Infrared optical constants of insulators determined by high-resolution electron-energy-loss spectroscopy

Abstract

High-resolution electron-energy-loss spectroscopy can be applied to insulators by use of an auxiliary electron gun. Fuchs-Kliewer phonons of the MgO(001) surface were recorded with excellent resolution (27 ${\mathrm{cm}}^{-1\mathrm{}}$). Specular intensities were analyzed for angles of incidence from 40° to 85°. Data processing by use of the dielectric-function theory yields optical constants as accurate as by IR spectroscopy: resonance frequency ${\omega }_{\mathrm{TO}}=393\mathrm{}\pm 2$ ${\mathrm{cm}}^{-1\mathrm{}}$; damping $\gamma =35\mathrm{}\pm 2$ ${\mathrm{cm}}^{-1\mathrm{}}$, and Szigeti charge $e^{*}=(0.83\mathrm{}\pm 0.07)e$.