In this work we present a new contribution for tracking the behavior of electron beam in gas and then in material placed in the chamber of a variable pressure scanning electron microscope using Monte Carlo simulation. Firstly our results for width and depth of interaction volume in high vacuum mode are compared and are consistent with those obtained by several relationships present in literature. Carbon and aluminum are considered as examples in order to establish the reliability of our approach and experimental data available from the literature. Then, we compared the evolution of width in both high (Re (HV ) ) and low (Re (LV ) ) vacuum modes with enlargement of skirt (Rs). The present work demonstrates that the best resolution conditions for energy, pressure and material, is given by Rs = Re (HV ) . Finally, the energy that must be used to get the best image resolution for given pressure and material is determined.

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