Focus: Atoms in 3D

Phys. Rev. Focus 7, 10
Pairs of atomic-scale images made from photoelectron diffraction with circularly polarized light can be merged into a stereoscopic, 3D view.
Figure caption
Phys. Rev. Lett. 86, 2034 (2001)
Two points of view. Pairs of atomic-scale images made from photoelectron diffraction with left and right circularly polarized light can be merged into a stereoscopic, 3D view (tungsten crystal shown here).

What do The Creature From the Black Lagoon and atomic microscopy have in common? More than you might think, according to a paper in the 5 March PRL. A Japanese physicist proposes a method for creating three-dimensional images of atoms by applying the same stereoscopic techniques used to make 3D pulp-fiction movies. Unlike other methods that require complex calculations, the process is simple, fast, and might even someday allow for real-time 3D video of atoms and molecules.

Since the early 20th century, researchers have learned about atomic arrangements using diffraction–the scattering of x rays and electrons from crystals. But the traditional methods can be tedious and require many trial-and-error calculations. Within the past 15 years, physicists have developed several more direct techniques. One scheme, called photoelectron diffraction, uses high energy photons to knock electrons loose inside the sample. These electrons then pass through the sample and generate a diffraction pattern. Some researchers believe that the peaks in the diffraction pattern can be related directly to the distance between the emitter and scattering atoms. This means that the structure of the crystal can be obtained directly from diffraction data, without more complex analysis.

For several years, Hiroshi Daimon of the Nara Institute of Science and Technology in Japan has studied an unusual feature of photoelectron diffraction. He has bombarded his samples with circularly polarized light, which contains photons with spin angular momentum. This angular momentum is transferred to the electrons and changes their trajectories, creating a diffraction pattern that is rotated slightly–either clockwise or counter-clockwise, depending on the light’s direction of rotation.

Inspired by 3D stereograms in magazines, Daimon came up with a use for this phenomenon. Stereograms require a pair of colored glasses to separate blue and red images and create a three-dimensional illusion. It turns out that the equations for stereoscopic images are similar to those for circularly polarized photoelectron diffraction. Just as the blue and red images each illustrate a scene from a slightly different point-of-view, the two diffraction patterns represent slightly different views of a crystal. Daimon demonstrated the technique by making a stereoscopic pair of images of the atoms inside a tungsten crystal.

But Brian Tonner of the University of Central Florida in Orlando is uncertain whether such a technique could truly work. “The notion that a diffraction pattern like this can be interpreted in terms of real space and time positions is still under scientific debate,” he says. Still, Tonner concedes, it is not implausible that this technique could work and, because it is so simple, could even permit real time imaging of molecules, a prospect that he describes as “very exciting.”

–Geoff Brumfiel

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