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1993 (3)
1Author    J. R. Schmitz, H. Schulte-Schrepping, A. Berthold, S. Mourikis, W. SchülkeRequires cookie*
 Title    Performance of the Compton Spectrometer at HARWI/HASYLAB  
 Abstract    Performance, resolution and spectral throughput both of the sagittally focusing monochromator and of the alternately installed two analysing systems, a Cauchois-type cylindrically bent crystal analyser for Compton-profile measurements, and a spherically bent crystal analyser for S(q, (^-mea-surements, of the new Compton spectrometer at the HARWI (harter Röntgen Wiggler) of the DORIS storage ring are presented together with two typical applications. 
  Reference    Z. Naturforsch. 48a, 279—282 (1993); received December 24 1991 
  Published    1993 
  Keywords    X-ray spectrometer, Inelastic X-ray scattering, Focusing X-ray optics, Compton pro-file, Dynamic structure factor 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0279.pdf 
 Identifier    ZNA-1993-48a-0279 
 Volume    48 
2Author    A. Berthold, K.-J Gabriel, W. SchülkeRequires cookie*
 Title    The Dynamic Structure Factor of LiC 6 and KC 8 : Inelastic Synchrotron X-Ray Scattering Results  
 Abstract    The dynamic structure factor S(q, &>) of electrons in lithium-intercalated graphite (LiC 6) and potassium-intercalated graphite (KC 8) for momentum transfer q || c-axis has been measured by inelastic synchrotron X-ray scattering. The dielectric function s{q, a>) was deduced from the data and compared with e(q, co) of pristine graphite. The main feature in the different Im [e(q, tt>)]-spectra, a more or less intense peak around 14 eV, can be assigned to maxima of the symmetry-projected joint density of occupied and unoccupied electron states near the Fermi level. Knowing the position of the occupied bands by photoemission experi-ments, predictions about the unoccupied n and interlayer states can be made. In the case of LiC 6 , a shift and broadening of the first Im [e(q, a>)]-peak was found, which can be explained by a decrease of the energy of the interlayer-band because of the strong hybridization of this graphite-derived band with the Li metal 2s-band. In the case of KC 8 , a weakening of the first peak of Im [e(q, co)] was observed, which we attribute both to a decreasing overlap of the occupied 7t-derived state with the empty interlayer state and to a change of symmetry of the occupied er-derived states as well as of the empty rc-derived states. 
  Reference    Z. Naturforsch. 48a, 283—288 (1993); received December 30 1991 
  Published    1993 
  Keywords    Inelastic X-ray scattering, Dynamic structure factor, Graphite, Graphite intercalation compounds, Interlayer state 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0283.pdf 
 Identifier    ZNA-1993-48a-0283 
 Volume    48 
3Author    K. SturmRequires cookie*
 Title    Dynamic Structure Factor: An Introduction  
 Abstract    The doubly differential cross-section for weak inelastic scattering of waves or particles by many-body systems is derived in Born approximation and expressed in terms of the dynamic structure factor according to van Hove. The application of this very general scheme to scattering of neutrons, x-rays and high-energy electrons is discussed briefly. The dynamic structure factor, which is the space and time Fourier transform of the density-density correlation function, is a property of the many-body system independent of the external probe and carries information on the excitation spectrum of the system. The relation of the electronic structure factor to the density-density response function defined in linear-response theory is shown using the fluctuation-dissipation theorem. This is important for calculations, since the response function can be calculated approximately from the independent-par-ticle response function in self-consistent field approximations, such as the random-phase approxima-tion or the local-density approximation of the density functional theory. Since the density-density response function also determines the dielectric function, the dynamic structure can be expressed by the dielectric function. 
  Reference    Z. Naturforsch. 48a, 233—242 (1993); received December 10 1991 
  Published    1993 
  Keywords    Scattering theory, Dynamic structure factor, Inelastic photon scattering, Inelastic elec-tron scattering, Inelastic neutron scattering, Dielectric function 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0233.pdf 
 Identifier    ZNA-1993-48a-0233 
 Volume    48