MICROANALYSIS OF INDIVIDUAL SILVER-HALIDE MICROCRYSTALS

Elemental distributions and contents of tabular and cubic silver halid e microcrystals were analyzed by backscattered electron imaging, scann ing transmission electron imaging, X-ray mapping and X-ray analysis in the spot mode by scanning transmission electron microscopy (STEM) com bined with energy-dispersive X-ray spectrometry (EDXS). By using a liq uid nitrogen cryostage, damage to the microcrystals and drift of the s ample under electron bombardment were minimized. Monte Carlo simulatio n shows the electron trajectories in the silver halide microcrystals f or different experimental conditions and directs the selection of the beam position for X-ray spot analysis. The backscattered electron imag es, scanning transmission electron images and X-ray maps were acquired after selecting the optimal operation parameters of the image process ing system. The quality of backscattered electron images was improved by processing the images off line. The X-ray maps directly show the el emental distribution in individual microcrystals, the backscattered el ectron images and the scanning transmission electron images do so indi rectly. 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 microcryst als, even cubic ones.