The talk will deal with phase transitions and behavior of small molecule organic semiconductors (OSMs) as induced by various factors. At the beginning, I will give a short introduction to x-ray
scattering techniques, which are main tools in the presented research, and physics and chemical nature of OSMs. Thereafter, individual cases of observed phase behavior will be discussed: (I) metal surface modification induced ultra-thin film phase and bulk phase orientation for para-sexiphenyl grown on Cu(110) surfaces; (II) thickness hindered β-phase nucleation and two-step phase transition observed for 5,11-bis(triethyl silylethynyl) anthradithiophene on amorphous substrates; (III) molecular mixing induced anisotropic ordering and smectic C phase appearance in pentacene-diindenorperylene binary mixture. Explanations for the observed behavior in the
individual systems (I-III) will be provided based on substrate surface morphology and strain accumulation in molecular film; competition between entropy, molecules' steric properties, and
anisotropic inter-molecular interactions; and competition between bulk and surface energy of molecular crystallites, respectively.