AN AFM INVESTIGATION OF SURFACE ENERGY OF PENTACENE FILMS ON PARYLENE-C AND BENZOCYCLOBUTENE

In view to put in light morphology peculiarities of pentacene, the widely used material for organic transistors, a detailed atomic force microscopy (AFM) investigation of the pentacene growth mode in relationship with the film thickness (in the range 6–60 nm) is reported. Local surface energy measurements based on contact AFM spectroscopy were performed to explain the thickness dependent morphology of the pentacene films onto two polymer dielectrics (parylene-C and benzocyclobutene). Our analysis provided an exhaustive description not only of the accessible film surface but also of its inner structural properties. Evidenced by these approaches, a critical thickness of 30 nm was found in relation with a transition from the orthorhombic thin film phase to triclinic bulk phase for pentacene growth on parylene-C and benzocyclobutene. This thickness was previously observed to be corresponding to organic field effect transistors (OFETs) with optimized mobility.