Orientation of para-phenylene crystals nucleated on alkali-halide stepped substrates

The influences of substrate steps on crystallographic orientation of para-quaterphenylene (p-4P) thin films deposited on potassium chloride (KCl) (0 0 1) cleaved in ultrahigh vacuum have been studied in needle-shaped crystals preferentially nucleated at the step edges of the substrates. Surprisingly, most of the crystals nucleated on the so-called tartan zone of the KCl (0 0 1) substrate did not grow epitaxially, but became aligned in the directions of the cleaved steps, indicating the onset of grapho-epitaxy. The effects of step height and width on the nucleation and growth of p-4P crystals have been discussed.