Ultra-High Frame-Rate Pixelated Direct Electron STEM Detector

Multi-color electron microscopy (EM) is a powerful new technique for studying biological ultrastructure with selective lanthanide-ion tagging of specific components of interest. The technique is analogous to multi-color fluorescence microscopy, but at about 100× higher magnification. However, the current method for acquiring multi-color EM data based on energy-filtered TEM (EFTEM) requires high-priced energy-filter equipment and makes us of <1% of incident electrons, making it laborious and inefficient, often producing noisy images that are difficult to unambiguously interpret. To improve the throughput, efficiency, and resolution of multi-color EM, we are developing a new multi- color EM technique based on four-dimensional (4D) scanning transmission electron microscopy (STEM), which uses a pixelated detector to capture signals from the vast majority of the primary electrons that interact with the specimen. Multi-color EM using 4D-STEM is based on the scattering of elastically scattered electrons, which represents about 30% of the incident electrons, to get elemental discrimination in the STEM. Our proposed development of an ultra-high frame-rate pixelated direct electron STEM detector will make this multi-color EM fast, efficient, and greatly improve the scientific results that can be obtained, aligning well with the Department of Energy’s goal of developing powerful new tools for structural characterization of biological systems from the atomic to the cellular scale. During Phase I of this project, we developed a demonstrator detector, a synchronized scan controller, and software for performing preliminary studies using this technique on a state-of-the-art STEM. The first results with biological specimens were far superior in information content and required significantly less time to acquire than would have been necessary using the previous EFTEM-based technique. The Phase I 4D-STEM results were used to finalize the requirements for a new ultra-high frame-rate pixelated direct detection sensor and camera system, capable of readout at more than 100,000 frames per second (fps), that would be required to make the technique useful for large field-of-view, high-resolution multi-color EM studies of biological ultrastructure. The sensor and camera designs were progressed through completion of the architecture and schematic phases. During Phase II we will complete the development of this new ultra-fast 4D-STEM camera system, further refine edge-computing hardware and software to efficiently handle the enormous volumes of data produced, and then demonstrate multi-color EM with 4D-STEM at about 20,000 scan points per second in order to capture a full 4096 × 4096 field-of-view on a biological specimen. Multi-color EM is broadly applicable, so a lower cost and significantly more efficient system that enables this technique is easily commercially viable. An ultra-fast pixelated detector for 4D-STEM is also useful for a variety of other applications in both biological and materials science research at the nanoscale, and thus the impact of this project should extend far beyond the application of multi-color EM.