RESUMEN
The effect of the specimen inclination on the electron distribution at the specimen surface in an HPSEM was investigated by Monte Carlo simulation. A broadening of the electron profile versus the tilt angle was obtained and a relationship between the r(0.9) radius and this tilt angle is proposed. The plot of the electron distribution at the sample surface shows that the classical scattering profile in the standard conditions is modified so that an inclined truncated shape is obtained. This result confirms the difficulty to carry out X-ray microanalysis in low vacuum conditions.
RESUMEN
Helium gas and air are commonly used in the high pressure scanning electron microscope (HPSEM). The presence of a gaseous environment in the specimen chamber modifies the electron beam profile. In order to fully understand the beam-gas interaction, we have investigated the beam-diameter effect for two gases (helium and air) by Monte Carlo simulation. In this calculation, we have assumed that the electron beam is Gaussian and we have explored the influence of the nature of the gas at low voltage. When the beam diameter varies between 1 and 100 nm, there is no influence on the beam profile for these two gases. The resolving power of the HPSEM is not affected by the beam-gas interaction. These theoretical results have been compared with experimental images obtained at low voltage under air and helium gases. The variation of image quality at low voltage has confirmed the interest of helium for use in a Field Emission Gun SEM (FEGSEM) in high pressure (or low vacuum) conditions.