Electron localization in (7x7) reconstructed and hydrogen- covered Si(111) 
surfaces as seen by NMR on adsorbed Li

Winnefeld, H.; Czanta, M.; Fahsold, G.; Jansch, H. J.; Kirchner, G.; Mannstadt, W.; Paggel, J. J.; Platzer, R.; Schillinger, R.; Veith, R.; Weindel, C.; Fick, D.

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Electron localization in (7x7) reconstructed and hydrogen- covered Si(111) surfaces as seen by NMR on adsorbed Li

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Fick, D.
Prof. Dirk Schwalm, Emeriti, MPI for Nuclear Physics, Max Planck Society;

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Citation

Winnefeld, H., Czanta, M., Fahsold, G., Jansch, H. J., Kirchner, G., Mannstadt, W., et al. (2002). Electron localization in (7x7) reconstructed and hydrogen- covered Si(111) surfaces as seen by NMR on adsorbed Li. Physical Review B, 65(19): 195319, pp. 195319-195319.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0011-8343-1

Abstract

The observation of "Korringa-like" nuclear-spin-lattice relaxation of Li-8 probe atoms, adsorbed at extremely low coverages on the Si(111)-(7x7) surface (10(-4) ML and below) points to the existence of a correlated two-dimensional electron gas. The observed high relaxation rates as compared to adsorption of Li-8 on metals are in accordance with an enhanced electron localization in the adatom dangling bonds. For Li-8 adsorbed on semiconducting hydrogen covered Si(111) surfaces (now at coverages around 10(-3) ML) "Korringa-like" spin- lattice relaxation is also observed, quite surprisingly. Independent of the preparation of the hydrogen coverage, i.e., in vacuum or wet chemically terminated, the relaxation rates are moreover all of the same size. This points to a narrow band at the Fermi energy generated by the adsorbed Li itself. Quantitative ab initio all-electron density-functional calculations for Li coverage as low as 0.04 on the perfectly hydrogen-terminated Si(111) surface together with a qualitative reasoning following Mott's arguments on semiconductor-metal transitions support this view.