Nano-interfacial space charge and single electron tunneling conduction in metal/polyimide/metal junctions

The surface potential of metal/polyimide (PI) ultra-thin film, prepared by spin-coat technique, was measured by Kelvin probe method at a temperature of 16 K. The photoirradiation effect on the surface potential was examined as the functions of the wavelength and irradiation time. It was found that the wavelength of 400 nm photoirradiation caused the charge injection from the metal electrode to PI films, rather than that of 600 nm. The behaviors of the metal/PI interfacial space charge estimated by the surface potential measurement well explained the photocurrent observed in the current-voltage characteristics of Au/PI/Al junctions, and the threshold voltage shift appeared in the Coulomb staircase of Au/PI:C60/Al junction.