The effect of annealing temperature and film thickness on the phase of pentacene on the p⁺-Si substrate

This paper investigates the morphology and crystallization properties of the two crystalline phases of pentacene grown by thermal evaporation on p^+-Si substrates at room temperature by the methods of atomic force microscopy and x-ray diffraction. This kind of substrate induces a thin film phase and a triclinic phase which are formed directly onto p^+-Si substrates and constitute a layer consisting of faceted grains with a step height between terraces of 15.8 Å (1 Å=0.1 nm) and 14.9 Å, respectively. Above the critical thickness of the thin film phase, lamellar structures are found with an increasing fraction with the increase of the film thickness. When the film thickness is fixed, the fraction of lamellar structures increases with the increase of annealing temperature. These lamellar structures are identified as the second phase with a interplanar distance of 14.9 Å corresponding to the pentacene triclinic phase. Furthermore, the thin film phase consisting of several micrometre sized uniformly oriented grains at an annealing temperature of less than 80^\circC and a deposition rate of 0.6 Å/s is observed.