Gold highly dispersed on metal oxide supports has unexpectedly been found to be highly active for a number of catalytic reactions. However, the electronic nature of the gold species in active catalysts has not been fully elucidated. We have applied a modified version of the gas phase condensation combined with Arc plasma method for the metal nanoparticle synthesis. Which is not only convenient in synthesizing highly dispersive metal nanoparticle with cleaner surface but also is suitable for the size controlling. In addition, this method also shows advantage in synthesizing metal nanoparticle with simple shape on a supporting material (Si Ta, TaN, HOPG). The performance of the gas phase condensation and Arc plasma method for the size control has been confirmed in the earlier work [1]. In this study, we report the investigations of the thermal stabilities, crystallographic structure and the size dependence of electronic structures of Au ant Pt nanoparticles in range of 1.5 ~ 5nm in diameter. The Au nanoparticle were characterized by the TEM, AFM, XPS and UPS. Drastic change have observed in the 4f level photoemission spectrum when the size of Au particle down to 1.5nm. The spectrum is characterized by component of an oxidized doublet states of Au₂O₃ coexisting with the doublet states of pure Au. The vanishing of component of Au₂O₃ doublets has been observed with increasing the annealing temperature of the sample in the reduction atmosphere.

[1]. G. Kutluk, S. Yagi, H. Sumida, H. Namatame, M. Taniguchi, Mater. Res. Soc. Symp. Proc. Vol. 915 R06-18 2006

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