Ultrasmall Metal Clusters Act Metallic | February 7, 2011 Issue - Vol. 89 Issue 6 | Chemical & Engineering News
Volume 89 Issue 6 | p. 27 | Concentrates
Issue Date: February 7, 2011

Ultrasmall Metal Clusters Act Metallic

Bucking prior theory, sodium clusters with as few as three atoms have metallic character analogous to bulk metals
Department: Science & Technology
Keywords: metal cluster, dipole moment, superatom, electric field

Metal clusters with as few as three atoms have metallic character analogous to bulk metals, according to experiments done at Georgia Institute of Technology (Phys. Rev. Lett., DOI: 10.1103/physrevlett­.106.043401). A classical metal is one that can’t support an internal electric field and therefore has no permanent electric dipole moment. Theoretical analysis had predicted that small clusters would show a dipole moment and therefore should not be considered metallic, even for a traditional metal such as sodium. John Bowlan, Anthony Liang, and Walter A. de Heer evaluated the dipole moments of sodium clusters by measuring how molecular beams of clusters were deflected by an electric field. They found that the theory had “vastly overestimated” cluster dipole moments, de Heer says. Instead, even three-atom clusters show almost entirely metallic character. The team has observed similar results for other elements and even for mixed-element clusters. As with molecules, dipole moments play a role in cluster chemistry. The inability of theory to predict such properties would therefore affect modeling of cluster catalysis and the behavior of superatoms, which are molecules or collections of atoms that act like single atoms, de Heer adds.

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