Structure, conductivity, and optical absorption of Ag2−xO films

Evaporation of Ag in the presence of an electron cyclotron resonance (ECR) oxygen plasma was used to deposit Ag_2−xO films with a range of stoichiometries onto r-plane sapphire substrates. A quartz crystal oscillator (QCO) was used to accurately measure the silver and oxygen arrival rates and establish the O/Ag flux ratio needed to produce films with nominal Ag₂O stoichiometry. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis indicates that the Ag_2−xO films are not single phase but contain signatures of coexisting Ag₂O and AgO components. XRD shows that the lattice matching with the r-plane sapphire substrate causes the Ag₂O phase to grow with <002> heteroepitaxial crystallites coexisting with crystallites having <111> normal and random in-plane orientation. The AgO phase also forms with crystallites having <002> heteroepitaxy as well as crystallites with <111> normal and random in-plane orientation. The mixed phase Ag_2−xO films exhibit approximately 77% optical transmission over the visible range (500 nm to 700 nm) and have a single absorption edge near 3.3 eV. Four-point van der Pauw conductivity and Hall effect measurements indicate that the Ag_2−xO films are p-type with a conductivity on the order of 3 × 10^− 3 Ω^− 1 cm^− 1.     

Very low voltage, normally-off asymmetric Fabry-Perot reflection modulator

Using the electro-absorptive properties of approximately=150 AA quantum wells in an asymmetric Fabry-Perot modulator (AFPM), a normally-off reflection modulator with very low drive voltage was demonstrated. With this device contrasts of more than 6 Db at normal incidence in reflection have been achieved, with a voltage swing of only 3.5 V and >     

Observation of contact phenomena in glass/metal systems

Microscopic observation of the wetting of glass sessile drops on platinum has revealed the presence of glassy droplets in the vicinity of the wetting edge. A study of the droplets has Clarified the deposition process and the influence of the platinum grain structure on their nucleation and growth, and has allowed comment to be made on the mode of grainboundary movement during grain growth.     

Application of quantitative fluorescence and absorption-edge computed microtomography to image metal compartmentalization in Alyssum murale

This paper shows that synchrotron-based fluorescence and absorption-edge computed microtomographies (CMT) are well-suited for determining the compartmentalization and concentration of metals in hyperaccumulating plant tissues. Fluorescence CMT of intact leaf, stem, and root samples revealed that Ni concentrated in stem and leaf dermal tissues and, together with Mn, in distinct regions associated with the Ca-rich trichomes on the leaf surface of the nickel hyperaccumulator Alyssum murale "Kotodesh". Metal enrichment was also observed within the vascular system of the finer roots, stem, and leaves but absent from the coarser root, which had a well-correlated metal coating. Absorption-edge CMT showed the three-dimensional distribution of the highest metal concentrations and verified that epidermal localization and Ni and Mn co-localization at the trichome base are phenomena that occurred throughout the entire leaf and may contribute significantly to metal detoxification and storage. Ni was also observed in the leaf tips, possibly resulting from release of excess Ni with guttation fluids. These results are consistent with a transport model where Ni is removed from the soil by the finer roots, carried to the leaves through the stem xylem, and distributed throughout the leaf by the veins to the dermal tissues, trichome bases, and in some cases the leaf tips.     

In-line Fabry-Perot optical waveguide filter with quasi-chirpedgratings

The authors propose and demonstrate a novel InP-based waveguide filter, the in-line Fabry-Perot. The device is designed to give a number of sharp equally spaced FP like transmission peaks without the need of cleaved mirror facets. Fabricated devices give more than 18 clear 1 nm spaced transmission peaks     

Atmospheric attenuation at submillimetre wavelengths

A high-resolution interference spectrometer has been used to observe the absorption of water vapour in the 500?1500 Gc/s region. The centre frequencies and relative strengths of the resonances are compared with earlier theoretical calculations of several workers and point to an extrapolation error in one previous experimental measurement.     

Do superconductors change as fast as possible when quenched?

If superconductors change as fast as possible as they pass through a phase transition, then the initial domain structure is constrained by causality. We shall see that Josephson junctions do indeed display such behaviour. However, we shall argue that causal bounds arise through the Gaussian nature of the order parameter, which can be thought of as a consequence of instabilities growing as fast as possible.     

Plutonium oxidation and subsequent reduction by Mn(IV) minerals in Yucca Mountain tuff

Plutonium oxidation state distribution on Yucca Mountain tuff and synthetic pyrolusite (beta-MnO2) suspensions was measured using synchrotron X-ray micro-spectroscopy and microimaging techniques as well as ultrafiltration/solventextraction techniques. Plutonium sorbed to the tuff was preferentially associated with manganese oxides. For both Yucca Mountain tuff and synthetic pyrolusite, Pu(IV) or Pu(V) was initially oxidized to more mobile Pu(V/VI), but over time, the less mobile Pu(IV) became the predominant oxidation state of the sorbed Pu. The observed stability of Pu(IV) on oxidizing surfaces (e.g., pyrolusite), is proposed to be due to the formation of a stable hydrolyzed Pu(IV) surface species. These findings have important implications in estimating the risk associated with the geological burial of radiological waste in areas containing Mn-bearing minerals, such as at the Yucca Mountain or the Hanford Sites, because plutonium will be predominantly in a much less mobile oxidation state (i.e., Pu(IV)) than previously suggested (i.e., Pu(V/VI).