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O: Oberflächenphysik

O 20: Elektronische Struktur (Experiment und Theorie) (II)

O 20.1: Vortrag

Dienstag, 24. März 1998, 16:15–16:30, H37

Collective surface excitations in and adsorption at SiC(100) — •V.M. Polyakov¹, T. Balster¹, H. Ibach², and J.A. Schaefer¹ — ¹TU Ilmenau, Inst. f. Physik, Pf. 100565, 98684 Ilmenau — ²Forschungszentrum Jülich, IGV, D-52425 Jülich

Collective surface excitations (Fuchs-Kliewer phonons and plasmons) at Si-terminated (2x1)- and C-terminated c(2x2)-surfaces of heavily n-doped (∼2.5x10¹⁸cm⁻³) SiC(100) are systematically examined experimentally and theoretically by high-resolution electron-energy- loss spectroscopy (HREELS) in a wide range of primary electron-beam energies. The measured spectra are fit by using the dipole scattering approach, including smooth free-electron density profiles calculated self-consistently by Schrödinger and Poisson equations. The measured spectra for all primary electron-beam energies are well reproduced by the applied model. However, when including only the contributions from lattice vibrations (phonons) and plasma oscillations of bulk free electrons (plasmons) the substantial discrepancy between the measured and calculated spectra is revealed. The latter is more pronounced for SiC(100) c(2x2). A better fit is obtained by the modified surface loss function contributed additionally from the quasi-two-dimensional electron gas at the surface. We attribute the latter to a weak metallicity of the SiC(100) c(2x2)-surface due to the presence of the surface states in the bulk band gap. In addition, the interaction of atomic hydrogen with the (2x1)- and c(2x2)- reconstructed surfaces in a low-exposure regime is also considered.