Nanoscale surface morphology and rectifying behavior of a bulk single-crystal organic semiconductor

A nanoscale investigation of the critical interface between bulk crystals of rubrene and air by means of scanning tunneling microscopy (STM) and current-voltage spectroscopy was analyzed. The periodic 2D organization of individual molecules of rubrene, an organic semiconductor with potential applications in electronics have been observed on the a-b plane of a bulk crystal where they form a highly ordered step and terrace surface. In order to explore whether the p-type rectifying behavior of rubrene crystals is a property inherent to these samples, the scanning tunneling spectroscopy (STS) and point-contact diode I-V characteristics under white illumination light were recorded. The light induces booth electrons and holes but for positive biases, the current remains extremely weak and is unaffected by light excitation. The results reveal the nanoscale morphology and electrical properties of the active interfaces of field-effect transistors fabricated with these materials.