Gaseous Cascade Amplification in He-H2O Gas Mixture in an Environmental Scanning Electron Microscope

This paper deals with the gaseous cascade amplification in He-H2O mixture in an ESEM. It is shown that such a mixture has the same behavior and gas amplification gain slightly modified with the increase of the (pd) parameter as compared to pure Helium. The use of the mixture gives rise to higher gain with respect to water vapor and more efficiency in the electrical neutralization of the specimen surface compared to He. All in all, the mixture exhibits high Townsend ionization coefficient, high gain and low operating voltage, which allows an expected increase of the signal to noise ratio.