A new microscope may facilitate nanotech developments by combining nanometer scale spatial resolution with temporal resolution in the millisecond to femtosecond range. ScienceDaily brings us this news release from Caltech: “Caltech 4D Microscope Revolutionizes the Way We Look at the Nano World“:
More than a century ago, the development of the earliest motion picture technology made what had been previously thought “magical” a reality: capturing and recreating the movement and dynamism of the world around us. A breakthrough technology based on new concepts has now accomplished a similar feat, but on an atomic scale–by allowing, for the first time, the real-time, real-space visualization of fleeting changes in the structure and shape of matter barely a billionth of a meter in size.
Such “movies” of atomic changes in materials of gold and graphite, obtained using the technique, are featured in a paper appearing in the November 21 issue of the journal Science [abstract]. (4D microscopy videos can be viewed at http://ust.caltech.edu/movie_gallery/.) A patent on the conceptual framework of this approach was granted to the California Institute of Technology (Caltech) in 2006.
The new technique, dubbed four-dimensional (4D) electron microscopy, was developed in the Physical Biology Center for Ultrafast Science and Technology, 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–atoms uniting into molecules, then breaking apart back into atoms–occurring at the timescale of the femtosecond, or one millionth of a billionth of a second. The work “captured atoms and molecules in motion,” Zewail says, akin to the freeze-frame stills snapped by 19th-century photographer Eadweard Muybridge of a galloping horse (which proved for the first time that a horse does indeed lift all four hooves off the ground as it gallops) and other moving objects.
Snapshots of molecules in motion “gave us the time dimension,” Zewail says, “but what we didn’t have was the dimensions of space, the structure. We didn’t know what the horse looked like. Did it have a long tail? Beautiful eyes? My dream since 1999 was to come up with a way to look not just at time but also at the spatial domain; to see the architecture of a complex system at the atomic scale, as it changes over time, be it for physical or biological matter.”
…As reported in the Science paper, Zewail and colleagues applied their new 4D electron microscopy to observe the behavior of the atoms in superthin sheets of gold and graphite. Graphite, the material in pencils, consists of layers of carbon atoms locked into a sheet-like array. The atoms move in a unique and coherent way on the femtosecond timescale.
However, the researchers found that on a slightly longer, picosecond (one thousandth of a billionth of a second) scale, the graphite nanosheets produce sound waves. In the images, they directly visualized the elastic movements of the sheets and determined the force holding them together, which is described by a stress-strain property known as “Young’s modulus.” The 4D movies produced from the frames revealed the behavior in space and time.
In a second paper in the current issue of the journal Nano Letters [abstract], Zewail and his colleagues described their visualization of the changes in a nanometer-thick graphite membrane on a longer time scale, up to a thousandth of a second. The researchers first blasted the sample with a pulse of heat. The heated carbon atoms began to vibrate in a random, nonsynchronized fashion. Over time, however, the oscillations of the individual atoms became synchronized as different modes of the material locked in phase, emerging to become a heartbeat-like “drumming.” Digital video, slowed down more than a billion times, illustrates this nano-drumming mechanical phenomenon, which displays a well-defined resonance that is nearly 100 times higher than can be detected by the human eardrum.
—Jim
