Silicon cage clusters

Silicon is a vital material for the vast semiconductor industry and is one of the most studied elements in all of science. Unlike pure carbon, which can form C₆₀ buckyballs, pure Si cannot form stable, closed cages. Nevertheless, researchers at the Joint Research Center for Atom Technology in Japan have managed to create just such configurations of Si atoms, but with lone transition metal atoms trapped inside. In fact, the experimentalists found that a metal ion served as a reaction site, nucleating a cluster of Si atoms until it was completely covered. The number of Si atoms that formed the cage cluster depended on the chemical identity of the metal atom. For example, hafnium was stably surrounded by 14 Si atoms, tantalum by 13, tungsten by 12, rhenium by 11, and iridium by 9. The remarkable stability of these compounds could allow them to be used as tunable building blocks for new nanostructures. The scientists note in particular that the cage clusters efficiently isolate their guest metal atoms from the surrounding environment, a characteristic that could make them useful in a quantum computer, where a cluster could store a single bit of information in the spin state of the enclosed metal atom. (H. Hiura et al., Phys. Rev. Lett. 86 , 1733, 2001 http://dx.doi.org/10.1103/PhysRevLett.86.1733 .)