Specific Characteristics of Noble Metal Nanoparticles on Sulfide Minerals Observed by XPS and STS

Synchrotron radiation X-ray photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy (STM/STS) have been used to characterize gold and silver species spontaneously deposited from HAuCl4 or AgNO3 solutions onto sulfide minerals at room temperature. The reacted substrates were studied too. It was found that Au 4f7/2 binding energies increase up to 1 eV with decrease in the size of Au0 nanoparticles in the range 3 to 30 nm. This is attributed to a temporal charging of the particles, lessening kinetic energies of the photoelectrons via interaction with final-state photoholes. STS revealed a positive correlation between the current magnitude and the diameter of Au particles, tentatively explained by Coulomb blockade effects. Silver deposited on the minerals exhibited neither shifts of Ag 5d bands, nor Coulomb blockade in STS. Possible mechanisms behind the suppression of electronic tunneling and its potential role for the charge transfer steps in reactions of gold nanoparticles were considered