Systematic shape evolution of gold nanocrystals with sizes between 100 and 300 nm was observed in a modified polyol process. By adding a surface‐regulating polymer and foreign ions, one can readily access the distinct shapes of tetrahedron, cube, octahedron, and icosahedron (dubbed platonic nanocrystals, see picture) with high yield and good uniformity.

We describe the construction and performance of dye-sensitized solar cells (DSCs) based on arrays of ZnO nanowires coated with thin shells of amorphous Al 2 O 3 or anatase TiO 2 by atomic layer deposition. We find that alumina shells of all thicknesses act as insulating barriers that improve cell open-circuit voltage (V OC ) only at the expense of a larger decrease in short-circuit current density (J SC ). However, titania shells 10-25 nm in thickness cause a dramatic increase in V OC and fill factor with little current falloff, resulting in a substantial improvement in overall conversion efficiency, up to 2.25% under 100 mW cm -2 AM 1.5 simulated sunlight. The superior performance of the ZnO-TiO 2 core-shell nanowire cells is a result of a radial surface field within each nanowire that decreases the rate of recombination in these devices. In a related set of experiments, we have found that TiO 2 blocking layers deposited underneath the nanowire films yield cells with reduced efficiency, in contrast to the beneficial use of blocking layers in some TiO 2 nanoparticle cells. Raising the efficiency of our nanowire DSCs above 2.5% depends on achieving higher dye loadings through an increase in nanowire array surface area.

The III nitrides have been intensely studied in recent years because of their huge potential for everything from high-efficiency solid-state lighting and photovoltaics to high-power and temperature electronics. In particular, the InGaN ternary alloy is of interest for solid-state lighting and photovoltaics because of the ability to tune the direct bandgap of this material from the near-ultraviolet to the near-infrared region. In an effort to synthesize InGaN nitride, researchers have tried many growth techniques. Nonetheless, there remains considerable difficulty in making high-quality InGaN films and/or freestanding nanowires with tunability across the entire range of compositions. Here we report for the first time the growth of single-crystalline In(x)Ga(1-x)N nanowires across the entire compositional range from x=0 to 1; the nanowires were synthesized by low-temperature halide chemical vapour deposition and were shown to have tunable emission from the near-ultraviolet to the near-infrared region. We propose that the exceptional composition tunability is due to the low process temperature and the ability of the nanowire morphology to accommodate strain-relaxed growth, which suppresses the tendency toward phase separation that plagues the thin-film community.