XPS and AFM studies of monodispersed Pb/PbO core-shell nanostructures.

A probe of the core-shell formation and the interfacial properties of monodispersed 30 nm Pb nanoparticles are presented. A direct correlation between the structures of the particle to its chemical states is done, by a careful Ar+ ion depth profiling followed by X-ray Photoelectron Spectroscopy and Atomic Force Microscopy. The study provides a unique insight into the structure of the nanoparticles. A PbO shell of 4 nm is observed to cover a 15-nm core, with a 5 nm interfacial region. The valence band spectra show the movement of the valence band maxima towards and beyond the Fermi-level during the insulator to metal transition along the particle depth. Evidence is also provided for an enhanced preferential sputtering of the PbO shell and an ion induced penetration of PbO into the Pb core.