EVOLUTION OF STEPS ON VICINAL (0001)-SURFACES OF ALPHA-ALUMINA

Evolution of the step arrangement on vicinal (0001) surfaces of an a-a lumina crystal annealed for 1 h in the range of 1000-1500 degrees C in air was investigated by atomic force microscopy. For T < 1200 degrees C, coalescence of monosteps (h(1) = 0.2 nm) forms mainly parallel dou ble-height steps. At temperatures 1200 degrees C, steps with larger he ights grow either due to direct coalescence or due to the displacement of single steps. During coalescence of steps in the whole temperature range investigated, the direction of the higher steps keeps parallel to that of the initial monosteps over hundreds of microns although it does not correspond to any low index crystalline orientation. Differen t mechanisms of growth of the steps are discussed. A quantitative esti mation of the activation energy of one effective self diffusion proces s can be performed. (C) 1998 Elsevier Science B.V. All rights reserved .