Dynamic Redistribution of Excess Charge During Photoemission in an Electron Bombarded Glass-Ceramic

Abstract

ABSTRACTWe have measured the energy distribution of excess charge trapped by an electron irradiated mica-glass ceramic, Macor™. Photoelectron emission as a function of incident wavelength shows two distinctly different contributions to the measured density of electron trap states. First, there is a broad continuum of binding states which extends well above the Fermi level. This results in spontaneous electron emission which depletes the excess charge in these states rapidly at room temperature and more slowly at 170K. The free decay of charge emission can be described semiclassically. Second, localized trap states appear as peaks on the continuum distribution which occur at 2.7 and 3.1 eV. These correspond to two thermionic emission peaks which occur during heating at 550K and 595K respectively. Photoemission at high intensities using the 458, 488, and 514 nm wavelengths of an argon ion laser and the 632 nm wavelength of a He-Ne laser greatly enhances the depletion of excess charge from the sample. The laser-induced emission intensity is initially high and drops rapidly, followed by a more gradual decrease. The initial intensity measures the population of electrons with binding energies less than the photon energy. The later emission is related to the repopulation of these states by the dynamic redistribution of electrons from deeper states. This behavior may lead to a model for the mechanism of electron redistribution in charged insulating materials.