Mineral diagnostics: SEM-EDS Monte Carlo strategy for optimised measurements of ultrathin fragments in cultural heritage studies

The availability of minute quantities of sampling material is often an issue in the context of cultural heritage and archaeology due, for instance, to the value of the sample, its uniqueness or the small amount of residual material which testify the original form of the art to be restored. In this context, electron-excited energy-dispersive X-ray spectrometry (EDS) performed in a scanning electron microscope (SEM) has proven to be a primary methodology for analysing minute quantities of material thanks to its morphological and microanalytical capability. However, when dealing with micro- and sub-micrometre specimens, as can be the case in ultrathin glass and metal fragments, several effects resulting from the physics and operational settings of the measurement must be considered to avoid quantification errors. In this paper, a detailed study of the effects of micro- and nanometric-sized glass and gold-alloy fragments on SEM-EDS microanalysis is presented. Monte Carlo simulations of different kinds of elongated glass fragment, with a square section and a thickness of 0.1 to 10 µm, and of some gold alloys demonstrated a strong influence in terms of the fragment size and operational conditions (beam energy, detector position, etc.). This work can be used to devise an appropriate and optimised measurement strategy.