The soft and polar nature of quasi‐2D (PEA)2PbBr4 perovskite, and robust photo‐generated excitons lead exciton‐polaritons and exciton‐polarons as the important phenomena near the band edge for ...application in the lighting aspect. In this work, a convenient methodology is proposed based on the polariton resonant modes in temperature‐dependent (77 K to RT) spectroscopy, and investigate the effect of these quasi‐particles on refractive index dispersion. The large binding energy (≈335 meV) of quasi‐2D excitons is obtained by the reflectance measurements at 77 K. Stable exciton‐polaritons and exciton‐polarons are confirmed by energy dispersions and the observation of self‐trapped exciton‐polaron state, respectively. Furthermore, the large negative thermal‐optic coefficient due to damping effect of exciton‐phonon scattering is observed. The phenomenon is opposite to those observed in conventional semiconductors (e.g., Si, Ge, GaN, AlN, GaAs, AlAs, and ZnO etc.). The observed stable negative thermal‐optic coefficients from 160 K to RT indicate that the quasi‐2D perovskite can be used as a phase compensator for conventional semiconductor materials.
The shrinkage of the energy difference between lower polariton branches (LPs) and upper polariton branches (UPs) proves that oscillator strength decreases when the temperature rises from 77 to 300 K. Therefore, the strong damping effect of exciton‐phonon interactions reduces the oscillator strength when the temperature rises, and further result in the negative thermal‐optic behaviors of quasi‐2D (PEA)2PbBr4 perovskite.
The effects of atomic size difference on the microstructure and mechanical properties of single face-centered cubic (FCC) phase high-entropy alloys are studied. Single FCC phase high-entropy alloys, ...namely, CoCrFeMnNi, Al
CoCrFeMnNi, and Al
CoCrCu
FeNi, display good workability. The recrystallization and grain growth rates are compared during annealing. Adding Al with 0.2 molar ratio into CoCrFeMnNi retains the single FCC phase. Its atomic size difference increases from 1.18% to 2.77%, and the activation energy of grain growth becomes larger than that of CoCrFeMnNi. The as-homogenized state of Al
CoCrCu
FeNi high-entropy alloy becomes a single FCC structure. Its atomic size difference is 3.65%, and the grain growth activation energy is the largest among these three kinds of single-phase high-entropy alloys. At ambient temperature, the mechanical properties of Al
CoCrCu
FeNi are better than those of CoCrFeMnNi because of high lattice distortion and high solid solution hardening.
Constructing polaritonic devices in monolithic, ultra‐compact photonic architectures with monolayer‐featured exciton‐emitters is decisive to exploit the coherent superposition between entangled ...photonic and excitonic eigenstates for potential realizations of optical nonlinearities, macroscopic condensations, and superfluidity. Here, a feasible strategy for exciton‐polariton formations is demonstrated by implementing a Tamm‐plasmon (TP) polaritonic device with the active material composed of single‐monolayered perovskite (CsPbBr3) quantum dots (QDs). The metallic character of the TP configuration is able to concentrate its resonance mode into a confined region beyond the diffraction limit, which highly overlaps, both spatially and spectrally, with the single‐monolayered CsPbBr3 QDs embedded inside. The mode volume of the device is hence reduced dramatically, leading to an enhanced light–matter coupling strength for the polaritonic emission at room temperature. In particular, it is found that the dispersion relation of the TP polaritonic device is tunable by detuning the excitonic and photonic eigenmodes and that the polariton–polariton interaction energy is strongly dependent on the polariton's spin state. The presented strategy is a determinant step toward the realization of strong light–matter coupling and polariton spintronics in the CsPbBr3 QDs with a single‐monolayered feature.
This work demonstrates a feasible strategy for room temperature polaritonic emissions by implementing a Tamm‐plasmon polaritonic device embedded with the CsPbBr3 quantum dots with a single‐monolayered feature.
The Rabi-splitting energy represents the strength of light–matter interaction. This quantity is a good benchmark for evaluating the performance of light-modulation devices. Herein, we adopt ZnO ...microrods as microcavities for whispering gallery modes and propose a convenient method for estimating the light–matter coupling strength based on the shifts of resonant modes in temperature-dependent photoluminescence spectra from 295 to 77 K. Both temperature-dependent index dispersion and Rabi splitting can be extracted. Additionally, the Rabi-splitting energy of bulk ZnO at 0 K is estimated to be about 289 meV.
An equiatomic CoCrFeMnNi high-entropy alloy under hydrostatic compression is investigated using in-situ angular-dispersive X-ray diffraction to explore the polymorphism in high entropy alloy systems. ...The metallic system is of face-centered-cubic structure at ambient condition and applied hydrostatic pressures up to 20 GPa via diamond anvil cell. The angle-resolved diffraction-intensity evolutions of multiple diffraction peaks were collected simultaneously to elucidate the phase stability examinations. The phase transformation from face-centered-cubic to hexagonal-close-packed structure was evidently observed in CoCrFeMnNi alloy accompanied by a deviatoric strain subjected to the hydrostatic compression. We found lattice-asymmetric crossover before and after the phase transformation subjected to hydrostatic compression surroundings. Deviatoric strain triggers fcc-hcp phase transformation as local heterogeneity-driven lattice distortion is significant for CoCrFeMnNi alloy.
•Lattice-asymmetric crossover occurs before and after phase transformation subjected to hydrostatic compression surroundings.•Manganese promotes the deviatoric deformation, triggering fcc-to-hcp phase transformation in CoCrFeMnNi.•The anisotropic lattice straining and induced local shearing govern the deformation model.•The dominant deformation in CoCrFeMnNi is the twinning-assisted phase transformation.
Welding and relevant studies are indispensable to employ high-entropy alloys for practical applications. In this study, Al
CoCrCu
FeNi high-entropy alloy with single FCC phase was used to make ...“bead-on-plate” friction stir welds at different rotational speeds, and the effects on microstructure and mechanical properties were studied. Several banded structures containing oxide or nitride particles were observed in the stir zone (SZ), and the chemical wear of the polycrystalline cubic boron nitride tool was confirmed. The microhardness distribution of the welds showed higher hardness in the SZ because of grain refinement and the presence of deformed grains. The electron backscattered diffraction results suggested that the high-entropy alloy with low stacking-fault energy experienced recrystallization during friction stir welding, which was similar to other conventional materials with low stacking-fault energy.
We realized a single-mode laser with an ultra-high quality factor in individual cesium lead bromide (CsPbBr3) perovskite micro-hemispheres fabricated by chemical vapor deposition. A series of lasing ...property analysis based on cavity size was reported under this material system. Due to good optical confinement capability of the whispering gallery resonant cavity and high optical gain of CsPbBr3 perovskite micro-hemispheres, single-mode lasing behavior was achieved with an ultra-high quality factor as large as 11,460 at room temperature. To study in detail the physical effects between lasing threshold and cavity, a set of cavity size dependence photoluminescence analyses were performed. We found that the lasing threshold increases while the cavity size decreases. Time-resolved PL analysis was conducted to confirm the relation between cavity size and lasing threshold. The larger cavity stands for longer PL lifetime and indicates easier-to-achieve carrier population inversion. Strong Purcell enhancement could be further investigated by the spontaneous emission coupling factor β and internal quantum efficiency as a function of cavity size. A high β-factor of 0.37 could be obtained from a 2.2 μm diameter hemisphere microcavity and a high Purcell factor of 14 in a 1.9 μm diameter hemisphere microcavity showing strong Purcell enhancement effect in our system.
We construct the ZnO-based superluminescent light-emitting diodes (SLEDs) by spin-coating ZnO nano-particles onto p-GaN/sapphire substrate. By inserting another thin Al layer to form an ...n-ZnO/Al/n-ZnO/p-GaN sandwich structured SLD, the intensities of the photoluminescence and electroluminescence were greatly enhanced, which can be attributed to the surface plasmon resonance of this Al layer. The tendency of the intensities of the entire electroluminescence spectra shows a super-linearly behavior with increasing the forward bias. Besides, the spectral bandwidth is narrowed down enormously owing to the achievement of the SLD. Furthermore, the interfacial emissions between ZnO/GaN are effectively suppressed by partially oxidizing the Al layer.
The CsPbBr
3
microwires with unique isosceles right triangle cross-sections are commonly observed via chemical vapor deposition method. In this work, we study the correlations between measured ...multi-mode lasing behaviors and the simulation of the mode patterns inside the triangular-rod microcavity. We confirm that lasing action with higher-order transverse modes can well sustain, even when these modes experience large optical loss due to the isosceles triangle cross-section. By comparing the experimental and simulation results, the higher-order transverse modes tend to show up prior to the fundamental transverse modes for wider microwires. We attribute this behavior to the nonuniform field distribution caused by the high absorption efficiency of CsPbBr
3
. We also elaborate on the difficulties to sustain the whispering gallery mode in the CsPbBr
3
triangular-rod microcavity, which implies that the lateral dimension and geometry of the cavity should be considered carefully for the future design of low threshold wire-based laser devices.
The extraordinary dynamics of microstructures, such as various dislocations, stacking faults, twinning, and polymorphism transformations, dominate the mechanical performance of high-entropy alloys. ...To reveal the phase transformation kinetics, we precisely detect the microstructure evolution in CoCrFeMnNi high-entropy alloy (HEA) and CrFeNi medium-entropy alloy (MEA) subjected to high-pressure compression using in situ angular-dispersive synchrotron X-ray diffraction. We find that controlling the initial microstructural state using cold-rolling can significantly reduce the stacking fault energy of CoCrFeMnNi and CrFeNi alloys, which results in lower onset pressures for phase transformations. The microstructure-induced stacking-fault energy reduction facilitates the formation of twins, which can act as nucleation sites for hexagonal close-packed (HCP) phase formation and recrystallization. The microstructure evolution-driven deviatoric deformation mechanism of CoCrFeMnNi HEA and CrFeNi MEA under quasi-hydrostatic compression is explored. Beyond the FCC phase, twinning in the HCP phase of CoCrFeMnNi alloy under high pressure is observed for the first time. This implies that the deformation mechanism of CoCrFeMnNi HEAs in the HCP phase is dominated by twinning-induced plasticity, which is verified using transmission electron microscopy.
•Twins can act as nucleation sites for HCP phase formation and recrystallization.•Phase ratio and stability are controlled by stacking fault energy reduction.•Deformation mechanism of CoCrFeMnNi is dominated by twinning-induced plasticity.
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