Watching the nanoworld in 4-D
Caltech researchers have developed a new technique named 4-D electron microscopy to capture images of atoms in real time. They claim that their 4-D microscope will revolutionize the way we look at the nanoworld. Caltech adds that Ahmed Zewail, winner of the 1999 Nobel Prize in Chemistry, and his colleagues, have introduced the time dimension into high-resolution electron microscopy. The Caltech news release is so enthusiastic about 'this revolutionary development' that it's better to look at the technical papers published by the research team. Discover them...
You can see above what the research team dubs 'nanodrumming' of graphite, visualized with 4-D electron microscopy. (Credit: Nano Letters; images produced at Caltech, link to a larger version). "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."
And here is a description of the 4-D electron microscopy used to visualize the nanodrumming phenomenon. (Credit: Nano Letters; images produced at Caltech, link to a larger version).
This specific research work has been published in the current issue of Nano Letters under the title "Nanoscale Mechanical Drumming Visualized by 4D Electron Microscopy" (Volume 8, Issue 11, Pages 3557–3562, November 12, 2008). Here is the beginning of the abstract. "With four-dimensional (4D) electron microscopy, we report in situ imaging of the mechanical drumming of a nanoscale material. The single crystal graphite film is found to exhibit global resonance motion that is fully reversible and follows the same evolution after each initiating stress pulse. At early times, the motion appears “chaotic” showing the different mechanical modes present over the micron scale. At longer time, the motion of the thin film collapses into a well-defined fundamental frequency of 1.08 MHz, a behavior reminiscent of mode locking."
This research work has been conducted at the Caltech's Physical Biology Center for Ultrafast Science & Technology, directed by Professor Ahmed Zewail. Please look at the 4D Microscopy and Diffraction page for more information.
Now, let's return to the Caltech news release. "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."
This is what the researchers have described in an article published by Science, "4D Imaging of Transient Structures and Morphologies in Ultrafast Electron Microscopy" (Volume 322, Issue 5905, Pages 1227-1231, November 21, 2008). Here is the beginning of the abstract. "With advances in spatial resolution reaching the atomic scale, two-dimensional (2D) and 3D imaging in electron microscopy has become an essential methodology in various fields of study. Here, we report 4D imaging, with in situ spatiotemporal resolutions, in ultrafast electron microscopy (UEM). The ability to capture selected-area-image dynamics with pixel resolution and to control the time separation between pulses for temporal cooling of the specimen made possible studies of fleeting structures and morphologies. We demonstrate the potential for applications with two examples, gold and graphite."
Finally, here is a link to some short videos at Caltech about 'nano drumming' and a 'nano penguin.'
Sources: Caltech news release, November 20, 2008; and various websites
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