Structural and morphological phase control by supersonic beams on titanyl phthalocyanine: An investigation on the growth

Titanyl Phthalocyanine (TiOPc) is a cyclic oligomer widely used in organic electronics for its good stability, optical properties and charge mobility. Several polymorphs of TiOPc are known, showing different physical properties and consequently, in particular in the growth of thin films, the full control over the crystal phase formation is critical to effectively tune the conductive properties of the material. As a consequence, the availability of growth techniques allowing a precise control of both the morphology and crystal phase of the obtained films is crucial for the production of devices. In this work the structural properties and polymorphism of titanyl phthalocyanine thin films, grown on silicon substrates, have been systematically studied by synchrotron radiation grazing incidence X-rays diffraction and atomic force microscopy. Films obtained by the use of hyperthermal seeded supersonic beams technique allowed to unveil the key role played by the kinetic energy of the molecules in stabilizing specific polymorphs of TiOPc. The different growth conditions lead to grain dimensions in a range from the nanometric to the micrometric scale, depending on the substrate temperature and on the kinetic energy of the beam, while a high degree of fiber-like crystallographic order is observed in all the analyzed samples. The excellent control over phase selection, grain size and shape together with the production of well oriented high quality crystals makes of the hyperthermal seeded supersonic beams technique a promising tool for the realization of TiOPc thin films with structural and morphologic properties suitable for electronic application.