CHARGING PHENOMENA IN LOW-VOLTAGE ELECTRON-MICROSCOPY OF LASER-FRACTURED FLUORIDE SURFACES

Surfaces of fluoride crystals, fractured by a single excimer laser pul se and then covered by a thin conductive layer, are imaged by scanning electron microscopy in the low-voltage secondary electron mode. As a result of charging, at lower primary electron energies a contrast enha ncement can be obtained for surface fragments that are no longer tight ly attached to the crystal. This differs from high-energy (>10 keV) im aging which only yields topographic contrasts and allows the analysis of the fractured structure by edge and shadowing effects. Even contras t inversion from positive to negative charging of an entire fragment c an be achieved, depending on the primary electron energy. It is shown that this effect can be utilized to discriminate between fragments wit h a good mechanical contact to the bulk and partially detached ones by systematically studying the contrast as a function of electron energy and specimen inclination. (C) 1996 American Institute of Physics.