Hall carrier density and magnetoresistance measurements in thin film vanadium dioxide across the metal-insulator transition

Temperature dependent magneto-transport measurements in magnetic fields of up to 12 Tesla were performed on thin film vanadium dioxide (VO2) across the metal-insulator transition (MIT). The Hall carrier density increases by 4 orders of magnitude at the MIT and accounts almost entirely for the resistance change. The Hall mobility varies little across the MIT and remains low, ~0.1cm2/V sec. Electrons are found to be the major carriers on both sides of the MIT. Small positive magnetoresistance in the semiconducting phase is measured

The Effect of Disease Modifying Therapies on Disability Progression in Multiple Sclerosis: A Systematic Overview of Meta-Analyses

Background: Disease modifying therapy (DMT) efficacy trials make an essential contribution to the development of evidence-based clinical treatments and practices for people with multiple sclerosis (MS). Meta-analysis is a critical part of this process and provides a powerful tool to assess the effects of DMT on MS progression. However, although there have been several meta-analyses on the effect of DMT on MS disease progression, they often do not reach the same conclusions.Objective: Our aim was to better understand and contextualize the results of meta-analyses evaluating DMT, identify differences in methodology that might explain their differing conclusions, and highlight areas for future research that will improve our ability to develop clinical recommendations.Methods: We conducted an overview of systematic reviews with meta-analyses assessing the efficacy of DMT on disability progression in people with MS in PubMed (Medline) and the Cochrane Database of Systematic Reviews.Results: We included 22 meta-analyses in this overview: eight general (on >3 DMT), 11 specific (on ≤3 DMT), 2 that evaluated subsets, and 1 that evaluated long-term effects. We found that there is good evidence that DMT improve short-term (≤2–3 years) disability progression outcomes relative to placebo in people with relapsing-remitting MS. However, results varied substantially between meta-analyses, and there is little evidence of their efficacy in other populations or over longer periods. The relative effects of individual DMT also remain unclear. The variance in results between meta-analyses may be related to the substantial differences in inclusion criteria, which was reflected in the limited overlap in included studies, as well as the year of meta-analysis publication. Of the 123 total unique studies included in the general meta-analyses, 77 (62.6%) were included in only one meta-analysis. This incongruence was also evident in the included DMT. Six of the 16 (37.5%) DMT evaluated in the general meta-analyses were only included in one meta-analysis.Conclusions: Translating DMT efficacy studies into evidence-based clinical practice requires greater methodological consistency in meta-analyses, more data on the relative effects of DMT through head-to-head clinical trials, and better reporting of adverse events

Reclassification of Subspecies of \u3ci\u3eAcidovorax avenae\u3c/i\u3e as \u3ci\u3eA. Avenae\u3c/i\u3e (Manns 1905) emend., \u3ci\u3eA. cattleyae \u3c/i\u3e (Pavarino, 1911)comb.nov., \u3ci\u3eA. citrulli\u3c/i\u3e Schaad et al.,1978)comb.nov., and proposal of \u3ci\u3eA. oryzae \u3c/i\u3esp. nov.

The bacterium Acidovorax avenae causes disease in a wide range of economically important monocotyledonous and dicotyledonous plants, including corn, rice, watermelon, anthurium, and orchids.Genotypic and phenotypic relatedness among strains of phytopathogenic A. avenae sub sp. avenae, A. avenae sub sp. citrulli, A. avenae subsp. cattleyae and A. konjaci, as well as all other Acidovorax species, including A. facilis, the type strain of Acidovorax, was determined.The16s rDNA sequencing confirmed previous studies showing the environmental species to be very distant from the phytopathogenic species. DNA/DNA reassociation assays on the different strains of A. avenae revealed four(A, B, C, and D) distinct genotypes. Taxon A included six A. avenae subsp. avenaestrains from corn that had a mean reciprocal similarity of 81%; taxon B included six A. avenae sub sp. avenae strains from rice that had a mean reciprocal similarity of 97%; taxon C contained 11 A. avenae sub sp. citrulli strains from cucurbits (cantaloupe, watermelon, and pumpkin) that had a mean reciprocal similarity of 88%, and taxon D contained four A. avenae sub sp. cattleyae strains from orchids that had a mean similarity of 98%

Persistent Photoconductivity Studies in Nanostructured ZnO UV Sensors

The phenomenon of persistent photoconductivity is elusive and has not been addressed to an extent to attract attention both in micro and nanoscale devices due to unavailability of clear material systems and device configurations capable of providing comprehensive information. In this work, we have employed a nanostructured (nanowire diameter 30–65 nm and 5 μm in length) ZnO-based metal–semiconductor–metal photoconductor device in order to study the origin of persistent photoconductivity. The current–voltage measurements were carried with and without UV illumination under different oxygen levels. The photoresponse measurements indicated a persistent conductivity trend for depleted oxygen conditions. The persistent conductivity phenomenon is explained on the theoretical model that proposes the change of a neutral anion vacancy to a charged state

Electrical Transport Properties in Zinc Oxide

This chapter contains sections titled: Introduction Hall-Effect Analysis Donor States and n-type Doping Hydrogen Acceptor States and p-type Doping Photoconductivity Summary Reference

Electrical and Optical Properties of n-Type and p-Type ZnO

In recent years, ZnO has been proposed for new electronic and optoelectronic devices, such as transparent transistors and UV light-emitting diodes (LEDs). The LED application will require both n-type and p-type ZnO, but the latter is difficult to produce, and progress in this area will require a detailed knowledge of the various impurities and defects that affect the electrical and optical properties. The dominant donors in as-grown ZnO are usually thought to be interstitial H and substitutional AlZn, with activation energies of about 40 and 65 meV, respectively. However, interstitial Zn and its associated complexes may also contribute free electrons. The dominant acceptor, at least in vapor-phase-grown material, is the Zn vacancy; however, substitutional NO is also present, although sometimes passivated by H. To produce p-type ZnO, it is necessary to dope with acceptor-type impurities, and some success has been achieved with N, P, As, and Sb. However, only N has been proven to have simple substitutional character (NO), and more complicated acceptor structures, such as AsZn-2VZn, have been proposed for some of the other group V elements. Both homostructural and heterostructural UV LEDs have been fabricated, although not of high luminescent power so far. The main objective of this paper is to review the Hall-effect and photoluminescence results on n-type and p-type ZnO

Electrical and Optical Properties of n-Type and p-Type ZnO

In recent years, ZnO has been proposed for new electronic and optoelectronic devices, such as transparent transistors and UV light-emitting diodes (LEDs). The LED application will require both n-type and p-type ZnO, but the latter is difficult to produce, and progress in this area will require a detailed knowledge of the various impurities and defects that affect the electrical and optical properties. The dominant donors in as-grown ZnO are usually thought to be interstitial H and substitutional AlZn, with activation energies of about 40 and 65 meV, respectively. However, interstitial Zn and its associated complexes may also contribute free electrons. The dominant acceptor, at least in vapor-phase-grown material, is the Zn vacancy; however, substitutional NO is also present, although sometimes passivated by H. To produce p-type ZnO, it is necessary to dope with acceptor-type impurities, and some success has been achieved with N, P, As, and Sb. However, only N has been proven to have simple substitutional character (NO), and more complicated acceptor structures, such as AsZn-2VZn, have been proposed for some of the other group V elements. Both homostructural and heterostructural UV LEDs have been fabricated, although not of high luminescent power so far. The main objective of this paper is to review the Hall-effect and photoluminescence results on n-type and p-type ZnO

Electrical Transport Properties in Zinc Oxide

This chapter contains sections titled: Introduction Hall-Effect Analysis Donor States and n-type Doping Hydrogen Acceptor States and p-type Doping Photoconductivity Summary Reference

Electron and Hole Traps in N-Doped ZnO Grown on p-Type Si Substrate by MOCVD

Electron and hole traps in N-doped ZnO were investigated using a structure of n+-ZnO:Al/i-ZnO/ZnO:N grown on a p-Si substrate by metalorganic chemical vapor deposition (for growth of the ZnO:N layer) and sputtering deposition (for growth of the i-ZnO and n+-ZnO:Al layers). Current-voltage and capacitance-voltage characteristics measured at temperatures from 200 to 400 K show that the structure is an abrupt n+−p diode with very low leakage currents. By using deep level transient spectroscopy, two hole traps, H3 (0.35 eV) and H4 (0.48 eV), are found in the p-Si substrate, while one electron trap E3 (0.29 eV) and one hole trap H5 (0.9 eV) are observed in the thin ZnO:N layer. Similarities to traps reported in the literature are discussed

Vapor-Phase Growth of High-Quality ZnO Micro- and Nano-Structures

Micro- and nano-structures of ZnO have been grown on substrates from flowing carrier gases in a tube furnace. We have investigated how variations in the carrier gas composition, gas flow rate and the position of the substrate control the formation and the morphology of the nanostructures. The source material was pure zinc powder evaporated in the temperature range 500ºC to 650ºC in flowing Ar plus oxygen at atmospheric pressure. It was found that precise control of the gas composition, gas flow rate, and growth time was necessary for reliable deposition. It was also found that zinc powder must be washed to remove the surface oxide. Scanning electron microscopy (SEM) images of samples grown from a Zn powder source show forested needles approximately 100 nm in diameter by 1 micron long, and faceted rods from 500nm to 700nm thick. Photoluminescence measurements at 4 K show a dominant line at ~3.36eV with additional features at 3.32 and 3.37eV. The line widths are ~ 3.5meV, indicating good quality material. The usual green-band emission is also observed