Ion-beam “photography”

Many of the beautiful colors in stained glass windows are the result of light scattering off metal or oxide nanoclusters dispersed in the material. However, the mechanism of nanocluster formation is usually obscured in the complexities of glass chemistry. Now, researchers at the Universities of Orsay and Paris, collaborating with glass experts, have found that by shooting MeV ions into a room-temperature glass containing a metal oxide, they can nucleate and control the density of pure metal nanoclusters. The nucleation requires exceeding a threshold of energy going into electron motion in the glass. Moreover, the nanoclusters grow only upon subsequent heating of the sample, allowing control over their size, and all the clusters grow simultaneously. This is analogous to the photographic process, with ions replacing photons, metal oxide in the glass replacing metal-containing salts in the emulsion, and heat replacing the developer. The ion-beam method allows the density of nucleation sites to be predicted precisely, and standard lithographic techniques could be used to design spatial patterns of clusters, leading to applications in optoelectronics. (E. Valentin et al., Phys. Rev. Lett. 86, 99, 2001 http://dx.doi.org/10.1103/PhysRevLett.86.99 .)