This image might look like an impressionist sunset, but it is actually a vector map of the measured deflections of an atomic-sized electron beam scanned across different polar domains in the ferroelectric bismuth ferrite. The image was recorded in about a minute by the new electron microscope pixel array detector.Image courtesy of: Cornell University
The Science
At Cornell University, the Sol M. Gruner (SMG) detector group has developed and demonstrated a new type of imaging electron detector that records an image frame in 1/1000 of a second, and can detect from 1 to 1,000,000 electrons per pixel. This is 1000 times the intensity range, and 100 times the speed of conventional electron microscope image sensors.
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The Impact
Capture of all the transmitted electrons allows quantitative measurement of materials properties, such as internal electric and magnetic fields, which are important for use of the materials in memory and electronics applications.
Summary
At Cornell University, we developed and tested a new detector for electron microscopes that enables quantitative measurements of electric and magnetic fields from micrometers down to atomic resolution. The device is an adaptation of a solid-state x-ray detector technology we have developed over the last fifteen years, now modified to function as a high-speed, high dynamic range electron diffraction camera. Dynamic range denotes the maximum range of signals that can be detected by a pixel. The resulting electron microscope pixel array detector records an image frame in under a millisecond, and can detect from 1 to 1,000,000 primary electrons per pixel per image frame. This is 1000 times the dynamic range, and 100 times the speed of conventional electron image sensors. These properties allow us to record the entire unsaturated diffraction pattern in scanning mode, and simultaneously capture bright field, dark field, and phase contrast information, as well as analyze the full scattering distribution, opening the way for new multichannel imaging modes. From the analysis of the spatially resolved diffraction patterns, we can extract local strains, tilts, rotations, polarity, and even electric and magnetic fields.
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Funding
Pixel array detector (PAD) development in SMG’s lab is supported by the U.S. Department of Energy (DOE), Office of Science (SC), grant DE-FG02-10ER46693 and by the Cornell High Energy Synchrotron Source (CHESS), which is supported by the National Science Foundation (NSF) and the National Institutes of Health (NIH) National Institute of General Medical Sciences via grant DMR-1332208. The PAD architecture used was developed as an x-ray detector over the last decade and a half as a collaboration between SMG’s group and Area Detector Systems Corp. (Poway, CA) under NIH grant R44 RR014613 and DOE/SC grant DE-FG02-97ER62443.
The adaptation of the x-ray PAD to the scanning transmission electron microscope (STEM) was supported by the Kavli Institute at Cornell for Nanoscale Science.
Electron microscope data acquisition (KXN, DAM) was supported by the Cornell Center for Materials Research, an NSF Materials Research Science and Engineering Center (MRSEC) under grant DMR-1120296.
Paul Fischione of Fischione Instruments provided the base annular dark field detector housing.
Publications
M. W. Tate, P. Purohit, D. Chamberlain, K. X. Nguyen, R. M. Hovden, C. S. Chang, P. Deb, E. Turgut, J. T. Heron, D. G. Schlom, D. C. Ralph, G. D. Fuchs, K. S. Shanks, H. T. Philipp, D. A. Muller, and S. M. Gruner, "High Dynamic Range Pixel Array Detector for Scanning Transmission Electron Microscopy". Microscopy and Microanalysis 22, 237-249 (2016). [DOI: 10.1017/S1431927615015664].
