CONTACT:
Chris Chandler at (847) 491-3115 or e-mail at [email protected]
FOR RELEASE: Immediate
CLEAREST IMAGES TO DATE OF SILICON SURFACE
EVANSTON, Ill. --- Silicon is one of the most common elements on earth, and yet its surface structure is probably the most complicated of all --- a three-layered geometric construction of atoms with tiny holes at its peaks.
Researchers at Northwestern University and the NEC Corporation in Japan have made the clearest images to date of this complex surface. Using a High Resolution Electron Microscope (HREM), the researchers have developed images that reveal a beautiful symmetry when the jagged surface is seen from above.
"These images are the first to show all three levels of atoms at the same time," said Lawrence Marks, professor of materials science and engineering at the McCormick School of Engineering at Northwestern University. "They are the clearest and most detailed images to date of the surface of silicon," he added.
The images, which first appeared in Physical Review Letters, will be displayed this fall as part of a permanenet exhibition at the Research Institute of Discrete Mathematics at the University of Bonn.
The images also confirm the model of the surface's structure first proposed by K. Takayanagi and associates in 1985. That model describes a basic unit of 112 atoms arranged in a parallelogram of three layers, with 12 atoms on the top layer which all rest on atoms in the next two layers. These 12 atoms appear as black in the High Resolution Electron Microscope (HREM) imagery. -more-
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There are only a handful of such microscopes now in use, with one at Northwestern and a second at the Fundamental Research Labs of the NEC Corp. in Tsukuba, Japan. The more common Scanning Tunneling Microscope (STM) uses low-energy electrons to generate images of surfaces.
The HREM uses high-energy electrons, and, as these images demonstrate, is capable of providing the most detailed information about the surfaces of materials.
Marks and his team of researchers used noise reduction filters to clarify the images originally obtained in Japan and transmitted via the internet to his lab in Evanston, Illinois. His Japanese collaborators, were T. Ichihashi, P.M. Ajayan and S. Iijima. Also contributing were graduate students E. Bengu and R. Plass.
The wealth of detail provided by HREM can be clearly seen when the images are compared with images obtained with scanning tunneling microscopes. -30- 2/18/97 (Marks can be reached at (847) 491-3996 or by e-mail at [email protected]) (Chandler can be reached at (847) 491-3115 or e-mail [email protected])
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