Monte Carlo simulation of electron-solid interactions in cement-based materials

Knowledge of the size of the electron-solid interaction volume and the sampling volume of various signals within it is important for interpretation of images and analytical results obtained from electron microscopy. In this study we used a Monte Carlo technique to simulate electron trajectories in order to investigate the shape and size of the interaction volume, the spatial and energy distribution of backscattered electrons and characteristic X-rays in cement-based materials. We found that the maximum penetration depth of the electron trajectories ranges from 0.75 to 1.5 μm at 10 keV and from 2.5 to 5.0 μm at 20 keV. For backscattered electrons, the maximum sampling depth is about 30% of the interaction volume depth and its lateral dimension is close to the interaction volume depth. The sampling volume size of characteristic X-rays is a substantial fraction of the interaction volume. For ettringite, the amount of material analysed in X-ray microanalysis is in the order of 1 to 100 μm3 at conventional SEM accelerating voltages of 10 to 20 keV.