Study of the surface morphology of the (100) cleavage planes of MgO single crystals by atomic force microscopy

Some experimental observations made on the nature and distribution of nearly circular and polygonal closed steps, and arrays of semicircular steps arranged between two multilayer steps on the (100) cleavage planes of MgO single crystals by atomic force microscopy are described. The results show that: (1) the formation of disc-shaped elevations and depressions, and series of semicircular steps takes place by a mechanism similar to the Frank-Read source [Phys. Rev. 79 (1950) 722]; (2) the diameters of disc-shaped structures are related with shear stresses of the order of the yield stress of the crystal; and (3) with an increase in the size of closed steps, their rounded shape changes to polygonal due to a lower edge free energy of the [010] and [011] steps compared to that of steps of other orientations. (C) 1999 Elsevier Science B.V. All rights reserved.