Morphology Evolution and Crystal Alignment of Copper Phthalocyanine Thin Film under Thermal Annealing

The surface film morphology and nanostructure of small molecule-based thin films play a great role in gas sensor and photovoltaic applications. The morphology evolution of copper phthalocyanine (CuPc) thin films is studied with atomic force microscopy after thermal annealing in vacuum. The concurrently deposited samples are individually annealed in vacuum at temperatures up to 300°C for 30 minutes. The small round CuPc crystals measure around 20nm in diameter as deposited. At the 150°C annealing temperature, they become noticeably elongated, but are randomly oriented. At even higher annealing temperatures, 250°C, the crystals elongate more and start to form domains of similarly aligned crystals. This work demonstrates how the post-annealing procedure can affect the structural properties of small molecular thin films.