Natural porous materials such as bone, wood and pith evolved to maximize modulus for a given density. For these three-dimensional cellular solids, modulus scales quadratically with relative density. But can nanostructuring improve on Nature's designs? Here, we report modulus-density scaling relationships for cubic (C), hexagonal (H) and worm-like disordered (D) nanoporous silicas prepared by surfactant-directed self-assembly. Over the relative density range, 0.5 to 0.65, Young's modulus scales as (density)n where n(C)

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The optical properties of solution-grown ZnO nanorods were investigated using photoluminescence and cathodoluminescence. The as-grown nanorods displayed a broad yellow-orange sub-band-gap luminescence and a small near-band-gap emission peak. The sub-band-gap luminescence can only be observed when exciting above band gap. Scanning cathodoluminescence experiments showed that the width of the sub-band-gap luminescence is not due to an ensemble effect. Upon reduction, the sub-band-gap luminescence disappeared and the near-band-gap emission increased. Compared to ZnO powders that are stoichiometric and oxygen deficient, we conclude that the yellow-orange sub-band-gap luminescence most likely arises from bulk defects that are associated with excess oxygen.

We present persistence data from the 5D manifolds of europium (3+)-activated Y2O3, after excitation by ultraviolet photons. For europium concentrations below 1 at. %, the persistence is largely consistent with multiphonon relaxation. For europium concentrations at and above 1 at. %, the persistence shows evidence for energy transfer interactions between europium activators. Interactions involving one activator in an upper (5D3, 5D2 or 5D1) manifold and another in a ground state (7F) manifold affect the kinetics of the relaxation of the upper 5D manifolds but do not degrade phosphor efficiency. Interactions involving two activators in excited manifolds ultimately dissipate, by phonon emission, excitation that might be emitted as photons. The interactions involving two activators in excited manifolds appear to be related to both concentration quenching and the reduction of phosphor efficiency at high excitation density.

Nanostructural characterization of amorphous diarnondlike carbon (a-C) films grown on silicon using pulsed-laser deposition (PLD) is correlated to both growth energetic and film thickness. Rarnan spectroscopy and x-ray reflectivity probe both the topological nature of 3-and 4-fold coordinated carbon atom bonding and the topographical clustering of their distributions within a given film. In general, increasing the energetic of PLD growth results in films becoming more "diarnondlilce", i.e. increasing mass density and decreasing optical absorbance. However, these same properties decrease appreciably with thickness. The topology of carbon atom bonding is dfferent for material near the substrate interface compared to material within the bulk portion of an a-C film. A simple model balancing the energy of residual stress and the free energies of resulting carbon topologies k proposed to provide an explanation of,thg evolution of topographical bonding clusters in a growing a-C film.