Electron scattering by gas in the Environmental Scanning Electron Microscope (ESEM): Effects on the image quality and on the X-ray microanalysis

Abstract
in this work, we studied the electron beam scattering due to the introduction of two gases : water vapour and helium within the specimen chamber of the Environmental Scanning Electron Microscope (ESEM) and the effects of this phenomenon on the image quality and on the microanalysis results. An increase in the pressure involves an amplification of the electron beam scattering phenomenon up to 160 microns when water vapour is used. The best results are obtained with helium. The use of this gas allowed a better focusing of the electron beam on the micronic particle which led to an improvement of the chemical contrast of the images, like the stability of the results of microanalysis X. In addition, with helium we showed an improvement in the signal-to-noise ratio which not only leads to obtain images of good quality but also to improve the limit of detection of the microanalysis system. In spite of the advantages of the use of helium, an important focusing of the electron beam, can induce an increase in the temperature of the surface of the sample by causing its degradation especially for fragile materials or a dehydration of hydrated samples.