During epidemics of cholera in two rural sites (Bakerganj and Mathbaria), a much higher proportion of patients came for treatment with severe dehydration than was seen in previous years. V. cholerae O1 isolated from these patients was found to be El Tor in its phenotype, but its cholera toxin (CT) was determined to be that of classical biotype. Whether the observed higher proportion of severe dehydration produced by the El Tor biotype was due to a shift from El Tor to classical CT or due to other factors is not clear. However, if cholera due to strains with increased severity spread to other areas where treatment facilities are limited, there are likely to be many more cholera deaths.

Barium copper sulfur fluoride thin films with a face-centered cubic phase in the Fm3m space group were synthesized via RF magnetron sputtering. The results of a detailed optical and electronic characterization of the films are presented. As-deposited, they exhibit degenerate p-type conductivity at room temperature of approximately 260 S/cm – higher than that of any previously reported p-TC. Their conductivity after post-deposition processing increases to as high as 800 S/cm. The films exhibit bandgaps ranging from 1.45-1.75 eV. They are typically deposited with a substrate temperature between room temperature and 100°C, making them suitable for deposition on plastic as well as glass or crystalline substrates. It was found that a silica protective layer reduces degradation in film transparency that is caused by exposure to air.

We report on the investigation of X-ray strains and surface elevation of ion-implanted GaN as a function of ion fluence. Si, Mg and Ar ion implantation are examined. A continuous increase in lattice constants, a and c occur for doses up to near 1 × 1015/cm2. At higher doses there emerges a volume expansion of the GaN perpendicular to the surface which is an order of magnitude larger than any observed out-of-plane change in strain. The rapid expansion correlates with the onset of GaN amorphization. Transmission electron microscopy indicates that cavities form after 5 × 1016/cm2, 100 keV Ar+ implantation. For low temperature implantation, the cavities lie near the peak of the ion range For room temperature implantation, the cavities coalesce at the surface and push out the GaN perpendicular to the surface. AFM measurements confirm the presence of large bumps on the surface. The very high dose ion implantation have important consequences to etching rates of GaN and to the ability to produce n+, but not p+ doping with ion implantation.

The optical transparencies and electrical conductivities of thin films of In2O3 mixed with ZrO2 have been investigated. These films were deposited on glass substrates at room temperature using pulsed-laser deposition. Indium–zirconium oxide films with a ZrO2 content up to a 15 wt% were conducting and more than 80% transparent from 450 to 700 nm. As the ZrO2 content increased from 0 to 15 wt%, the electrical resistivities increased from 1.28 × 10−3 to 6.48 × 10−2 Ω cm, the carrier densities were decreased from 2.14 × 1020 to 1.0 × 1018/cm3, and the Hall mobilities decreased from 21 to 5 cm2 V−1 s−1, all monotonically.

Epitaxial films of (100) Ag were deposited onto (100) MgO substrates to a thickness of 4 μm with no evidence of (111) nucleation. Deposited films were smooth and had large areas, 50 × 50 microns square, free of morphological defects. Films were deposited using a two-step process. First, pulsed laser deposition was used to grow a 1000 Å Ag (100) seed layer on the MgO substrate. Second, e−beam evaporation was used to grow the film to the desired thickness. The high quality of the resulting films will allow them to be used as templates for further epitaxial deposition of other applied materials.

With low energy x-rays, such as those from a Cu x-ray tube, only the outer few microns of a metallic sample can be probed. This low penetrating power prohibits structural studies from being carried out on the interior of an electrode in an electrochemical cell because of absorption by the cell material, electrodes and the electrolyte. The work described in this paper circumvents this problem by utilizing high energy, high brightness x-rays produced on the superconducting wiggler beam line, X-17C, at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory. The penetrating power of the higher energy x-rays allowed Pd diffraction spectra to be obtained in-situ on a 1 mm diameter Pd wire cathode during electrolysis of heavy water. Moreover, the beam (28 × 28 μm in cross-section) allowed diffraction spectra to be acquired as a function of distance across the sample. Spectra were recorded in 50 μm steps from the edge of the Pd wire to its core. This was done at 2 minute intervals as a function of electrolysis time. The α-β phase transition induced in the Pd while deuterium was electrochemically absorbed was observed by monitoring the Pd-(422) diffraction peaks. Results allowed the diffusion rate and the diffusivity of deuterium atoms in the Pd wire to be determined. Other features of the structural changes associated with the absorption of deuterium into Pd are reported.

Single phase BaxSr1−xTiO3 (BST) films (∼0.5-7 μm thick) have been deposited onto single crystal substrates (MgO, LaAlO3, SrTiO3) by pulsed laser deposition. Silver interdigitated electrodes were deposited on top of the ferroelectric film. The room temperature capacitance and dielectric Q (1/tanδ) of the film have been measured as a function of electric field (≤80 kV/cm) at 1 - 20 GHz. The dielectric properties of the film are observed to strongly depend on substrate type and post-deposition processing. After annealing (≤1000° C), it was observed that the dielectric constant and % tuning decreased and the dielectric Q increased for films deposited onto MgO, and the opposite effect was observed for films deposited onto LaA1O3. Presumably, this change in dielectric properties is due to the changes in film stress. Very thin (∼50 Å) amorphous BST films were successfully used as a stress-relief layer for the subsequently deposited crystalline BST (∼5000 Å) films to maximize % tuning and dielectric Q. Films have been deposited from stoichiometric targets and targets that have excess Ba and Sr. The additional Ba and Sr has been added to the target to compensate for deficiencies in Ba and Sr observed in the deposited BST (x=0.5) films. Films deposited from compensated targets have higher dielectric constants than films deposited from stoichiometric targets. Donor/acceptor dopants have also been added to the BST target (Mn, W, Fe ≤4 mol.%) to further improve the dielectric properties. The relationship between the dielectric constant, the dielectric Q, the change in dielectric constant with electric field is discussed.

Here we report a nanoparticulate route to Y2O3 nanofibers (~50 nm in diameter and a few micrometers in length) and for the radial growth of ZnS spheres (200-800 nm diameter). Well-defined higher order structures are developed upon thermostatically aging the dispersions of monomeric nanocrystals. The shapes of the “macromolecules„ are correlated to primary monomeric nanocrystallites, the growing time and temperature, and surfactant templating agents. It is anticipated that this approach should inspire fabrication of nanoparticulate structures by using primary nanoparticles as monomers.

We experimentally demonstrate the annealing and electrical activation of doped silicon without the direct application of heat as in conventional thermal annealing or pulsed laser annealing. 25 × 25 × 3 mm samples of silicon doped by neutron transmutation were irradiated with a short pulse from a 1.06-micron laser. The few joule laser pulse was focused to mm-diameter surface spot which resulted in high power (∼ 1011W/cm2) capable of launching shocks into the entire sample. In a few instances the entire silicon slab, including regionsfar outside the illuminated spot, was annealed and electrically activated. In the annealed samples electrical activation of donors throughout the slab, measured with a four-point probe, was uniform and comparable to that of thermally annealed control samples. Far-infrared spectroscopy and Hall measurements also showed that the donor species was activated and Raman spectroscopy demonstrated marked improvement in the crystal structure. We conjecture that the annealing was caused by the mechanical energy that was launched into the slab by the laser pulse. Results of experiments on an ion-implanted silicon sample are also discussed.

Thin films of the colossal magnetoresistive material La0.67Ca0.33MnO3 (LCMO) have been grown by off-axis sputtering from a single target of the LCMO material onto various substrates and studied by electrical transport, x-ray diffraction, scanning electron microscopy and atomic force microscopy. The LCMO films typically grow with the (002) direction oriented normal to the film. We find magnetoresistances at 6 T of ≈ 90%. We observe a scaling between the temperature of the resistivity peak (Tp) and the relative change in resistivity between room temperature and the resistance peak for Tp varying from 90 to 270 K. This scaling is consistent with an activated resistivity above the peak, with an activation temperature of ≈ 940 K. Films of LCMO grown on cubic zirconia exhibit an upturn in resistivity at low temperatures. Bilayers of LCMO and the superconductor YBa2Cu3O7-δ have been grown and compared to see the effects of having either the magnetic or superconducting layer first in the sequence.

High-quality thin-film superlattices of permalloy (NiFe) and silver (Ag) have been grown by pulsed laser deposition (PLD) for the first time. The alternating metallic layers weregrown from individual NiFe and Ag targets utilizing an automated multi-target holder coupled to a conventional PLD system. The targets were ablated at a base pressure of 4×10−7 Torr and the material deposited on room-temperature (100) silicon and on fused silica substrates. The films were characterized by X-ray diffraction (XRD), magnetic field-dependent resistivity, and ferromagnetic resonance (FMR). XRD was used to confirm uniform bilayer thicknesses. The magnetic field-dependent resistance measurements indicated the presence of magnetoresistance in the deposited films. An as-deposited film with a bilayer thickness of 75 Å demonstrated a roomtemperature magnetoresistive effect of 0.15 %. FMR has been used to determine the relationship between NiFe magnetism and the observed magnetoresistance.

The growth of Fe/ZnSe/Fe multilayers on (001) and (111) GaAs substrates is reported. The samples were characterized in-situ by reflection high energy electron diffraction (RHEED), and ex situ by vibrating sample magnetometry (VSM), ferromagnetic resonance (FMR), cross sectional transmission electron microscopy (TEM), and x-ray diffraction. On the (001) surface, the quality of the layers deteriorated significantly with the growth of the first ZnSe spacer layer. In Fe/ZnSe/Fe trilayer structures, TEM revealed a well-defined layered structure, with a high density of defects in both the ZnSe spacer layer and the subsequent Fe layer. VSM and FMR clearly showed the presence of two Fe films with distinct coercive fields, with the higher coercive field attributed to the lower crystalline quality of the second Fe layer. θ-2θ xray diffraction measurements performed on samples grown on (001) GaAs substrates indicated that the ZnSe spacer layer (grown on (001) Fe) grew in a (111) orientation. Growth on GaAs(111) substrates produced better RHEED patterns for all layers with little deterioration in film quality with continued layer growth, so that the magnetic properties of the individual Fe layer could not be distinguished.

Several high Tc compounds containing Tl (thallium) were prepared starting from different initial compositions. Superconducting properties and the structure were determined for each sample. Electron diffraction and transmission electron microscopy showed the existence of polytypic high Tc compounds with the same a- and b-axes but different c-axis values. The c-axis appears to increase approximately in integral multiples of 0.15 nm with varying composition and is associated with the insertion of Cu–Ca or Cu–Tl layers in each unit cell. Several random stacking faults were also noted, which give rise to diffuse streaking in the electron diffraction pattern.

Artificially multilayered copper/nickel thin films with bilayer repeat lengths between 1.6 and 12 nm were produced by ion beam sputtering. The mechanical properties of these films were investigated by low load microhardness and nanoindentation (force versus depth) techniques. It was found that none of the films displayed bilayer repeat length dependent enhanced elastic behavior (the supermodulus effect) as measured during unloading in the nanoindenter. However, enhancements in hardness, as measured by both the nanoindenter and the low load microhardness tester, were observed in films with small bilayer repeat lengths. These measurements displayed a Hall-Petch-type relationship, using the individual layer thickness (equal to half the bilayer repeat length) as the characteristic “grain size.” This hardness behavior can be understood in terms of a mechanism involving dislocation pinning at the interfaces analogous to the mechanism of grain boundary hardening.

In order to grow large single crystals of the La2‐xSrxCuOy and Bi2+xSr2‐zCuOy families of high Tc superconductors, we have studied the relationships between nominal Sr composition in the starting materials and the Sr compositions of the resulting products. We present growth, x‐ray, and composition data for these samples.

During the past quarter-century, the field of high pressure research has undergone a quiet revolution. This has resulted from the creation and development of the diamond-anvil cell (DAC). Because diamonds are the hardest known materials, the highest static pressures can be attained and indefinitely held in these devices, recent pressure records have surpassed 400 GPa.