pinecone/core-2020-05-10-deduplication huggingface dataset:
Thermoelectric power factor enhancement by spin-polarized currents – a nanowire case study

In this work, thermoelectric (TE) measurements have been performed on the workhorses of today’s data storage devices, namely nanostructured materials exhibiting either the giant or the anisotropic magnetoresistance effect (GMR and AMR). In particular, the temperature-dependent (50 K - 300 K) and magnetic field-dependent (up to 1 T) TE power factor (PF) has been determined for several Co-Ni alloy nanowires with varying Co:Ni ratios as well as for Co-Ni/Cu multilayered nanowires with various Cu layer thicknesses, which were all synthesized via a template-assisted electrodeposition process. A systematic investigation of the resistivity, (rho), as well as the Seebeck coefficient, S, was performed for Co-Ni alloy nanowires exhibiting AMR and Co-Ni/Cu multilayered nanowires exhibiting GMR. At room temperature, measured values of TE PFs up to 3.6 mWK-2m-1 for AMR samples and 2.0 mWK-2m-1 for GMR nanowires were obtained. Furthermore, the TE PF was found to increase by up to 13.1 % for AMR Co-Ni alloy nanowires and by up to 52 % for GMR Co-Ni/Cu samples in an external applied magnetic field. According to these measurements, the magnetic nanowires exhibit TE PFs that are of the same order of magnitude as TE PFs of Bi-Sb-Se-Te based thermoelectric materials and, additionally, give the opportunity to adjust the TE power output to changing loads and hot spots through external magnetic fields
Spin orbit coupling controlled spin pumping effect

Effective spin mixing conductance (ESMC) across the nonmagnetic metal
(NM)/ferromagnet interface, spin Hall conductivity (SHC) and spin diffusion
length (SDL) in the NM layer govern the functionality and performance of pure
spin current devices with spin pumping technique. We show that all three
parameters can be tuned significantly by the spin orbit coupling (SOC) strength
of the NM layer in systems consisting of ferromagnetic insulating Y3Fe5O12
layer and metallic Pd1-xPtx layer. Surprisingly, the ESMC is observed to
increase significantly with x changing from 0 to 1.0. The SHC in PdPt alloys,
dominated by the intrinsic term, is enhanced notably with increasing x.
Meanwhile, the SDL is found to decrease when Pd atoms are replaced by heavier
Pt atoms, validating the SOC induced spin flip scattering model in polyvalent
PdPt alloys. The capabilities of both spin current generation and spin charge
conversion are largely heightened via the SOC. These findings highlight the
multifold tuning effects of the SOC in developing the new generation of
spintronic devices.Comment: 16 pages, 4 figure
Gate-tunable transport properties of in-situ capped Bi$_2$Te$_3$
  topological insulator thin films

Combining the ability to prepare high-quality, intrinsic Bi$_2$Te$_3$
topological insulator thin films of low carrier density with in-situ protective
capping, we demonstrate a pronounced, gate-tunable change in transport
properties of Bi$_2$Te$_3$ thin films. Using a back-gate, the carrier density
is tuned by a factor of $\sim 7$ in Al$_2$O$_3$ capped Bi$_2$Te$_3$ sample and
by a factor of $\sim 2$ in Te capped Bi$_2$Te$_3$ films. We achieve full
depletion of bulk carriers, which allows us to access the topological transport
regime dominated by surface state conduction. When the Fermi level is placed in
the bulk band gap, we observe the presence of two coherent conduction channels
associated with the two decoupled surfaces. Our magnetotransport results show
that the combination of capping layers and electrostatic tuning of the Fermi
level provide a technological platform to investigate the topological
properties of surface states in transport experiments and pave the way towards
the implementation of a variety of topological quantum devices.Comment: 10 pages, 4 figures and 1 tabl
Superconducting YBa2Cu3O7-δ nanocomposites using preformed ZrO2 nanocrystals : growth mechanisms and vortex pinning properties

Although high temperature superconductors are promising for power applications, the production of low-cost coated conductors with high current densitiesat high magnetic fieldsremains challenging. A superior superconducting YBa2Cu3O7- nanocomposite is fabricated via chemical solution deposition (CSD) using preformed nanocrystals (NCs). Preformed, colloidally stable ZrO2 NCs are added to the trifluoroacetic acid based precursor solution and the NCs' stability is confirmed up to 50 mol% for at least 2.5 months. These NCs tend to disrupt the epitaxial growth of YBa2Cu3O7-, unless a thin seed layer is applied. A 10 mol% ZrO2 NC addition proved to be optimal, yielding a critical current density J(C) of 5 MA cm(-2) at 77 K in self-field. Importantly, this new approach results in a smaller magnetic field decay of J(C)(H//c) for the nanocomposite compared to a pristine film. Furthermore, microstructural analysis of the YBa2Cu3O7- nanocomposite films reveals that different strain generation mechanisms may occur compared to the spontaneous segregation approach. Yet, the generated nanostrain in the YBa2Cu3O7- nanocomposite results in an improvement of the superconducting properties similar to the spontaneous segregation approach. This new approach, using preformed NCs in CSD coatings, can be of great potential for high magnetic field applications
Microwave Admittance of Gold-Palladium Nanowires with Proximity-Induced
  Superconductivity

We report quantitative electrical admittance measurements of diffusive
superconductor--normal-metal--superconductor (SNS) junctions at gigahertz
frequencies and millikelvin temperatures. The gold-palladium-based SNS
junctions are arranged into a chain of superconducting quantum interference
devices. The chain is coupled strongly to a multimode microwave resonator with
a mode spacing of approximately 0.6 GHz. By measuring the resonance frequencies
and quality factors of the resonator modes, we extract the dissipative and
reactive parts of the admittance of the chain. We compare the phase and
temperature dependence of the admittance near 1 GHz to theory based on the
time-dependent Usadel equations. This comparison allows us to identify
important discrepancies between theory and experiment that are not resolved by
including inelastic scattering or elastic spin-flip scattering in the theory.Comment: 8 pages, 6 figure
Source-Gated Transistors Based on Solution Processed Silicon Nanowires for Low Power Applications

The solution-based assembly of field-effect transistors using nanowire inks, processed at low temperatures, offers an enormous potential for low power applications envisioned for the “Internet of Things,” including power management sensor circuits and electronics for in vivo bioimplants. Such low-temperature assembly, however, yields substantial contact potential barriers, with limited capacity for high current applications. In this study, the Schottky effect in a specific transistor configuration is utilized to achieve much reduced power consumption, with low saturation voltages (≈1 V), with relatively thick 230-nm SiO2 dielectrics. These source-gated transistors (SGTs) employ solution-deposited silicon nanowire arrays. A range of metal electrode work functions are investigated as device contacts and SGT operation is realized only in the structures with high source contact barriers. Such devices show very early drain current pinch-off, abruptly saturating at low drain voltages. The authors show that drain-current modulation is achieved via the gate field acting on the source barrier and lowering it through image force effects. Activation energy measurements reveal gate-induced source barrier lowering of ≈3 meV V−1. Numerical simulations show excellent correlation with the experimental data. These features, coupled with flat current saturation characteristics, are ideal for a range of low power applications, including wearable electronics and autonomous systems
Luminescent Downshifting by Photo-Induced Sol-Gel Hybrid Coatings: Accessing Multifunctionality on Flexible Organic Photovoltaics via Ambient Temperature Material Processing

A novel high-durability multifunctional organic-inorganic hybrid coating material is presented in this work as luminescent down-shifting (LDS) host matrix system for flexible organic photovoltaic (OPV) devices. Such new LDS coating is obtained by incorporating a convenient fluorescent organic dye in an appropriately functionalized fluoropolymeric resin that can be readily crosslinked by means of a dual-cure mechanism with a single-step ambient-temperature photo-induced sol-gel process. Due to its peculiar characteristics, the newly proposed system may be readily implemented in heat-sensitive flexible devices. By carefully tuning the amount of organic fluorophore in the hybrid coating material, a maximum increase in power conversion efficiency exceeding 4% is achieved on devices incorporating the new LDS layer with respect to control systems. This represents the highest efficiency enhancement reported to date on flexible OPVs by means of a polymer-based LDS layer. In addition, long-term accelerated weathering tests (>550 h) highlight the excellent stability of LDS-coated OPV devices, which can retain 80% of their initial performance, as opposed to the dramatic efficiency decay experienced by control uncoated devices. The approach presented here opens the way to the straightforward incorporation of versatile multifunctional light-managing layers on flexible OPV systems for improved device efficiency and lifetime
First-Principles Modeling of Point Defects and Complexes in Thin-Film Solar-Cell Absorber CuInSe2

Point defects and complexes may affect significantly physical, optical, and electrical properties of semiconductors. The Cu(In,Ga)Se2 (CIGSe) alloy is an absorber material for low-cost thin-film solar cells. Several recently published computational investigations show contradicting results for important point defects such as copper antisite substituting indium (CuIn), indium vacancy (VIn), and complexes of point defects in CuInSe2. In the present work we study effects of the most important computational parameters especially on the formation energies of point defects. Moreover, related to defect identification by the help of their calculated properties we discuss possible explanations for the three acceptors, which occur in photoluminescence measurements of Cu-rich samples. [S. Siebentritt et al., Progress in Photovoltaics: Research and Applications 2010, 18, 390, S. Siebentritt et al., Physica Status Solidi (c) 2004, 1, 2304.] Finally, new insight into comparison between theoretical and experimental results is presented in the case of varying chemical potentials and of formation of secondary phases.Non Peer reviewe
Defect Dynamics in Proton Irradiated CH3NH3PbI3  Perovskite Solar Cells

Perovskite solar cells have been shown to be of extraordinary radiation hardness,  considering high energetic  68 MeV  proton irradiation with doses  up to 1013 p cm amp; 8722;2. In this study electrical and photoelectrical properties of  perovskite solar cells with and without proton irradiation are analyzed in  detail. The results reveal that proton irradiation improves the open circuit  voltage, fill factor, and recombination lifetime of photogenerated charge  carriers in perovskite solar cells. These enhancements are mainly a result of  the lower nonradiative recombination losses in the proton irradiated devices.  The proton treatment creates shallow traps, which may be associated with  the proton induced point defects due to the displacements of atoms in the  inorganic Pb I framework, which act as unintentional doping sources and  partially compensate deep traps originated from the photodegradation of  methylammonium molecule
Mixed-Mode Electro-Optical Operation of Ge2Sb2Te5 Nanoscale Crossbar Devices

This is the author accepted manuscript. The final version is freely available from Wiley via the DOI in this record.The use of phase-change materials for a range of exciting new optoelectronic applications from artificial retinas to ultrahigh-resolution displays requires a thorough understanding of how these materials perform under a combination of optical and electrical stimuli. This study reports for the first time the complex link between the electronic and optical properties in real-world crossbar nanoscale devices constructed by confining a thin layer of Ge2Sb2Te5 between transparent indium tin oxide electrodes, forming an optical nanocavity. A novel proof-of-concept device that can be operated by a combination of optical and electrical stimuli is presented, leading the way for the development of further applications based on mixed-mode electro-optical operation.CONACYT. Grant Number: 215365. EPSRC. Grant Numbers: EP/J018783/1, EP/M015173/1, EP/M015130/1, EP/J018694/
The Influence of Backbone Fluorination on the Dielectric Constant of Conjugated Polythiophenes

The ability to modify or enhance the dielectric constant of semiconducting polymers can prove valuable for a range of optoelectronic and microelectronic applications. In the case of organic photovoltaics, increasing the dielectric constant of the active layer has often been suggested as a method to control charge generation, recombination dynamics, and ultimately, the power conversion efficiencies. In this contribution, the impact that the degree and pattern of fluorination has on the dielectric constant of poly(3-octylthiophene) (P3OT), a more soluble analogue of the widely studied conjugated material poly(3-hexylthiophene), is explored. P3OT and its backbone-fluorinated analogue, F-P3OT, are compared along with a block and alternating copolymer version of these materials. It is found that the dielectric constant of the polymer thin films increases as the degree of backbone fluorination increases, in a trend consistent with density functional theory calculations of the dipole moment
Neuromorphic Time-Dependent Pattern Classification with Organic Electrochemical Transistor Arrays

Based on bottom‐up assembly of highly variable neural cells units, the nervous system can reach unequalled level of performances with respect to standard materials and devices used in microelectronic. Reproducing these basic concepts in hardware could potentially revolutionize materials and device engineering which are used for information processing. Here, an innovative approach that relies on both iono‐electronic materials and intrinsic device physics to show pattern classification out of a 12‐unit biosensing array is presented. The reservoir computing and learning concept to demonstrate relevant computing based on the ionic dynamics in 400 nm channel‐length organic electrochemical transistor is used. It is shown that this approach copes efficiently with the high level of variability obtained by bottom‐up fabrication using a new electropolymerizable polymer, which enables iono‐electronic device functionality and material stability in the electrolyte. The effect of the array size and variability on the performances for a real‐time classification task paving the way to new embedded sensing and processing approaches is investigate
Atomic Layer Deposition of Tin Monosulfide Thin Films

Thin film solar cells made from earth-abundant, non-toxic materials are needed to replace the current technology that uses \(Cu(In,Ga)(S,Se)_2\) and \(CdTe\), which contain scarce and toxic elements. One promising candidate absorber material is tin monosulfide (\(SnS\)). In this report, pure, stoichiometric, single-phase SnS films were obtained by atomic layer deposition (ALD) using the reaction of \(bis(N,N′-diisopropylacetamidinato)tin(II)\) \([Sn(MeC(N-^{i}Pr)_{2})_{2}]\) and hydrogen sulfide \((H_2 S)\) at low temperatures (100 to 200 \(°C\)). The direct optical band gap of SnS is around 1.3 eV and strong optical absorption \((\alpha > 10^4 cm^{−1})\) is observed throughout the visible and near-infrared spectral regions. The films are p-type semiconductors with carrier concentration on the order of \(10^{16} cm^{−3}\) and hole mobility \(0.82–15.3cm^{2}V^{−1}s^{−1}\) in the plane of the films. The electrical properties are anisotropic, with three times higher mobility in the direction through the film, compared to the in-plane direction.Chemistry and Chemical Biolog
Incorporation of Indium Tin Oxide Nanoparticles in PEMFC Electrodes

Carbon materials suffer from corrosion at the cathode of polymer electrolyte membrane fuel cells (PEMFCs). In the presence of water, carbon support materials are oxidized to carbon dioxide even at low potentials. Hence, nowadays it is very fashionable to look for alternative support materials, like oxides or conductive polymers. To gain the maximum performance for a new material one should also consider an appropriate electrode structure. This study shows the results for the incorporation of nanosized alternative support materials into advanced electrode architectures. Commercially available indium tin oxide (ITO) nanoparticles (<50 nm) are used as support for Pt nanoparticles in combination with Nafion‐coated multi‐walled carbon nanotubes (MWCNTs) on the cathode side of a PEMFC. The MWCNTs promote a high electronic conductivity and help to form a porous network, which could accommodate the Pt/ITO nanoparticles. The microscopic investigations show a homogeneous electrode structure composed of Pt/ITO and MWCNT/Nafion multilayer. Single cell measurements show a maximum power density of 73 mW cm −2  and a Pt utilization of 1468 mW mg Pt  −1  for the cathode. The performance data and the Pt utilization are comparable to a standard Pt/carbon black electrode possessing the same Pt loading in the electrode. Beside this, it is shown for the first time that ITO serves as support material under real fuel cell conditions.     Oxide support materials decorated with Pt nanoparticles  are embedded in a carbon nanotube network by a multilayer preparation technique. The corrosion‐stable support in combination with the porous structure offered by the CNTs leads to a high Pt utilization and a good electrochemical performance. Further optimization of the structure could result in stable, cost efficient, and easy to prepare electrodes
Skutterudite unicouple characterization for energy harvesting applications

Skutterudites are promising thermoelectric materials because of their high figure of merit, ZT, and good thermomechanical properties. This work reports the effective figure of merit, ZT[subscript eff], and the efficiency of skutterudite legs and a unicouple working under a large temperature difference. The p- and n-type legs are fabricated with electrodes sintered directly to the skutterudite during a hot pressing process. CoSi[subscript 2] is used as the electrode for the n-type skutterudite (Yb[subscript 0.35]Co[subscript 4]Sb[subscript 12]) and Co[subscript 2]Si for the p-type skutterudite (NdFe3.5Co0.5Sb12). A technique is developed to measure the ZTeff of individual legs and the efficiency of a unicouple. An ZT[subscript eff] of 0.74 is determined for the n-type legs operating between 52 and 595 °C, and an ZT[subscript eff] of 0.51 for the p-type legs operating between 77 and 600 °C. The efficiency of the p–n unicouple is determined to be 9.1% operating between ∼70 and 550 °C.Center for Clean Water and Clean Energy at MIT and KFUPMUnited States. Dept. of Energy. Office of Science (Award DE-SC0001299)United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-FG02-09ER46577
Molecular weight dependence of exciton diffusion in poly(3-hexylthiophene)

Z.M. is grateful to the Government of Brunei Darussalam for financial support. The research at St Andrews leading to these results has received funding from the Engineering and Physical Sciences Research Council of the UK, and from the European Union Seventh Framework Programme under grant agreement number 321305.A joint experimental and theoretical study of singlet exciton diffusion in spin-coated poly(3-hexylthiophene) (P3HT) films and its dependence on molecular weight is presented. The results show that exciton diffusion is fast along the co-facial pi-pi aggregates of polymer chromophores and about 100 times slower in the lateral direction between aggregates. Exciton hopping between aggregates is found to show a subtle dependence on interchain coupling, aggregate size, and Boltzmann statistics. Additionally, a clear correlation is observed between the effective exciton diffusion coefficient, the degree of aggregation of chromophores, and exciton delocalization along the polymer chain, which suggests that exciton diffusion length can be enhanced by tailored synthesis and processing conditions.PostprintPeer reviewe
Enhanced Near-Bandgap Response in InP Nanopillar Solar Cells

The article of record as published may be found at http://dx.doi.org/10.1002/aenm.201400061The effect of nanopillar texturing on the performance of InP solar cells is
investigated. Maskless, lithography-free reactive ion etching of InP nanopillars
improves the open-circuit voltage, reduces refl ectance over a broad
spectral range, and enhances the near-bandgap response compared to a fl at,
non-textured cell with comparable refl ectance in the infrared. Electron-beam
induced current measurements indicate an increased effective minority carrier
collection length. The response at short wavelengths decreases due to
the formation of a defective surface layer with strong non-radiative recombination.
Plasma oxidation and wet etching partially restore the blue response
resulting in a power conversion effi ciency of 14.4%.C.B. and J.X. contributed equally to this work. InP solar cell fabrication and characterization was funded by the Bay Area Photovoltaics Consortium (BAPVC). C.B. acknowledges support from the Zeno Karl Schindler Foundation
A Scalable Nanogenerator based on Self-Poled Piezoelectric Polymer Nanowires with High Energy Conversion Efficiency

Energy harvesting from vibrations is demonstrated using a nanogenerator composed of piezoelectric polymer nanowires with high energy conversion efficiency. Nanowires of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) grown using a simple, scalable, and cost-effective template-wetting technique are shown to be successfully exploited in high-performance nanogenerators without the need for electrical poling.SKN is grateful for support from the Royal Society through a Dorothy Hodgkin Fellowship. VN acknowledges the Herchel Smith Fund, University of Cambridge for a Fellowship. This work was supported by the EPSRC Cambridge NanoDTC, EP/G037221/1.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/aenm.20140051
Enhanced light harvesting in semitransparent organic solar cells using an optical metal cavity configuration

Aquest article pot ser utilitzat per a fins no comercials, d'acord amb  els termes i condicions d’auto-arxiu de Wiley. https://authorservices.wiley.com/author-resources/Journal-Authors/licensing-open-access/open-access/self-archiving.htmlAn optical metal cavity configuration is used to trap near infrared light in a semitransparent organic solar cell. The efficiency for such cell, which has a higher than 20% transparency in the visible region, is equal to 90% of the efficiency of the corresponding opaque cell.Peer ReviewedPostprint (author's final draft