X‐ray microanalysis with Si(Li) detectors

Abstract

SUMMARYThe Si(Li) detector, with its relatively high collection solid angle, has brought X‐ray microanalysis within the operating current limits of both SEMs and transmission microscopes. At present, the main deficiencies arise in the low‐energy region of the spectrum, below about 2 keV. Here, detection efficiency falls off because of absorption in the entrance window, peaks invariably overlap and pile‐up rejection is less effective. High‐energy photons generated in transmission microscopes are responsible for new spectral artefacts and problems of overload. While computer processing of spectra can correct for most artefacts, background and peak overlaps, accuracy is fundamentally limited by counting statistics and the overall stability of the spectrometer. The technique will therefore benefit from improved design of both electronic circuitry and components. For example, advances in FET design may bring a substantial reduction in electronic noise which will not only improve resolution at low energies, but will also improve discrimination between small pulses and noise so that pile‐up rejection can be more effective. This will be most important when a very thin entrance window is used to permit observation down to the C Kα energy (282 eV) although the hazards involved in such ‘windowless' operation still limit its application. The stability of detection efficiency with time has been exploited in methods which attempt to remove the need for repetitive standardization of the spectrometer and new techniques have been developed for the analysis of thin films, particles and rough surfaces which make use of information contained in the bremsstrahlung continuum.