Environmental gas impact on the emission volume of X-rays near the interface in the variable pressure scanning electron microscopy.

In this paper, our previously developed model to account for the secondary X-ray fluorescence and absorption effects near the interface of two adjacent materials in a high-vacuum scanning electron microscope (Zoukel & Khouchaf, 2014) is adapted and extended to experimental conditions of low-vacuum mode (in the presence of a gaseous environment in the SEM analysis chamber). The position shifting effect of the two Gaussian peaks issued from the first derivative equation that can fit the experimental low-vacuum EDS profiles is investigated. The impact of the medium gas on the emission volume of secondary X-rays near the interface is qualitatively discussed. Water vapour and helium are successively used as gas environment, in order to link the resolution of microanalysis profiles with the effects of the X-ray fluorescence and absorption phenomenon. A close agreement between Monte Carlo simulation and experimental results is found.

Gas effect on the emission and detection of the backscattered electrons in a VP-SEM at low energy.

The effect of the electron beam skirting on the emission and detection of the backscattered electrons (BSE) in a low vacuum scanning electron microscope is investigated at low energy regime. Monte Carlo computed dependencies of the BSE distribution on the water vapor and air pressure shown a significant increase of the extent of the BSE exit zone. The pressure variation has however a little effect when helium gas is used. A new approach based on the comparison between the sizes of the skirt and the BSE exit zone on the specimen surface provides a useful tool to determine the operating pressure range that ensures minimal degradation of the lateral resolution in BSE imaging mode.