A group of scientists has introduced a groundbreaking transmission electron microscope that operates at an incredible temporal resolution of just one attosecond, enabling them to capture the first still image of an electron in motion.
Picture having a camera so advanced that it can freeze-frame a moving electron—an entity that moves fast enough to circle the Earth numerous times in a single second. Researchers at the University of Arizona have created the fastest electron microscope in the world that can achieve this feat.
The researchers believe their innovation will usher in revolutionary changes across fields like physics, chemistry, bioengineering, and materials science.
“When you upgrade to the latest smartphone, it usually comes with an enhanced camera,” said Mohammed Hassan, an associate professor of physics and optical sciences. “Our transmission electron microscope is akin to a cutting-edge camera in the latest smartphones; it enables us to capture images of phenomena previously beyond our sight—such as electrons. We aspire to enhance the scientific community’s understanding of quantum physics and the behavior and movement of electrons with this microscope.”
Hassan spearheaded a team from the physics and optical sciences departments that published their findings in the article “Attosecond electron microscopy and diffraction” in the Science Advances journal. His collaborators included Nikolay Golubev, assistant professor of physics; Dandan Hui, co-lead author and a former research associate now at the Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences; Husain Alqattan, co-lead author, a U of A alum, and assistant professor of physics at Kuwait University; and Mohamed Sennary, a graduate student focused on optics and physics.
A transmission electron microscope is a device that allows scientists and researchers to enlarge objects millions of times their actual size, revealing details too small for standard light microscopes. Unlike conventional microscopes that use visible light, a transmission electron microscope sends beams of electrons through the sample being examined. The interaction between the electrons and the sample is captured with lenses and detected by a camera sensor, producing intricate images of the sample.
Ultrafast electron microscopes that utilize these principles were first created in the 2000s, using lasers to generate pulsed beams of electrons. This technique significantly enhances a microscope’s temporal resolution—its capability to observe changes in a sample over time. With these ultrafast microscopes, the image quality isn’t dictated by the speed of a camera’s shutter; instead, it relies on the length of the electron pulse.
The quicker the pulse, the clearer the image.
Previous ultrafast electron microscopes operated by sending a series of electron pulses at speeds reaching a few attoseconds. An attosecond is one quintillionth of a second. These rapid pulses generated a sequence of images similar to movie frames; however, scientists could not capture the reactions and transitions of an electron that occurred between those frames as it dynamically evolved. To capture a stationary electron, the U of A team successfully produced a single attosecond electron pulse, matching the speed of electron movement, thereby greatly improving the microscope’s temporal resolution, akin to how a high-speed camera can capture previously invisible movements.
Hassan and his team built upon the Nobel Prize-winning achievements of Pierre Agostini, Ferenc Krausz, and Anne L’Huilliere, who received the 2023 Nobel Prize in Physics for generating the first extreme ultraviolet radiation pulse that could be measured in attoseconds.
Using this prior work as a foundation, the U of A scientists devised a microscope where a high-powered laser is divided and modified into two sections: a rapid electron pulse and two ultra-short light pulses. The initial light pulse, termed the pump pulse, energizes the sample, causing the electrons to move or undergo other swift transformations. The second light pulse, called the “optical gating pulse,” acts similarly to a gate, establishing a brief time window for generating the single attosecond electron pulse. Consequently, the gating pulse’s speed determines image resolution. By meticulously synchronizing the two pulses, the researchers regulate when the electron pulses probe the sample, enabling the observation of ultrafast processes at the atomic level.
“The enhancement of temporal resolution in electron microscopes has long been sought after and is a central focus for many research teams—because there’s a collective desire to visualize electron motion,” Hassan stated. “These movements occur in attoseconds. But now, for the first time, we have achieved attosecond temporal resolution with our transmission electron microscope—termed ‘attomicroscopy.’ Now we can observe parts of an electron in motion.”
