240.
This paper reports that monitoring the composition of the
c(0 0 0 1),
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 ArH
2 or ArO
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 ArO
2 and ArH
2. (ii) Potassium adsorption enhances the kinetics of step-bunching on the
c-surface under ArO
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 ArH
2, alumina surface diffusion is much slower than under ArO
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.
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