Structural Phase Transition induced by Molecular Substrate Interactions

Phthalocyanine thin films have unique properties in various electronic devices and sensors that are not commonly found in traditional semiconductors. These electric, optical, and magnetic properties are strongly dependent on their film structure including their crystalline size and orientation. As previously shown, when the substrate molecular interaction is stronger than the molecule-molecule interaction, the anisotropic molecule has its plane lying flat on the substrate surface. In contrast, if the molecule-molecule force dominates, the phthalocyanine molecules arrange in a standing configuration. For some substrates like gold surfaces, the roughness can also trigger this transition from flat lying to standing configuration. Here, we examine thin films of copper phthalocyanine deposited onto gold coated silicon substrates to show quantitative data of this molecular orientation transition using x-ray diffraction and atomic force microscopy. The gold roughness is varied with several methods and measured before a single co-deposition of phthalocyanine.