375 research outputs found
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Photocatalytic hydrogen generation coupled to pollutant utilisation using carbon dots produced from biomass
Carbon dots from biomass waste as efficient photoabsorbers for sustainable and scalable coupled solar-driven H2 evolution and pollutant utilisation.Christian Doppler Research Association (Austrian Federal Ministry for Digital and Economic Affairs and the National Foundation for Research, Technology and Development) and OMV
Unconventional Hall effect in oriented CaCoO thin films
Transport properties of the good thermoelectric misfit oxide
CaCoO are examined. In-plane resistivity and Hall resistance
measurements were made on epitaxial thin films which were grown on {\it c}-cut
sapphire substrates using the pulsed laser deposition technique. Interpretation
of the in-plane transport experiments relates the substrate-induced strain in
the resulting film to single crystals under very high pressure ( 5.5 GPa)
consistent with a key role of strong electronic correlation. They are confirmed
by the measured high temperature maxima in both resistivity and Hall
resistance. While hole-like charge carriers are inferred from the Hall effect
measurements over the whole investigated temperature range, the Hall resistance
reveals a non monotonic behavior at low temperatures that could be interpreted
with an anomalous contribution. The resulting unconventional temperature
dependence of the Hall resistance seems thus to combine high temperature
strongly correlated features above 340 K and anomalous Hall effect at low
temperature, below 100 K.Comment: Submitted to Physical Review B (2005
Electron transport properties in Al0.25Ga0.75N/AIN/GaN hetrostructures with different InGaN back barrier layers and GaN channel thickness grown by MOCVD
Cataloged from PDF version of article.The electron transport properties in Al0.25Ga0.75N/AlN/GaN/InxGa1-xN/GaN double heterostructures with various indium compositions and GaN channel thicknesses were investigated. Samples were grown on c-plane sapphire substrates by MOCVD and evaluated using variable temperature Hall effect measurements. In order to understand the observed transport properties, various scattering mechanisms, such as acoustic phonon, optical phonon, interface roughness, background impurity, and alloy disorder, were included in the theoretical model that was applied to the temperature-dependent mobility data. It was found that low temperature (T 160 K), optical phonon scattering is the dominant scattering mechanism for AlGaN/AlN/GaN/InGaN/GaN heterostructures. The higher mobility of the structures with InGaN back barriers was attributed to the large conduction band discontinuity obtained at the channel/buffer interface, which leads to better electron confinement. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Solar reforming of biomass with homogeneous carbon dots
A sunlight-powered process is reported that employs carbon dots (CDs) as light absorber for the conversion of lignocellulose into sustainable H2 fuel and organics. This photocatalytic system operates in pure and untreated sea water using a benign pH (2-8) at ambient temperature and pressure. The CDs can be produced in a scalable synthesis directly from biomass itself and their solubility allows for good interactions with the insoluble biomass substrates. They also display excellent photophysical properties with a high fraction of long-lived charge carriers and the availability of a reductive and an oxidative quenching pathway. The presented CD-based biomass photoconversion system opens new avenues for sustainable, practical, and renewable fuel production through biomass valorization
Dark Photocatalysis: Storage of Solar Energy in Carbon Nitride for Time-Delayed Hydrogen Generation
While natural photosynthesis serves as the model system for efficient charge separation and decoupling of redox reactions, bio-inspired artificial systems typically lack applicability owing to synthetic challenges and structural complexity. We present herein a simple and inexpensive system that, under solar irradiation, forms highly reductive radicals in the presence of an electron donor, with lifetimes exceeding the diurnal cycle. This radical species is formed within a cyanamide-functionalized polymeric network of heptazine units and can give off its trapped electrons in the dark to yield H , triggered by a co-catalyst, thus enabling the temporal decoupling of the light and dark reactions of photocatalytic hydrogen production through the radical's longevity. The system introduced here thus demonstrates a new approach for storing sunlight as long-lived radicals, and provides the structural basis for designing photocatalysts with long-lived photo-induced states.This work was supported by the Deutsche Forschungsgemeinschaft (project LO1801/1-1) and an ERC Starting Grant (B.V.L., grant number 639233), the Max Planck Society, the cluster of excellence Nanosystems Initiative Munich (NIM), and the Center for Nanoscience (CeNS). We acknowledge support by the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy, National Foundation for Research, Technology and Development) and the OMV Group (H.K., E.R.). V.W.-h.L. gratefully acknowledges a postdoctoral scholarship from the Max Planck Society
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Interfacial Engineering of a Carbon Nitride-Graphene Oxide-Molecular Ni Catalyst Hybrid for Enhanced Photocatalytic Activity
Abstract can be found here: https://doi.org/10.1021/acscatal.8b0196
Electrical conduction properties of Si δ-doped GaAs grown by MBE
The temperature dependent Hall effect and resistivity measurements of Si δ-doped GaAs are performed in a temperature range of 25-300 K. The temperature dependence of carrier concentration shows a characteristic minimum at about 200 K, which indicates a transition from the conduction band conduction to the impurity band conduction. The temperature dependence of the conductivity results are in agreement with terms due to conduction band conduction and localized state hopping conduction in the impurity band. It is found that the transport properties of Si δ-doped GaAs are mainly governed by the dislocation scattering mechanism at high temperatures. On the other hand, the conductivity follows the Mott variable range hopping conduction (VRH) at low temperatures in the studied structures. © 2009 Elsevier B.V. All rights reserved
Semiclassical wave equation and exactness of the WKB method
The exactness of the semiclassical method for three-dimensional problems in
quantum mechanics is analyzed. The wave equation appropriate in the
quasiclassical region is derived. It is shown that application of the standard
leading-order WKB quantization condition to this equation reproduces exact
energy eigenvalues for all solvable spherically symmetric potentials.Comment: 13 page
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