A true atomic movie shot by pulse twins with a giant X-ray laser
How do atoms move when a liquid flows or a hot glass changes shape? Their motion happens so quickly in a seemingly random manner. Yet researchers have now built a giant X-ray laser to take successive shots so quickly and precisely that it can record atoms as they drift. A story from Shuai Wei and colleagues first published in Aktuel Naturvidenskab.
In many materials, atoms are arranged in regular, repeating patterns, making them easier to study. In contrast, among the many examples of complex matter, glasses and liquids stand out. Their atoms are not ordered but instead are arranged in irregular ways and are constantly moving. In science, “glass” refers not only to transparent window glass or smartphone displays, but also broadly to many types of amorphous solids: metallic glasses, polymers, chalcogenide glasses, organic systems, and even amorphous ice. In fact, the latter is believed to be the most common form of water in the universe. As a result, this lack of structure makes it difficult to describe how these materials behave, even though they are widely used in everyday technologies.
Understanding Atomic Motion
To truly understand these materials, scientists need to observe how atoms are arranged and how they move over time. Therefore, researchers must use tools that act like ultra-fast cameras capable of resolving individual atoms. These cameras must also capture motion on extremely short timescales. To shoot a true atomic movie, we need a special camera with an extraordinarily fast “shutter”. In particular, two requirements are essential: (1) spatial resolution fine enough to see individual atoms, and (2) exposure times short enough to take two consecutive snapshots less than 10⁻¹² seconds apart, capturing atomic motion in progress.
An Ultra-Fast X-ray Camera
X-ray free-electron lasers, known as XFELs, make this possible. These large research facilities generate intense pulses of X-rays with wavelengths small enough to probe atomic structures. For example, in crystalline materials, where atoms are arranged in regular patterns, standard X-ray techniques work well because the repeating structure produces clear and predictable signals. However, in disordered materials like glass or liquids, this regularity is missing. As a result, the signals become more complex and much harder to interpret.
To address this challenge, researchers use coherent X-rays, where the light waves are perfectly synchronized. In this way, they can capture detailed, speckle-like patterns that act as fingerprints of the atomic arrangement, making it possible to study even highly disordered systems.
Capturing Motion with Pulse Twins
To track motion, scientists split a single X-ray pulse into two closely spaced pulses. First, one pulse interacts with the material, and then the second follows shortly after. Each pulse interacts with the material at a slightly different time, allowing researchers to take two snapshots in rapid succession. By comparing these images, they can follow how atoms rearrange on timescales of trillionths of a second.
Using this approach, researchers have now demonstrated the first steps toward creating “movies” of atomic motion in disordered materials. Interestingly, their results show that even in systems that appear random, atoms still form short-range structures over small distances. Moreover, these local arrangements constantly form and disappear, sometimes within less than a trillionth of a second.
What Comes Next
Although current experiments are still limited to only a few frames, the work represents an important breakthrough. Looking ahead, future XFEL facilities are expected to deliver faster measurements, more data, and improved sensitivity. This means that scientists will be able to follow atomic motion in much greater detail and over longer periods of time.
Understanding how atoms move in disordered materials is more than a fundamental challenge. Ultimately, it could help guide the design of advanced materials for energy storage, electronics, and sustainable technologies. In this way, by revealing the hidden dynamics inside these systems, X-ray lasers are bringing researchers closer to controlling materials at the most fundamental level.
More information
Read the full news article in Aktuel Naturvidenskab (in Danish).
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