Core level spectroscopy during sodium atom adsorption on gold nanoparticle surfaces

The electronic structure of Au nanoparticles deposited on a W surface with natural oxide was studied by in situ photoelectron spectroscopy in ultrahigh vacuum before and after adsorption of Na atoms. The photoemission spectra from the core levels of Au $4f$, Na $2s$, and Na $2p$ were analyzed under synchrotron excitation in the photon energy range of 80-600 eV. It was shown that heating of the Au nanoparticle film leads to an increase in photoemission from the Au $4f$ level, which is associated with an increase in the size of gold nanoparticles. Deposition of Na atoms leads to the formation of an adsorbed Na layer and diffusion of Na atoms deep into the gold film with the formation of the intermetallic compound Na$_x$Au$_y$. Two states were found: Na$^0$ and Na$^+$, which are associated with the adsorbed Na layer and the intermetallic compound Na$_x$Au$_y$, respectively.