Growth of PTCDA crystals on H:Si(1 1 1) surfaces

The room temperature deposition of PTCDA on hydrogen passivated Si(1 1 1), as a function of evaporation temperature and dosing time, has been studied by STM. At low evaporation temperature, 200 °C, clusters with an average size of 3.5 nm are formed on the surface. The mobility of the small clusters is so high, even at room temperature, that most of the clusters are trapped at surface defects. By increasing the evaporation temperature to 230 °C, larger clusters are formed which have lower mobility. The growth process is identified as a Volmer-Weber mechanism. On increasing the evaporation temperature further to 250 °C, crystals with dendritic shape are formed with an average size of 150 nm. The terraces of the crystal are formed with the (1 0 2) basal plane of the α-phase. Molecular resolution on the terrace also allows us to identify the molecular mechanism involved in the growth of the dendritic crystals.