Thermally induced phase transition in crystalline lead phthalocyanine films investigated by XRD and atomic force microscopy

Lead phthalocyanine films have been deposited at room temperature on to silicon substrates and than annealed in high vacuum at different temperatures. The samples have been analysed by X-ray diffraction (XRD) as well as atomic force microscopy (AFM) in order to get structural and morphological information on the samples. The as deposited film shows a monoclinic structure with a (320) orientation. Increasing the annealing temperature up to 170°C, crystallites with both triclinic and monoclinic phases are observed, although the triclinic phase seems unstable. Annealing the sample at 190°C the film consists mainly of monoclinic phase. The AFM topographic images suggest that at this temperature the triclinic crystallites evaporate, leaving wide holes in the films.