Figure 3. Probability of different numbers of electrons being emitted from a GNP following an ionisation by a 50 keV photon, as a function of the distance from the ionising event to the nanoparticle surface.

All ionising events in gold typically produce a large number of secondary Auger electrons, but many of these electrons are emitted at low energies and cannot escape because they are stopped in the GNP bulk. At distances a few nanometres within the GNP, a broad distribution of electron yields can be seen, as most Auger electrons can escape following ionisations near the surface. By contrast, at points further from the surface, the distribution is sharply peaked, with only one or two electrons generated following most ionising events.