Traditionally, scanning transmission electron microscopes (STEMs) use a highly focused beam of electrons across samples, creating images point by point. At each point, the beam pauses for a fixed time to accumulate signals, similar to cameras using photographic film. This conventional method risks excessive irradiation that may damage or destroy samples.
The new method rethinks the fundamental logic of imaging. Instead of observing over a fixed time and measuring detected "events" as electrons scatter from different sample parts, the team developed an event-based detection system. They measure the varying time taken to detect a set number of events.
Both methods provide equivalent "detection rate" image contrast, but the new theory shows that the first electron detected at each point provides significant information, while subsequent electron hits offer diminishing returns. Each electron on the specimen poses a damage risk.
The new method allows "shutting off" illumination at the peak of imaging efficiency, requiring fewer electrons to build a high-quality image.
The team patented a technology (Tempo STEM) jointly with IDES Ltd. to implement this method. This technology combines a high-tech "beam blanker" to shutter the beam once the desired precision at each measurement point is achieved.
Dr. Lewys Jones, Ussher Assistant Professor in Trinity College Dublin's School of Physics, Royal Society-Science Foundation Ireland University Research Fellow, and Funded Investigator in AMBER, the SFI Centre for Advanced Materials and Bioengineering Research, led the research. He said, "Combining two already state-of-the-art technologies in such an exciting way delivers a real leap in the microscope's capabilities. Giving microscopists the ability to 'blank' or 'shutter' the electron beam on and off in a matter of nanoseconds in response to real-time events has never been done before."
"Our approach reduces the overall dose of radiation needed to produce high-quality images, eliminates the excess dose that was only providing diminishing returns, and avoids causing unnecessary damage to the sample."
Dr. Jon Peters, Trinity, first author of the work, commented, "We tend to think of electrons as relatively mild from a radiation perspective, but when they are fired at a tiny biological sample at speeds of around 75% the speed of light, it's no surprise that they damage these samples. This has been a major issue for microscopy, as the images you get back could be unusable, or worse, misleading. This is obviously problematic if you need to make decisions on future battery materials or catalyst development."
Research Report:Event-responsive scanning transmission electron microscopy
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