pinecone/core-2020-05-10-deduplication huggingface dataset:
Shorter Exciton Lifetimes via an External Heavy-Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light-Emitting Diodes

Multiexcited‐state phenomena are believed to be the root cause of two exigent challenges in organic light‐emitting diodes; namely, efficiency roll‐off and degradation. The development of novel strategies to reduce exciton densities under heavy load is therefore highly desirable. Here, it is shown that triplet exciton lifetimes of thermally activated delayed‐fluorescence‐emitter molecules can be manipulated in the solid state by exploiting intermolecular interactions. The external heavy‐atom effect of brominated host molecules leads to increased spin–orbit coupling, which in turn enhances intersystem crossing rates in the guest molecule. Wave function overlap between the host and the guest is confirmed by combined molecular dynamics and density functional theory calculations. Shorter triplet exciton lifetimes are observed, while high photoluminescence quantum yields and essentially unaltered emission spectra are maintained. A change in the intersystem crossing rate ratio due to increased dielectric constants leads to almost 50% lower triplet exciton densities in the emissive layer in the steady state and results in an improved onset of the photoluminescence quantum yield roll‐off at high excitation densities. Efficient organic light‐emitting diodes with better roll‐off behavior based on these novel hosts are fabricated, demonstrating the suitability of this concept for real‐world applications.United States. Department of Energy (Grant DE‐FG02‐07ER46474
Ferroelectrics as smart mechanical materials

The mechanical properties of materials are insensitive to space inversion, even when they are crystallographically asymmetric. In practice, this means that turning a piezoelectric crystal upside down or switching the polarization of a ferroelectric should not change its mechanical response. Strain gradients, however, introduce an additional source of asymmetry that has mechanical consequences. Using nanoindentation and contact‐resonance force microscopy, this study demonstrates that the mechanical response to indentation of a uniaxial ferroelectric (LiNbO₃) does change when its polarity is switched, and use this mechanical asymmetry both to quantify its flexoelectricity and to mechanically read the sign of its ferroelectric domains
Bis-tridentate Ir(III) metal phosphors for efficient deep-blue organic light-emitting diodes.

Emissive Ir(III) metal complexes possessing two tridentate chelates (bis-tridentate) are known to be more robust compared to those with three bidentate chelates (tris-bidentate). Here, the deep-blue-emitting, bis-tridentate Ir(III) metal phosphors bearing both the dicarbene pincer ancillary such as 2,6-diimidazolylidene benzene and the 6-pyrazolyl-2-phenoxylpyridine chromophoric chelate are synthesized. A deep-blue organic light-emitting diode from one phosphor exhibits Commission Internationale de l'Eclairage (CIE(x,y)) coordinates of (0.15, 0.17) with maximum external quantum efficiency (max. EQE) of 20.7% and EQE = 14.6% at the practical brightness of 100 cd m−2
Highly Efficient Rubrene–Graphene Charge-Transfer Interfaces as Phototransistors in the Visible Regime

This is the final version of the article. Available from Wiley via the DOI in this record.Atomically thin materials such as graphene are uniquely responsive to charge transfer from adjacent materials, making them ideal charge-transport layers in phototransistor devices. Effective implementation of organic semiconductors as a photoactive layer would open up a multitude of applications in biomimetic circuitry and ultra-broadband imaging but polycrystalline and amorphous thin films have shown inferior performance compared to inorganic semiconductors. Here, the long-range order in rubrene single crystals is utilized to engineer organic-semiconductor–graphene phototransistors surpassing previously reported photogating efficiencies by one order of magnitude. Phototransistors based upon these interfaces are spectrally selective to visible wavelengths and, through photoconductive gain mechanisms, achieve responsivity as large as 10^7 A/W and a detectivity of 9 × 10^11 Jones at room temperature. These findings point toward implementing low-cost, flexible materials for amplified imaging at ultralow light levels.S.R. and M.F.C. acknowledge financial support from EPSRC (Grant 464 Nos. EP/J000396/1, EP/K017160/1, EP/K010050/1, EP/G036101/1, EP/M001024/1, and 465 EP/M002438/1), from Royal Society international Exchanges Scheme 2012/R3 and 466 2013/R2 and from European Commission (No. FP7-ICT-2013-613024-GRASP)
Structure Formation in Soft Matter Solutions Induced by Solvent
  Evaporation

Solvent evaporation in soft matter solutions (solutions of colloidal
particles, polymers and their mixtures) is an important process in material
making and in printing and coating industries. The solvent evaporation process
determines the structure of the materials, and strongly affects their
performance. Solvent evaporation involves many physico-chemical processes:
flow, diffusion, crystallization, gelation, glass transition, etc., and is
quite complex. In this article, we report recent progresses in this important
process, with a special focus on theoretical and simulation studies.Comment: 13 pages, 4 figures, Research News for an Advanced Materials Special
  Issue celebrating the 65th Anniversary of Beihang Universit
Highly Crystalline C8-BTBT Thin-Film Transistors by Lateral Homo-Epitaxial Growth on Printed Templates

Highly crystalline thin films of organic semiconductors offer great potential for fundamental material studies as well as for realizing high-performance, low-cost flexible electronics. The fabrication of these films directly on inert substrates is typically done by meniscus-guided coating techniques. The resulting layers show morphological defects that hinder charge transport and induce large device-to-device variability. Here, a double-step method for organic semiconductor layers combining a solution-processed templating layer and a lateral homo-epitaxial growth by a thermal evaporation step is reported. The epitaxial regrowth repairs most of the morphological defects inherent to meniscus-guided coatings. The resulting film is highly crystalline and features a mobility increased by a factor of three and a relative spread in device characteristics improved by almost half an order of magnitude. This method is easily adaptable to other coating techniques and offers a route toward the fabrication of high-performance, large-area electronics based on highly crystalline thin films of organic semiconductors.status: publishe
Coupling Mechanical and Electrical Properties in Spin Crossover Polymer Composites

Spin crossover particles of formula[Fe{(Htrz)2(trz)}0.9(NH2-trz)0.3](BF4)1.1 and average size of 20 nm ± 8 nm are homogeneously dispersed in poly(vinylidene,fluoride-co-trifluoro-ethylene), P(VDF-TrFE), and poly(vinylidene fluoride)PVDF) matrices to form macroscopic (cm-scale), freestanding, and flexible nanocomposite materials. The composites exhibit concomitant thermal expansion and discharge current peaks on cycling around the spin transition temperatures, i.e., new “product properties” resulting from the synergy between the particles and the matrix. Poling the P(VDF-TrFE) (70–30 mol%) samples loaded with 25 wt% of particles in 18 MV m−1 electric field results in a piezoelectric coefficient d33 = −3.3 pC N−1. The poled samples display substantially amplified discharges and altered spin transition properties. Analysis of mechanical and dielectric properties reveals that both strain (1%) and permittivity (40%) changes in the composite accompany the spin transition in the particles, giving direct evidence for strong electromechanical couplings between the components. These results provide a novel route for the deployment of molecular spin crossover materials as actuators in artificial muscles and generators in thermal energy harvesting devices
Engineering Extracellular Vesicles with the Tools of Enzyme Prodrug Therapy.

Extracellular vesicles (EVs) have recently gained significant attention as important mediators of intercellular communication, potential drug carriers, and disease biomarkers. These natural cell-derived nanoparticles are postulated to be biocompatible, stable under physiological conditions, and to show reduced immunogenicity as compared to other synthetic nanoparticles. Although initial clinical trials are ongoing, the use of EVs for therapeutic applications may be limited due to undesired off-target activity and potential "dilution effects" upon systemic administration which may affect their ability to reach their target tissues. To fully exploit their therapeutic potential, EVs are embedded into implantable biomaterials designed to achieve local delivery of therapeutics taking advantage of enzyme prodrug therapy (EPT). In this first application of EVs for an EPT approach, EVs are used as smart carriers for stabilizing enzymes in a hydrogel for local controlled conversion of benign prodrugs to active antiinflammatory compounds. It is shown that the natural EVs' antiinflammatory potential is comparable or superior to synthetic carriers, in particular upon repeated long-term incubations and in different macrophage models of inflammation. Moreover, density-dependent color scanning electron microscopy imaging of EVs in a hydrogel is presented herein, an impactful tool for further understanding EVs in biological settings
Efficient and stable perovskite solar cells using low-cost aniline-based enamine hole-transporting materials

Metal‐halide perovskites offer great potential to realize low‐cost and flexible next‐generation solar cells. Low‐temperature‐processed organic hole‐transporting layers play an important role in advancing device efficiencies and stabilities. Inexpensive and stable hole‐transporting materials (HTMs) are highly desirable toward the scaling up of perovskite solar cells (PSCs). Here, a new group of aniline‐based enamine HTMs obtained via a one‐step synthesis procedure is reported, without using a transition metal catalyst, from very common and inexpensive aniline precursors. This results in a material cost reduction to less than 1/5 of that for the archetypal spiro‐OMeTAD. PSCs using an enamine V1091 HTM exhibit a champion power conversion efficiency of over 20%. Importantly, the unsealed devices with V1091 retain 96% of their original efficiency after storage in ambient air, with a relative humidity of 45% for over 800 h, while the devices fabricated using spiro‐OMeTAD dropped down to 42% of their original efficiency after aging. Additionally, these materials can be processed via both solution and vacuum processes, which is believed to open up new possibilities for interlayers used in large‐area all perovskite tandem cells, as well as many other optoelectronic device applications
Incipient Metals: Functional Materials with a Unique Bonding Mechanism

Abstract While solid-state materials are commonly classified as covalent, ionic, or metallic, there are cases that defy these iconic bonding mechanisms. Phase-change materials (PCMs) for data storage are a prominent example: they have been claimed to show “resonant bonding,” but a clear definition of this mechanism has been lacking. Here, it is shown that these solids are fundamentally different from resonant bonding in the π-orbital systems of benzene and graphene, based on first-principles data for vibrational, optical, and polarizability properties. It is shown that PCMs and related materials exhibit a unique mechanism between covalent and metallic bonding. It is suggested that these materials be called “incipient metals,” and their bonding nature “metavalent”. Data for a diverse set of 58 materials show that metavalent bonding is not just a superposition of covalent and metallic cases, but instead gives rise to a unique and anomalous set of physical properties. This allows the derivation of a characteristic fingerprint of metavalent bonding, composed of five individual components and firmly rooted in physical properties. These findings are expected to accelerate the discovery and design of functional materials with attractive properties and applications, including nonvolatile memories, thermoelectrics, photonics, and quantum materials.Peer reviewe
Do images of Biskyrmions show Type-II bubbles?

The intense research effort investigating magnetic skyrmions and their applications for spintronics has yielded reports of more exotic objects including the biskyrmion, which consists of a bound pair of counter‐rotating vortices of magnetization. Biskyrmions have been identified only from transmission electron microscopy images and have not been observed by other techniques, nor seen in simulations carried out under realistic conditions. Here, quantitative Lorentz transmission electron microscopy, X‐ray holography, and micromagnetic simulations are combined to search for biskyrmions in MnNiGa, a material in which they have been reported. Only type‐I and type‐II magnetic bubbles are found and images purported to show biskyrmions can be explained as type‐II bubbles viewed at an angle to their axes. It is not the magnetization but the magnetic flux density resulting from this object that forms the counter‐rotating vortices
Driving spin and charge in quantum wells by surface acoustic waves

Recent experiments have shown the potential of surface acoustic waves as a
mean for transporting charge and spin in quantum wells. In particular, they
have proven highly effective for the coherent transport of spin-polarized wave
packets, suggesting their potential in spintronics applications. Motivated by
these experimental observations, we have theoretically studied the spin and
charge dynamics in a quantum well under surface acoustic waves. We show that
the dynamics acquires a simple and transparent form in a reference frame
co-moving with the surface acoustic wave. Our results, e.g., the calculated
spin relaxation and precession lengths, are in excellent agreement with recent
experimental observations.Comment: 8 pages, 5 figure
UV-assisted low temperature oxide dielectric films for TFT applications.\ud

Solution-based oxide gate dielectric layers are prepared from metal nitrates using UV-assisted annealing at 150 °C. The leakage current densities of ZrO2 and Al2O3 dielectrics are less than about 10-9 A/cm2 at 1 MV/cm and comparable to those formed by annealing at higher temperatures. High dielectric constants and the low leakage current behavior of the dielectric layers provide excellent ZnO TFT performance, with a field effect mobility of 1.37 cm2/V.s and an off-current density of 10-12 A/cm2. This low fabrication temperature process is compatible with future plastic electronics technology. \u
Molecular design of antifouling polymer brushes using sequence-specific peptoids

Material systems that can be used to flexibly and precisely define the chemical nature and molecular arrangement of a surface would be invaluable for the control of complex biointerfacial interactions. For example, progress in antifouling polymer biointerfaces that prevents nonspecific protein adsorption and cell attachment, which can significantly improve the performance of an array of biomedical and industrial applications, is hampered by a lack of chemical models to identify the molecular features conferring their properties. Poly(N-substituted glycine) “pep- toids” are peptidomimetic polymers that can be conveniently synthesized with specific monomer sequences and chain lengths, and are presented as a versatile platform for investigating the molecular design of antifouling polymer brushes. Zwitterionic antifouling polymer brushes have captured significant recent atten- tion, and a targeted library of zwitterionic peptoid brushes with different charge densities, hydration, separations between charged groups, chain lengths, and grafted chain densities, is quantitatively evaluated for their antifouling properties through a range of protein adsorption and cell attachment assays. Specific zwit- terionic brush designs are found to give rise to distinct but subtle differences in properties. The results also point to the dominant roles of the grafted chain density and chain length in determining the performance of antifouling polymer brushes
Graphoepitaxy of High-Quality GaN Layers on Graphene/6H–SiC

The implementation of graphene layers in gallium nitride (GaN) heterostructure\ud
growth can solve self-heating problems in nitride-based high-power electronic\ud
and light-emitting optoelectronic devices. In the present study, high-quality GaN\ud
layers are grown on patterned graphene layers and 6H–SiC by metalorganic\ud
chemical vapor deposition. A periodic pattern of graphene layers is fabricated\ud
on 6H–SiC by using polymethyl methacrylate deposition and electron beam\ud
lithography, followed by etching using an Ar/O\ud
2\ud
gas atmosphere. Prior to GaN\ud
growth, an AlN buffer layer and an Al\ud
0.2\ud
Ga\ud
0.8\ud
N transition layer are deposited.\ud
The atomic structures of the interfaces between the 6H–SiC and graphene, as\ud
well as between the graphene and AlN, are studied using scanning transmission\ud
electron microscopy. Phase separation of the Al\ud
0.2\ud
Ga\ud
0.8\ud
N transition layer into an\ud
AlN and GaN superlattice is observed. Above the continuous graphene layers,\ud
polycrystalline defective GaN is rapidly overgrown by better quality single-crys-\ud
talline GaN from the etched regions. The lateral overgrowth of GaN results in\ud
the presence of a low density of dislocations (\ud
≈\ud
10\ud
9\ud
cm\ud
−\ud
2\ud
) and inversion domains\ud
and the formation of a smooth GaN surface
Giant switchable Rashba effect in oxide heterostructures

One of the most fundamental phenomena and a reminder of the electron's
relativistic nature is the Rashba spin splitting for broken inversion symmetry.
Usually this splitting is a tiny relativistic correction, hardly discernible in
experiment. Interfacing a ferroelectric, BaTiO$_3$, and a heavy 5$d$ metal with
a large spin-orbit coupling, Ba(Os,Ir)O$_3$, we show that giant Rashba spin
splittings are indeed possible and even fully controllable by an external
electric field. Based on density functional theory and a microscopic tight
binding understanding, we conclude that the electric field is amplified and
stored as a ferroelectric Ti-O distortion which, through the network of oxygen
octahedra, also induces a large Os-O distortion. The BaTiO$_3$/BaOsO$_3$
heterostructure is hence the ideal test station for studying the fundamentals
of the Rashba effect. It allows intriguing application such as the Datta-Das
transistor to operate at room temperature.Comment: This is the pre-peer reviewed version of the following article:Giant
  switchable Rashba effect in oxide heterostructures, advanced materials
  interfaces 2015, 1400445, which has been published in final form at
  http://dx.doi.org/10.1002/admi.20140044
Designing Durable Vapor-Deposited Surfaces for Reduced Hydrate Adhesion

The formation and accumulation of clathrate hydrates inside oil and gas pipelines cause severe problems in deep-sea oil/gas operations. In the present work, durable and mechanically robust bilayer poly-divinyl benzene/poly(perfluorodecylacrylate) coatings are developed using initiated chemical vapor deposition (iCVD) to reduce the adhesion strength of hydrates to underlying substrates (silicon and steel). Tetrahydrofuran (THF) dissolved in water with a wt% concentration of 0–70 is used to study the formation of hydrates and their adhesion strength. Goniometric measurements of the THF–water droplets on the substrates exhibit a reduction in advancing and receding contact angles with an increase in the THF concentration. The strength of hydrate adhesion experiences a tenfold reduction when substrates are coated with these iCVD polymers: from 1050 ± 250 kPa on bare silicon to 128 ± 100 kPa on coated silicon and from 1130 ± 185 kPa on bare steel to 153 ± 86 kPa on coated steel. The impact of subcooling temperature and time on the adhesion strength of hydrate on substrates is also studied. The results of this work suggest that the THF–water mixture repellency of a given substrate can be utilized to assess its hydrate-phobic behavior; hence, it opens a pathway for studying hydrate-phobicity.Chevron Corporation (MIT-Chevron University Partnership Program
Wide-Range Tunable Dynamic Property of Carbon Nanotube-Based Fibers

Carbon nanotube (CNT) fiber is formed by assembling millions of individual
tubes. The assembly feature provides the fiber with rich interface structures
and thus various ways of energy dissipation, as reflected by the non-zero loss
tangent (>0.028--0.045) at low vibration frequencies. A fiber containing
entangled CNTs possesses higher loss tangents than a fiber spun from aligned
CNTs. Liquid densification and polymer infiltration, the two common ways to
increase the interfacial friction and thus the fiber's tensile strength and
modulus, are found to efficiently reduce the damping coefficient. This is
because the sliding tendency between CNT bundles can also be well suppressed by
the high packing density and the formation of covalent polymer cross-links
within the fiber. The CNT/bismaleimide composite fiber exhibited the smallest
loss tangent, nearly as the same as that of carbon fibers. At a higher level of
the assembly structure, namely a multi-ply CNT yarn, the inter-fiber friction
and sliding tendency obviously influence the yarn's damping performance, and
the loss tangent can be tuned within a wide range, as similar to carbon fibers,
nylon yarns, or cotton yarns. The wide-range tunable dynamic properties allow
new applications ranging from high quality factor materials to dissipative
systems
‘Isofacet’ anatase TiO2 microcages : topotactic synthesis and ultrastable Li-ion storage

This work was financially supported by National Natural Science Foundation (NSF) of China and the Government of Guangdong Province for NSF (U1301242, 21271190 and S2012020011113), the Specialized Research Fund for the Doctoral Program of Higher Education (20130171130001) and industry (2012B09000026), and the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University (2012-01). Qili Wu and Xianfeng Yang contributed equally to this work.A new type of anatase TiO2 microcages assembled by oriented nanocrystals have been successfully fabricated through a topotactical conversion from CaTiO3 microcage precursor. The anatase microcages have all their six side faces dominated by anatase {001} facets, as revealed by detailed electron microscopy characterization. When used as the anode material for Li-ion storage, the unique microcages have the advantage of remarkable structural stability, high surface areas, and facile electronic conduction path. As a result, the TiO2 microcages-based anode achieves a high lithium storage performance especially at high current rates and long cycling stability, giving 175 mAh g-1 at 5C (850 mA g-1) after 800 cycles and 95 mAh g-1 at 50 C after 5000 cycles. Our comparison to the literature shows that this is a competitive and promising material for Li-ion battery and potentially also photocatalyst applications.PostprintPeer reviewe