Scanning tunnelling microscopy studies of α-Fe 2O 3(0001)

Abstract

Scanning tunnelling microscopy (STM) images of two different reconstructions of an α-Fe 2O 3(0001) crystal are presented. Annealing the sample to 1000 K creates a selvedge stabilised by a thin film of Fe 3O 4, with its (111) plane parallel to the basal plane of the underlying substrate. The STM images confirm that this surface is structurally equivalent to that previously reported for the surface of Fe 3O 4(111) single crystals, in that two coexisting terminations, denoted A and B, are present 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. Some regions of the sample are disordered but contain small triangular islands of termination A. This structure is attributed to Ar ion induced sputter damage. A different termination, created by annealing the sample at 1100 K in 1 × 10 −6 mbar O 2, has a distinctive hexagonal LEED pattern, with all the main beams floreted, being surrounded by a hexagon of smaller spots. The STM results show that this surface is stabilized by coexisting α-Fe 2O 3(0001) and Fe 1− x O(111) phases, with each phase existing in atomically well ordered islands of mesoscopic dimensions. The islands themselves are arranged to form a superlattice. The formation of this superlattice can be explained in terms of the lattice mismatch between the two types of oxygen sub-lattices.