Showing papers by "Alex H. Weiss published in 2021"
TL;DR: In this article, the authors applied positron annihilation induced Auger-gamma coincidence spectroscopy to identify important mechanisms responsible for the emission of low energy electrons following the sudden creation of holes in bilayer graphene on copper substrate.
Posted Content•
TL;DR: Auger-mediated positron sticking as mentioned in this paper is a technique to probe the electronic structure of the top-most atomic layer of a solid using the virtual photon exchange between a positron and a valence band electron.
Abstract: In this manuscript, we demonstrate a novel technique to probe the electronic structure of the top-most atomic layer of a solid using the virtual photon exchange between a positron and a valence band electron. This process, termed Auger-mediated positron sticking, is initiated by the coupling of the energy and momentum associated with the trapping of a positron in an image-potential-induced surface state to an electron in the material. We have used this quantum sticking of low-energy positrons to probe the valence band density of states of single-layer graphene and copper. The measured positron-induced electron spectra were successfully reproduced using a model which is principally composed of the valence band density of states. Our results demonstrate that Auger-mediated positron sticking is a top-most atomic layer selective probe of the electronic structure of fragile two dimensional surfaces which can complement existing photoemission spectroscopy techniques. The exceptional surface selectivity of Auger-mediated positron sticking arises because the excitation depth is limited to the Thomas-Fermi screening length. Finally, the analysis of the Cu spectrum in terms of the partial density of states reveals matrix element effects that suppress the contribution of valence 3d electrons relative to the 4s and 4p electrons.