Molecular Reorientation of Copper Phthalocyanine Thin Films on Gold Surfaces with Controlled Roughness

In many organic semiconductors the optical, magnetic and electric properties in various devices and sensors are determined by the precise ordering and orientation of the molecules in crystalline thin films. One strategy to modify the molecular orientation on a metallic substrate is by changing the substrate roughness. We examine thin films of the metal-organic planar molecule, copper phthalocyanine, deposited onto Au(111) surfaces with varying roughness. The molecular alignments were measured using x-ray diffraction and the roughness was extracted from atomic force microscopy images. We find a diminishing 27.7° diffraction peak and an emergence of the 6.8° diffraction peak as surface roughness increases, suggesting a re-orientation of the molecule on the gold surface.