High-temperature transformation of vicinal (0001) Al2O3-? surfaces: an AFM study

Development of the morphology of vicinal (0001) surfaces of α-alumina, induced by annealing in air at 1500 °C, was studied by AFM. Our investigation shows that the resulting surface morphology depends on both the duration of thermal treatment and the surface misorientation relative to crystallographic directions. The whole vicinal surface, which is initially covered by steps of 0.21 nm height, after heating can exhibit two kinds of morphologies due to step bunching or step faceting. Step bunching occurs even after a relatively short annealing time (1 h) and is found to depend on the miscut angle. Further annealing of bunched stepped surfaces leads to the disappearance of bunching, leaving sometimes a new faceted phase. In the general case of facets, the border of faceted steps follows the [10 10] crystallographic direction, and less closely the [11 20] direction, producing zigzags. The faceting process is triggered by the step height exceeding a certain value. The origin of incubation time for the faceting process is discussed. Copyright © 2000 John Wiley & Sons, Ltd.