AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP7
Two-dimensional Electronic Excitations in a Metallic Monolayer on a Semiconductor Surface

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Surface Science Poster Session
Presenter: T. Inaoka, Iwate University, Japan
Authors: T. Inaoka, Iwate University, Japan
T. Nagao, Tohoku University, Japan
S. Hasegawa, University of Tokyo, Japan
T. Hildebrandt, University of Hannover, Germany
M. Henzler, University of Hannover, Germany
Correspondent: Click to Email
There exists a surface-state band at the Si(111)-(@sr@3x@sr@3)-Ag surface created by depositing a monolayer of Ag on the Si(111) surface. An electron system in this band forms a realistic two-dimensional (2D) conduction-electron system. Recently, 2D plasmons (PLs) in this electron system have been clearly observed by high-resolution electron energy-loss spectroscopy in a broad wave-number range including PL decay due to electron-hole pair (EHP) excitations. In the present work, by means of the local-field-correction (LFC) theory, we evaluate the exchange-correlation (X-C) effects on the above electronic excitations. We compare three cases, namely, (i) random-phase approximation, (ii) Hartree-Fock approximation, and (iii) STLS approximation formulated by Singwi, Tosi, Land, and Sjölander. The X-C effects are neglected in (i), only the X effect is considered in (ii), and both the X and C effects are taken into account in (iii). We determine the electron density and the electron effective mass so that the calculated results in (iii) accord with the experimental ones. Our calculations give a good description of the experimental results of the energy dispersion and the energy-loss intensity of the 2DPL. When the X or both the X and C are switched on, with increase in wave number q, the dispersion curve begins to shift downward, and decays away due to EHP excitations at a smaller q value. Simultaneously, the integrated resonance intensity of the 2DPL in the energy dependence of the energy-loss function declines more quickly at smaller q values. This effect is more conspicuous in (iii) than in (ii). Our electron system has a large effective Bohr radius, and consequently a high effective density, because our electron system lies on a semi-infinite dielectric medium. However, owing to low dimensionality, the X-C effects appear remarkably in the 2DPL with increase in q.