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.