Electroluminescence efficiencies and stabilities of quasi-two-dimensional halide perovskites are restricted by the formation of multiple-quantum-well structures with broad and uncontrollable phase distributions. Here,...
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Electroluminescence efficiencies and stabilities of quasi-two-dimensional halide perovskites are restricted by the formation of multiple-quantum-well structures with broad and uncontrollable phase distributions. Here, we report a ligand design strategy to substantially suppress diffusion-limited phase disproportionation, thereby enabling better phase control. We demonstrate that extending the π-conjugation length and increasing the cross-sectional area of the ligand enables perovskite thin films with dramatically suppressed ion transport, narrowed phase distributions, reduced defect densities, and enhanced radiative recombination efficiencies. Consequently, we achieved efficient and stable deep-red light-emitting diodes with a peak external quantum efficiency of 26.3% (average 22.9% among 70 devices and cross-checked) and a half-life of ~220 and 2.8 h under a constant current density of 0.1 and 12 mA/cm, respectively. Our devices also exhibit wide wavelength tunability and improved spectral and phase stability compared with existing perovskite light-emitting diodes. These discoveries provide critical insights into the molecular design and crystallization kinetics of low-dimensional perovskite semiconductors for light-emitting devices.
Among two-dimensional lattices, both kagome and Lieb lattices have been extensively studied, showing unique physics related to their exotic flat and Dirac bands. Interestingly, we realize that the two lattices are in ...
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Among two-dimensional lattices, both kagome and Lieb lattices have been extensively studied, showing unique physics related to their exotic flat and Dirac bands. Interestingly, we realize that the two lattices are in fact interconvertible by applying strains along the diagonal direction, as they share the same structural configuration in the unit cell, i.e., one corner-site and two edge-center states. We study phase transitions between the two lattices using the tight-binding approach and propose one experimental realization of the transitions using photonic devices. The evolution of the band structure demonstrates a continuous evolution of the flat band from the middle of the Lieb band to the top/bottom of the kagome band. Though the flat band is destroyed during the transition, the topological features are conserved due to the retained inversion symmetry, as confirmed by Berry curvature, Wannier charge center, and edge state calculations. Meanwhile, the triply degenerate Dirac point (M) in the Lieb lattice transforms into two doubly degenerate Dirac points, one of which moves along M−Γ and the other moves along M−K/K′ directions that form the kagome band eventually. Interestingly, the Dirac cones in the transition states are strongly tilted, showing a coexistence of type-I and type-II Dirac points. We finally show that these transitions can be experimentally realized in photonic lattices using waveguide arrays.
We investigated thermal properties of the epoxy-based composites with a high loading fraction - up to ff ≈ 45 vol. % - of the randomly oriented electrically conductive graphene fillers and electrically insulating bor...
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We have investigated the interlayer shear and breathing phonon modes in MoS2 with pure 3R and 2H stacking order by using polarization-dependent ultralow-frequency Raman spectroscopy. We observe up to three shear branc...
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INTRODUCTION:Poor sleep may be a risk factor for neurodegeneration and Alzheimer's disease (AD). Few studies have examined objectively measured sleep with structural neuroimaging measures.METHODS:Vanderbilt Memory...
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INTRODUCTION:Poor sleep may be a risk factor for neurodegeneration and Alzheimer's disease (AD). Few studies have examined objectively measured sleep with structural neuroimaging measures.
METHODS:Vanderbilt Memory and Aging Project participants (N = 407; median age: 70 years) wore ActiGraph accelerometers for 10 days to estimate sleep regularity, timing, efficiency, duration, wake-after-sleep onset, and awakening length. Volume in brain regions of interest (ROIs) and AD signatures were quantified using 3T brain magnetic resonance imaging (MRI). Cross-sectional linear regression models were adjusted for sociodemographic and lifestyle factors, depression, cognitive status, and cardiovascular risk. ROI and McEvoy models were adjusted for total intracranial volume.
RESULTS:Greater sleep irregularity (β= -0.12, p = 0.005; β= -0.07, p = 0.024) and longer awakening length (β= -0.11, p = 0.009; β= -0.08, p = 0.012) were associated with smaller volumes in ROIs related to AD.
DISCUSSION:More irregular and fragmented sleep was associated with smaller volume in ROIs vulnerable to AD, indicating a potential link between poor sleep and neurodegeneration.
HIGHLIGHTS:Associations between sleep and brain health are poorly understood. Gray matter atrophy by irregular sleep may imply Alzheimer's disease (AD) decline. Increased sleep irregularity is associated with smaller brain region volume. Sleep disruption, estimated by awakening length, is linked to AD-related brain volume.
Image processing has become a critical technology in a variety of science and engineering disciplines. While most image processing is performed digitally, optical analog processing has the advantages of being low-powe...
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In article number 2007346, Dae-Hyeong Kim, Taeghwan Hyeon, Donghee Son, and co-workers develop a durable and fatigue-resistant soft bidirectional neuroprosthetic device composed of a biocompatible nanocomposite of gol...
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In article number 2007346, Dae-Hyeong Kim, Taeghwan Hyeon, Donghee Son, and co-workers develop a durable and fatigue-resistant soft bidirectional neuroprosthetic device composed of a biocompatible nanocomposite of gold-nanoshell-coated silver flakes dispersed in a tough, stretchable, and self-healing polymer. The electrical conductivity of our neuroprosthetics spontaneously recovers even after repetitive degradations by irregular and severe mechanical deformations.
Owing to the difficulty in detecting and manipulating the magnetic states of antiferromagnetic materials, studying their switching dynamics using electrical methods remains a challenging task. By employing heavy-metal...
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Owing to the difficulty in detecting and manipulating the magnetic states of antiferromagnetic materials, studying their switching dynamics using electrical methods remains a challenging task. By employing heavy-metal–rare-earth–transition-metal alloy bilayers, we experimentally study current-induced domain wall dynamics in an antiferromagnetically coupled system. We show that the current-induced domain wall mobility reaches a maximum at the angular momentum compensation point. With experiment and modeling, we further reveal the internal structures of domain walls and the underlying mechanisms for their fast motion. We show that the chirality of the ferrimagnetic domain walls remains the same across the compensation points, suggesting that spin orientations of specific sublattices rather than net magnetization determine Dzyaloshinskii-Moriya interaction in heavy-metal–ferrimagnet bilayers. The high current-induced domain wall mobility and the robust domain wall chirality in compensated ferrimagnetic material opens new opportunities for high-speed spintronic devices.
Lithium-intercalated layered transition-metal oxides, LixTMO2, brought about a paradigm change in rechargeable batteries in recent decades and show promise for use in memristors, a type of device for future neural com...
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We demonstrate a unidirectional motion of a quasiparticle without explicit symmetry breaking along the space-time coordinate of the particle motion. This counterintuitive behavior originates from a combined action of ...
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We demonstrate a unidirectional motion of a quasiparticle without explicit symmetry breaking along the space-time coordinate of the particle motion. This counterintuitive behavior originates from a combined action of two intrinsic asymmetries in the other two directions. We realize this idea with the magnon-driven motion of a magnetic domain wall in thin films with interfacial asymmetry. Contrary to previous studies, the domain wall moves along the same direction regardless of the magnon-flow direction. Our general symmetry analysis and numerical simulation reveal that the odd order contributions from the interfacial asymmetry is unidirectional, which is dominant over bidirectional contributions in the realistic regime. We develop a simple analytic theory on the unidirectional motion, which provides an insightful description of this counterintuitive phenomenon.
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