Investigation of space charge at pentacene/Au interface with UV/ozone treatment by a near-field microwave microprobe

The near-field microwave microprobe (NFMM) and Kelvin-probe measurements were performed to evaluate the conductivity in terms of surface potential of pentacene films on Au electrode. The UV/ozone treated and untreated Au electrodes were prepared to reveal the relationship between the electrical conductivity and interfacial electrostatic charging phenomena. For the pentacene film deposited on the Au electrode with UV/ozone treatment, holes were displaced from Au electrode to pentacene film, resulting the accumulation of apparent positive charges in the interfacial region of pentacene film around Au electrode. The NFMM measurement revealed that the reflection coefficient of microwave, S11 increased with UV/ozone treatment, indicating the resistance decrease of the surface. Accumulation of positive charge in the interfacial region of Au electrode/pentacene film is one of the essential reasons for the increase of the conductivity of pentacene film.