AVS 51st International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP20
XPS and AFM Study of K Promoted Supported Au Nanoclusters

Tuesday, November 16, 2004, 4:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: S.A. Sardar, University of California, Santa Barbara
Authors: Y. Yang, University of Calfornia, Santa Barbara
M.M. Sushchikh, University of California, Santa Barbara
S.A. Sardar, University of California, Santa Barbara
E.W. McFarland, University of California, Santa Barbara
Correspondent: Click to Email
It has been observed in high pressure reactors that K can increase the activity for CO oxidization of Au nanoclusters formed in block copolymer micelles and deposited on titania supports. UHV in situ characterization shows that the surface species, K@sub 3@ N and carbonates are discomposed after heating the surface to 800 K in UHV. K remains on the surface, however, the XPS signal from Au disappears during the heating process. Surprisingly, repeat XPS following exposure of the surface to air shows an observable Au signal. The appearance/disappearance of the Au XPS signal is reproduced by cyclically exposing the sample to the air then re-heating to 800 K in UHV. Sputtering the surface heated in UHV recovers the Au XPS signal. A K-shell model is proposed to explain the data with the formation of a K@sub 2@ CO@sub 3@ overlayer on the Au cluster during heating in UHV. The concentration ratio between Au and K is approximately1:1.