the CaF2 adlayer. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.