Positron trapping at quantum-dot-like particles on metal surfaces

Measurements of the positron annihilation-induced Auger electron (PAES) spectra from the Fe-Cu alloy surfaces with quantum-dot-like Cu nanoparticles embedded in Fe reveal a decrease of the Fe M2,3VV positron annihilation-induced Auger signal intensity and an enhancement of the Cu one for surfaces created by enriching the Cu content of the Fe-Cu alloy. These experimental results are analyzed by performing calculations of positron surface states and annihilation characteristics at the Fe(1 0 0) surface with quantum-dot-like Cu nanoparticles embedded in the top atomic layers of the host substrate. Estimates of the positron binding energy and annihilation characteristics reveal their strong sensitivity to the nanoparticle coverage. Theoretical core annihilation probabilities are compared with experimental ones estimated from the measured Auger peak intensities. The observed behavior of the Fe and Cu PAES signal intensities is explained by theoretical calculations as being due to trapping of positrons in the regions of Cu nanoparticles embedded in the top atomic layers of Fe.