Scanning Microscopy


Elemental distributions and contents of tabular and cubic silver halide microcrystals were analyzed by backscattered electron imaging, scanning transmission electron imaging, X-ray mapping and X-ray analysis in the spot mode by scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectrometry (EDXS). By using a liquid nitrogen cryostage, damage to the microcrystals and drift of the sample under electron bombardment were minimized. Monte Carlo simulation shows the electron trajectories in the silver halide microcrystals for different experimental conditions and directs the selection of the beam position for X-ray spot analysis. The backscattered electron images, scanning transmission electron images and X-ray maps were acquired after selecting the optimal operation parameters of the image processing system. The quality of backscattered electron images was improved by processing the images off line. The X-ray maps directly show the elemental distribution in individual microcrystals, the backscattered electron images and the scanning transmission electron images do so indirectly. X-ray analyses in the spot mode yield semiquantitative results. This work indicates that the combination of the different modes can be used to assess elemental distribution and content in the microcrystals, even cubic ones.

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