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.

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.

Density functional conformational study of 2-O-sulfated 3,6 anhydro-α-D-galactose and of neo-κ- and ι-carrabiose molecules in gas phase and water.

We examined the conformational preferences of the 2-O-sulfated-3,6-α-D-anhydrogalactose (compound I) and two 1,3 linked disaccharides constituting-κ or ι-carrageenans using density functional and ab initio methods in gas phase and aqueous solution. Systematic modifications of two torsion angles leading to 324 and 144 starting geometries for the compound I and each disaccharide were used to generate adiabatic maps using B3LYP/6-31G(d). The lower energy conformers were then fully optimized using B3LYP, B3PW91 and MP2 with several basis sets.

Electron distribution on a tilted sample in the high pressure SEM.

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 effect of beam diameter on the electron skirt in a high pressure scanning electron microscope.

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.