Trace Element Analysis in Geochemical Systems by STEM/EDS

Until recently, measurement of trace elements with ppm concentrations has been inaccessible to STEM EDS. Development of fast SDD detectors with solid angles > 1/2 steradian and faster processors are now making such measurements a reality. STEM EDS measurements already have a low brehmsstrahlung background owing to thin samples. However, the combination of high beam currents required to attain sufficient x-ray counts and high beam energy (typically 60-300 kV) tends to damage samples. The detection limits are therefore determined by the count rates obtainable from a given beam current, while still maintaining sample integrity.