X-ray Absorption Near-Edge Structure and X-ray Photoelectron Spectroscopy Studies of Interfacial Charge Transfer in Gold–Silver–Gold Double-Shell Nanoparticles

Charge transfer in heteromeric structures such as gold–silver core–shell (Au@Ag) nanoparticles (NPs) and gold–silver–gold double-shell (Au@Ag@Au) NPs was demonstrated using X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) techniques. XANES analyses confirmed that the d-orbital hole density of the Au atoms increases in the following order: Au foil ≅ Au NPs < Au@Ag NPs < Au@Ag@Au NPs. In conjunction with observed positive and negative shifts in the Au 4f and Ag 3d binding energies in XPS spectra of Au@Ag and Au@Ag@Au NPs, we conclude that d electrons are transferred from Au to Ag in the heteromeric NPs due to the charge compensation mechanism. By taking advantage of the charge transfer phenomenon, one can modify the electronic structure of heteromeric NPs with enhanced chemical stability and optical/electronic properties.