Computer Control of Energy Analysis in an Electron Microscope

Abstract

Recent experiments have shown that, for suitable alloy systems (Al-Cu, Al-Mg), it is possible to detect changes in composition ∼ 1 atomic wt. % with a spatial resolution 10nm, by measuring shifts in the energy loss spectrum of electrons transmitted through a specimen in an electron microscope. The sensitivity and accuracy of the technique for microanalysis is limited by several factors: (i) the energy-loss spectrum is recorded photographically and then traced on a photodensitometer; the resulting curve is smoothed by hand and the data points are transferred to a computer; (ii) since both voltage and intensity scales are non-linear at this stage, they are adjusted by reference to calibration plates; (iii) even for a monochromatic incident beam, the half-peak full width of the 15 eV plasmon loss in Al is 1 eV; for Al-Mg alloys a composition change of 1% corresponds to a shift in the plasmon peak of 0.055 eV and so curve-fitting techniques must be applied to the corrected data.