Search

The orientation and rearrangement of water on a gold electrode significantly influences its physicochemical heterogeneous performance. Despite numerous experimental and theoretical studies aimed at uncovering the structural characteristics of interfacial water, the orientational behavior resulting from electrode-induced rearrangements remains a subject of ongoing debate. Here, we employed molecular dynamics simulations to investigate the adaptive structure and dynamics properties of interfacial water on Au(111) and Au(100) surfaces by considering a polarizable model for Au atoms in comparison with the non-polarizable model. Compared to the nonpolarizable systems, the polarization effect can enhance the interaction between water molecules and the gold surface. Unexpectedly, the rotational dynamics directly associated with the orientational behavior of water adjacent to the gold surface is accelerated, thereby reducing the hydrogen bond lifetime. The underlying mechanism for this anomalous phenomenon originates from the polarization effect, which induces the attraction of the positive hydrogen atoms to the surface by the negative image charge. This leads to a change in orientation that disrupts the hydrogen bonds in the first water layer and subsequently accelerates reorientation dynamics of water molecules adjacent to the gold surface. These results shed light on the intricate interplay between polarization effects and water molecule dynamics on metal surfaces, establishing the foundation for the rational regulation of the orientation of interfacial water. [ABSTRACT FROM AUTHOR]

When it comes to simulate or calculate an optoelectronic tweezer (OET) response for a microparticle suspended in a given medium, a precise electrical conductivity (later referred to as conductivity) value for the microparticle is critical. However, there are not well-established measurements or well-referenced values for microparticle conductivities in the OET realm. Thus, we report a method based on measuring the escape velocity of a microparticle with a standard OET system to calculate its conductivity. A widely used 6 μm polystyrene bead (PSB) is used for the study. The conductivity values are found to be invariant around 2×10-3 S/m across multiple different aqueous media, which helps clarify the ambiguity in the usage of PSB conductivity. Our convenient approach could principally be applied for the measurement of multiple unknown OET-relevant material properties of microparticle-medium systems with various OET responses, which can be beneficial to carry out more accurate characterization in relevant fields. [ABSTRACT FROM AUTHOR]

Environment-friendly lead-free potassium sodium niobate-based piezoelectric materials have been widely used in acoustic device applications because of its high piezoelectric response, high Curie temperature, and low acoustic impedance. In our previous works, samarium modified 0.915(K0.45Na0.5Li0.05)NbO3–0.075BaZrO3–0.01(Bi0.5Na0.5)TiO3 (Sm–KNLN–BZ–BNT) ceramics have achieved high piezoelectric properties with good thermal stability. To further improve its properties and thermal stability, grain orientation-controlled methods have been introduced to Sm–KNLN–BZ–BNT ceramics. In this work, textured Sm–KNLN–BZ–BNT ceramics with a 93% ⟨001⟩c-oriented textured degree have been prepared. The samples have achieved a d33* value with 532 pm/V and better thermal stability between room temperature to 150 °C than the non-textured samples. Moreover, ultrasonic transducers with a 25 MHz center frequency have been designed and fabricated by the textured Sm–KNLN–BZ–BNT ceramics. The peak-to-peak of the transducers has reached a 1.78 V high level, which demonstrated the textured Sm–KNLN–BZ–BNT ceramics are a good candidate for acoustic applications. [ABSTRACT FROM AUTHOR]

Monolayer and few-layer CoPS3 have been successfully synthesized via an Au-assisted exfoliation technique, with their transport properties subsequently investigated by conductive atomic force microscopy. Rectification effects can be observed in CoPS3 nanosheets due to the Schottky junction formation at the Au/CoPS3 interface, especially in configurations comprising two or more layer flakes. The distinct transport properties between monolayer and few-layer samples demonstrate that the charge transport behavior in the vertical direction is associated with the van der Waals gap. The calculated electron affinity for CoPS3 is about 4.84 eV, as revealed by the thermionic emission model. The results obtained contribute to the knowledge base concerning the transport characteristics of ultrathin MPX3, facilitating further exploration of the transport behavior of these materials and their potential applications in novel electronic devices. [ABSTRACT FROM AUTHOR]

An impedance analysis for optically induced dielectrophoresis is presented. A circuit model is developed for this purpose. The model parameters are fully defined in terms of the geometrical and material properties of the system. It is shown that trapping force can only be generated when the material properties follow certain impedance matching conditions. The impedance match factor is introduced to succinctly quantify the phenomenon. It is used to calculate bounds on the allowed electrical conductivity of the suspension medium. Results from the proposed model are found to be in good agreement with full-wave numerical simulations. By computing the acceptable set of material parameters with little computational cost, the presented analysis can streamline ODEP system design for various applications. [ABSTRACT FROM AUTHOR]

Density functional theory calculations are performed to systematically investigate the electronic and magnetic properties of few-layer and bulk Fe3SiSe2 (FSS). We predict that the bulk FSS has a metallic ground state and a layered structure displaying intralayer ferromagnetic ordering and interlayer antiferromagnetic ordering. The itinerant magnetism in the FSS was determined by the Stoner criterion. Predictions of the absence of unstable phonon modes and a moderate cleavage energy of only 28.3 meV/Å2 suggest the possibility of stabilizing FSS in a monolayer form. The calculated spin–orbit coupling facilitates not only a large magnetocrystalline anisotropy energy, around 500 μeV/Fe, but also spontaneous valley polarization in odd-numbered layer systems. These systems have net magnetic moments as the magnetic moments of AFM-ordered layers are not fully compensated in the odd-numbered layer case and are predicted to show 2D metallic behaviors. The magnitude of the valley polarization in odd-numbered layered systems decreases from 18 meV with layer number but is absent in even-layered structures, thus showing an odd–even oscillation effect. Experimental realization of this bidimensional metallic magnet is, therefore, expected to widen the arena of two-dimensional materials that show exotic phenomena. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to study the adaptability and enhancement methods of ignition chips in complex electromagnetic environments. In this paper, combined with simulation and calculation technology, we first establish the electromagnetic–electrical–thermal coupling simulation model of ignition chips and analyze the influence of two electromagnetic environments, continuous electromagnetic wave and nuclear electromagnetic pulse, on the electrical–thermal coupling in the bridge area of the ignition chip. The results show that a continuous electromagnetic wave field strength of 1200 V/m, irradiated for 5 s, a nuclear electromagnetic pulse with a rise time of 5 ns, a half-height width of 24 ns, and a leg wire length of 350 mm will cause the ignition chip to fire accidently. In order to suppress its accidental firing, the electromagnetic protection is enhanced by using parallel Transient Voltage Suppressor (TVS) diodes. It has been shown that parallel TVS diodes provide good protection against both continuous electromagnetic waves and nuclear electromagnetic pulses. In particular, the peak induced current decreases by more than 64.7% during the action of continuous electromagnetic waves, and the maximum temperature in the bridge area decreases by 54.34% during the action of nuclear electromagnetic pulses. [ABSTRACT FROM AUTHOR]

Two-dimensional ferromagnetic topological semi-metals have attracted much interest owing to their fascinating spintronic applications. Using first-principles calculations, we propose a stable transition metal nitrogen halide compound, namely, VNI monolayer, to display intrinsic ferromagnetism with high Curie temperature TC (∼510 K) and strong out-of-plane magnetism. It is found to be a topological Weyl nodal line material, which can be fully spin-polarized by controlling the on-site Coulomb interaction. Its nodal line can be destroyed by orienting the magnetization axis. Additionally, biaxial strain enables efficient tuning of the magnetic properties by switching the easy magnetic axis from an out-of-plane to in-plane direction with an enhanced TC to 540 K. These results highlight the great application potential of a VNI monolayer in low-dimensional topological magnets. [ABSTRACT FROM AUTHOR]

The micro-actuator is a key element of the MEMS-based initiator. In order to ensure safety and achieve the function of detonation energy isolation and transmission of the micro-pyrotechnic sequence, it is necessary to set up a safety and arming device between the micro-heater and energetic materials on the next level in the initiator. In this paper, the MEMS safety and arming device was simulated and analyzed, and the actuator chip was made based on MEMS technology and then tested. The results showed that the maximum temperature and displacement generated by the silicon-based micro-actuator increased with increasing actuation voltage. When the actuation voltage was larger than 16 V, the device could not work normally because the maximum temperature of the device was higher than the melting point of silicon. Furthermore, the influence factors on the state-recoverable property of the device were studied by changing the actuation voltage, length, width, and thickness of the V-shaped beam in a single way. The results showed that when the actuation voltage remained unchanged and the other factors were changed in a single way, the smaller structural parameters resulted in the shorter response time and recovery time, while the displacement generated was smaller. Meanwhile, the larger structural parameters resulted in larger displacements, while the response time and recovery time were larger. In addition, the state-recoverable characteristics of the device were affected by the working environmental temperature. It is of great significance to the design of the MEMS-based initiator. [ABSTRACT FROM AUTHOR]

A scheme that combines optoelectronic tweezers (OET) with spectroscopic analysis is presented. Referred to as spectral tweezers, the approach uses a single focused light beam that acts both as the trapping beam for OET and the probe beam for spectroscopy. Having simultaneous manipulation and spectral characterization ability, the method is used to isolate single micro-samples from clusters and perform spectral measurements. Experimental results show that a characteristic spectral signature can be obtained for a given sample. The proposed approach can be easily integrated into the optical setups used for conventional OETs with only a few additional optical components, making it a convenient tool for bio-analytical applications. [ABSTRACT FROM AUTHOR]

Pyrotechnic device is the key initiating component of weapon system, and its function reliability will directly affect the triggering of detonation and actuation mechanism. In order to enhance the survival ability of pyrotechnic device in intricate electromagnetic interference environment, it is necessary to carry out in-depth research on the electromagnetic protection technique of pyrotechnic device. In this paper, a new electromagnetic protection circuit based on vertical punch through PN junction device is proposed, which monolithically integrates the circuit with polysilicon semiconductor bridge on a single chip. The Electro-static Discharge (ESD) test was carried out according to the method specified by standard electrostatic standard 500 pF/500 Ω/25 kV, and the ESD capability of the proposed new chip was not less than 25 kV. Compared with the electromagnetic protection circuit by transient voltage suppressor diode based on lateral punch through junction device structure, the new chip increases the effective junction area of PN junction, reduces the current density, and increases the current conduction ability and electrostatic roughness of the diode. The new chip has a larger diode effective junction capacitance, which not only improves the ESD capability but also improves the RF protection capability at the same time. [ABSTRACT FROM AUTHOR]

Textured process is considered an effective way to enhance the performance of piezoelectric ceramics. To obtain lead-free piezoelectric KNN-based ceramics with high performance, ⟨001⟩c-textured lead-free piezoelectric 0.915(K0.45Na0.5Li0.05)–0.075BaZrO3–0.01Bi0.5Na0.5TiO3 (KNLN–BZ–BNT) ceramics with the addition of 5 mol. % NaNbO3 templates were prepared, and the improved piezoelectric properties and thermal stability were expectedly achieved. For textured ceramics, the textured degree is one of the very important parameters and strongly depends on the amount of templates. Therefore, in this work, the effect of the amount of templates on the textured degree and electrical properties of ⟨001⟩c-textured KNLN–BZ–BNT ceramics were investigated in detail. It was found that the templates take a positive effect when the template amount is low, in which the textured degree and electrical properties increased with the amount of templates. In contrast, excess templates could induce a severe shift of stoichiometry within the textured ceramics, accompanied by degraded performances. As a result, for the ceramics with template amount less than 4 mol. %, enhanced textured degree and electrical properties were obtained. When the template amount exceeds 5 mol. %, the textured degree and electrical properties become degraded. The textured ceramic with the 4 mol. % template shows the highest textured degree of 93% and the highest piezoelectric constants of d33 = 360 pC/N and d 33 ∗ = 615 pm/V. Combining a vertical morphotropic phase boundary with an appropriate template amount of 4 mol. %, the ceramics exhibit superior thermal stability within the temperature range of 30–200 °C. [ABSTRACT FROM AUTHOR]

The safety and reliability of the initiating explosive devices (IEDs) are critical for the weapon system. As the core components of IEDs, the method of resistance designing and the performance of conversion energy of energy conversion components (ECCs) are worth being studied. In this paper, the design method for the resistance of ECCs is established based on the finite element discrete method, and the currents of melting and electric explosion are presented for evaluating the performance of ECCs. The results show that the resistance of the ECCs is 1 ± 0.05 Ω with consistency. The ECCs were designed by the established design method of resistance and manufactured by the established machining method. The melting current of ECCs is 1.8 A, which is calculated by the infrared temperature measurement and finite element simulation. The electric explosion current of ECCs is 5 A, which was obtained by combining the snapshot obtained via the high-speed camera and finite element simulation. [ABSTRACT FROM AUTHOR]

The recent discovery of infinite-layer nickel oxide superconductors has highlighted the importance of first-principles simulations. We predict an infinite-layer bismuth oxide superconductor BaBiO2, which is isostructural to NdNiO2. In this work, electronic structure, lattice dynamics, and electron–phonon interaction are studied, with special attention paid to the influence of spin–orbit coupling (SOC) on the above-mentioned quantities. Our calculations show that the structure will be dynamically stable under pressure and induce superconductivity, whether SOC is considered or not. In addition, SOC will significantly enhance the electron–phonon coupling (EPC), resulting in an increase in EPC constant λ from 0.43 to 0.73. We further find that the Fermi surface nesting is partially responsible for its superconductivity. A strong SOC changes the Fermi surface and enhances the nesting, and the EPC becomes stronger. Our results propose a bismuth-based superconductor, demonstrating the importance of SOC for its superconductivity and providing clues for further experimental synthesis. [ABSTRACT FROM AUTHOR]

Since the experimental observation of a rhombohedral phase of hafnium oxide, there remains controversy over whether this phase belongs to the R3 or R3m space group. Moreover, the origin of polarization in these two rhombohedral phases has not been comparatively elucidated. Here, we present a theoretical study comparing the relative stability and ferroelectricity of the R3 and R3m phases of HfO2, representing two potential forms of heavily Zr-doped ferroelectric thin films of hafnia found recently. We comprehensively investigate their structural stability and polarization response under in-plane compressive strain. A phase transition from R3 to R3m is discovered under biaxial compressive strain. The direction and magnitude of polarization in both phases can be tuned by strain. Through symmetry mode analysis, we elucidate the improper nature of ferroelectricity. These findings may advance understanding of ferroelectricity in hafnia thin films. [ABSTRACT FROM AUTHOR]

Nonvolatile multiferroic coupling that can be controlled by electric fields has a wide range of future electronic multistate applications. Through first-principles calculations, we have revealed such magnetoelectric effect in van der Waals heterostructure systems consisting of CuCrP2Se6 and VS2. The distinct magnetic moments for Se atoms on the upper and lower surfaces of the CuCrP2Se6 substrate lead to different interlayer magnetic coupling configurations. Meanwhile, by varying the number of substrate layers, we can manipulate the direction of V's magnetic moment during ferroelectric reversal. This intricate interplay of ferroelectricity, magnetism, and ferrovalley enables the creation of electric switchable states. These findings provide ideas for nonvolatile memories controlled directly through electric fields. [ABSTRACT FROM AUTHOR]

We present a device that can achieve controlled transport of colloidal microparticles using an array of micro-electrodes. By exciting the micro-electrodes in regular sequence with an AC voltage, a time-varying moving dielectrophoretic force-field is created. This force propels colloidal microparticles along the electrode array. Using this method, we demonstrate bidirectional transport of polystyrene micro-spheres. Electromagnetic simulation of the device is performed, and the dielectrophoretic force profile around the electrode array is mapped. We develop a Brownian dynamics model of the trajectory of a particle under the influence of the time-varying force-field. Numerical and experimental results showing controlled particle transport are presented. The numerical model is found to be in good agreement with experimental data. The developed numerical framework can be useful in designing and modeling lab-on-a-chip devices that employ external non-contact forces for micro-/nanoparticle manipulation. [ABSTRACT FROM AUTHOR]

We observe the strong photorefractive (PR)-like effect in silica micro-fibers, which is different from the previously reported nonlinear behaviors in optical fiber devices. The micro-fiber is fabricated by tapering a standard silica single-mode fiber using the hydrogen flame. Two fiber Bragg gratings are fused at each end of the micro-fiber to form a Fabry–Pérot cavity, enabling us to observe the nonlinear dynamics. By situating the silica micro-fiber in a gas medium (i.e., N2, Ar, He, and air), we observe the remarkable PR-like effect, especially under the low-pressure condition below 80 Torr. In fact, the nonlinear effect increases with the reduced pressure as a power function. Such a nonlinear effect is also affected by the laser wavelength detuning rate, input laser power, and micro-fiber diameter. Finally, a nonlinear cavity dynamics model is adopted to well describe the observed nonlinear effect. [ABSTRACT FROM AUTHOR]

Over the past decades, lead-based relaxor ferroelectrics have served as the model systems to unravel the relationship between electromechanical properties and local structure. Here, by employing pair distribution function analysis and the reverse Monte Carlo method, we investigate the local structural features and their temperature dependence in relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-xPbTiO3 with x = 0.15 (PZN-15PT), which has a tetragonal average structure, but displays frequency dependence at low temperatures. The refined atomic model suggests that ordered polar nanoregions (PNRs) originate from the strong atomic displacive correlation, and their polar directions are the same as the crystallographic symmetry axis. The dipoles in the disordered matrix have weak correlations and can be averaged into a global tetragonal symmetry. These findings establish a detailed picture of the local structure of lead-based relaxor ferroelectrics and provide a deeper insight into the nature of PNRs. [ABSTRACT FROM AUTHOR]

A peculiar topological Hall effect (THE) is reported in a noncentrosymmetric ternary carbide GdCoC2. The GdCoC2 reveals a magnetic ordering transition from paramagnetic to ferromagnetic state at the Curie temperature TC = 15.6 K, followed by a commensurate-incommensurate phase transition at Tt = 14.1 K. Below Tt, the competition between an external magnetic field and magnetic interactions, including the Dzyaloshinskii–Moriya interaction, would give rise to characteristic spin textures with non-zero scalar spin chirality χ ijk , or even topologically protected spin configurations like skyrmions, for which the exotic spin-charge coupled phenomena are induced. Besides a large negative magnetoresistance (MR) up to ∼−52% at 14 K, a remarkably sharp topological Hall signal is observed with almost no anomalous Hall resistivity below 10 K. The topological Hall resistivity ( ρ xy T ) of GdCoC2 reaches a maximum value of ∼0.23 μΩ cm at 3 K under μ0H = 0.6 T. The mechanism underlying the exceptional THE with relatively large ρ xy T value in GdCoC2 is discussed in detail. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) multiferroic materials with coexisting ferroelasticity (FA) and ferroelectricity (FE) have potential applications in high-density data storage and sonar detectors. Here, based on first-principles calculations, we predict a series of stable 2D FA-FE multiferroic structures, namely, γ-XOOH (X = Al, Ga, and In) monolayers. By analyzing the lattice symmetry and orientation distribution of hydroxyls, we find that XOOH monolayers possess both in-plane ferroelastic and ferroelectric polarization, as well as antiferroelectric ordering caused by the anti-parallel alignment of hydroxyls. Interestingly, the perpendicular reorientation of in-plane FE polarization accompanies 90° ferroelastic switching. Moreover, they show an unusual negative transverse piezoelectric effect originated from the clamped-ion term. The multiferroic properties of the XOOH monolayers provide an excellent platform to study electroelastic effects. [ABSTRACT FROM AUTHOR]

A peculiar topological Hall effect (THE) is reported in a noncentrosymmetric ternary carbide GdCoC2. The GdCoC2 reveals a magnetic ordering transition from paramagnetic to ferromagnetic state at the Curie temperature TC = 15.6 K, followed by a commensurate-incommensurate phase transition at Tt = 14.1 K. Below Tt, the competition between an external magnetic field and magnetic interactions, including the Dzyaloshinskii–Moriya interaction, would give rise to characteristic spin textures with non-zero scalar spin chirality χ ijk , or even topologically protected spin configurations like skyrmions, for which the exotic spin-charge coupled phenomena are induced. Besides a large negative magnetoresistance (MR) up to ∼−52% at 14 K, a remarkably sharp topological Hall signal is observed with almost no anomalous Hall resistivity below 10 K. The topological Hall resistivity ( ρ xy T ) of GdCoC2 reaches a maximum value of ∼0.23 μΩ cm at 3 K under μ0H = 0.6 T. The mechanism underlying the exceptional THE with relatively large ρ xy T value in GdCoC2 is discussed in detail. [ABSTRACT FROM AUTHOR]

We report the development of swept cavity-enhanced photoacoustic spectroscopy using a quartz tuning fork for ultra-sensitive and high-resolution molecular spectroscopy. By using a quantum cascade laser (QCL) as the mid-infrared light source, a dual-feedback Pound–Drever–Hall locking method is proposed to lock the QCL frequency to a continuously swept optical cavity. By placing an off-beam quartz-enhanced photoacoustic spectroscopy module in a 48-mm Fabry–Pérot cavity, we are able to achieve ultra-sensitive gas detection based on the doubly resonant photoacoustic effect. As a proof-of-concept, we use a distributed feedback QCL to exploit the CO line at 2190.02 cm−1, where the cavity-locked QCL is scanned over a spectral range of 10 GHz with a spectral resolution of ∼3 MHz. With the incident laser power of 7.3 mW, the optical cavity (finesse 1931) builds up the intracavity power beyond 3 W. Our photoacoustic spectrometer achieves the minimum detection limit of 375 part-per-trillion (ppt) at the averaging time of 150 s and the normalized noise equivalent absorption coefficient of 1.27 × 10−9 Wcm−1 Hz−1/2. [ABSTRACT FROM AUTHOR]

An optoelectronic tweezer (OET) device is presented that exhibits improved trapping resolution for a given optical spot size. The scheme utilizes a pair of patterned physical electrodes to produce an asymmetric electric field gradient. This, in turn, generates an azimuthal force component in addition to the conventional radial gradient force. Stable force equilibrium is achieved along a pair of antipodal points around the optical beam. Unlike conventional OETs where trapping can occur at any point around the beam perimeter, the proposed scheme improves the resolution by limiting trapping to two points. The working principle is analyzed by performing numerical analysis of the electromagnetic fields and corresponding forces. Experimental results are presented that show the trapping and manipulation of micro-particles using the proposed device. [ABSTRACT FROM AUTHOR]

Bismuth sodium titanate and related compounds are promising lead-free ferroelectric materials potentially useful in a wide range of piezoelectric applications. The domain structure plays an important role in determining the piezoelectric and ferroelectric properties and thereby the performance of electromechanical transducers. In this work, piezoresponse force microscopy (PFM) is used to gain insights into the mesoscopic-scale domain structure and its evolution under electric field in the (1−x)Bi0.5Na0.5TiO3-xBaTiO3 (BNT-BT) piezoceramics with compositions varying from x = 0 to x = 0.08. A phase transition from the rhombohedral phase to the tetragonal phase is observed with increasing BT contents. A relationship is established between the relaxor behavior and the domain structures imaged by PFM, i.e., short-range polar regions without visible domains in relaxor ceramics of pure BNT, while long-range ordered polar states with clear domains in ferroelectric ceramics with the addition of BT content. Distinct micro-domains are observed in the ceramics with compositions close to the morphotropic phase boundary (MPB), but the domain size drops to nanometers in the MPB composition with an increasing domain wall density. An electric field can induce the transformation from the relaxor behavior to a ferroelectric state, accompanied by an increase in domain sizes and a rearrangement/reorientation of the polar domains. This study of domain structure and its evolution in BNT-BT provides a better understanding of the relationship between the crystal structure, mesoscopic-scale domains, and macroscopic properties in these important lead-free piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

The heterogeneous epitaxial system of BaTiO3/Ge (BTO/Ge) is of great interest for both fundamental research and device applications, thanks to its quasi-lattice-matching feature and the integration of functional oxides on semiconductors. Currently, the heteroepitaxial growth of crystalline BTO films on Ge includes the utilization of ultrahigh vacuum tools and complex surface passivation pre-treatment as well as careful control of oxygen partial pressure during the growth. Meanwhile, oxygen vacancies in oxides strongly impact their structural and electrical properties. Here, we report a facile method to directly grow single crystalline BTO films on Ge using pulsed laser deposition. The strict control of oxygen partial pressure ensures a sharp interface with an atom-to-atom registry and also leads to the oxygen-deficient characteristics of BTO. The epitaxial relationship of BTO and Ge is [110] BTO (001)//[100] Ge (001). Detailed crystallographic studies on BTO films with different thicknesses show that, for the films with a thickness less than 20 nm, BTO shows a mixture of tetragonal and cubic phases due to the oxygen vacancies and the strain from the Ge substrate and the cubic phase eventually dominates as the film thickness increases. Such oxygen-deficient BTO films reveal conducting characteristics rather than dielectric properties. The oxygen vacancies can be partly "cured" after a low temperature annealing process. These results not only demonstrate the possibility to directly grow single crystalline oxides on semiconductors without surface passivation but also highlight the importance of oxygen vacancies and lattice strain on the crystallographic and electrical properties of BTO films. [ABSTRACT FROM AUTHOR]

The orthorhombic O and O′ structure phases of ABO3-type perovskites possess the same symmetry and quite different physical properties. In this work, a pressure induced isostructural O′–O phase transition with volume expansion and less distortion in DyFeO3 orthoferrite was experimentally observed and studied by high-pressure x-ray diffraction and Raman spectroscopy measurements. Up to 35.2 GPa, DyFeO3 crystallizes in an orthorhombic Pbnm symmetry structure. With no change in the symmetry group, distinct O′-phase and O-phase were verified below 13.1 GPa and above 15.1 GPa, respectively. Meanwhile, the lattice becomes less distorted and metrically pseudo-cubic on the high-pressure side. The cell volume expands by a step in the intermediate pressure window accompanied by a decrease in spontaneous strain. It is suggested that FeO6 octahedra are more compressible than DyO12 sites under pressure. This work claimed the physical mechanism underlying phonon dynamics and variation of local structure symmetry of DyFeO3, which can be considered as the basic view for RFeO3 perovskites. [ABSTRACT FROM AUTHOR]

MEMS electric energy utilization rate is the key parameter affecting firing performance. It has important relationship with its preparation technology, microscale and structure morphology. In order to improve the theory of energy exchange element design for MEMS pyrotechnics, reduce the design error of transducer parameters at microscale. To ensure the performance of MEMS pyrotechnics, in this paper, the influence of the central line of the thin film transducer element on the electrothermal conversion is simulated and analyzed. The electrothermal conversion and temperature characterization of different central lines in the transducer bridge area are calculated by the finite element method. The influence of the central line on the thermal efficiency under microscale is revealed. The corresponding data are obtained. [ABSTRACT FROM AUTHOR]

The NiCr igniter is a key element of MEMS-based electro-explosive device (mEED), while electrostatic discharge (ESD) may excite the igniter accidentally. To protect the NiCr igniter from damage by ESD, a novel NiCr igniter by integrating the igniter onto a TVS diode based substrate was designed and fabricated through semiconductor technology. The microscope photograph, resistivity, breakdown voltage, firing performance, and ESD protection ability were tested. The results show that the surface of the chip is smooth, the edges of key structures are clear, and there are no major scratches, cracks, and other phenomena on the whole device. The resistivity of all the TVS-mNiCr igniters is between 5 and 7 Ω, and the TVS diode resistance value is normal. The breakdown voltages of the eight types of TVS diodes with different structures are all between 3.5 and 5 V, and the TVS-mNiCr igniters can fire reliably at a constant current of 2 A. After the ESD test, the microscope of the igniter does not change significantly, meaning that the TVS-mNiCr igniter chip has a certain ability of ESD protection. It is of vital importance to guide the design of electrostatic tolerant ability for the MEMS-based electro-explosive device. [ABSTRACT FROM AUTHOR]

In order to improve the ignition ability of reactive film, in this paper, the effects of copper oxide and silicon nitride on the flame height of the TaN@(Al/Ni) energy exchanger were investigated by using a high-speed photographic system. The insulating layer material was applied to the preparation TaN@(Al/Ni) by the MEMS process. The experimental results showed that the flame height of (Al/Ni)–TaN energy exchanger was obviously higher than that of silicon nitride when copper oxide was used as the insulation layer, which indicates that the oxygen-containing insulation layer could increase the flame height of the energy exchanger. [ABSTRACT FROM AUTHOR]

The plasmonic response of a nano C-aperture is analyzed using the Vector Field Topology (VFT) visualization technique. The electrical currents that are induced on the metal surfaces when the C-aperture is excited by light is calculated for various wavelengths. The topology of this two-dimensional current density vector is analyzed using VFT. The plasmonic resonance condition is found to coincide with a distinct shift in the topology which leads to increased current circulation. A physical explanation of the phenomenon is discussed. Numerical results are presented to justify the claims. The analyses suggest that VFT can be a powerful tool for studying the physical mechanics of nano-photonic structures. [ABSTRACT FROM AUTHOR]

Density functional theory calculations have been performed for the structural, electronic, magnetic, and ferroelectric properties of a mixed-valence Fe(ii)–Fe(iii) formate framework [NH2(CH3)2][FeiiiFeii(HCOO)6]. Recent experiments report a spontaneous electric polarization, and our calculations are in agreement with the reported experimental value. Furthermore, we shed light onto the microscopic mechanism leading to the observed value, as well as on how to possibly enhance the polarization. The interplay between charge ordering, dipolar ordering of DMA+ cations, and the induced structural distortions suggest new interesting directions to explore in these complex multifunctional hybrid perovskites. [ABSTRACT FROM AUTHOR]

Strong coupling between light and matter occurs when the two interact such that new hybrid modes, the so-called polaritons, are formed. Here, we report on the strong coupling of both the electric and the magnetic degrees of freedom to an ultrafast terahertz (THz) frequency electromagnetic wave. In our system, optical phonons in a slab of ferroelectric lithium niobate are strongly coupled to a THz electric field to form phonon-polaritons, which are simultaneously strongly coupled to magnons in an adjacent slab of canted antiferromagnetic erbium orthoferrite via the magnetic-field component of the same THz pulse. We juxtapose experimental results of bare slabs consisting of the two materials with a photonic crystal cavity, consisting of a two-dimensional array of air holes cut into the hybrid slab. In both cases, the strong coupling leads to the formation of new magnon-phonon-polariton modes, which we experimentally observe in the time domain as a normal-mode beating and which corresponds in the frequency domain to an avoided crossing. Our simple yet versatile waveguide platform provides a promising avenue through which to explore ultrafast THz spintronics, quantum electrodynamics, sensing, and spectroscopic applications. [ABSTRACT FROM AUTHOR]

As the reach points of different phases with complex structural features, a morphotropic phase boundary (MPB) in ferroelectric and ferromagnetic solid solutions can significantly enhance the piezoelectric performance and magnetostrictive response, respectively. Recently, the phase-change functional responses related to the multiferroic MPB are proposed to be a promising way to enhance the magnetoelectric coupling in BiFeO3-based single phase multiferroics. In this work, we verify the tunable magnetic ordering and the construction of the multiferroic MPB by engineering the chemical concentrations of the ferroelectric/non-magnetic PbTiO3 end in the (1 – x)Bi0.9Dy0.1FeO3-xPbTiO3 binary solid solution ceramic system. Based on the results obtained in this work and reported in the literature, the structure-ferroic properties phase diagram of the BiFeO3-DyFeO3-PbTiO3 ternary system is established, where a compositional region with coexisting ferroelectric polarization and ferromagnetic moment is found. More importantly, a multiferroic MPB line separating two chemical regions with distinct crystal structures and ferroic orderings is discovered in the phase diagram. The phase changing nature of MPB compositions with temperature and compositions is investigated from room temperature to high temperature paraelectric phase. This work could provide a promising system to explore the highly desired colossal effects on magnetoelectric coupling in single phase multiferroics by phase-change functional responses. [ABSTRACT FROM AUTHOR]

LaN/rare earth nitride (REN) superlattices, having magnetic REN as one of the parent components, are constructed and studied by first-principles calculations. In particular, they are found to be mechanically and dynamically stable with (anti-)ferromagnetic and ferroelectric orderings. We reveal that the volume matching condition is applicable to these superlattices, which results in the elastic constant C33 softening and, when combined with a small c/a value, induces a huge piezoelectric response near the unstrained state. We also show that in-plane biaxial strain can precisely control the nature (indirect or direct) and value of the electronic bandgap. Moreover, the unpaired magnetically active 4f-electrons reduce the c-direction off-centric distortion of the wurtzite structure, making possible the switching of the ferroelectric polarization. This work, therefore, reveals that the volume matching condition also applies to magnetic materials and provides guidance for the design of multiferroic rare-earth nitride superlattices in piezoelectric devices. [ABSTRACT FROM AUTHOR]

The ever-increasing demand for larger surface area, well-defined, and conformal multi-layer nanostructures in gas sensor, catalyst and solar cell applications has propelled the exploration of such nanostructures within an atomic resolution. The atomic layer deposition (ALD) technique is ideal for the synthesis of these nanostructures due to its excellent step coverage ability on high aspect ratio nanostructures. In this work, different coaxial nanotube networks are successfully fabricated by electrospinning and ALD, with a well-controlled phase. We systematically studied the temperature-induced microstructures and photoluminescence property evolution of the nanotube network. The Al2O3/ZnO/Al2O3 tri-layer nanotube network is obtained by sintering at 400 °C, and a ZnAl2O4 core-shell nanotube structure has formed by the Kirkendall effect by further post-annealing at 700 °C. Oxygen accumulation is clearly observed at the small neck feature, but the Zn and Al elements are uniformly distributed along the whole nanotube. Photoluminescence emission obtained in this work is so broad that it almost covers the whole visible light wavelength range. The results indicate that the microstructures and photoluminescence properties can be well-controlled by the post-annealing temperature. It provides an available platform for realizing conformal 3D nano-devices. [ABSTRACT FROM AUTHOR]

Topological semimetals represent one of the most interesting classes of materials that continue to attract worldwide interest. Here, we report magnetotransport properties of MPn2-type (M=Nb, Ta; Pn=P, As, Sb) NbSb2 single-crystal semimetals with a centrosymmetric C12/m1 space group, paramagnetic ground state, and non-saturation parabolic-like magnetoresistance. The NbSb2 crystals show metallic conductivity down to 2K and undergo a metal-to-insulator-like transition under a magnetic field B (B ≥ 4 T) and exhibit a resistivity plateau in the lowtemperature region (T ≤ 10K), where the value of resistivity strongly depends on the magnitude and direction of the magnetic field. Upon sweeping the magnetic field from 0 to 14.5 T in the transverse configuration at T=1.5K, the NbSb2 crystal shows a large positive magnetoresistance (4.2 x 10³% at B=14.5 T) with Shubnikov-de Haas (SdH) oscillation. Hall measurements reveal that both the carrier compensation between electrons and holes and the high mobility and large mean free path of carriers contribute to the large magnetoresistance. Fast Fourier transform analyses of angle-resolved SdH oscillation indicate that the Fermi surface of the NbSb2 crystal is quasi-two-dimensional with three-dimensional components. These findings, together with the theoretically calculated electronic band structure obtained within the framework of density functional theory, suggest that NbSb2 is a good candidate compensated semimetal for further theoretical and experimental investigation of this family of materials. [ABSTRACT FROM AUTHOR]

A sodium bismuth titanate-based thin film is widely investigated lead-free piezoelectrics with potential applications for modern micro-devices such as PiezoMEMS. In this work, a 0.9Na1/2Bi1/2TiO3–0.1BaZr0.2Ti0.8O3 thin film was deposited on a Pt/Ti/SiO2/Si (001) substrate by the sol–gel spin coating method. The deposited piezoelectric film shows low dielectric loss and high remnant polarization. The measured ferroelectricity loop showed a coercive field of 110 kV/cm and a saturation polarization of 46.83 μC/cm2. The piezoelectric response of this thin film does not decrease from room temperature to around 100 °C. The fabricated piezoelectric device with bottom and top electrodes showed a large macro-scale strain value of ∼4% under the DC (30 V) and AC voltages (f = 800 kHz, Vpp = 10 V). [ABSTRACT FROM AUTHOR]

Infrared detection by binary phosphides is of great interest due to their high carrier mobility, excellent stability, and high absorbance coefficient, as they have a wide range of applications in civil and military fields. As the only metastable phase in gold phosphide, Au2P3 has attracted great attention in fundamental research and optoelectronic applications. Here, we synthesized high-quality and environmentally stable Au2P3 nanosheets through a modified facile one-step mineralization-assisted chemical vapor transport method. Through systematic infrared photoluminescence characterizations, it is found that the as-synthesized Au2P3 nanosheets display an impressive mid-infrared luminescence band centered at about 6.64 μm (0.187 eV) at room temperature. Furthermore, Au2P3-based self-powered photodetectors display outstanding infrared detection performance with D* = 2.9 × 1010 Jones at 1550 nm and D* = 1.9 × 108 Jones at 2611 nm, respectively. Our results suggest that the synthesized Au2P3 nanosheets could be promising candidates for future chip-based infrared nanophotonic and optoelectronic circuitry. [ABSTRACT FROM AUTHOR]

We predict the presence of gapped electronic structures in an artificial superlattice of graphene embedded in (111)-oriented BiFeO3 layers based on first-principles calculations. Due to the electron transfer and the proximity effect at the BiFeO3/graphene interface, we find that magnetic moments of Fe atoms near a graphene layer were slightly less than that of bulk Fe atoms. Regarding the ferromagnetic moment orientation of Fe atoms in perovskite BiFeO3, we reveal that the in-plane magnetization gives the ground state. The bandgap depends on the magnetization direction and the separation between the graphene layer and the perovskite BiFeO3 slab, which might be adjusted by applying external uniaxial stress in an experiment. Our results provide a route for designing hybrid 2D materials with emerging properties that are not available in single materials alone. [ABSTRACT FROM AUTHOR]

In this work, the solidification of liquid iron with or without external magnetic field was investigated by using two molecular dynamics methods, namely direct cooling and two-phase simulation. The influence of external magnetic field on the solidification is characterized by the critical temperature and radial distribution functions. Our computational results show that under external magnetic field, the solidification point tends to decrease significantly. By further analyzing the diffusion coefficients and viscosity, we attribute the effect to the stronger fluctuation of liquid iron atoms driven by the external magnetic field. [ABSTRACT FROM AUTHOR]

Zn1-xYbxO (0⩽x⩽0.02) thin films have been prepared by inductively coupled plasma enhanced physical vapor deposition method. All the Yb-doped ZnO thin films show room-temperature ferromagnetism. The correlation between oxygen vacancy and magnetism in Yb-doped ZnO thin films is studied. It is found that Yb irons initially substitute for Zn sites when x⩽0.01 and then enter the interstitial sites of ZnO with increasing Yb concentration of x>0.01. The ferromagnetism is induced by the coexistence of oxygen vacancy and Yb point defects. A strong correlation between oxygen vacancy and saturation magnetization is observed. [ABSTRACT FROM AUTHOR]

Field effect transistors (FETs) using two-dimensional molybdenum disulfide (MoS2) as the channel material has been considered one of the most potential candidates for future complementary metal-oxide-semiconductor technology with low power consumption. However, the understanding of the correlation between the device performance and material properties, particularly for devices with scaling-down channel lengths, is still insufficient. We report in this paper back-gate FETs with chemical-vapor-deposition grown and transferred MoS2 and Zr doped HfO2 ((Hf,Zr)O2, HZO) high-k dielectric gates with channel lengths ranging from 10 to 30 µm with a step of 5 µm. It has been demonstrated that channels with the length to width ratio of 0.2 lead to the most superior performance of the FETs. The MoS2/HZO hybrid FETs show a stable threshold voltage of ∼1.5 V, current on/off ratio of >104, and field effect mobility in excess of 0.38 cm2 V−1 s−1. The impact of the channel lengths on FET performance is analyzed and discussed in depth. A hysteresis loop has been observed in the Ids − Vgs characteristics of the hybrid FETs, which has been further studied and attributed to the charge effect at the interfaces. The HZO films show a relatively weak ferroelectric orthorhombic phase and thus serve mainly as the high-k dielectric gate. Charge trapping in the HZO layer that might induce hysteresis has been discussed. Our results show that MoS2/HZO hybrid FETs possess great potential in future low power and high-speed integrated circuits, and future work will focus on further improvement of the transistor performances using ferroelectric HZO films and the study of devices with even shorter MoS2 channels. [ABSTRACT FROM AUTHOR]

As state-of-the-art fabrication techniques are approaching the 3 nm size, the traditional silicon-based circuit faces huge challenges. Transistors based on two-dimensional (2D) materials have attracted much attention as potential alternative candidates. However, critical performances including the subthreshold swing (SS), on/off ratio, and magnitude of the on-state current for 2D transistors around 3 nm size are far less to be studied well. In this work, we propose in-plane Schottky-barrier field-effect transistors (SBFETs) with a 4-nm channel based on the lateral heterostructure of monolayer 1T/2H MoTe2 and WTe2. The electric transport properties are investigated by first-principles quantum transport simulations. At a 0.64 V bias, the WTe2 SBFET has an on-state current of 3861 μA/μm, with a 4.5 × 104 on/off ratio and an SS of 87 mV/dec, while the MoTe2 SBFET has an on-state current of 1480 μA/μm, with a large on/off rate of 3.6 × 105 and an SS of 78 mV/dec. Our results suggest that FETs based on the lateral heterostructure of 1T/2H MoTe2 (WTe2) are promising candidates for high-performance 2D transistors. [ABSTRACT FROM AUTHOR]

A transportable fountain clock with high reliability is important for high-precision time-frequency measurements. Because of its relatively small cold atoms' collision frequency shift and ease of attaining high quantum state preparation efficiency, the rubidium atomic fountain clock has an indicated higher stability and reliability. This paper reports the design and operation of a transportable rubidium atomic fountain clock developed by the Shanghai Institute of Optical and Fine Mechanics, Chinese Academy of Science. After being transported more than 1000 km from Shanghai to the Changping Campus of the National Institute of Metrology, China, the optical platform and other hardware of the fountain clock did not need to be adjusted. The rubidium fountain clock maintained a stability of 4.0 × 10−13τ1/2, reaching 5.0 × 10−16 at 300 000 s. After transportation, the rubidium fountain clock and a cesium fountain clock (NIM5) were operated together against the reference frequency of a hydrogen maser. In three separate operating periods, over a total of nearly three months, the average frequency repeatability of the rubidium fountain was less than 3.8 × 10−15. [ABSTRACT FROM AUTHOR]

Nitrides are of increasing interest since they are usually wide-bandgap semiconductors and the available environmental raw materials are abundant. Using first-principles predictions, we reveal that Mg2XN3 (X = V, Cr) compounds show remarkably large ferroelectric polarization and piezoelectric response. Quantitative theoretical analysis further indicates the asymmetric orbital hybridization to be the origin of the ferroelectricity. Since Cr has one more 3d electron than V, it is found that Mg2CrN3 is multiferroic with a ferromagnetic ground state. We further show that the epitaxial strain can regulate the piezoelectricity, and thus, both Mg2CrN3 and Mg2VN3 exhibit a larger piezoelectric response than the reported nitride piezoelectric materials under appropriate tensile epitaxial strain. Our findings provide guidance for potential applications of nitride materials in spintronics, sensors, and memory devices. [ABSTRACT FROM AUTHOR]

PbZrO3-based antiferroelectric crystals are of great interest in both fundamental and applied research, not only because of the antiferroelectric feature at room temperature but also because of the existence of a peculiar intermediate state at elevated temperatures. Here, we report a detailed description of domain structure change at the temperature-induced antiferroelectric-to-ferroelectric phase transition. A complex process of different types of domains is revealed to appear at different stages of the phase transition. A hierarchical ferroelastic domain structure forms in the stabilized intermediate state, where the dense domain walls show potential impact on the physical properties of the crystal. [ABSTRACT FROM AUTHOR]

With the development of small size and high energy output of initiators, how to improve the safety of the system becomes an urgent problem. Therefore, a novel Micro-electro-mechanical System (MEMS) initiator with a built-in safety-and-arming (S&A) device is introduced in this paper. The MEMS initiator is composed of the MEMS ignitor and the MEMS S&A device. A movable barrier with a fire hole is controlled by the MEMS S&A device. Driven by the electro-thermal principle, the barrier can be moved backward or forward to open or close the fire channel, and the status conversion between the armed mode and the safe mode can be realized. The test results show that under specific control signals, the MEMS S&A device can generate 1 mm output displacement. Under the armed mode, the flame can burst out from the fire channel when stimulated by 64 V pulse voltage. Under the safe mode, the barrier hit by the flame can stay intact, and the explosion energy is blocked in the fire channel successfully. The silicon wafer and silicon-on-insulator wafer are used to fabricate the MEMS S&A device. Integrated with the MEMS ignitor, the total chip size is 11 × 12 × 1.2 mm3. [ABSTRACT FROM AUTHOR]

A monolayer 1T′-WTe2 film is grown on SrTiO3(001) with in-plane tensile strain. A height of ∼0.7 nm, obvious charge transfer, and incommensurate charge fluctuations in 1T′-WTe2 suggest strong coupling to the STO substrate. Scanning tunneling spectroscopy on the surface reveals that a large energy gap opens at the Fermi level with nearly zero conductance. The opened energy gap decreases with the increase in the WTe2 island size. The lack of the metallic edge state on monolayer 1T′-WTe2/SrTiO3(001) indicates the absence of the quantum spin Hall (QSH) state. Our study here demonstrates that the energy gap of monolayer 1T′-WTe2 can be tuned by lattice strain and illustrates the importance of interface coupling to realize the metallic edge state and QSH in monolayer 1T′-WTe2. [ABSTRACT FROM AUTHOR]

A synergetic effect of Li/Nd at the A site and W/Mn at the B site co-substitution on electrical properties of calcium bismuth niobate (CaBi2Nb2O9, CBNO)-based ceramics is proposed in this paper. CBNO primarily shows mixed p-type and ionic conduction due to a trace of oxygen vacancies (VO••). Both bulk resistivity (ρb) and activity energy (Ea) for conduction are dramatically increased by the co-substitution in Ca0.92(Li1/2Nd1/2)0.08Bi2Nb2−x(W3/4Mn1/4)xO9 [CBNO-LN-x(WM), x = 0–0.02]. Consequently, the modified compositions almost show an intrinsic conducting mechanism due to a significant suppression of the VO•• concentration. Furthermore, the synergetic effect of Li/Nd at the A site and W/Mn at the B site greatly improves the piezoelectricity coefficient (d33), which is up to ∼21.1 pC/N in the optimized composition [CBNO-LN-10(WM)]. This combined with a high Curie temperature (TC = ∼946 °C) and high resistivity indicates that CBNO-LN-10(WM) is a good promising material in high-temperature piezoelectric applications. [ABSTRACT FROM AUTHOR]