On the roughening of ceramic surfaces

The faceting of single-crystal ceramic surfaces has been investigated by atomic force microscopy, scanning electron microscopy and transmission electron microscopy. Single-crystals of α-Al2O3 (alumina) with different nominal surface orientations were annealed and used as a model system to investigate the faceting of a polished ceramic surfaces. The {101̄0} orientation of α-alumina, which facets into a hill-and-valley morphology, provides a dramatic representation of the different stages by which a surface facets. This surface starts faceting with the growth of an individual facet. The growth of this facet creates local surface disturbances that promote the nucleation of adjacent facets; thus, domains of faceted surface form on the otherwise smooth surface. Through time, these domains coalesce and the facets coarsen into a hill-and-valley morphology. Surfaces which facet into a terrace-and-step structure, such as (0001) and {112̄0} surfaces of alumina, are characterized for their progression of surface faceting and are compared with the stages of faceting observed for the {101̄0} surface.