Heteroepitaxial growth of GaP/ZnS nanocable with superior optoelectronic response.

We demonstrate the controlled growth of coaxial nanocables composed of GaP/ZnS core-shell structures by a facile chemical vapor deposition method. Structural analysis confirms that the cubic GaP (111) plane and wurtzite ZnS (0001) plane present close similarities in terms of hexagonal-arranged atomic configuration with small in-plane lattice mismatch, and the ZnS shell is epitaxially grown on the (100) plane of the cubic GaP core. Compared with the unitary ZnS nanobelts, the GaP/ZnS coaxial nanocables exhibit improved optoelectronic properties such as high photocurrent and excellent photocurrent stability. This approach opens up new strategy to boost the performance of ZnS-based photodetectors.

Surface-emitting fiber lasers.

All fiber lasers to date emit radiation only along the fiber axis. Here a fiber that exhibits laser emission that is radially directed from its circumferential surface is demonstrated. A unique and controlled azimuthally anisotropic optical wave front results from the interplay between a cylindrical photonic bandgap fiber resonator, anisotropic organic dye gain, and a linearly polarized axial pump. Low threshold (86nJ) lasing at nine different wavelengths is demonstrated throughout the visible and near-infrared spectra. We also report the experimental realization of unprecedented layer thicknesses of 29.5 nm maintained throughout meter-long fibers. Such a device may have interesting medical applications ranging from photodynamic therapy to in vivo molecular imaging, as well as textile fabric displays.

Caenorhabditis elegans glutamylating enzymes function redundantly in male mating.

Microtubule glutamylation is an important modulator of microtubule function and has been implicated in the regulation of centriole stability, neuronal outgrowth and cilia motility. Glutamylation of the microtubules is catalyzed by a family of tubulin tyrosine ligase-like (TTLL) enzymes. Analysis of individual TTLL enzymes has led to an understanding of their specific functions, but how activities of the TTLL enzymes are coordinated to spatially and temporally regulate glutamylation remains relatively unexplored. We have undertaken an analysis of the glutamylating TTLL enzymes in C. elegans We find that although all five TTLL enzymes are expressed in the embryo and adult worm, loss of individual enzymes does not perturb microtubule function in embryonic cell divisions. Moreover, normal dye-filling, osmotic avoidance and male mating behavior indicate the presence of functional amphid cilia and male-specific neurons. A ttll-4(tm3310); ttll-11(tm4059); ttll-5(tm3360) triple mutant, however, shows reduced male mating efficiency due to a defect in the response step, suggesting that these three enzymes function redundantly, and that glutamylation is required for proper function of the male-specific neurons.

The interplay of structural and optical properties in individual ZnO nanostructures.

Semiconductor nanostructures exhibit unique properties distinct from their bulk counterparts by virtue of nanoscale dimensions; in particular, exceptionally large surface area-to-volume ratios relative to that of the bulk produce variations in surface state populations that have numerous consequences on materials properties. Of the low-dimensional semiconductor nanostructures, nanowires offer a unique prospect in nanoscale optoelectronics due to their one-dimensional architecture. Already, many devices based upon individual nanowires have been demonstrated, but questions about how nano-size and structural variations affect the underlying materials properties still remain unanswered. Here, we focus on understanding the growth mechanism and kinetics of ZnO nanowires and related nanowalls, and their effects on nanoscale structural and optical properties.

Controlled growth of ternary alloy nanowires using metalorganic chemical vapor deposition.

We report the growth and characterization of ternary AlxGa1- xAs nanowires by metalorganic chemical vapor deposition as a function of temperature and V/III ratio. Transmission electron microscopy and energy dispersive X-ray spectroscopy show that, at high temperatures and high V/III ratios, the nanowires form a core-shell structure with higher Al composition in the nanowire core than in the shell. We develop a growth model that takes into account diffusion of reactants and decomposition rates at the nanowire catalyst and stem to describe the compositional difference and the shell growth rate. Utilizing this model, we have successfully grown compositionally uniform Al0.16Ga0.84As nanowires. The ability to rationally tune the composition of ternary alloy nanowires broadens the application range of nanowires by enabling more complex nanowire heterostructures.