Figure 3: Results of theoretical calculations.

(a) Cut through the ground-state positron probability density (top panel) and the potential experienced by the positron near the top atomic layers (bottom panel) along a C–C bond on single layer graphene (SLG) on a Cu (111) substrate (The (110) plane of the unit cell is shown in the Supplementary Fig. 1). Our result shows that the positron is localized predominantly in its image potential well at the vacuum side of the graphene layer, giving signals almost exclusively from the SLG. The 2D contour plot of the potential in the bottom panel shows the position of the Cu and C atoms. (b) One-dimensional plot of the potential (turquoise) and the positron density (purple) averaged over the xy plane. It can be seen in this plot that the positron overlap with Cu atoms is small compared with the overlap with the C atoms. As a consequence, most of the annihilation and annihilation induced signal is due to the graphene layer consistent with our experimental results. (c) Density of the electronic valence (turquoise) and conduction (purple) states. The vacuum level is indicated by the dashed line. The yellow curve shows the calculated distribution of annihilation induced holes that initiate the VVV Auger process (the distribution of electronic valence states and the distribution of hole states have been scaled to agree at the peak). The calculations show that the distribution of annihilation-induced holes closely resembles the valence band density of states due to the fact that the positron partial annihilation rate is relatively constant for states in the valence band.