Abstract – Ben McMorranApril 26, 2019 10:18 am
Phase Contrast Imaging of Materials and Magnetic Fields using Scanning Electron Interferometry
The advent of efficient nanoscale diffractive electron optics, direct electron imaging detectors, and improved electron microscopes enable a new form of separated-path scanning electron interferometry. We use a single nanoscale grating as an amplitude-dividing beam splitter that can coherently divide an electron beam into two more than two probes. Improvements to the phase profile imprinted onto the electron wavefunction by the grating provide control over the relative probability current in each diffraction order, and can also be used to holographically remove aberrations and prepare electrons in desired spatial modes. We demonstrate the use of a single grating in a conventional scanning transmission electron microscope (STEM) to provide a flexible Mach-Zehnder electron interferometer in which electrons are divided into multiple paths separated up to 80 micrometers apart and each focused down to sub-nanometer diameters. The interferometer can be scanned across a transparent specimen or interaction region, and the interference pattern imaged directly at each position. We demonstrate using this technique to provide phase contrast of electron-transparent materials with atomic spatial resolution. Additionally, Aharonov-Bohm phases are used to image nanoscale magnetic fields. This new technique, requiring only an imaging detector and a modified condenser aperture in a STEM instrument, could be applied to future experiments in quantum electron microscopy or to coherently probe correlations in quantum systems.