Size and temperature dependence of phase stability in nanocrystalline pentacene thin films

Pentacene thin films are frequently used to fabricate organic molecular electronic materials. It is believed that the orthorhombic phase is transformed into the triclinic phase in a process that is dominated by thin film thickness and substrate temperature. In this work, a thermodynamic model was established to describe the polymorphic behavior of pentacene thin films with respect to contributions in surface (interface) energy and surface stress to the total Gibbs free energy. The accuracy of the developed model was verified with the reported experimental data. It reveals that a lower surface energy and surface stress coupled with a higher volume Gibbs free energy induces crystallization of the orthorhombic phase on the nanometer scale.