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We report the first direct observation of electron emission into the vacuumas a result of a VVV Auger transition resulting from the relaxation of a deephole in the valence band. A beam of low energy (<1.25eV) positrons was used todeposit positrons onto the surface of samples consisting of single layergraphene, multi-layer graphene and graphite. The distribution of electronsemitted from the samples as a result of the annihilation of the positron showedpeak extending up to ~12 eV with a maximum at ~4eV. The observed peak was ~17times larger than the previously observed annihilation induced C KVV peak. Ananalysis based upon a density functional theory calculation of the positronannihilation rates indicates that the width and intensity of the peak isconsistent with electron emission resulting from VVV Auger transition excitedby the annihilation of valence band electrons. Good agreement was found betweenthe data from the single layer graphene on Cu surface with a theoretical lineshape found from a self-folding of the density of states for a free standinggraphene layer. The agreement between the theoretical and measured intensitiesfor the KVV and VVV transitions indicates that the branching ratio for holes todecay via an Auger transition is nearly the same in both cases (i.e. close to100%). Our results suggest the possibility of using annihilation induced VVVAuger spectroscopy to study the properties of the local density of states andthe hole decay processes in materials in which the valence band width exceedsthe work function.

Direct observation of electron emission as a result of a VVV Auger transition in the valence band of Graphene