Abstract
Electron diffraction gratings can be used to imprint well-defined phase structure onto an electron beam. For example, diffraction gratings have been used to prepare electron beams with unique phase dislocations, such as electron vortex beams, which hold promise for the development of new imaging and spectroscopy techniques for the study of materials. However, beam intensity loss associated with absorption, scattering, and diffraction by a binary transmission grating drastically reduces the current in the beam, and thus the possible detected signal strength it may generate. Here we describe electron-transparent phase gratings that efficiently diffract transmitted electrons. These phase gratings produce electron beams with the high current necessary to generate detectable signal upon interaction with a material. The phase grating design detailed here allows for fabrication of much more complex grating structures with extremely fine features. The diffracted beams produced by these gratings are widely separated and carry the designed phase structure with high fidelity. In this work, we outline a fabrication method for high-efficiency electron diffraction gratings and present measurements of the performance of a set of simple prototypical gratings in a transmission electron microscope. We present a model for electron diffraction gratings that can be used to optimize the performance of diffractive electron optics. We also present several new holograms that utilize manipulation of phase to produce new types of highly efficient electron beams.
Highlights
Scanning transmission electron microscopy (STEM) has recently offered a large number of critical insights into the structure and behavior of materials at the atomic scale [1, 2, 3]
High-quality gratings may be produced with highresolution focused ion beam (FIB) milling, electron beam-induced deposition (EBID), and electron beam lithography (EBL); the choice of technique places some limitations on the structure of the gratings produced but is primarily a question of practical considerations
We consider prototypical electron diffractive optics produced by focused ion beam (FIB) milling, as FIB instruments are present in many TEM labs and can be used safely to produce an electron diffraction grating with minimal training
Summary
Scanning transmission electron microscopy (STEM) has recently offered a large number of critical insights into the structure and behavior of materials at the atomic scale [1, 2, 3]. One recent demonstration of electron vortex production employed an amplitude diffraction grating which produced a beam separation of 3 μrad [9], or, equivalently, a real-space separation on the order of 5 nm in the specimen plane of a modern high-resolution STEM instrument. To address these challenges, in our work developing electron vortex beams [18, 10] we have devoted considerable effort towards developing electron-transparent phase grating structures [19] that modulate the phase of the electron wave rather than the amplitude.
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