IN SITU XPS STUDY OF Pd NANOPARTICLE FABRICATED BY GAS EVAPORATION METHOD

The Pd nanoparticles were fabricated by the gas evaporation method without any capping molecules. It is found that the average diameter of the nanoparticles are 1.7 nm with standard deviation of 0.8 nm by AFM observations. The chemical states of the nanoparticles were measured by the in situ XPS. The XPS results indicate that the chemical states of the nanoparticles become almost the same as the bulk Pd. The chemical states of the air-exposed Pd nanoparticles were also observed by the ex situ XPS and NEXAFS methods. Both ex situ XPS and NEXAFS measurements indicate that the nanoparticles were naturally oxidized under an atmospheric environment. Considering from the behavior of Pd 3d XPS and the diameter of nanoparticles, it is suggested that the depth of oxidized Pd layer is less than 1.4 monolayer from the nanoparticles surface.