ANALYTICAL ELECTRON-MICROSCOPY AND THE PROBLEM OF POTASSIUM DIFFUSION

Adularia and muscovite show different diffusion profiles during analytical electron microscopy (AEM); for muscovite a strong dependence of diffusion on crystallographic orientation has been observed. Conditions giving rise to reliable chemical data by AEM are the use of a wide scanning area and/or large beam size to reduce the effect of diffusion of alkali elements, a specimen thickness greater than about 1000 A, constant instrument operating conditions, and the use of a homogeneous, well-characterized standard sample. The optimum thickness range was obtained by determining the element intensity ratio vs. thickness curve for given operating conditions.