The Orientation Overgrowth of Polycyclic Aromatic Quinones on the Cleavage Surface of Alkali Halide Single Crystals

Vacuum-condensed films of polycyclic aromatic quinones (flavanthrone, indanthrone, and pyranthrone) were found to grow epitaxially on the cleavage faces of NaCl and KCl. Electron microscopy studies have shown that all the films on NaCl were composed of small, needle-like crystallites crossing orthogonally. The needle axis of the crystals coincides with the 〈110〉 directions of NaCl. When a cleavage surface of KCl was used as the substrate, vacuum-condensed films of flavanthrone and indanthrone were composed of dendroid crystals which assumed the standing b-axis orientation with an apparent C4v symmetry. On the other hand, a pyranthrone film on KCl was composed of wedge-like crystals which assumed the standing b-axis orientation. The electron-diffraction pattern of the film revealed that the b-axis of each crystal tilts against the normal of the substrate face at an angle of 29° and takes a random orientation. When the films assume the standing b-axis orientation, the planar molecule in the crystal comes into parallel contact with the cleavage face of KCl. It may be presumed that the nitrogen atoms in both flavanthrone and indanthrone molecules are placed on potassium ions in the (001) plane of KCl.