Morphological, Optical, and Electronic Consequences of Coexisting Crystal Orientations in β-Copper Phthalocyanine Thin Films

The crystal structure of the β phase of copper phthalocyanine (CuPc) is a monoclinic herringbone, which is commonly created in thin films by either thermal annealing of α-CuPc at 300 °C or deposition on heated substrates. Of the several known CuPc crystal polymorphs, the β phase is of particular interest due to its thermodynamic stability. We observe three coexisting crystal orientations for thin films of β-CuPc to be (101), (105), and (502) using grazing incidence wide-angle X-ray scattering. Each of the three crystal orientations have distinct surface roughness, as measured by atomic force microscopy, but are electrostatically similar by Kelvin probe force microscopy. However, local optical properties, as measured by micro-UV-vis spectroscopy, are very different in the different domains.