Epitaxial Growth and Defect Structures of Quaterrylene Studied Using High Resolution Electron Microscopy

Vapor deposited epitaxial films of quaterrylene on (001) of KCl were investigated using high-resolution electron microscopy and electron diffraction. The crystal c-axis is parallel and perpendicular to the substrate surface at a lower and at a higher temperature, respectively. This means that the long axis of the quaterrylene molecule is in the film plane at a lower temperature and becomes perpendicular to it at a higher temperature. High-resolution images revealed the detailed features of an edge dislocation, twin boundaries and small angle grain boundaries. Differing from the normal part of the crystal, the unit cells are deformed and the orientation of molecules are varied from unit cell to unit cell. In addition, solitary molecular columns are seen to occupy empty spaces formed at the dislocation core or at the grain boundaries in order to relax the lattice distortion.