Extracting elemental composition of topmost-atomic layers using Doppler Broadening Spectroscopy (DBS)

Our recent results have shown that the Doppler broadened gamma spectra originating from the annihilation of surface trapped positrons can provide elemental information of the topmost atomic layer even with the enhanced annihilation of positrons with valence electrons and the presence of positronium annihilation induced gamma. Here, we show that it is possible not only to identify but also to obtain quantitative chemical composition of the top surface through the analysis of Doppler Broadened annihilation gamma line shape. We have simulated Doppler broadened annihilation gamma spectra as measured by a high purity germanium detector representing annihilations from the surface of various elements (Cu, Si, C, Au, Ag, O). The simulated experimental spectra include statistical uncertainties, white noise, and background due to the inelastic scattering of the annihilation gamma. We show that it is possible to obtain the concentration of the trace element (<10% on surface) through the analysis of Doppler spectra. Our results open pathway for a positron-based technique that can provide quantitative chemical composition of inaccessible surfaces as the annihilation gamma can escape from inner surfaces of the sample without any loss of information.