Plasmons in core-level photoemission spectra of Al(111)

The line shape and intensity of surface and bulk plasmon excitations in Al $2s$ and $2p$ core-level spectra of Al(111) have been studied as functions of the photoelectron emission angle ({θ}). For both surface and bulk plasmons, an asymmetric line shape is observed in normal emission, which becomes more symmetric in grazing emission. The asymmetric line shape is in good agreement with theory. The relative contributions of the intrinsic, extrinsic, and interference processes to the surface plasmon intensity are determined from its variation with {θ} and from theoretical line-shape calculations. We show the importance of the interference process in determining the intensity and line shape of the plasmons. From the intensity variation of multiple $(n=1--6)$ bulk plasmons (nωₚ) with n, the intrinsic and extrinsic bulk plasmon probabilities are determined.