Evolution of the surface morphology of rubrene under ambient conditions

Evolution of the surface morphology and local conductivity on cleaved surfaces of rubrene single crystals is characterized with atomic force microscopy. The cleaved surface was found to exhibit molecular reorganization that results in the formation of nanoscale beads aligned along molecular step edges and fingers, narrow molecular structures, one molecule high, and in excess of 1 μm long. The beads show insulating behavior and a band bending effect on the surface nearby. Their formation has a strong environmental dependence, which has implications for the operation of rubrene field-effect transistors in the ambient environment.