PHYSICAL VAPOR GROWTH OF CENTIMETER-SIZED CRYSTALS OF ALPHA-HEXATHIOPHENE

The processes in physical vapor transport: vaporization, transport and crystal growth, the regimes for transport: molecular flow path limite d, diffusion-limited, convection-limited and forced-convection-limited are analyzed and the results are used to guide a systematic investiga tion of physical vapor transport and crystal growth of alpha-hexathiop hene (alpha 6T), a promising thin-film transistor organic material. Su ccessful growth occurred when the gas pressure was such that the regim e was convective and when deliberate inert-gas flow (forced convection ) improved volatilization. Plate-like growth morphology and thickness differences between the high-temperature and low-temperature polymorph s is explained on the basis of differing atomic structure. Conditions for the reproducible growth of crystals of up to 1 cm in size are repo rted. We feel that the analyses and procedures reported here can be us ed to grow crystals of other organic materials.