Amorphous Silicon Laid Bare | Chemical & Engineering News
Volume 90 Issue 9 | p. 52 | Concentrates
Issue Date: February 27, 2012

Amorphous Silicon Laid Bare

Computer models challenge decades-old understanding of the element’s structure
Department: Science & Technology
Keywords: silicon, electron microscopy, computational chemistry, materials science
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This TEM image shows amorphous silicon; a structural model is overlaid. The model contains ordered silicon clusters (red) in a less structured matrix (blue).
Credit: Courtesy of Michael Treacy
TEM image of amorphous silicon with the new model of its atomic structure (ball and stick). The model contains highly ordered paracrystalline structures (red) and a less-structured matrix (blue).
 
CLOSE-UP
This TEM image shows amorphous silicon; a structural model is overlaid. The model contains ordered silicon clusters (red) in a less structured matrix (blue).
Credit: Courtesy of Michael Treacy

Amorphous silicon’s atomic structure has more order to it than previously thought, according to a report (Science, DOI: 10.1126/science.1214780). The structural insights could be useful for improving solar cells or liquid-crystal displays, two of the many products for which the material has applications. Amorphous silicon is an allotrope of elemental silicon. Since the 1930s, most scientists have represented amorphous silicon’s structure by what’s called the continuous random network model, in which the silicon atoms form a disordered network and some atoms have less than fourfold coordination. The model agrees with structural data obtained by X-ray diffraction, but it isn’t consistent with data from electron microscopy. Arizona State University’s Michael M. J. Treacy and the University of Oxford’s Konstantin B. Borisenko used computer models to show that another structure—an inhomogeneous paracrystalline structure—is in better agreement with all the available data. The paracrystalline model suggests the structure consists of 1- to 2-nm ordered clusters of silicon atoms embedded in a less structured matrix of silicon atoms.

 
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