The optical and structural properties of high-quality single-crystal epitaxial MgZnO films deposited by pulsed-laser deposition were studied. In films with up to ∼36 at. % Mg incorporation, we have observed intense ultraviolet band edge photoluminescence at room temperature and 77 K. The highly efficient photoluminescence is indicative of the excitonic nature of the material. Transmission spectroscopy was used to show that the excitonic structure of the alloys was clearly visible at room temperature. High-resolution transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectroscopy/ion channeling were used to verify the epitaxial single-crystal quality of the films and characterize the defect content. Post-deposition annealing in oxygen was found to reduce the number of defects and to improve the optical properties of the films. These results indicate that MgZnO alloys have potential applications in a variety of optoelectronic devices.

Nitrogen-rich transition-metal nitrides hold great promise to be the next-generation catalysts for clean and renewable energy applications. However, incorporation of nitrogen into the crystalline lattices of transition metals is thermodynamically unfavorable at atmospheric pressure; most of the known transition metal nitrides are nitrogen-deficient with molar ratios of N:metal less than a unity. In this work, we have formulated a high-pressure route for the synthesis of a nitrogen-rich molybdenum nitride through a solid-state ion-exchange reaction. The newly discovered nitride, 3R-MoN2, adopts a rhombohedral R3m structure, isotypic with MoS2. This new nitride exhibits catalytic activities that are three times more active than the traditional catalyst MoS2 for the hydrodesulfurization of dibenzothiophene and more than twice as high in the selectivity to hydrogenation. The nitride is also catalytically active in sour methanation of syngas with >80% CO and H2 conversion at 723 K. Our formulated route for the synthesis of 3R-MoN2 is at a moderate pressure of 3.5 GPa and, thus, is feasible for industrial-scale catalyst production.

No abstract

Indices of refraction for Mg x Zn 1Ϫx O epitaxial films grown by pulsed-laser deposition on sapphire substrates with x up to 0.36 were determined in the range of wavelength 457-968 nm by analysis of optical transmission spectra and prism-coupled waveguide measurements. The dispersion follows the first-order Sellmeier dispersion equation. Absorption coefficients, exciton energy gaps, and binding energies of Mg x Zn 1Ϫx O alloys were determined by transmission spectroscopy. The excitonic absorption features were clearly visible at room temperature despite alloy broadening. These results provide important information for the design and modeling of ZnO/MgZnO heterostructure optoelectronic devices.

This article describes the design of a new and attractive minimally-invasive bicomponent microneedle sensing device for the electrochemical monitoring of the excitatory neurotransmitter glutamate and glucose. The new device architecture relies on the close integration of solid and hollow microneedles into a single biosensor array device containing multiple microcavities. Such microcavities facilitate the electropolymeric entrapment of the recognition enzyme within each microrecess. The resulting microneedle biosensor array can be employed as a minimallyinvasive on-body transdermal patch, obviating the extraction/sampling of the biological fluid, thereby simplifying device requirements. The new concept is demonstrated for the electropolymeric entrapment of glutamate oxidase and glucose oxidase within a poly(o-phenylenediamine) (PPD) thin film. The PPD-based enzyme entrapment methodology enables the effective rejection of coexisting electroactive interferents without compromising the sensitivity or response time of the device. The resulting microneedle-based glutamate and glucose biosensors thus exhibit high selectivity, sensitivity, speed, and stability in both buffer and undiluted human serum. High-fidelity glutamate measurements down to the 10 mM level are obtained in serum. The attractive recess design also serves to protect the enzyme layer upon insertion into the skin. This simple, yet robust microneedle design is well-suited for diverse biosensing applications in which real-time metabolite monitoring is a core requirement.

We present eight epochs of 43‐GHz, dual‐polarization VLBA observations of the gravitational lens system PKS 1830‐211, made over fourteen weeks. A bright, compact ‘core’ and a faint extended ‘jet’ are clearly seen in maps of both lensed images at all eight epochs. The relative separation of the radio centroid of the cores (as measured on the sky) changes by up to 87 μ as between subsequent epochs. A comparison with the previous 43‐GHz VLBA observations made 8 months earlier shows even larger deviations in the separation of up to 201 μas. The measured changes are most likely produced by changes in the brightness distribution of the background source, enhanced by the magnification of the lens. A relative magnification matrix that is applicable on the milliarcsecond scale has been determined by relating two vectors (the ‘core–jet’ separations and the offsets of the polarized and total intensity emission) in the two lensed images. The determinant of this matrix, −1.13 ( ± 0.61), is in good agreement with the measured flux density ratio of the two images. The matrix predicts that the 10‐mas‐long jet, which is clearly seen in previous 15‐ and 8.4‐GHz VLBA observations, should correspond to a 4‐mas‐long jet trailing to the south‐east of the south‐western image. The clear non‐detection of this trailing jet is a strong evidence for substructure in the lens and may require more realistic lens models to be invoked, such as that of Nair & Garrett.

Implants containing antimicrobial metals may reduce morbidity, mortality, and healthcare costs associated with medical device-related infections. We have deposited diamondlike carbonsilver (DLC-Ag), diamondlike carbon-platinum (DLC-Pt), and diamondlike carbon-silverplatinum (DLC-AgPt) thin films using a multicomponent target pulsed laser deposition process.Transmission electron microscopy of the DLC-silver and DLC-platinum composite films revealed that the silver and platinum self-assemble into nanoparticle arrays within the diamondlike carbon matrix. The diamondlike carbon-silver film possesses hardness and Young's modulus values of 37 GPa and 331 GPa, respectively. The diamondlike carbon-metal composite films exhibited passive behavior at open-circuit potentials. Low corrosion rates were observed during testing in a phosphate-buffered saline (PBS) electrolyte. In addition, the diamondlike carbon-metal composite films were found to be immune to localized corrosion below 1000 mV (SCE). DLC-silver-platinum films demonstrated exceptional antimicrobial properties against Staphylococcus bacteria. It is believed that a galvanic couple forms between platinum and silver, which accelerates silver ion release and provides more robust antimicrobial activity.Diamondlike carbon-silver-platinum films may provide unique biological functionalities and improved lifetimes for cardiovascular, orthopaedic, biosensor, and implantable microelectromechanical systems.

No abstract