Plasmon Loss in Al 2p Core-level Photoelectron Spectroscopy.

Abstract

In core-level photoemission spectra of simple metals, distinct plasmon loss peaks appear due to excitation of plasma oscillations. This process can be classified into intrinsic and extrinsic ones. Here, plasmon excitation processes by the core-hole potential are called intrinsic and inelastic plasmon losses during photoelectron transport to the surface are called extrinsic. Although there have been many attempts to distinguish these two processes in photoemission spectra, some controversies still remain. Moreover there can be quantum mechanical interference between these two processes. This interference effect has been often neglected in the analyses of experimental data. In this research, we performed angle-resolved Al 2p core-level photoemission experiments and analyzed plasmon loss peak intensity at relatively low photoelectron kinetic energy. Consequently, we found characteristic behavior of plasmon loss peaks as a function of the angle between the polarization vector of incident photons and photoemission direction . We also performed full quantum-mechanical calculation taking into account the interference, which satisfactorily predicted the experimental re sults.

How is it possible to obtain buried interface information through very thick films using a hard-X-ray PEEM?

“…Here only extrinsic losses are of importance. The momentum of a plasmon is much smaller than the momentum of the primary electrons [7]. Consequently the electrons undergo only small changes in direction, and the lateral position on the surface at which secondary electrons are emitted does not deviate significantly from the lateral position of the atom which was initially excited.…”

Theoretical study of plasmon losses from Li 1s level in core‐level photoemission spectra

“… Their results show that the quantum Landau formula gives results quite similar to those without use of the high‐energy approximation in the photoelectron kinetic energy range from 60 to 1000 eV. Uwatoko et al have measured and calculated single plasmon loss spectra associated with Al 2p photoemission on the basis of Hedin's formalism, which shows rather good results as far as we include the interference. However, plasmon peaks are strongly influenced by the photoelectron diffraction, and it is thus important to consider the elastic scatterings to analyze the experimental results in detail.…”

Theoretical Study of Plasmon Losses in Core-level Photoemission Spectra

“…As pointed out before β(ω) depends on p, so that plasmon loss bands show the angular dependence. At low energy prominent angular dependence of the plasmon loss spectra is observed, whereas no angular dependence is observed at high-energy excitation (ε p > 1 keV ) [7]. Some experimental results show that the relative plasmon loss intensity changes very slowly as a function of photoelectron energy [22,23] in the high-energy region, but rapidly changes in the low-energy region.…”

“…The extrinsic losses were first discussed by Berglund and Spicer in their three step model, excitation, transport to the surface, and passage through the surface [1]. These two loss mechanisms are not possible to separate: They can interfere each other [2][3][4][5][6][7]. On the other hand the three step model has widely been used for practical purposes [8][9][10][11].…”