Surface morphology and composition of c-, a- and m-sapphire surfaces in O2 and H2 environments

This paper reports that monitoring the composition of the c(0001), a(11-20)and m(10-10) sapphire surfaces is essential for a proper interpretation of the surface morphologies obtained after annealing at 1253 and 1473 K in Ar-H-2 or Ar-O-2 atmospheres. Our experimental investigations, which have used Auger electron spectroscopy (AES) and atomic force microscopy (AFM) on the surfaces of 99.99% pure sapphire wafers, have led to the following original conclusions: (i) Calcium segregates at the c-surface of sapphire both under Ar-O-2 and Ar-H-2. (ii) Potassium adsorption enhances the kinetics of step-bunching on the c-surface under Ar-O-2. (iii) The step edges on the a-surface may develop a comb-like morphology made of parallel strips along the [10-10] direction. (iv) At 1253 K, clean m-surfaces may be stable. (v) Under Ar-H-2, alumina surface diffusion is much slower than under Ar-O-2 for all surface orientations, the surface concentration of impurities is low, and the Al-O ratio of the AES signals at the surface is significantly larger. (C) 2009 Elsevier B.V. All rights reserved.