Often advances in science go hand-in-hand with advances in scientific instrumentation. The ability to capture atoms in motion, that is, images at the atomic level over a period of time, is a major advancement. The achievement required combining the power of a conventional three-dimensional electron microscope with the ability to capture the images in an extremely short interval (in a phrase, the world’s fastest movie camera).

One of the main problems with capturing atomic level images is motion. The problem is not much different than capturing images of anything moving rapidly, a speeding bullet or a running athlete. If the interval of exposure for the image isn’t short enough, there will be blurring. Of course, with atoms in motion the speed, distance, and corresponding interval of exposure must be incredibly short. In fact, it’s usually measured in femtoseconds (one millionth of a billionth of a second).

Four-dimensional (4D) microscopy—the methodology upon which the new techniques were based—was developed at Caltech’s Physical Biology Center for Ultrafast Science and Technology. The center is directed by Ahmed Zewail, the Linus Pauling Professor of Chemistry and professor of physics at Caltech, and winner of the 1999 Nobel Prize in Chemistry.

Zewail was awarded the Nobel Prize for pioneering the science of femtochemistry, the use of ultrashort laser flashes to observe fundamental chemical reactions occurring at the timescale of the femtosecond (one-millionth of a billionth of a second). The work “captured atoms and molecules in motion,” Zewail says, but while snapshots of such molecules provide the “time dimension” of chemical reactions, they don’t give the dimensions of space of those reactions—that is, their structure or architecture.

Zewail and his colleagues were able to visualize the missing architecture through 4D microscopy, which employs single electrons to introduce the dimension of time into traditional high-resolution electron microscopy, thus providing a way to see the changing structure of complex systems at the atomic scale.

[Source: EurekAlert]

One way of looking at the new techniques is to think of the stream of electrons beamed at the target material as ‘lighting’. Traditional ‘lighting’ for an electron microscope is continuous. It can illuminate the shape of atoms (the traditional three dimensions) but does not help with atoms in motion. The researchers’ innovation was to create a different source of ‘lighting’ in the form of electron pulses generated by a wafer of crystalline silicon struck by extremely short pulse of laser light. The resulting femtoseconds pulse of ‘lighting’ captures the motion of the atoms without blurring. This is much like photographers using a sequence of flash exposures to capture motion. The series of images can then be played-back and just like a motion-picture, providing a view of the motion of atoms.

There are a great many potential applications for this technique, not the least of which is fundamental research into the behavior of atoms under various conditions.