Ultra High Energy Resolution Electron Spectrometer for Atomic Resolution Studies
Department of Energy
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1102 8th St., Kirkland, WA, 98033-5666
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AbstractIf the energy resolution of electron energy loss spectroscopy (EELS) carried out in a scanning transmission electron microscope (STEM), with an atom-sized electron probe, could be improved to 10 meV or better, a new way of studying materials at the atomic scale, by recording and analyzing their vibrational energies, would become possible. No STEM system capable of such performance has yet been developed. Up to a few months ago, the best energy resolution that could be obtained with monochromated EELS systems capable of forming a small probe was about 40 meV, i.e. a factor of 4 too poor. Using a new monochromator we have recently built and an improved Gatan spectrometer, we have shown that resolution of 10 meV and eventually 5 meV will become possible, if the spectrometer part of our new instrument is brought up to the same design standards as the new monochromator. Building such a spectrometer is what we plan to do in the proposed project. In Phase I we built and brought up a monochromated STEM that uses a new type of a Nion- designed monochromator, and achieved unprecedented levels of performance. The spectrometer used in this project was Gatans latest design, the Enfinium, with two enhancements for extra stability. The system was able to reach 12 meV energy resolution in spectra taken with very short acquisition times, but not in spectra taken with acquisition times of around 1 s. Pushing the whole system to reach unprecedented levels of energy resolution has taught us what is and what is not important in ultra-high resolution EELS. We used this knowledge to design a new spectrometer with improved electron optics, and detectors optimized for detecting weak spectral features next to an intense zero loss peak. The newly designed spectrometer will be built, in two stages during Phase II. Stage A spectrometer will be built in the first year. It will reach 10 meV energy resolution at 60 keV, and it will provide a test bed for key design elements of stage B. The Stage B spectrometer, which will be mostly built in the first year and brought up and optimized in the second year, will be designed to reach 5 meV energy resolution. Commercial Applications and Other Benefits: Elements as light as hydrogen will become detectable, and their bonding arrangements determined from the observed vibrational energies. This will increase our understanding of energy conversion and storage devices needed for a green economy. The new spectrometer and the associated equipment (a complete monochromated scanning transmission electron microscope) will open up a new market segment in research instrumentation, which we estimate will be worth about $20M per year for Nion.
* information listed above is at the time of submission.