Observed Line Shapes of Collective Excitations in Al, Be, and Ge†

Line shapes of the major characteristic electron energy-loss peaks of Al, Be, and Ge, attributed to collective excitations of the valence electrons, have been measured at 20 keV primary electron energy and zero scattering angle. The primary-beam line shape has been unfolded from the observed energy-loss peak to obtain the natural-loss line shape. The results are discussed in terms of a Lorentzian line and the Drude model. The unfolded line shapes of Al and Ge are compared with optical measurements of − Im(1/∊). An expected correlation between the loss-peak halfwidth and the value of ∊2 at the peak maximum is in fair agreement with the observed data for Al and Ge.