Electron Interferometry Using an Amplitude Dividing Grating Beamsplitter: Development and Application
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Date
2019-09-18
Authors
Yasin, Fehmi
Journal Title
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Publisher
University of Oregon
Abstract
Electron microscopes can be used for atomic resolution imaging myriad materials including semiconductor nanomaterials integral to modern technology, biomolecular materials that compose all of life and the carbon energy cycle, and 2-D materials with various potential applications. Due to the high electron dose required to form contrast in conventional electron microscopy imaging techniques, many biomolecular and low atomic number materials are destroyed before an image can be formed. Electron interferometry shows promise as a lower dose imaging technique due to the difference in how contrast is formed. Electron holography, for example, uses an electrostatic charged wire as an electron biprism in order to overlap the interaction and vacuum electron waves to form interference fringes. These fringes can be imaged directly and processed to measure the object transmission function, providing both spatial information such as atomic locations, and quantitative phase and amplitude information, necessary for thickness and electric and magnetic field measurement within the specimen. In this work, we combine electron holography with Scanning Transmission Electron Microscopy (STEM), which forms a focussed probe beam at the specimen and raster scans the beam over a field of view. We've experimentally realized a path-separated electron interferometer in this mode, called STEM holography (STEMH), and apply it to image gold nanoparticles on thin amorphous carbon at subnanometer resolution. STEMH simultaneously forms efficient, interpretable contrast for both of these materials, allowing us to confirm the presence of string-like structure within the amorphous carbon, previously thought to be randomly bonded and oriented. Additionally, we've devised and implemented a multi-biprism design that enables tuning of the path separation between the arms of the interferometer at the specimen plane, and we demonstrate the largest path-separated amplitude division electron interferometer to date. This flexible STEMH enables large geometry experiments and a means to precisely place the probes in the specimen plane, enabling imaging around beam-sensitive materials and probing fundamental physical phenomena in or around materials. On its own, STEMH can probe fundamental fields with atomic resolution, and advances in detector technology may allow STEMH to image beam-sensitive materials without destroying them in the process.
This dissertation includes previously published co-authored material.
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Keywords
Electron Holography, Electron Interferometry, Electron Microscopy, STEM Holography