Quantitative X-ray microanalysis in stem—on the nature of disturbing surface films

Abstract

We have tested the quantitative capabilities of a new commercial transmission electron microscope equipped with an energy-dispersive spectrometer. Metallic solid solutions of known compositions were used. The thin film ratio method was employed, the Cliff-Lorimer factor being included in the software of the system. In most cases the correct compositions were obtained by the automatic system without difficulties. However, in a relatively few cases when examining very thin areas (close to the edge) of the transmission specimens, the wrong compositions were evaluated. This so-called ‘edge-effect’ is due to the formation of thin surface layers during electropolishing. These disturbing surface films, previously discussed in the literature, could not be made visible in the transmission electron microscope and were considered to be hypothetical. In the case of Al-Cu alloys, we resolved these layers as being ‘island structures’ which were described earlier in quite a different context by Kaiser and Kaesche (1980, Werkst. u. Korr.31: 347–353.) The disturbing surface layers could be removed successfully by additional ion beam milling.