772 research outputs found
Inverse melting of the vortex lattice
Inverse melting, in which a crystal reversibly transforms into a liquid or
amorphous phase upon decreasing the temperature, is considered to be very rare
in nature. The search for such an unusual equilibrium phenomenon is often
hampered by the formation of nonequilibrium states which conceal the
thermodynamic phase transition, or by intermediate phases, as was recently
shown in a polymeric system. Here we report a first-order inverse melting of
the magnetic flux line lattice in Bi2Sr2CaCu2O8 superconductor. At low
temperatures, the material disorder causes significant pinning of the vortices,
which prevents observation of their equilibrium properties. Using a newly
introduced 'vortex dithering' technique we were able to equilibrate the vortex
lattice. As a result, direct thermodynamic evidence of inverse melting
transition is found, at which a disordered vortex phase transforms into an
ordered lattice with increasing temperature. Paradoxically, the structurally
ordered lattice has larger entropy than the disordered phase. This finding
shows that the destruction of the ordered vortex lattice occurs along a unified
first-order transition line that gradually changes its character from
thermally-induced melting at high temperatures to a disorder-induced transition
at low temperatures.Comment: 13 pages, 4 figures, Nature, In pres
Three-Dimensional Optical Transformer - Highly Efficient Nanofocusing Device
Using electron-beam-induced deposition and focused-ion-beam milling, we have fabricated and demonstrated a nanofocusing optical transformer with a 3-dimensionally tapered tip.
At the tip, the light is confined to 13-by-80-nm area with intensity enhancement exceeding 1500
Thermally activated delayed fluorescent dendrimers that underpin high-efficiency host-free solution-processed organic light emitting diodes
This project has received funding from the European Unionâs Horizon 2020 research and innovation program under the Marie SkĆodowska-Curie grant agreements No. 838009 (TSFP) and No 812872 (TADFlife). D.S. acknowledges support from the Marie SkĆodowska-Curie Individual Fellowship (TSFP), the National Postdoctoral Program for Innovative Talents (BX201700164), and the Jiangsu Planned Projects for Postdoctoral Research Funds (2018K011A). S.B. acknowledges support from the German Science Foundation (392306670/HU2362). The St Andrews team thank the Leverhulme Trust (RPG2016047) and EPSRC (EP/P010482/1) for financial support. X.Z. would like to thank the support from the National Key Research & Development Program of China (Grant No. 2020YFA0714601, 2020YFA0714604), the National Natural Science Foundation of China (Grant No. 52130304, 51821002), Suzhou Key Laboratory of Functional Nano & Soft Materials, Collaborative Innovation Center of Suzhou Nano Science & Technology, the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), the 111 Project, Joint International Research Laboratory of Carbon-Based Functional Materials and Devices. E. Z.-C. is a Royal Society Leverhulme Trust Senior Research fellow (SRF\R1\201089).The development of high-performance solution-processed organic light-emitting diodes (OLEDs) remains a challenge. An effective solution, highlighted in this work, is to use highly efficient thermally activated delayed fluorescence (TADF) dendrimers as emitters. Here, the design, synthesis, density functional theory (DFT) modeling, and photophysics of three triazine-based dendrimers, tBuCz2pTRZ , tBuCz2mTRZ , and tBuCz2m2pTRZ , is reported, which resolve the conflicting requirements of achieving simultaneously a small ÎEST and a large oscillator strength by incorporating both meta- and para-connected donor dendrons about a central triazine acceptor. The solution-processed OLED containing a host-free emitting layer exhibits an excellent maximum external quantum efficiency (EQEmax) of 28.7%, a current efficiency of 98.8 cd Aâ1, and a power efficiency of 91.3 lm Wâ1. The device emits with an electroluminescence maximum, λEL, of 540 nm and Commission International de l'Ăclairage (CIE) color coordinates of (0.37, 0.57). This represents the most efficient host-free solution-processed OLED reported to date. Further optimization directed at improving the charge balance within the device results in an emissive layer containing 30 wt% OXD-7, which leads to an OLED with the similar EQEmax of 28.4% but showing a significantly improved efficiency rolloff where the EQE remains high at 22.7% at a luminance of 500 cd mâ2.Publisher PDFPeer reviewe
Regiochemistry of donor dendrons controls the performance of thermally activated delayed fluorescence dendrimer emitters for high efficiency solution-processed organic light-emitting diodes
This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie SkĆodowska-Curie grant agreement No. 838009 (TSFP) and No 812872 (TADFlife). D.S. acknowledges support from the Marie SkĆodowska-Curie Individual Fellowship, the National Postdoctoral Program for Innovative Talents (BX201700164), the Jiangsu Planned Projects for Postdoctoral Research Funds (2018K011A). E.Z.-C. is a Royal Society Leverhulme Trust Senior Research fellow (SRFâR1â201089). The St Andrews team would also like to thank the Leverhulme Trust (RPG-2016047) and EPSRC (EP/P010482/1) for financial support. This work was also supported by Comunidad de Madrid (Spain) â multiannual agreement with UC3M (âExcelencia para el Profesorado Universitarioâ â EPUC3M14) â Fifth regional research plan 2016-2020 and by the Spanish Ministry of Science, Innovation and Universities (MICINN) through project RTI2018-101020-B-100. X.Z. would like to thank the support from the National Key Research & Development Program of China (Grant No. 2020YFA0714601, 2020YFA0714604), the National Natural Science Foundation of China (Grant No. 52130304, 51821002), Suzhou Key Laboratory of Functional Nano & Soft Materials, Collaborative Innovation Center of Suzhou Nano Science & Technology, the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), the 111 Project, Joint International Research Laboratory of Carbon-Based Functional Materials and Devices.The potential of dendrimers exhibiting thermally activated delayed fluorescence (TADF) as emitters in solution-processed organic light-emitting diodes (OLEDs) has to date not yet been realized. This in part is due to a poor understanding of the structureâproperty relationship in dendrimers where reports of detailed photophysical characterization and mechanism studies are lacking. In this report, using absorption and solvatochromic photoluminescence studies in solution, the origin and character of the lowest excited electronic states in dendrimers with multiple dendritic electron-donating moieties connected to a central electron-withdrawing core via a para- or a meta-phenylene bridge is probed. Characterization of host-free OLEDs reveals the superiority of meta-linked dendrimers as compared to the already reported para-analogue. Comparative temperature-dependent time-resolved solid-state photoluminescence measurements and quantum chemical studies explore the effect of the substitution mode on the TADF properties and the reverse intersystem crossing (RISC) mechanism, respectively. For TADF dendrimers with similarly small âEST, it is observed that RISC can be enhanced by the regiochemistry of the donor dendrons due to control of the reorganization energies, which is a heretofore unexploited strategy that is distinct from the involvement of intermediate triplet states through a nonadiabatic (vibronic) coupling with the lowest singlet charge transfer state.Publisher PDFPeer reviewe
The Manhattan effect: When relationship commitment fails to promote support for partnersâ interests
Research on close relationships has frequently contrasted oneâs own interests with the interests of the partner or the relationship and has tended to view the partnerâs and the relationshipâs interests as inherently aligned. The present article demonstrated that relationship commitment typically causes people to support their partnerâs personal interests but that this effect gets weaker to the extent that those interests misalign or even threaten the relationship. Studies 1a and 1b showed that (a) despite their strong correlation, partner-oriented and relationship-oriented concerns in goal-directed behaviors are separable and (b) relationship commitment strengthens only the link between relationship-oriented motivation and the goal pursuit (not the link between partner-oriented motivation and the goal pursuit). The remaining 7 studies zero in on circumstances in which the partnerâs and the relationshipâs interests are in conflict, demonstrating that (c) relationship commitment reliably increases the tendency to support the partnerâs personal interests when those interests do not pose a strong threat to the relationship but that (d) this effect becomes weakerâand even reverses directionâas the relationship threat posed by the partnerâs interests becomes stronger. The reduction or reversal of the positive link between relationship commitment and propartner behaviors in such situations is termed the Manhattan effect. These findings suggest that the partner-versus-relationship conflicts provide fertile ground for novel theorizing and empirical investigations and that relationship commitment appears to be less of a partner-promoting construct than relationship science has suggested; instead, its role appears to be focused on promoting the interests of the relationship
Radiation Engineering of Optical Antennas for Maximum Field Enhancement
Optical antennas have generated much interest in
recent years due to their ability to focus optical energy beyond
the diffraction limit, benefiting a broad range of applications
such as sensitive photodetection, magnetic storage, and surfaceenhanced
Raman spectroscopy. To achieve the maximum field
enhancement for an optical antenna, parameters such as the
antenna dimensions, loading conditions, and coupling efficiency
have been previously studied. Here, we present a framework,
based on coupled-mode theory, to achieve maximum field
enhancement in optical antennas through optimization of optical antennasâ radiation characteristics. We demonstrate that the
optimum condition is achieved when the radiation quality factor (Q_(rad)) of optical antennas is matched to their absorption quality
factor (Q_(abs)). We achieve this condition experimentally by fabricating the optical antennas on a dielectric (SiO2) coated ground
plane (metal substrate) and controlling the antenna radiation through optimizing the dielectric thickness. The dielectric thickness at
which the matching condition occurs is approximately half of the quarter-wavelength thickness, typically used to achieve
constructive interference, and leads to âŒ20% higher field enhancement relative to a quarter-wavelength thick dielectric layer
Characterization of Extended Width Optical Dipole Antennas
Optical dipole antennas with varying length and width are fabricated using e-beam lithography. Antennas with wider width are shown to exhibit stronger scattering while preserving the same resonance frequency
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