Interface structure of the rubrene crystal field effect transistor

The gate voltage effect on the surface structure of a rubrene field effect transistor (FET) is investigated by means of x-ray crystal truncation rod (CTR) scattering. Gate voltage ranging between 0 V and −70 V does not alter the CTR intensity profile of the rubrene FET, which reflects both the rubrene–air interface and the rubrene–substrate interface structures. Two possible structural models that explain the experimental results are proposed: (1) the gate voltage does not affect the structures of the two interfaces, or (2) the gate voltage does not affect the structure of the rubrene–air interface, and the other interface does not contribute to the CTR profile, because of the embossing of the rough substrate surface to the flat rubrene crystal surface.