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Optical analog computation is garnering increasing attention due to its innate parallel processing capabilities, swift computational speeds, and minimal energy requirements. However, traditional optical components employed for such computations are usually bulky. Recently, there has been a substantial shift toward utilizing nanophotonic structures to downsize these bulky optical elements. Nevertheless, these nanophotonic structures are typically realized in planar subwavelength nanostructures, demanding intricate fabrication processes and presenting limitations in their numerical apertures. In this study, we present a three-layer thin-film optical coating different from the conventional Fabry–Pérot nanocavity. Our design functions as a real-time Laplacian operator for spatial differentiation, and it remarkably boasts an ultrahigh numerical aperture of up to 0.7, enabling the detected edges to be sharper and have closely matched intensities. We also experimentally demonstrate its capacity for effective edge detection. This ultracompact and facile-to-fabricate thin-film spatial differentiator holds promising prospects for applications in ultrafast optical processing and biomedical imaging. [ABSTRACT FROM AUTHOR]

Antiferroelectric materials hold great potential for energy storage applications. However, a significant challenge lies in the disparity ΔW between the rapid discharge energy density Wdis and the recoverable energy density Wre. Quantitative analysis is still lacking, and the ultra-fast reverse ferroelectric–antiferroelectric (FE–AFE) transition behavior at the microsecond scale remains unknown. In this study, a pulse technique was employed instead of the Sawyer–Tower method to obtain the "μs P-E loop" during rapid charge–discharge processes. The "μs P-E curve" clearly illustrates the distinct FE–AFE transition behavior during rapid discharge in comparison to low-frequency conditions. Under pulsed conditions, the FE–AFE transition field was observed to decrease, and even a "remanent polarization" was observed, leading to a reduction in discharge energy during fast discharge. Moreover, through the enhancement of relaxor behavior and the increased diffuseness of FE–AFE switching, the μs P-E loop tended to resemble that observed at low frequencies, thereby resulting in more efficient discharge performance. This study introduced a technique for investigating the ultra-fast FE–AFE transition. Furthermore, it unveiled the origin of ΔW and provided an effective method for achieving high discharge energy density. [ABSTRACT FROM AUTHOR]

Vanadium dioxide (VO2) has been one of the most significant functional materials for its prominent property change during phase transition. Here the modulation in crystallinity and morphology of VO2 thin film is achieved by femtosecond laser direct writing. Both the local crystallization from an amorphous phase and self-organized periodical structures are generated due to the well-controlled femtosecond laser energy deposition and controlled accumulation. The dynamic evolution of either the volumetric or surface nano-/micro-structure depends strongly on the femtosecond laser conditions, revealed by changes of the Raman bands and reflectance spectra at visible wavelengths. Based on the distinguishable color display performance of differently processed regions, a four-color-level image has been drawn on a VO2 thin film. This work proposes an elaborate "annealing by light" and optical property modulation method for the VO2, paving the way to producing complex integrated multi-functional devices for color display and data storage. [ABSTRACT FROM AUTHOR]

Since the first example of linearly polarized organic light-emitting diodes (LP-OLEDs) reported by Dyreklev et al. [Adv. Mater. 7, 43 (1995)], remarkable efforts have been devoted to the development of LP-OLEDs, particularly in recent years. LP-OLEDs, as a next-generation light source, have attracted increasing interest for their capability of directly generating linearly polarized light as well as for their wide potential applicability in optical data storage, high-contrast display, and three-dimensional (3D) imaging. In this review, we systematically summarize the recent advances in LP-OLEDs that are roughly divided into three categories, including mechanical treatment, structural assistance, and self-assembled materials. This review is expected to provide an updated and impressive perspective on high efficiency and high polarization LP-OLEDs for a broad range of scientists in a multi-disciplinary field and draw more attention to this growing research field. [ABSTRACT FROM AUTHOR]

There are still challenges in the precise control of microwave energy for the industrial production, one of which is the effective inhibition of microwave hotspots or thermal runaway during microwave radiation, which has become a long-standing problem for improving heating uniformity and further expanding applications. Nevertheless, the evolution process and the underlying mechanism of microwave hotspots in high-dielectric dimers within different applied dielectrics are not fully understood due to the difficulty of internal temperature measurement. In this Letter, an optical indirect observation method has been proposed to characterize the hotspots distribution inside the applied dielectric. The grapes with high relative permittivity have been selected, which are easy to cut and absorb microwave, to conduct an in situ investigation of microwave hotspots evolution for dimers in a domestic microwave oven using the thermal and optical imaging. The results show that with the increase in the relative permittivity of applied dielectric, the starting of microwave plasma is prevented, and the focused hotspots disappear. Most significantly, the heating uniformity of dimers in water is improved by about ten times compared to that in air. The reduction of the calculated focused energy density near the contact point verifies the weakening effect of applied dielectric on the microwave cooperative resonance of dimers and explains the experimental phenomenon. These findings can be directly applied to inhibit the formation of focused hotspots for dimers or even multi-particle systems during the microwave processing and also provide a better understanding for cooperative interaction of Mie resonances. [ABSTRACT FROM AUTHOR]

Ceramic-based capacitors with excellent recoverable energy storage density (Wrec) and efficiency (η) are greatly desired for pulsed capacitors but challenge as well. In this work, the high energy storage performance with an Wrec of 5.1 J/cm3, an η of 93.4%, and an ultrafast discharge–charge speed t0.9 of 72 ns is achieved in unusual interstitial and substitutional hybrid solid solution of Sr0.64Bi0.18Na0.18TiO3-ZnO (SBNT-Zn), in which two Zn2+ ions occupy one A-site, while one Zn2+ ion occupies one B-site of ABO3 perovskite lattice simultaneously. The addition of Zn2+ increases lattice distortion and breaks long-range ferroelectric order, resulting in more highly dynamic polar nanoregions, higher relaxation behaviors as well as larger polarization (ΔP). Moreover, the extraordinary hybrid solid solution configuration enhances the bandgap of SBNT-Zn and ZnO as a sintering aid refines grain size, both help to enhance electric breakdown strength. This work affirms the feasibility and reliability of forming a hybrid solid solution to develop high-performance ferroelectric materials. [ABSTRACT FROM AUTHOR]

Anharmonicity as a fundamental issue inspires numerous interesting phenomena in phase transition, electronic structure, thermal transport, and so on. Here, we find that the peculiar A 1 u phonon mode of in-plane rotational vibration of group-IB-atom ring introduces the anharmonicity into the s(I) and s(II) phases of two-dimensional group-IB chalcogenides. Compared to the high-symmetry s(I) phase, the A 1 u phonon mode is always active and the anharmonicity is stronger in the symmetry-breaking s(II) phase by releasing the strain energy. The temperature-hardened A 1 u mode stabilizes the s(I) phase and reduces the lattice thermal conductivity by strengthening the anharmonicity. The strain-softened A 1 u mode drives the s(II)-to-s(I) phase transition and enhances the lattice thermal conductivity by weakening the anharmonicity. We also establish the relationships of the anharmonicity vs the band structure and Poisson's ratio. As the anharmonicity is weakened during the strain-induced s(II)-to-s(I) phase transition, the bandgap significantly increases. Meanwhile, the weaker anharmonicity implies the lower Poisson's ratio, which further drops much faster with the strain. Our work realizes the tuning of anharmonicity by the peculiar phonon mode in 2D group-IB chalcogenides, which provides a useful guidance for further understanding the anharmonic effect. [ABSTRACT FROM AUTHOR]

The energy density of dielectrics could be evaluated both via low-frequency P–E loop (quasi-static recoverable energy density, Wre) and fast discharge current (dynamic discharge energy density, Wdis). The value of Wdis represents the useful energy, which can be converted to electrical energy while most work about high-energy-density dielectrics is focused on enhancing Wre. In this work, we investigated the relationship between Wdis and Wre in (Pb1 − 3x/2Lax)[(Zr0.45Sn0.55)0.99Ti0.01]O3 antiferroelectrics. Tuning the phase transition properties could improve the fast discharge capability by reducing the difference between Wdis and Wre and accelerating the energy release rate. At 300 kV/cm, the composition with x = 0 has the highest Wre of 6.7 J/cm3 but a lower Wdis of only 4 J/cm3 and longer discharge time duration, indicating a "high-energy-density" (highest Wre) quasi-static performance but "low-energy-density" (lower Wdis) and slow discharge performance during fast discharge. A highest Wdis of 5.9 J/cm3 and power density were achieved in composition with x = 0.2 though with lower Wre. The various fast energy release performance was explained by their different domain mobility and phase switching behavior. Thus, purely pursing high Wre is with limitation and suppressing the difference between Wdis and Wre is with great significance. This work will give an approach for the development of energy storage dielectrics by connecting their fast discharge performance with polarization mechanism. [ABSTRACT FROM AUTHOR]

Spin pumping converting sub-terahertz electromagnetic waves to DC spin currents has recently been demonstrated in antiferromagnets (AFMs) with easy-axis magnetic anisotropy. However, easy-plane AFMs such as NiO, which are easier to prepare experimentally, are considered to be bad candidates for spin pumping because the Néel vector oscillation is linearly polarized, placing a major restriction on the material choice for practical applications. Through a case study of NiO, we show that an applied magnetic field below the spin–flop transition can substantially modify the polarization of the resonance eigenmodes, which enables coherent sub-terahertz spin pumping as strong as that in easy-axis AFMs. In addition, we find that an applied magnetic field can significantly reduce the threshold of Néel vector auto-oscillation triggered by spin-transfer torques. These prominent field-assisted effects can greatly facilitate spintronic device engineering in the sub-terahertz frequency regime. [ABSTRACT FROM AUTHOR]

Silicon is a long-standing photosensitive material because of its unique photoelectronic properties and mature manufacturing technology. However, silicon photodetectors are generally limited by weak photoresponse in the near-infrared region. In this work, pressure is used as an effective means of tuning the photoresponse of silicon, specifically in the near-infrared region. Silicon has two different types of photoresponse under pressure. In the pressure range from 1 atm to 10 GPa, huge pressure-enhanced photocurrent is observed under illumination by a xenon lamp and near-infrared light (1064 nm). At 10 GPa, the photocurrent density (Jph), responsivity (R), and external quantum efficiency are increased 40-fold from those at 1.2 GPa. Interestingly, above 10 GPa, a unique pressure-induced positive–negative photoresponse switch is found along with the phase transformation from the semiconductive phase (Si I) to the metallic phase (β-tin). Further experiments show that the photothermal effect is the main factor for negative photoresponse. All these pressure-induced properties give silicon more possibilities in the further design of visible and infrared photodetectors. [ABSTRACT FROM AUTHOR]

Magnon excitations in antiferromagnetic materials and their physical implications have helped to facilitate the emergence of device concepts not presently available in ferromagnets. A unique characteristic of antiferromagnetic magnons is the coexistence of opposite spin polarization, which mimics the electron spin in a variety of transport phenomena. Among them, the most prominent spin-contrasting phenomenon is the magnon spin Nernst effect (SNE), which refers to the generation of a transverse pure magnon spin current through a longitudinal temperature gradient. We introduce selected recent progress in the study of magnon SNE in collinear antiferromagnets with focus on its underlying physical mechanism entailing profound topological features of magnon band structures. By reviewing how the magnon SNE has inspired and enriched the exploration of topological magnons, we offer our perspective on this emerging frontier that holds potential in future spintronic nano-technology. [ABSTRACT FROM AUTHOR]

Antiferroelectrics (AFEs) with high energy density and fast discharge speed are greatly needed to improve the performance of capacitors. In the present work, La-doped PbHfO3 ceramics were fabricated and the antiferroelectricity was investigated. The complicated phase transition behavior at both high electric field and rising temperature in composition Pb0.94La0.04HfO3 was revealed. Multiple phase transition was observed at high field, and when rising the temperature to 110 °C, an intermediate phase transition to another AFE phase was observed. The Pb0.94La0.04HfO3 ceramics have a high recoverable energy density of 10.2 J/cm3 and efficiency of 81.7%. Double P–E loop could be observed even at 180 °C, ensuring the high energy density at high temperature. In addition, a high current density of 2109 A/cm2 and a power density of 369 MW/cm3 could be obtained. This work revealed the antiferroelectricity in La-doped PbHfO3 ceramics and proved their potential for high energy and power density applications. [ABSTRACT FROM AUTHOR]

Using high-resolution angle-resolved photoemission spectroscopy, we studied the surface state of Ta3SiTe6, a candidate of topological semimetal protected by nonsymmorphic symmetry. Through photon-energy dependent measurements, the surface state near the Fermi level was detected. By determining the band dispersions, we found that the surface state is topological trivial. Around the surface Brillouin zone center, the surface bands disperse linear-like, forming a band crossing (zero energy gap) point at about 0.2 eV below the Fermi level. In Ta3SiTe6's rectangular surface Brillouin zone, the surface bands only cross the Fermi level along one axis, forming two hole-like Fermi pockets near surface Brillouin zone boundaries. Although the observed surface state is not topological, we proposed that its anisotropic Fermi surface topography could be potentially useful for future applications. [ABSTRACT FROM AUTHOR]

The gasification of carbonaceous feedstocks usually takes place in high-pressure, high-temperature reactors, making it difficult to have direct access to the reaction site. Since the greenhouse gas CO2 is a major component in gasification, there is an urgent need for a better understanding of these processes. In this study, we investigate carbon gasification in a CO2 atmosphere using the ultrabroadband, coherent anti-Stokes Raman spectroscopy (CARS). In contrast to conventional three beam CARS, this approach allows the simultaneous determination of the temperature of the CO2 atmosphere and the concentration of the reaction product CO. We show that temperature drop and increase in CO are directly linked to the feedstock conversion measured by thermogravimetric analysis. Due to gasification, a considerable temperature drop of up to 200 K was measured, which was predicted by simulations in the literature but has not been confirmed experimentally yet. [ABSTRACT FROM AUTHOR]

Twin boundaries (TBs) can increase interface scattering to reduce the lattice thermal conductivity. InSb has good electronic transport properties, but its high thermal conductivity constrains its thermoelectric application. In this work, we aim to study the role of TBs on lattice thermal conductivity of InSb. We use non-equilibrium molecular dynamics simulation to investigate how the TB spacing and orientation influence the lattice thermal conductivity of InSb. We find that TBs can hinder the heat flow, leading to decreased temperature gradient and, hence, remarkably reduced lattice thermal conductivity. The relationship between κL and λ can be described by a proportional function. Nanotwinned InSb with TB spacing of 1.1 nm has a lattice thermal conductivity of 12.6 W/m K, a decrease in 22.2% compared with its single crystal (16.2 W/m K). We also find that a minimum lattice thermal conductivity of InSb can be obtained when the TB orientation is perpendicular to the direction of heat flow. These findings provide a theoretical guidance for TBs engineering to reduce the thermal conductivity of thermoelectric materials. [ABSTRACT FROM AUTHOR]

The unique liquid nature and strong magnetic response ability enable ferrofluid droplets to split and self-assemble into reconfigurable three-dimensional structures. Although the manipulation of a ferrofluid droplet in a static or quasi-static state has been well studied, the splitting and self-assembly of ferrofluids in a dynamic state remain unexplored. Here, we report the impingement-assisted self-assembly of ferrofluids on superhydrophobic surfaces, whereby the required magnetic field is greatly reduced. In particular, the coupling between the magnetic field strength and Weber number endows a precise regulation of the ferrofluid post-impact dynamics, which facilitates the optimization of the self-assembly behavior. Finally, we demonstrate that the impingement-assisted self-assembly of ferrofluids can be generalized on various surfaces with different wettability. The fundamental understanding and the ability to self-assembly during droplet impingement can provide important insight into the dynamics of ferrofluid droplets as well as the applicability in multifunctional analytical and fluidic devices. [ABSTRACT FROM AUTHOR]

We report the fabrication of highly ordered arrays of GaAs/AlGaAs quantum dots (QDs) by droplet epitaxy using in situ direct laser interference patterning. Two-dimensional arrays of Ga droplets with a periodicity of ∼300 nm are initially formed on nanoisland structured AlGaAs surfaces due to the localized surface diffusion under the influence of a thermal gradient imposed by the light pulse. After crystallization under an arsenic flux, precisely ordered arrays of GaAs single dots are obtained. The size distribution and optical properties of the ordered GaAs QDs are shown to be optimized by the careful choice of parameters for nucleation and droplet formation. [ABSTRACT FROM AUTHOR]

The Seebeck effect or thermopower relates the temperature gradient to the electric voltage drop. Seebeck coefficient α measures the transport entropy, which could either linearly increase with temperature T like metallic conducting or decrease as 1 / T like semiconducting behavior. It could become more complicated in the temperature dependence for a number of disordered systems but still in a monotonic way. However, several recent experiments reported the "abnormal" non-monotonic temperature dependence of the Seebeck coefficient in doped conducting polymers, for instance, first increasing and then decreasing. Through a one-dimensional tight-binding model coupled with the Boltzmann transport equation, we investigate theoretically the doping effect for the Seebeck coefficient. We find that the abnormal behavior comes from multi bands' contribution and a two-band model (conduction or valence band plus a narrow polaronic band) can address such an abnormal Seebeck effect, namely, if there exists (i) a small bandgap accessible for thermal activation between the two bands; and (ii) a large difference in the bandwidth between the polaronic band and the conduction band (or valence band), then the Seebeck coefficient increases with temperature first, then levels off, and finally drops down. [ABSTRACT FROM AUTHOR]

In an easy-plane antiferromagnet with the Dzyaloshinskii–Moriya interaction (DMI), magnons are subject to an effective spin-momentum locking. An in-plane temperature gradient can generate interfacial accumulation of magnons with a specified polarization, realizing the magnon thermal Edelstein effect. We theoretically investigate the injection and detection of this thermally driven spin polarization in an adjacent heavy metal with a strong spin Hall effect. We find that the inverse spin Hall voltage depends monotonically on both temperature and the DMI but non-monotonically on the hard-axis anisotropy. Counterintuitively, the magnon thermal Edelstein effect is an even function of a magnetic field applied along the Néel vector. [ABSTRACT FROM AUTHOR]

The phenomenon of ferrofluid-water mixing is investigated using a double-layer magnetic micromixer, in which a layer of micromagnet bars is placed immediately below the fluid layer. A wavy pattern of the ferrofluid–water interface is surprisingly observed at each micromagnet responsible for improved mixing. The mechanism causing the wavy mixing is discovered and analyzed through experimental measurements and numerical simulations, and the mixing efficiency under different flow conditions is discussed. For flows with Re ≪ 1, the resultant steep gradient of opposing magnetic forces by micromagnets in the ferrofluid region gives rise to a local pressure source that induces a transverse/spanwise pressure gradient and activates momentum transfer between fluids. The current finding enables effective localized mixing of ferrofluids with a small footprint and, thus, has great potential to achieve fast mixing for high-throughput flows with an integrated parallel system of multiple microfluidic channels and micromagnets. [ABSTRACT FROM AUTHOR]

In this work, the breakdown characteristics and the electroluminescence (EL) spectra of a Schottky-metal/p-GaN/AlGaN/GaN device under forward bias were investigated at different temperatures. The failure of the metal/p-GaN junction, which was caused by electron transport in the p-type Schottky junction, was identified as the first step in the device breakdown process. The breakdown voltage increased with higher temperatures. Under a forward bias of 8 V, the intensity of the EL emission increased more than two orders of magnitude, while the current increased by a factor of 4 as the temperature increased from 0 °C to 200 °C. This unambiguously demonstrated thermally enhanced hole injection at the Schottky-metal/p-GaN interface. We proposed that more electrons were annihilated by the thermally enhanced hole injection, resulting in the positive temperature dependence of the device breakdown. [ABSTRACT FROM AUTHOR]

We demonstrate the growth and surface characterization of laterally ordered arrays of InAs quantum dot molecules (QDMs) on GaAs (100) substrates produced by a combination of in situ interferometric nanopatterning and molecular beam epitaxy growth. Four-beam ultraviolet laser interference is applied during the growth process resulting in the formation of quasi two-dimensional islands due to localized surface diffusion. With further InAs deposition, the edges of the islands are observed to act as preferential sites for the nucleation of InAs quantum dots. Well-ordered square arrays of lateral QDMs with a period of 300 nm and site occupancy ranging from single dot up to hexa-molecules are obtained by varying the InAs coverage from 1.55 ML to 1.75 ML. [ABSTRACT FROM AUTHOR]

In this work, NaEuF4 nanoparticles (NPs) with high dispersity and uniformity were synthesized using a hydrothermal method and introduced into the TiO2 mesoporous layer of perovskite solar cells (PSCs) for testing as high efficiency, downconversion materials. NaEuF4 can convert high-energy photons into low-energy photons for absorption by CH3NH3PbI3 and generation of more electron–hole pairs; we tested the hypothesis that this would extend the sunlight absorption range and improve the photovoltaic performance of PSCs. When NaEuF4 NPs were incorporated into TiO2 mesoporous layers, PSCs achieved power conversion efficiencies of 14.51%, which were better than those of the control PSCs. The use of NaEuF4 NPs for improving PSC photovoltaic performance, as shown herein, could encourage the greater use of solar energy. [ABSTRACT FROM AUTHOR]

We investigate the ultrafast carrier dynamics and spin–lattice interaction in strained and unstrained LaMnO3 films via temperature-dependent femtosecond transient optical spectroscopy. The transient reflectivity measurements show two characteristic relaxation processes in both types of films, which are attributed to electron–phonon coupling and phonon-assisted spin–lattice interaction, respectively. The carrier dynamics and coupling between lattice and spin system are well described with the three-temperature model; the spin–lattice relaxation time constant is dominated by the temperature-dependent spin specific heat. Both the electron–phonon coupling and the spin–lattice interaction are enhanced in the strained film, as a result of the modified band structure and orbital ordering under biaxial compressive strain. Our results reveal the critical role of strain in the photo-induced dynamical interactions in LaMnO3. [ABSTRACT FROM AUTHOR]

Bipolar plasticity for synaptic emulation of indium gallium zinc oxide thin-film transistors (TFTs) with HfOxNy–HfO2–HfOxNy sandwich-stack films as the gate dielectric was investigated. The postsynaptic current increased when a negative pulse train was applied to the gate of TFTs; when a positive pulse was applied, the postsynaptic current was reduced. This result is discussed based on the charge trapping/releasing process with the assistance of ferroelectric behavior of the enwrapped oxygen-deficient-HfO2 layer. The dual response of this synaptic transistor shows promising prospect in the mimicking of biological neurons. [ABSTRACT FROM AUTHOR]

Pseudo-binary GeSbTe alloys, best known as phase-change materials, are quasi-two-dimensional semiconductors in their stable trigonal phases with high electrical conductivity and low thermal conductivity, but their thermoelectric properties have not been systematically investigated. Here, in this letter, we prepared polycrystalline Ge2Sb2Te5, GeSb2Te4, and GeSb4Te7 bulk materials and studied the thermoelectric transport properties. Large anisotropy in Seebeck coefficient as well as in electrical conductivity is observed, which is not commonly reported in polycrystalline thermoelectric materials. Combining experimental study and theoretical calculations, one can find that this phenomenon is attributed to the asymmetry of a material's band structure. Maximal zT values of 0.46–0.60 are achieved at 750 K, indicating that GeSbTe-based compounds are promising thermoelectric materials for mid-temperature applications. [ABSTRACT FROM AUTHOR]

For advanced electronic device applications including printable, flexible organic electronics and bioelectronics, it is crucial to develop novel dielectric materials with high dielectric strength and low-temperature processability compatible with plastic substrates for producing flexible and low-voltage organic thin-film transistors (OTFTs). Herein, we report the facile fabrication of rationally designed, high-capacitance hybrid gate dielectric films for low-voltage OTFTs on plastic substrates via a room-temperature solution process. To create room-temperature-processed gate dielectrics with high dielectric strength, we designed organic-inorganic hybrid gate dielectric films by including ZrOx networks as inorganic high-k oxide materials for obtaining large capacitance and 1,6-hexanediol diacrylate as a bifunctional UV cross-linking agent and a flexible organic component for increasing the density and flexibility of films and ensuring room-temperature processability. The UV cross-linked ZrOx-based hybrid composite films with a 15 nm thickness showed excellent dielectric properties with a leakage current density of ∼10−6 A/cm2 and a capacitance of 640 nF/cm2. The film surfaces were modified with hydrophobic self-assembled monolayers to match the surface energy of organic semiconductors for enhancing the OTFT performance. The utility of the hybrid dielectrics for flexible OTFTs was demonstrated by realizing pentacene TFTs on plastic substrates with a low operating voltage at –2.5 V, a high on/off current ratio of 105, a threshold voltage as low as –0.7 V, and a hole mobility up to 0.47 cm2 V−1 s−1, which are comparable to those performed on Si substrates. [ABSTRACT FROM AUTHOR]

The large size and electromagnetic interference of microphone arrays are long standing challenges for sound source localization. Here, an all-fibre vector acoustic sensor based on crossed microfiber Bragg gratings (micro-FBGs) has been proposed and experimentally demonstrated that enables the two-dimensional sound source localization with a size less than 1.5 mm. Two micro-FBGs inscribed in the Co2+-doped fibre are fabricated through a hydrofluoric acid solution, which are placed parallel to each other to form a micro-FBG pair. Based on the self-heating and asymmetric temperature distribution of two Co2+-doped fibres, the crossed micro-FBGs provide a direct two-dimensional measurement of the acoustic particle velocity. The experimental results show that an orientation sensitivity of 1.57 mV/deg for the micro-FBGs is achieved with a figure-of-eight response of the acoustic source direction. Meanwhile, the direction responses of two crossed pairs of micro-FBGs are exactly orthogonal to each other, which could detect the sound source localization. The all-fibre vector acoustic sensor is immune to electromagnetic interference, which appears to have a variety of potential applications, including research in acoustic communication, pipeline monitoring and navigation, etc. [ABSTRACT FROM AUTHOR]

The interaction of domain structure and defects in ferroelectric thin films has been studied for decades. However, the role of dislocations and thermal stability of microstructures is still poorly studied. By combining transmission electron microscopy, x-ray diffraction experiments, and phase-field simulations, we show that dislocation pairs induced by post-annealing above 550 °C provide a stress field stabilizing a domains in 30 nm thick tetragonal PbTiO3 films on SrTiO3 substrate, initially exhibiting pure c domains. Based on phase-field simulations, we further discuss the effects of single dislocations and dislocation pairs on the nucleation of a-domains and the occurrence of non-ferroelastic 180° domains. Dislocations, and the possibility to tune them using an appropriate thermal annealing process, offer a path for modulating the domains and domain wall states and, thus, the physical properties of ferroelectric films. [ABSTRACT FROM AUTHOR]

This study demonstrates superior electrical and electroluminescence performance of inverted quantum-dot light-emitting diodes (QD-LEDs) with a V2O5/poly(N-vinylcarbazole) (PVK) hole conduction layer. Hole- and electron-only device measurements reveal a more balanced charge carrier injection as well as the higher hole conduction capability in the inverted QD-LED than the standard one. Smooth stepwise hole conduction energy levels with a remarkably reduced hole barrier height (Δh) from 1.74 to 0.89 eV at QD/PVK are found to be responsible for high hole conduction and high luminous efficiency in the inverted QD-LED, which is validated by ultraviolet photoelectron spectroscopy measurements. The down-shifted electronic energy levels of PVK for reducing the Δh are discussed from the point of view of molecular orientation of PVK governed by interfacial atomic interaction with underlayers of V2O5 and QD for standard and inverted device structures, respectively. [ABSTRACT FROM AUTHOR]

Surface plasmon-coupled emission has been widely used in fluorescence imaging, biochemical sensing, and enhanced Raman spectroscopy. A self-referenced directional enhanced Raman scattering for simultaneous detection of surface and bulk effects by using plasmon waveguide resonance (PWR) based surface plasmon-coupled emission has been proposed and experimentally demonstrated. Raman scattering was captured on the prism side in Kretschmann-surface plasmon-coupled emission. The distinct penetration depths (∂) of the evanescent field for the transverse electric (TE) and transverse magnetic (TM) modes result in different detected distances of the Raman signal. The experimental results demonstrate that the self-referenced directional enhanced Raman scattering of the TE and TM modes based on the PWR can detect and distinguish the surface and bulk effects simultaneously, which appears to have potential applications in researches of chemistry, medicine, and biology. [ABSTRACT FROM AUTHOR]

This study investigates the influence of voids on the electroluminescence (EL) emission color of ZnO microdisk/p-GaN heterojunction light-emitting diodes (LEDs). For this study, position-controlled microdisk arrays were fabricated on patterned p-GaN via wet chemical epitaxy of ZnO, and specifically, the use of trisodium citrate dihydrate (TCD) yielded high-density voids at the bottom of the microdisk. Greenish yellow or whitish blue EL was emitted from the microdisk LEDs formed with or without TCD, respectively, at reverse-bias voltages. Such different EL colors were found to be responsible for the relative EL intensity ratio between indigo and yellow emission peaks, which were originated from radiative recombination at p-GaN and ZnO, respectively. The relative EL intensity between dichromatic emissions is discussed in terms of (i) junction edge effect provoked by interfacial voids and (ii) electron tunneling probability depending on the depletion layer geometry. [ABSTRACT FROM AUTHOR]

Hydrogen-terminated diamond surfaces, emerging as a promising two-dimensional (2D) electron platform with great thermal and electronic properties, hold great potential for the next-generation high power and high frequency field effect transistor (FET). However, ideal gate dielectrics with high crystallinity and defect-free surfaces are still largely elusive. In this work, using the contamination-free pickup transfer method, hexagonal boron nitride (h-BN) flakes were fabricated on top of the hydrogen-terminated diamond surface to serve as a gate material and the passivation layer. The morphological and optical characterizations revealed the formation of homogeneous and intimate interface between h-BN and diamond. Benefiting from the h-BN gate dielectric layer, the maximum drain current density, subthreshold swing, and on/off ratio of diamond FET are measured to be −210.3 mA mm−1, 161 mV/dec, and 106, respectively. Especially, the transport measurement shows an almost constant Hall mobility of around 260 cm2 V−1 s−1 in the hole density range of 2 − 6 × 1012 cm−2, suggesting the excellent gate controllability of h-BN. Our results indicate that h-BN could form high-quality interface with hydrogen-terminated diamond, paving the way for the development of diamond-based electronic applications. [ABSTRACT FROM AUTHOR]

Single-crystal SnSe has been found to exhibit exceptional thermoelectric performance, but the efficiency of polycrystalline samples is still far from satisfactory. In this work, with an intention to effectively suppress heat conduction and minimally affect hole transport, we alloyed p-type polycrystalline SnSe with PbSe. Single-phase Sn1-xPbxSe solid solutions were formed up to x-0.12. The lattice thermal conductivity was reduced from 1.4 to 0.85W m-1 K-1 by 12 at. % PbSe alloying due to strain and mass fluctuations. Interestingly, the Seebeck coefficient and carrier concentration were nearly unchanged by Pb substitution, indicating a constant effective mass and an undisrupted valence band maximum. A peak figure of merit (ZT) of 0.85 at 800K was obtained in the x=0 sample, and relatively high performance was also achieved in solid solutions. A concise model was developed involving multiple carrier scattering mechanisms, capturing the dependence of the mobility on composition and temperature. [ABSTRACT FROM AUTHOR]

The energy in pulse capacitors need to discharge rapidly to obtain high peak power. However, the discharge energy density of antiferroelectric (AFE) dielectrics for pulse capacitors is traditionally evaluated by hysteresis loop (defined as quasi-static method). To verify whether the quasi-static method is suitable for pulse applications, AFE ceramics Pb0.94La0.04[(Zr0.70Sn0.30)0.86Ti0.14]O3 were prepared, and their discharge energy density was calculated by hysteresis loop and pulse current (defined as dynamic method), respectively. A significant difference was found between these two kinds of results. Under 36 kV/cm, the discharge energy density calculated by 1Hz hysteresis loop was 0.35 J/cm3 while that by pulse discharge current was only 0.18 J/cm3. It was found that the discharge energy density declined with increasing test frequency (0.1 Hz–100 Hz) and decreased further via dynamic hysteresis loop in microseconds scale. This declination can be explained by the viscous force during the motion of the domain wall. Thus, for pulse capacitors, it is more reasonable and practical to evaluate discharge energy density of AFE by pulse current than by quasi-static hysteresis loop. [ABSTRACT FROM AUTHOR]

We report the tailoring of the electronic structure of poly(N-vinylcarbazole) (PVK) using a mixture layer of polyaniline:poly(p-styrenesulfonic acid) (PANI:PSS) in organic multilayer PVK/PANI:PSS/poly(3,4-ethylenedioxythiophene):PSS heterojunctions. The overall electronic structure of the PVK overlayer was systematically down-shifted while the work function of PANI:PSS increased as a function of the PSS-to-PANI weight ratio for the ratio range from 1 to 11 in the PANI:PSS film. The down-shift in the highest occupied molecular orbital of PVK markedly reduced the hole injection barrier from PVK to quantum-dot (QD) layers in QD-light emitting diode (QD-LED) structures, resulting in superior electrical and electroluminescent characteristics for QD-LEDs. The influences of PANI:PSS thickness on the electronic structure of PVK and the performance of QD-LEDs are also discussed. [ABSTRACT FROM AUTHOR]

Ferroelectric-field-effect-tunable modulation of terahertz waves in graphene/Si:HfO2/Si stack structure was observed. The modulation shows distinct behaviors when the samples under different gate polarities. At a negative voltage, a transmission modulation depth up to ~74% was present without depending on the photo illumination power, whereas, at a positive voltage, the modulation of Thz wave shows dependence on the illumination power, which is ascribed to the creation/ elimination of an extra barrier in Si layer in response to the polarization in the ferroelectric Si:HfO2 layer. Considering the good compatibility of HfO2 on Si-based semiconductor process, the ferroelectricity layer of Si:HfO2 may open up an avenue for the tunable modulation of Thz wave. [ABSTRACT FROM AUTHOR]

Greatly improved resistance performance, including high resistance ratio between the high resistance state and the low resistance state, long-time retention, and reliable endurance, was observed in TiN/Si:HfO2/oxygen-deficient HfO2/TiN memory cells. The enhanced resistance ratio is ascribed to the creation/elimination of an extra barrier in oxygen-deficient HfO2 layer in response to the polarization reversal in the ferroelectric Si:HfO2 layer. Along with the enhanced resistance ratio, the long retention and good endurance make the proposed device a promising candidate for non-volatile resistive memories. [ABSTRACT FROM AUTHOR]

Greatly enhanced blue emission was observed at room temperature in the single-crystal silicon with HfO2 filled into its microcavities. The broad blue band light was emitted from both the HfO2 dielectric and the porous Si. The ferroelectricity of HfO2 enhances the blue emission from Si by its filling into the microcaivities. At the same time, HfO2 contributes to the light emission for the transitions of the defect levels for oxygen vacancy. The observation of greatly enhanced blue light emission of the porous Si filled with HfO2 dielectric is remarkable as both HfO2 and Si are highly compatible with Si-based electronic industry. [ABSTRACT FROM AUTHOR]

Resistive switching (RS) of Ti/HfO2/Pt memory devices was studied using X-ray photoelectron spectroscopy. Hf4+ monotonously decreases with depth increasing towards to HfO2/Pt interface in low resistance state, while a fluctuation distribution of Hf4+ is shown in high resistance state (HRS) and in the pristine Ti/HfO2/Pt devices (without any SET or RESET process). It is explained by the existence of locally accumulated oxygen vacancies (clusters) in the oxide bulk layer in HRS and pristine states. A dynamic model of RS processes was proposed that the oxygen vacancy clusters dominantly determines the resistivity by the connecting/rupture between the neighbor cluster sites in the bulk. [ABSTRACT FROM AUTHOR]

SnS is intrinsically a p-type semiconductor, and much effort has been made to attain n-type conduction. In this letter, we performed density functional theory calculations to seek an effective doping route for n-type SnS. It was found that aliovalent doping of SnS by Sb or Bi is not effective due to their high formation enthalpies; while the isovalent Pb-substitution of the Sn sites largely reduces formation enthalpies of Sn and Pb interstitials, which explain the recently demonstrated n-type conduction in the Sn1-xPbxS films fabricated under low H2S pressures. [ABSTRACT FROM AUTHOR]

Thyroglobulin (Tg) is a sensitive indicator of persistent or recurrent differentiated thyroid cancer of follicular cell origin. Detection of Tg in human serum is challenging as bio-receptors, such as anti- Tg, used in immunoassay have relatively weak binding affinity. We engineer sensing surfaces using the competitive adsorption of proteins, termed the Vroman Effect. Coupled with Surface Plasmon Resonance, the "cross-responsive" interactions of Tg on the engineered surfaces produce uniquely distinguishable multiple signature patterns, which are discriminated using Linear Discriminant Analysis. Tg-spiked samples, down to 2ng/ml Tg in undiluted human serum, are sensitively and selectively discriminated from the control (undiluted human serum). [ABSTRACT FROM AUTHOR]

Nanoindentation is used to assess mechanical properties of ordered mesoporous titania thin films with pore sizes in the range of 8-16 nm. Estimates of strut properties are obtained under the standard scaling assumptions widely used in porous media. The inferred hardness and fracture toughness of individual struts are found to correspond to anatase titania, indicating the absence of obvious size effects in the nanostructured ceramic. This is in marked contrast to nanoporous metals, where size effects often play a crucial role in determining material properties at similar length scales. [ABSTRACT FROM AUTHOR]

We demonstrate sheath-free vertical concentration and positioning of cells induced by fluid viscoelasticity in a rectangular channel. The high uniformity in depth position and the reduction in cell overlap eliminate out-of-focus blurring and increase detection sensitivity. Additionally, orientational ordering of red blood cells improves the monitoring and counting performance of an optical imaging system. As a proof of concept of vertical focusing and cell ordering, we demonstrate counting and monitoring of red blood cells flowing in a microchannel using phase-contrast holographic microscopy for quantitative phase imaging. [ABSTRACT FROM AUTHOR]

SnS epitaxial films were grown on MgO (100) substrates by pulsed laser deposition using a H2S gas as an S source. High growth temperature and high H2S gas flow rate caused re-evaporation and etching of the deposited films; therefore, the optimum condition was limited to a narrow region around 400 °C. The measured bandgap 1.08 eV is consistent with the previously reported theoretical calculation. The films with a S/Sn ratio of ∼1.0 showed the largest mobility of ∼37 cm2/(Vs). The hole transport was dominated by domain boundary potential barriers ∼0.05 eV in height. [ABSTRACT FROM AUTHOR]

We synthesize nanoporous copper (NP Cu) through electrochemical dealloying of amorphous Cu0.41Si0.59 under compressive residual stress. Transmission Electron Microscopy reveals that struts are nanocrystalline with grain size equal to the strut thickness. Moreover, a significant population of twins with spacing ∼7 nm is present within each imaged grain. The hardness of this nanocrystalline, nanotwinned NP Cu is approximately one order of magnitude greater than reports on NP Cu in the literature. The yield strength of individual struts inferred through dimensional analysis is approximately an order of magnitude greater than bulk copper and compares well with other nanostructured copper systems. [ABSTRACT FROM AUTHOR]

A method of manufacturing three-dimension microneedle electrode arrays is presented in this paper using the micromolding technology with liquid metal at room temperature, based on the physical property of the Bi-In-Sn liquid metal alloy, being its melting point especially low. Observed under scanning electron microscopy, the needle body of the electrode chip manufactured using this method has a good consistency. Skin penetration test in-vitro indicates that the microneedle electrode can pierce the stratum corneum and cross the high-impedance layer to acquire electrical signals. Electrical impedance and polarization voltage experimental results show that the electrode chips have great electric characteristics and meet the practical application demands. [ABSTRACT FROM AUTHOR]

We report a highly tunable graphene embedded waveguide which overall modal index is in linear relationship with the in-plane permittivity of graphene and the electro-refraction effect has been significantly enhanced after graphene is embedded. An eight-layer graphene embedded Mach-Zender modulator has been theoretically demonstrated with the advantage of ultra-compact footprint (4 × 30 μm2), high modulation efficiency (20 V·μm), fast modulation speed, and large extinction ratio (35 dB). Our results may promote various on-chip active components, boosting the utilization of graphene in optical applications. [ABSTRACT FROM AUTHOR]

We identify the microscopic structural origins determining the bandgaps in the deep-ultraviolet borates, and propose an efficient method for the prediction of their bandgaps. This method considers only the chemical bond lengths around oxygen atoms and achieves the very high precision with the relative error <5% typically. Its validity is verified by the first-principles studies, which reveal the strong dependence of bandgaps on the coordination environment around oxygen atoms. Our studies have great implications on the search and design of optoelectronic functional materials with large bandgap. [ABSTRACT FROM AUTHOR]

The physical interaction between a lipid vesicle and a silver nanoparticle (AgNP)-human serum albumin (HSA) protein 'corona' has been examined. Specifically, the binding of AgNPs and HSA was analyzed by spectrophotometry, and the induced conformational changes of the HSA were inferred from circular dichroism spectroscopy. The fluidity of the vesicle, a model system for mimicking cell membrane, was found to increase with the increased exposure to AgNP-HSA corona, though less pronounced compared to that induced by AgNPs alone. This study offers additional information for understanding the role of physical forces in nanoparticle-cell interaction and has implications for nanomedicine and nanotoxicology. [ABSTRACT FROM AUTHOR]