Vibrations and Some Electronic Excitations of Adsorbed Alkali Metal Monolayers
A. Hamawi, S.-A. Lindgren, C. Svensson and L. Wallden
Physics Department, Chalmers University of Technology, 41296 Göteborg, Sweden
Received: July 16, 1991; in revised form September 3, 1991
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We discuss briefly data obtained for adsorbed alkali metal monolayers with three different techniques (HREELS, UPS and SHG). The vibrational spectra provide support for the traditional picture of a fractionally charged adsorbate at low coverage and a neutral one at high coverage. We ascribe a vibrational overtone reported in previous work to contamination due to residual water vapour. UPS, uncharacteristically, gives little information of interest for low coverages except for substrates with a band gap and with a surface state in the gap. For Na on Si(100) we monitor the metallization of the surface region in the monolayer coverage range and observe metal induced gap states at higher coverages. For Cs on Cu(111) the optical second harmonic generation (SHG) shows a strong monolayer coverage dependence which we ascribe to optical transitions between surface bands and to surface barrier photoabsorption indicating the potential of SHG as a probe of the details of the surface electronic structure.
DOI: 10.12693/APhysPolA.81.7
PACS numbers: 68.35.Ja, 73.20.Dx, 79.60.Gs, 78.65.Ez, 42.65.Ky