Regensburg 1998 – wissenschaftliches Programm

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DF: Dielektrische Festkörper

DF 4: Elektrische und optische Eigenschaften II

DF 4.2: Vortrag

Dienstag, 24. März 1998, 14:50–15:10, H11

Inelastic X-Ray Scattering of Diamond and LiF — •W. Caliebe^1,2, C.-C. Kao¹, J. Hastings¹, and K. Hämäläinen³ — ¹NSLS, BNL, Upton NY 11973, USA — ²IFF, FZ-Jülich, 52425 Jülich — ³Dep. of Physics, Univ. of Helsinki, Helsinki, Finland

Inelastic X-ray scattering (IXS) with high energy resolution has been used to investigate the dynamical structure factor S(q,ω) of diamond and LiF. The advantages of IXS are the high penetration depth of hard X-rays which makes IXS rather insensitive to the surface, and the finite momentum of hard X-rays which allows to measure S(q,ω) in several Brillouin zones. The limiting factor is the low cross section which requires long counting times and which limits the statistics. The experiments have been performed at the inelastic X-ray scattering beamline X21 at the National Synchrotron Light Source (USA). The overall energy resolution in this experiment was 0.7 eV at a photon energy of 8 keV. LiF is considered to be the "fruit-fly" of the insulators due to its large band gap of 14.4 eV and the low number of bands which are involved in transitions with energy transfers below 20 eV. It has been studied for a better understanding of the method and interpretation of the data. In diamond, S(q,ω) was measured in [100]- and [111]-direction for several momentum transfers between the first and third Brillouin zone. Special attention was focussed on the indirect band gap in [100]-direction. The band gap was not observed in the first Brillouin zone but in the second one instead at the expected position.