Self-Organization of Organic Molecules on Surfaces

Organic semiconductors have advantages over their inorganic counterparts due to their eco-friendliness, cheap producibility, and applications in flexible electronics. However, organic semiconductors tend to have a lower conductivity than their inorganic counterparts. One possible method to increase the conductivity of organic semiconductors is self-assembly driven by a surface reconstruction that is a repeating topography across the surface of a substrate.  This work examines pentacene, an organic semiconductor, on a very simple surface of graphite or graphene both experimentally and computationally. Experimentally we see limited evidence of a lowest energy orientation for pentacene that is thermally evaporated onto highly ordered pyrolytic graphite (HOPG). This is in agreement with computational DFT calculations that show, despite an AB stacking structure being the lowest energy orientation, this is a very shallow minima. Several orientations of pentacene, shifted laterally across the surface and rotated at each position, have a similar final energy.