Two-process model of PSEE from scratched metals

When photoillumination is interrupted, the exoelectron emission from scratched metal samples decays quickly. When the illumination is resumed, however, the recovered exoelectron emission shoots up to a value significantly higher than before and then decreases gradually - a fact overlooked by previous researchers. To explain this “storage effect” in PSEE (photo- stimulated exoelectron emission), the authors have proposed a model, according to which there are two excitation processes competing during PSEE; one is the photoexcitation of the electrons at energy levels within the band gap of surface oxide layers, and the other is the tunneling transition of electrons in bulk metals to occupy the vacant levels of the oxide layers. From the rate equations based on this model and also from the PSEE data obtained for scratched aluminum and zinc, three kinds of quantities, i.e., the number of exo-active sites, the emission rate from the sites and the rate of activating exo-inactive sites, are successfully estimated. Other PSEE phenomena such as the peculiar emission intensity versus time profiles can also be elucidated in view of this model.