Shadow Imaging for Charge Distribution Analysis

Abstract

We briefly review the shadow imaging method for charge distribution analysis developed at Brookhaven. It is a unique electron-diffraction technique. Instead of focusing a small electron probe on the sample in conventional convergent beam electron diffraction, we focus the probe above (or below) the sample, resulting in parallel recording of dark-field images (shadow images), or PARODI. Because the method couples diffraction with imaging, it is thus suitable for studying crystals as well as their defects. We used this technique to accurately describe charge transfer that determines the functionality of technologically important materials. Examples are given for MgB2 superconductor and CaCu3Ti4O12 oxide that exhibits giant dielectric response. Discussions on non-spherical electron scattering factors and their parameterizations for direct observations of electron orbitals in atomic images are also included.