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Single metal nanoparticles and nanoaggregates are known to emit intense bursts of surface-enhanced Raman scattering (SERS) in an intermittent on and off fashion. The characteristic "blinking" timescales range from milliseconds to seconds. Here we report detailed temperature dependence (both heating and cooling) and light-intensity studies to further examine the origins of this intriguing phenomenon. The results indicate that blinking SERS contains both a thermo-activated component and a light-induced component. Several lines of evidence suggest that the observed fluctuations are caused by thermally activated diffusion of individual molecules on the particle surface, coupled with photo-induced electron transfer and structural relaxation of surface active sites or atomic-scale roughness features.

Novel open-framework alkali metal uranyl periodates, having the formula A[(UO2)3(HIO6)(OH)(O)(H2O)].1.5H2O (A = Li, Na, K, Rb, Cs), have been prepared through mild hydrothermal synthesis. These isostructural compounds contain distorted UO7 pentagonal bipyramids that are linked through a uranyl (UO22+) to uranyl cation-cation interaction. This interaction arises from a single axial uranyl oxygen coordinating at an equatorial site of an adjacent uranyl unit. These uranium oxide polyhedra are further bound by IO6 distorted octahedra creating an open-framework structure whose channels contain the alkali metal cations.

An increase in the concentration of K + in denned seawater medium induces settlement and metamorphosis in larvae of the marine molluscs Phestilla sibogae, Haliotis rufescens, and Astraea undosa, and in larvae of the marine annelid Phragmatopoma californica. The effect is dose-dependent, optimal at approximately double the normal concentration of K + in seawater, and specific for the K + ion. The ability of K + to directly influence cell membrane potential is proposed as an explanation for its broad effectiveness as a metamorphic inducer for larvae that recruit to different habitats. Depolarization of externally accessible, excitable cells thus is suggested to be a mechanism common to the induction of settlement and metamorphosis of a number of species. For Phestilla and Haliotis, the inductive effect of excess K + is additive with that of the substratum-derived inducers or analogs. The sensitivity of induction by K + to external tetraethylammonium (TEA, a K + -channel blocker) reported previously for Haliotis (Baloun and Morse, 1984) is not present in Phestilla or Phragmatopoma. Results presented here indicate that the addition of excess K + may provide a widely useful technique for inducing metamorphosis, and for analyzing the mechanisms which govern this process, in other marine invertebrate larvae.