Experimental energy-loss function,Im[−1ε(q,ω)], for aluminum

We describe highly accurate (0.2-1%) intensity measurements for the inelastic scattering of 75-keV electrons in ∼ 1000-Å-thick polycrystalline aluminum films in the region of (0.0-3.1)-${\mathrm{\AA }}^{-1\mathrm{}}$ transferred wave vector and (0-100)-eV energy loss. The work was performed on the Cornell University electron spectrometer-microscope-computer system. These measurements clarify some experimental problems associated with multiple scattering which obscure the single scattering distribution. We present a new method for eliminating the distribution of intensity attributable to multiple scattering involving quasielastic events. This subtraction method is accurate to ∼0.01% of the single-bulk-plasmon intensity. Next, we extend an earlier correction method to obtain the single scattering energy-loss function $\mathrm{Im}(-\frac{1}{\epsilon })$ from the residue of the first process, which consists of multiple plasmons and quasiparticle transitions. Details of the specific procedures are included. We point out several features in the result—the bulk-plasmon intensity, dispersion, and width, the quasi-particle continuum, and a simultaneous two-plasmon scattering. The latter is, for the first time, characterized completely as to intensity, dispersion, and energy width. Finally, we present a comparison of the measured bulk-plasmon dispersion with some recent model calculations.