The Effect of Atmospheric Doping on the Interfacial Electronic Structure of Phthalocyanine Thin Films as Studied by UPS

Abstract

AbstractThe effect of oxygen doping on titanyl phthalocyanine (TiOPc) films was investigated by ultraviolet photoelectron spectroscopy (UPS). The energy of the electronic levels of TiOPc films probed by UPS was clearly different between the film deposited in ultrahigh vacuum (UHV) and in oxygen atmosphere. The film deposited in UHV showed downward band bending characteristic of n-type semiconductor. On the other hand, the film deposited in oxygen atmosphere showed upward band bending characteristic of p-type semiconductor. Such trends are in excellent correspondence with reported field effect transistor characteristics. In order to examine the Fermi level (EF) alignment between TiOPc film and the substrate, the HOMO energy of TiOPc relative to the EF of the metal substrate was determined for various substrates. Although EF alignment was not achieved for the TiOPc film prepared in UHV, possibly because of insufficient charge density in the TiOPc film, it was achieved in the case of TiOPc film exposed to oxygen, probably by p-type doping effect of oxygen.