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

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 cm^-1). 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 ωTO=393±2 cm^-1; damping γ=35±2 cm^-1, and Szigeti charge e*=(0.83±0.07)e.