Core-Shell Charge Transfer in Plasmonic Fe@Ag Nanoparticles on MgO Film

In this work we report the interfacial charge transfer between the Fe core and Ag shell in self-organized nanoparticles on MgO films on Mo(001). Predeposited Fe nanoparticles organize in a square network with long-range order on the oxide surface guided by the MgO coincidence lattice. When Ag is added, it covers the Fe nanoparticles, forming a shell. By means of XPS and UPS we show that a charge transfer occurs between the Fe core and the Ag shell, determining the oxidation of part of the Fe atoms and a negative charging of the Ag shell. This is confirmed by band bending and core level shifts. As a consequence of the Fe@Ag morphology and composition the plasmonic response of the nanoparticles is modified with respect to pure Ag nanoparticles.