Amorphous Silicon Laid Bare

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.