Mitigating Thermal Beam Damage with Metallic Coats in Low Voltage FEG-EPMA of Geological Materials

Field emission gun electronprobe microanalysis (FEG-EPMA) provides the analyst with the opportunity to characterize very small volumes of material. Using a low voltage source the irradiated volume is submicron. It is well known that some geological phases e.g. volcanic glass, carbonates, phosphates, hydrous silicates suffer beam damage under high beam current condition [e.g.1,2] and several authors suggest mechanisms either to mitigate beam damage (e.g. cryostage cooling, reduced beam currents, metallic coats etc. [2,3,4.5]) or to use the time dependent intensity to interpolate the count rate back to the original composition at zero time [5].