The effect of surface preparation on the structure and electrical transport in an organic semiconductor

Self-assembled monolayers (SAMs) with a variety of structures and terminal groups were evaluated as underlayers for pentacene deposition. It was found that the most critical factor in the formation of highly oriented thin film pentacene with large grain size was the geometric structure of the monolayer. Monolayers with terminal bonds parallel to the surface produce large pentacene grains with an angular rather than the dendridic structure normally observed on octadecyltrichlorosilane (OTS) coated substrates. The grain size, X-ray scattering, carrier mobility, and current on/off ratios are all improved with monolayers of the appropriate geometry.