Accurate measurements of mean inner potential of crystal wedges using digital electron holograms

The mean inner potential of a solid is a fundamental property of the material and depends on both composition and structure. By using cleaved crystal wedges of known angle, combined with digital recording of off-axis electron holograms and with theoretical calculations of dynamical effects, the mean inner potential of Si (9.26 ± 0.08 V), MgO (13.01 ± 0.08 V), GaAs (14.53 ± 0.17 V) and PbS (17.19 ± 0.12 V) is measured with high accuracy of about 1%. Dynamical contributions to the phase of the transmitted beam are found by Bloch wave calculations to be less than 5% when the crystal wedges are tilted away from zone-axis orientations and from major Kikuchi bands. The accuracy of the present method is a factor of 3 better than previously achieved by reflection high-energy electron diffraction and electron interferometry. The major causes of uncertainty were specimen imperfections and errors in phase measurement and magnification calibration.