Electron-energy-loss spectroscopy studies of icosahedral-phase plasmons

Previous electron-energy-loss spectroscopy (EELS) measurements on amorphous and icosahedral (i-phase) ${\mathrm{Al}}_6$Mn show a broader plasmon excitation in the i-phase than in the amorphous phase [Chen et al., Phys. Rev. Lett. 57, 743 (1986)]. This broadening is presumed to arise from differences between the electronic structures of the phases. We present measurements on i-phase ${\mathrm{Al}}_6$Mn that confirm these earlier results. We also present measurements that show plasmon widths that are similar in i-phase and amorphous ${\mathrm{Pd}}_{58.8}$ ${\mathrm{U}}_{20.6}$ ${\mathrm{Si}}_{20.6}$, and in i-phase and amorphous ${\mathrm{Al}}_{75}$ ${\mathrm{Cu}}_{15}$ ${\mathrm{V}}_{10}$. Thus, the additional broadening in i-phase ${\mathrm{Al}}_6$Mn is not a general feature of the icosahedral phase. The phase independence of plasmon widths in ${\mathrm{Pd}}_{58.8}$ ${\mathrm{U}}_{20.6}$ ${\mathrm{Si}}_{20.6}$ and ${\mathrm{Al}}_{75}$ ${\mathrm{Cu}}_{15}$ ${\mathrm{V}}_{10}$ suggests that the amorphous and icosahedral phases in these systems have similar short-range ordering.