AVS 49th International Symposium
    Surface Science Thursday Sessions
       Session SS-ThM

Paper SS-ThM10
Low Dimensional Metallic States in Heavily Irradiated CaF@sub 2@ Thin Films on Si(111)

Thursday, November 7, 2002, 11:20 am, Room C-108

Session: Electronic Structure and Stimulated Processes
Presenter: A.A. Bostwick, University of Washington
Authors: A.A. Bostwick, University of Washington
J.A. Adams, University of Washington
A. Klust, University of Washington
E. Rotenberg, Advanced Light Source
M.A. Olmstead, University of Washington
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Calcium fluoride is a wide band gap ionic insulator that undergoes photosimulated desorption of fluorine. It has been previously reported by Karlsson et al.@footnote 1@ that heavily irradiated thin (2.5 – 4 triple layers) CaF2/Si(111) films show a sharp metallic defect state associated with an ordered array of surface fluorine vacancies. We find two additional states in thicker, irradiated films (5-10 triple layer), one at higher binding energy and one at lower energy than the surface state. These states also cross the Fermi level dispersing upwards from normal emission. The zone-center energies of these states depend on the thickness of the initial CaF2 film, hinting that the electrons are confined in the growth direction. The upper state could lie within the band gap of the silicon substrate, but the lower state, which is more than 1.5 eV below the Fermi level at the zone-center, does not. These states are observed after prolonged irradiation, much longer than that necessary to produce the surface state. We postulate that these new states are due to the formation of fluorine vacancy clusters (Ca metal quantum dots) within the CaF2. Funded by DOE grant DE-FG03-97ER45646/A0003. @FootnoteText@ @footnote 1@ Karlsson et al., Phys. Rev. Lett. 57,1247 (1986).