Temperature and coverage driven condensation of pentacene on the Si(111)-(√3 x √3) R30°-Ag surface

The adsorption and self-assembly behavior of pentacene molecules on the Si(111)-(root 3 x root 3) R30 degrees-Ag surface has been studied by variable-temperature scanning tunneling microscopy (STM). By cooling the surface from room temperature to 120 K we observed the condensation of a two-dimensional molecular gas phase to a new ordered solid phase (P2). The structure models of this phase and the high-density brick-wall phase (P1) are proposed consistently based on a systematic investigation of the morphology, chirality and domain boundary structures of the two phases. The self-assembly mechanism of pentacene molecules driven by temperature and molecular coverage is discussed.