SCANNING-TUNNELING-MICROSCOPY STUDIES OF ALPHA-FE2O3(0001)

Scanning tunnelling microscopy (STM) images of two different reconstru ctions of an alpha-Fe2O3(0001) crystal are presented. Annealing the sa mple to 1000 K creates a selvedge stabilised by a thin film of Fe3O4, with its (111) plane parallel to the basal plane of the underlying sub strate, The STM images confirm that this surface is structurally equiv alent to that previously reported for the surface of Fe3O4(111) single crystals, in that two coexisting terminations, denoted A and B, are p resent separated by alternate steps. Termination A has been identified with 1/4 ML of O atoms capping 3/4 ML of Fe atoms, while termination B consists of 1/2 ML of Fe atoms overlaying a close-packed O layer. So me regions of the sample are disordered but contain small triangular i slands of termination A. This structure is attributed to Ar ion induce d sputter damage. A different termination, created by annealing the sa mple at 1100 K in 1 x 10(-6) mbar O-2, has a distinctive hexagonal LEE D pattern, with all the main beams floreted, being surrounded by a hex agon of smaller spots. The STM results show that this surface is stabi lized by coexisting alpha-Fe2O3(0001) and Fe1-xO(111) phases, with eac h phase existing in atomically well ordered islands of mesoscopic dime nsions. The islands themselves are arranged to form a superlattice. Th e formation of this superlattice can be explained in terms of the latt ice mismatch between the two types of oxygen sub-lattices. (C) 1998 El sevier Science B.V.