Grating-Based Beam Shaping and Inelastic Interferometry with Free Electrons

Abstract

Here I present studies for the manipulation of free electrons using materialholograms and the application of holographically structured electrons in interferometry. The research in this dissertation can be divided into two main sections. First, is the design and nanofabrication of off-axis material holograms for free electrons that can be used to arbitrarily shape the amplitude and phase of the electron wavefront. Focused ion beam gas-assisted etching is presented as a method to reliably achieve the fabrication resolution required to produce the intended grating groove profiles to optimize diffraction efficiency and meet the precise hologram depth profiles required to impart a desired structured wavefront. An analytical method for finding hologram groove profiles is also outlined and experimental tests are performed to verify its accuracy. In the second portion, binary straight diffraction gratings are placed in a transmission electron microscope to create a scanning two-grating Mach-Zehnder interferometer. The sensitivity of the relative phases in the interferometer output are shown through the relative alignment of the gratings, as well as by introducing external phase shifts from static potentials to the path separated probes. The interferometer's capability to achieve phase sensitive nanoscale imaging is also demonstrated. Finally, the interferometer is used to measure interference between a coherent superposition of electrons inelastically scattered from the dipole plasmon of a gold nanoparticle. This dissertation contains previously published and unpublished material.