Taking images of individual atoms in color
Researchers at Cornell University are using a new kind of scanning transmission electron microscope (STEM) to take pictures of individual atoms in color for the first time. It seems odd, but 'the current generation of electron microscopes can be thought of as expensive black and white cameras where different atoms appear as different shades of gray,' said one of the researchers. This new microscope incorporates new aberration-correction technology and can deliver images in about 30 seconds, 50 to 100 times faster than in conventional STEMs. But read more...
As you can see on the left, this microscope doesn't look like the one you received for Christmas when you were a kid. And it costs considerably more... (Credit: NION). This microscope has been developed by the NION Company of Kirkland, Washington. As states this page, the NION's UltraSTEM has produced atomic-resolution elemental maps in less than a minute. for more information about this microscope, you can read An electron microscope for the aberration-corrected era, a technical paper published in Ultramicroscopy, an Elsevier journal (PDF format, 17 pages, 1.22 MB).
Now, let's go back to the researchers who are using this microscope for their research. They include David Muller, Cornell associate professor of applied and engineering physics and his research group, as well as John Silcox, professor of engineering at Cornell and his research group. Ondrej Krivanek of NION was also involved in the project with other scientists from Japan and South Korea.
After introducing the researchers, what will they be doing with such a microscope? "It allows scientists to peer inside a material or a device and see how it is put together at the atomic scale where quantum effects dominate and everyday intuition fails. One of the most important applications of the new instrument will be to conduct what Silcox calls 'materials pathology' to aid researchers in their development of new materials to use in electronic circuits, computer memories and other nanoscale devices. 'We can look at structures people have built and tell them if they've built what they thought they did,' Silcox explained."
And I guess you all want to know how a STEM works. It "shoots an electron beam through a thin-film sample and scans the beam across the sample in subatomic steps. In addition to forming an image, the new microscope can identify atoms in its path by a process called electron energy-loss spectrometry. Atoms in the path of the beam absorb energy from some of its electrons to kick their own electrons into higher orbits. The amount of energy this takes is different for each kind of atom. The detector that collects electrons emerging from the sample measures the energy losses, and from this the atoms in the path of the beam can be identified. The detector can simultaneously produce multiple images -- one for every different species of atom in the sample, and these can be color-coded, each color representing a different electron energy signature."
Finally, this research work has been published in Science under the title "Atomic-Scale Chemical Imaging of Composition and Bonding by Aberration-Corrected Microscopy" (Volume 319, Issue 5866, Pages 1073-1076, February 22, 2008). Here are two links to the abstract and to the figures illustrating the artticle.
Sources: Cornell University news release, via EurekAlert!, February 21, 2007; and various websites
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