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The electron momentum density ͑EMD͒ of two different modifications of graphite has been measured and the results of the measurements have been compared with theoretical calculations from three different theories: a full potential linear muffin-tin orbital, a modified augmented plane wave, and a pseudopotential calculation. Experimental results have been obtained by two different methods. The complete three-dimensional EMD is determined by inelastic photon-electron scattering, i.e., by the so-called (␥,e␥) experiment, and by electronelectron scattering, the (e,2e) experiment, cuts in the spectral electron momentum density are studied. For the (␥,e␥) experiment 180 keV synchrotron radiation from the PETRA storage ring at the Deutsches Elektronen-Synchrotron has been used with coincident detection of the recoil electrons. The (e,2e) experiments were carried out at the new (e,2e) spectrometer at the Australian National University using 40 keV primary electron energy and simultaneous detection of the outgoing electrons in an equal energy sharing mode. As samples we have prepared approximately 20 nm thin self-supporting graphite foils either by thermal evaporation ͑TE͒ or by laser plasma ablation ͑LPA͒. They are thin enough to suppress in essence electron multiple scattering. Electron diffraction analysis revealed that the LPA foil contains graphitic basal planes with a random distribution of c axes, whereas the TE foil was strongly c-axis oriented in the sense that the basal planes were parallel to the foil surface. In the analysis of the results special attention was devoted to anisotropies in the EMD revealed by comparison of TE and LPA foils. The (e,2e) measurements showed furthermore a strong orientation dependence of the intensity of and states ͑here we have for comparison additionally measured highly oriented pyrolytic graphite͒. The EMD's obtained by both techniques show anisotropies in the momentum distribution of graphite and are discussed in view of the theoretical results.

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We report on the three-dimensional electron momentum densities (EMD) of graphite and fullerene obtained by a so-called (,e) experiment, i.e. the coincident detection of an inelastically scattered hard x-ray photon with its recoil electron. A monochromatized flux of 1012 photons s-1 at 150 keV from the high-energy x-ray wiggler beamline of the ESRF was directed onto thin graphite or fullerene targets. Comparison with a pseudopotential and a full-potential linear muffin-tin orbital calculation in the case of graphite is made. Inclusion of electron correlation via the Lam-Platzman correction is discussed. The experimental EMD of C60 shows stronger electron delocalization in the `buckyball' compared to graphite, which is supported by theory.

We report on the measurement of the three-dimensional electron momentum density ͑EMD͒ of a 22 nm Cu/22 nm Ni sandwich foil and of a Cu 0.50 Ni 0.50 alloy film with the same thickness, which was obtained from an identical sandwich by interdiffusion. The EMD's were measured by coincident detection of a Compton scattered photon with its recoil electron. The experiments were performed at the High-Energy beamline of the European Synchrotron Radiation Facility. The experimentally observed small change of the EMD due to alloying is reproduced by the Korringa-Kohn-Rostoker coherent-potential approximation scheme ͓Benedek et al.