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Variable temperature photoluminescence of ZnO thin films deposited by a reactive laser ablation of metallic zinc was investigated. Free and bound exciton emissions are absent at cryogenic temperature, and the near band edge (NBE) emission is independent of measurement temperature for the ZnO thin film deposited at room temperature. Annealing at 700 °C results in the removal of defects, reappearance of exciton emission, and a temperature dependent NBE emission. The experimental data suggest that defects play an important role in the band edge emission in terms of both spectra shape and temperature dependence. Our observations will have an impact on device applications using ZnO, especially for optoelectronics that utilizes the exciton emission. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotubes have been modified using dodecanethiol as the reaction agent. The thiolated nanotubes form a stable suspension in toluene, and can be used for Langmuir-Blodgett deposition of monolayers. The nanotube conductance decreases by three orders of magnitude and acquires a gate dependence with a memory effect. The conductance for the on and off states with 0 V applied to the gate differs by more than two orders of magnitude. These effects are explained in terms of a chemical reaction between the tube wall and the thiol. The thiolation process is also observed on the exposure of the nanotubes to toluene solutions of dodecanethiol-stabilized Au nanoparticles. The nanoparticles can thus be used for labeling or manipulating the location of the chemical reaction sites on the tube wall. The reaction is followed using optical-absorption measurements. [ABSTRACT FROM AUTHOR]

Structural, optical, and field-emission properties of ZnO nanowire arrays grown at 90 °C are investigated. Single-crystalline ZnO nanowires with low level of oxygen vacancies are obtained at low temperatures. The nanowire growth is strongly dependent on the seeding method used but independent of the substrate materials, which enable large scale growth of ZnO arrays on all kinds of substrates including polymers. We have demonstrated stable electron emission at low-field strengths for nanowires grown on polystyrene and polyethylene foils, making them promising candidates for fabrication of flexible cold cathodes. Deposition of a few nanometers of gold on ZnO nanowires significantly lowers the field required for electron emission, which is explained in terms of additional field enhancement from Au islands on top of the ZnO nanowires. [ABSTRACT FROM AUTHOR]

Fe50Ni50 thin films were prepared by dc magnetron sputtering with a field of ∼40 mT applied parallel to the plane of the film. The microstructure and magnetic anisotropy of the films have been studied as a function of film thickness, which was varied from 13–1100 nm. Vibrating sample magnetometer and magnetic force microscope measurements show that only the very thinnest films (13 nm) showed an out-of-plane magnetic component. The in-plane anisotropy strongly depended on the thickness of the film: films with thickness of <=20 nm were magnetically isotropic with perfectly square B-H loops; when the thickness increased to 30 nm, the film began to show in-plane anisotropy with the magnetic easy axis parallel to the direction of the magnetic field applied during sputtering. The easy axis direction was confirmed by both magneto-optic Kerr effect and B-H loop tracer measurements. [ABSTRACT FROM AUTHOR]

Lower Eocene flowers with Pistillipollenites macgregorii pollen represent the earliest megafossil evidence of the Gentianaceae. The Paleocene occurrence of P. macgregorii, the fossil's modern floral structure, and suggested trends in the evolution of pollen in the Gentianaceae indicate a considerably earlier origin for the family. Floral morphology typical of bee-pollinated flowers provides the earliest, albeit indirect, fossil evidence of bees.