An AFM study of the thermal development of the (0 0 1) surface of KCl from room temperature up to the melting point

The topographical development of the (0 0 1) surface of KCl was investigated from room temperature up to the melting point by atomic force microscopy in UHV. Cleavage topographies of air-cleaved surfaces show extended growth hills formed by large numbers of rounded, mostly monatomic steps caused by the re-crystallization of crystal material dissolved in adsorbed water layers. Vacuum cleaved surfaces are more irregular. They exhibit among others sharp cleavage tips, which seem to be characteristic for ionic crystals. At moderately heated surfaces, 673 K, closed loop lamella systems as well as different types of spiral systems originating from edge and screw dislocations, respectively, are observed. High resolution images of spiral centers exhibit the emergence of mono and diatomic steps from the surface. The centers of closed loop step systems could not be visualized. After stronger heating, at 773 and 873 K, extended evaporation pits with macro-steps of heights between 20 and 35 nm are found. After shortly exceeding the melting point at about 1013 K, the surface is covered by macro-steps of heights between 3 and 5 nm and mono and diatomic steps running diagonally across the terraces between the high steps.