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Wave Vector Dependence of the Electron Energy Loss Functions of Graphite
Author(s) -
Venghaus H.
Publication year - 1974
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220660115
Subject(s) - electron , wave vector , anisotropy , momentum (technical analysis) , physics , atomic physics , dispersion (optics) , g band , graphite , electron energy loss spectroscopy , perpendicular , spectral line , condensed matter physics , optics , materials science , geometry , nuclear physics , quantum mechanics , raman spectroscopy , mathematics , finance , economics , composite material
Electron energy loss measurements were performed on graphite single crystals with 55 keV electrons. From spectra taken with transferred momentum hq parallel to the c‐axis and recorded for different absolute values of |q| the wave vector dependent energy loss function Im [−l/ϵ‖( E , q )] was determined for 0< E ⪅ 8 eV and 0.25 Å −1 <|q|< < 0.75 Å −1 . Apart from the dispersion of the energy loss maximum in the 5 to 6 eV region the main feature of Im [−1/ϵ‖( E , q )] is the appearence of a band gap E g , increasing from E g ≪ 1 eV for |q| = 0 up to E g ≈ 1 eV for |q| as 0.7 Å −1 . Additional measurements made with transferred momentum ħ q perpendicular to the c‐axis confirmed the dispersion of the π‐plasmon, exhibiting an anisotropy for large wave vectors and different orientation of the latter within the layer planes of graphite.