Investigation of the temperature-dependent surface morphology of p-sexiphenyl thin films on KCl(001)

Investigation into the temperature dependence of the surface morphology of a thin film of p-sexiphenyl (p-6P) on KCl(001) was carried out by atomic force microscopy (AFM). An individual p-6P film was prepared by vapor deposition at a base pressure of similar to1x10(8) mbar onto a KCl(001) surface which was maintained at 323 K during deposition. The AFM was carried out in a separate vacuum chamber, in situ, at a base pressure of similar to1x10(-6) mbar. The p-6P film was cooled and maintained at discrete temperatures in the range from 294 K to 128 K as AFM measurements were performed. Similar surface morphologies are observed for film temperatures maintained at 294, 264, and 227 K, and 188 and 128 K during the AFM measurements. AFM images for the first set of film temperatures (294 - 227 K) indicate the presence of block-like islands of p-6P, with well-defined crystallite boundaries. AFM images of the films in the second set (188 and 128 K) indicate the presence of triangular wedge-shaped structures of p-6P preferentially aligned nearly in the direction of the [110](KCl.) Comparison of these wedge-shaped structures at the indicated film temperatures reveals they are rotated by approximately 180degrees with respect to each other. Subsequent images of the surface of the p-6P film captured again at 294 K, after the final 128 K temperature study was completed, revealed the same surface features found for the initial 294 K film temperature.