http://mr.caltech.edu/media/Press_Releases/PR13207.htmlCaltech 4D Microscope Revolutionizes the Way We Look at the Nano World
PASADENA, Calif.-- 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. (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.
Nanodrumming of graphite, visualized with 4D microscopy. (Nano Letters; image produced at Caltech)
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."
Scientists can observe the static structure of objects with a resolution that is better than a billionth of a meter in length using electron microscopes, which generate a stream of individual electrons that scatter off objects to produce an image. Electrons are used to visualize the smallest of objects, on the atomic scale, because the wavelength of the radiation source used by a microscope must be shorter than the space between the atoms. This can be accomplished using electrons, and in particular--because the wavelength of an electron shrinks as its velocity increases--by electrons that have been accelerated to dizzying speeds.
But just having electrons isn't sufficient to capture the behavior of atoms in both space and time; the electrons have to be carefully doled out, so that they arrive at the sample at specific time intervals. Zewail and his colleagues have achieved this by introducing the fourth dimension of time into high-resolution electron microscopy, in what has been termed ultrafast "single-electron" imaging, where every electron trajectory is precisely controlled in time and space.
The resulting image produced by each electron represents a femtosecond still at that moment in time. Like the frames in a film, the sequential images generated by many millions of such images can be assembled into a digital movie of motion at the atomic scale....
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