Surface photovoltage of thin organic films studied by modulated photoelectron emission

Surface photovoltage (SPV) investigations of ultrathin organic films on a metal substrate with a unique sensitivity of <1 mV are reported. For this, a novel phase-sensitive method was developed, based on an accurate measurement of the light-induced shift of the ultraviolet or X-ray photoemission spectrum under power-modulated illumination of the sample. The study of the SPV provides access to electronic properties of semiconductor surfaces and interfaces, including also organic–inorganic interfaces, as demonstrated for thin films of perylene-tetracarboxylic dianhydride on Cu(1 0 0).