Plasmon energy losses in shear bands of metallic glass

TL;DR

This study investigates how shear bands in metallic glass affect plasmon energy losses using EELS, revealing density-related energy shifts and damping variations linked to medium-range order changes.

Contribution

It provides a detailed analysis of plasmon energy shifts in shear bands of metallic glass, highlighting the roles of damping and medium-range order in these shifts.

Findings

Maximum bulk plasmon energy shifts of about 38 and 14 meV in shear band segments.

Damping is larger in denser regions of shear bands.

Plasmon energy variations are explained by changes in damping and ionic density, predicted to be in the meV range.

Abstract

Shear bands resulting from plastic deformation in cold-rolled Al$_{88}$Y$_{7}$Fe$_{5}$ metallic glass were observed to display alternating density changes along their propagation direction. Electron-energy loss spectroscopy (EELS) was used to investigate the volume plasmon energy losses in and around shear bands. Energy shifts of the peak centre and changes in the peak width (FWHM) reflecting the damping were precisely determined within an accuracy of a few meV using an open source python module (Hyperspy) to fit the shapes of the plasmon and zero-loss peaks with Lorentzian functions. The maximum bulk plasmon energy shifts were calculated for the bright and dark shear band segments relative to the matrix to be about 38 and 14 meV, respectively. The damping was observed to be larger for the denser regions. The analysis presented here suggests that the changes in the plasmons are caused by two contributions: (i) Variable damping in the shear band segments due to changes in the medium-range order (MRO). This affects the static structure factor S(k), which, in turn, leads to either reduced or increased damping according to the Ziman-Baym formula. (ii) The ionic density and the effective electron mass appearing in the zero-momentum plasmon frequency formula $E_p(q=0)$ are coupled and give rise to small variations in the plasmon energy. The model predicts plasmon energy shifts in the order of meV.