Thin film properties and surface morphology of metal free phthalocyanine films grown by organic molecular beam deposition

The structure, optical properties and surface morphology of thin films of m etal free phthalocyanine (H2Pc) deposited in an ultra-high vacuum environme nt by organic molecular beam deposition have been studied using a variety o f ex-situ techniques. The growth conditions have a strong influence on the properties of the films. H2Pc undergoes a phase transition (alpha -->beta) at a deposition temperature of similar to 330 degrees C, or upon post annea ling a film grown at room temperature. Both the structure and optical prope rties of the films change and powder X-ray diffraction, electronic absorpti on spectroscopy, Raman and photoluminescence spectroscopies are used to cha racterise the differences between the two phases. Atomic force microscopy a nd Nomarski interference microscopy show that the lower temperature alpha-p hase is characterised by a smooth morphology with spherical islands that sh ow no apparent long-range order. By contrast, the beta-phase has a much gre ater root mean square roughness and long thin needle-like crystals are obse rved on the surface of the films. The morphology of the beta-phase depends on the method of preparation and there are two distinct types, beta(1) and beta(2). The crystallites show a preferential orientation and alignment wit h respect to each other for growth at room temperature followed by annealin g (beta(1)), but are randomly oriented for films grown at elevated substrat e temperatures (beta(2)).