Thermally and Optically Stimulated Exoelectron Emission from an Electron‐beam Irradiated Glass–ceramic Material
The American Institute of Physics
Journal of Vacuum Science Technology A
The exposure of insulating materials to an electron beam results in the trapping of excess charge on the surface. We have studied the thermally and optically stimulated emission of this excess charge in an electron‐bombarded, fluorophlogopite mica glass–ceramic material (Macor). The total electron emission from the surface is measured either as a function of the sample temperature during heating or the photon wavelength. The emission as a function of temperature has four characteristic peaks whose relative intensity depends on the beam dose, energy, initial sample temperature, and history (accumulation of beam‐induced defects). One peak occurs immediately upon heating and is related to the total surface charge. Two peaks occur at fixed temperatures of 280 and 325 °C and are associated with the discrete energy trap states. The highest temperature peak is only observed after prolonged beam exposure and is due to the annihilation of defects. Illumination in the ultraviolet is required to produce photoemission for an uncharged sample. However, after electron bombardment, electron emission is observed over a broad range of visible wavelengths. In addition, two photoemission thresholds at about 2.7 and 3.1 eV suggest electron trap states which can be associated with the thermally emitted peaks. The thermally and optically stimulated emission is a valuable tool to measure the electron state distribution in charged insulating materials.