The momentum-dependent dielectric function of Zn was measured using electron-energy-loss spectroscopy ͑EELS͒ in transmission. The loss function in the low-energy region is found to be a superposition of a sharp absorption feature due to the excitation of electrons from the 3d level at a binding energy of 9.4 eV and a broad not well pronounced feature at about 14 eV, which is attributed to the collective plasmon excitation of the free charge carriers. This latter feature becomes more pronounced

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... ith increasing momentum transfer due to a strong decrease of the core-level oscillator strength. The decrease of oscillator strength leads to an initially vanishing dispersion of the plasmon, and to a reduction of the plasmon line width with increasing momentum transfer. This behavior can qualitatively be understood in the framework of a Drude-Lorentz approach.