230 research outputs found
Enhanced critical current densities in MgB2 by mixing relatively impure boron powders.
Polycrystalline MgB2 samples were prepared from 99.98% purity Mg powder and different mixtures of relatively impure boron (99% pure crystalline boron and 95–97% amorphous boron) precursor powders. At both 6 and 20 K, for the mixed boron samples a doubling in Jc was observed over the highest values for single precursor samples. It is shown that the enhanced Jc results from the mixing effect of using different reaction rates of the different boron precursor powders. The work represents a cost-effective means of significantly improving current carrying Performance in MgB2 conductors
The critical current density of polycrystalline MgB2 prepared by using boron mixture
In this study, boron powders with varying purity and form were mixed in different proportion to serve as precursors for reaction with Mg forming polycrystalline MgB2 bulks. The inductively measured superconducting transition temperature, Tc and the critical current density, J c were compared to that of samples prepared from the respective single boron. Overall, Tc remains largely unchanged for all samples. It was found that Jc at 6 K and 20 K did not degrade significantly up to 4.6 T as a result of adding impure boron as much as 10 wt.% indicating comparable Jc can be obtained without dependence of use of expensive high purity boron powder alone. The systematic decrease of Jc with increasing impure boron additions shows that a compromise between desired and cost reduction can be made by varying the boron powder proportion. Finally, samples prepared from the mixture of both impure crystalline and amorphous borons even show enhanced Jc up to 3 T at 20 K. The increase in Jc correlates with the retention of strain level in these samples probably resulted from the more similar reaction rate of the respective borons
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High Yield Transfer of Clean Large-Area Epitaxial Oxide Thin Films
Highlights: A new way to achieve high yield and large area oxide thin film transfer is developed. Three different film compositions are demonstrated: SrRuO3, CeO2, and CeO2/STO nanocomposite films. Cracks, wrinkles, and damages are prevented by the new transfer method. They are commonly introduced by conventional transfer processes. Vertically aligned nanocomposite (VAN) structures can further improve the transfer yield. Possible mechanisms related to increased fracture toughness are proposed. We have opened up a route to large-scale oxide thin-film-based electronic device applications
Strain-gradient effects in nanoscale-engineered magnetoelectric materials
Understanding strain gradient phenomena is of paramount importance in diverse areas of condensed matter physics. This effect is responsible for flexoelectricity in dielectric materials, and it plays a crucial role in the mechanical behavior of nanoscale-sized specimens. In magnetoelectric composites, which comprise piezoelectric or ferroelectric (FE) materials coupled to magnetostrictive (MS) phases, the strain gradient can add to any uniform strain that is present to boost the strength of the coupling. Hence, it could be advantageous to develop new types of functionally graded multiferroic composites (for information technologies) or magnetic-field-driven flexoelectric/magnetostrictive platforms for wireless neurons/muscle cell stimulation (in biomedicine). In MS or FE materials with non-fully constrained geometries (e.g., cantilevers, porous layers, or vertically aligned patterned films), strain gradients can be generated by applying a magnetic field (to MS phases) or an electric field (to, e.g., FE phases). While multiferroic composites operating using uniform strains have been extensively investigated in the past, examples of new nanoengineering strategies to achieve strain-gradient-mediated magnetoelectric effects that could ultimately lead to high flexomagnetoelectric effects are discussed in this Perspective
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Electrochemical removal of anodic aluminium oxide templates for the production of phase-pure cuprous oxide nanorods for antimicrobial surfaces.
Antimicrobial surfaces are ones that incapacitate or kill pathogens landing on them, which could allow for self-sanitising surfaces for hospitals or implants, ensuring healthier stays and procedures. Cuprous compounds such as Cu2O are especially effective at incapacitating both viruses and bacteria, and nanorod arrays have been shown to prevent the adhesion of pathogens and mechanically deform bacteria to the point that their cell walls rupture. A Cu2O nanorod array should therefore allow for the exploitation of both of these effects. In the present work, an electrochemical method is introduced, where Cu2O nanorods formed in a substrate-supported anodic aluminium oxide (AAO) template are held at a stable electrochemical potential throughout the removal of the AAO template. This avoids the partial reduction of the nanorods from Cu2O to Cu that was observed during chemical removal of the template, which was attributed to the presence of residual aluminium from the template fabrication process that reacts with the etchant and lowers the electrochemical potential of the nanorods to a value that favours reduction. Using the electrochemical removal method, the reliable production of phase-pure, free-standing, crystalline Cu2O nanorod arrays on ITO/glass substrates is demonstrated. This simple method is compatible with nanorod arrays of any size
Tuning of defects in ZnO nanorod arrays used in bulk heterojunction solar cells.
With particular focus on bulk heterojunction solar cells incorporating ZnO nanorods, we study how different annealing environments (air or Zn environment) and temperatures impact on the photoluminescence response. Our work gives new insight into the complex defect landscape in ZnO, and it also shows how the different defect types can be manipulated. We have determined the emission wavelengths for the two main defects which make up the visible band, the oxygen vacancy emission wavelength at approximately 530 nm and the zinc vacancy emission wavelength at approximately 630 nm. The precise nature of the defect landscape in the bulk of the nanorods is found to be unimportant to photovoltaic cell performance although the surface structure is more critical. Annealing of the nanorods is optimum at 300°C as this is a sufficiently high temperature to decompose Zn(OH)2 formed at the surface of the nanorods during electrodeposition and sufficiently low to prevent ITO degradation.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are
Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO.
Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.The authors acknowledge the support of the Cambridge Overseas and Commonwealth Trust, the Rutherford Foundation of New Zealand, Girton College Cambridge. This work has been funded by ERC Advanced Investigator Grant, Novox, ERC-2009-adG247276 and by the EPSRC (under RGS3717)
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Tailoring physical functionalities of complex oxides by vertically aligned nanocomposite thin-film design
Abstract: Self-assembled nanocomposite thin films couple two materials into a single film, typically, in the form of vertically aligned nanopillars embedded in a matrix film. High-density vertical heterointerfaces provide a great platform for engineering new physical properties and novel multifunctionalities, as well as for nanoscale device integration. Tremendous research efforts have been devoted to developing different nanocomposite systems. In this article, we summarize recent progress on vertically aligned nanocomposite thin films for enhanced functionalities such as ferroelectricity, tunable magnetoresistance, multiferroicity, dielectricity, magnetic anisotropy, perpendicular exchange bias, novel electrical/ionic properties, interfacial conduction, and resistive switching. Using specific examples, we discuss how and why the fundamental physical properties can be significantly tuned/improved in vertically aligned nanocomposites. Finally, we propose future research directions to achieve further enhanced performance as well as practical devices
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