Controlled polymorphism in titanyl phthalocyanine on mica by hyperthermal beams: A micro-raman analysis

The polymorphism of titanyl phthalocyanine films, grown on atomically flat mica substrates, has been systematically studied by micro-Raman spectroscopy, correlating structure and optical properties. Different growth regimes, using hyperthermal seeded supersonic beams, have been explored as a function of the substrate temperature. Specific signatures in micro-Raman spectra, correlated to different phases, are identified and discussed. We demonstrate the unprecedented ability to grow crystalline films at low temperature, with improved structural order, and we show that different regimes lead to grain dimensions in a range from the nanometric to the micrometric scale. The local micro-Raman analysis, carried out on crystallites with regular shapes, allows discriminating different structural phases of the single crystalline grains. We provide evidence that different growth regimes are achieved and controlled, paving the way to phase selection, which is envisaged as a key feature to improve device performance.