Investigation of the surface potential formed in Alq3 films on metal surface by Kelvin probe and nonlinear optical measurement

Polar orientation of Alq3 (Tris(8-quinolinolato)aluminum) evaporated lms on metal electrode was investigated by Kelvin probemethod and optical second harmonic generation (SHG) measurement. For as-deposited lms under the dark condition, a largepotential formed across the lms was conrmed and it decreased drastically by light irradiation with a wavelength of 400 nm. Froma viewpoint of the interfacial electrostatic phenomena, there are two contributions to the surface potential, i.e. space charge eectcharges contribute mainly to the surface potential after irradiation. According to the SHG measurement, decrease of the signal fromAlq3 lms was observed after light irradiation. It is also found that using the fundamental light with a wavelength of 900 nm, SHintensity decreases steeply during the SH measurement in the absence of 400 nm irradiation possibly due to the two-photonexcitation.