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In two-dimensional valleytronics, the controllability of anomalous valley Hall effect is the key to its practical application. However, most of the previously proposed control methods are volatile or irreversible. Here, using first principles calculations, we demonstrate that the GdF2/Sc2CO2 multiferroic heterojunction can exhibit nonvolatile switching of its electronic band structures. Interestingly, the polarization switching of the ferroelectric monolayer induces movement in the valley polarization band of GdF2, enabling manipulation of the valley Hall effect. This allows the memory state encoded in the ferroelectric monolayer to be read out via the anomalous valley Hall signal of the heterostructures. The switchable anomalous valley Hall effect can also be achieved by applying biaxial strain in the GdF2/Sc2CO2 multiferroic heterojunction. By harnessing this intriguing anomalous valley Hall effect switching characteristic, we develop a nonvolatile valleytronics memory device. This work provides a way to achieve nonvolatile control in valleytronics and promotes the design of memory devices. [ABSTRACT FROM AUTHOR]

In this article, we analyzed the experimental data based on the TaOx memristor and found that the threshold switching (TS) characteristics are related to temperature, and its logarithmic I–V curve is in good agreement with the space charge limiting current conduction mechanism. We use this mechanism to establish a TS physical model and then use the physical model to build an LTspice model. The model data are fitted with the experimental data, which is basically consistent. Next, using the TS memristor to simulate a leaky integrate-and-fire neuron circuit, the basic dynamics are realized. By changing the external temperature of the memristor, the output frequency of the neuron will be more intense as the temperature increases. Finally, an artificial spiking neural network (SNN) was built based on this neuron circuit for MNIST recognition task. In this SNN, the input signals fused both voltage amplitude and temperature to achieve neuromorphic multimodal preprocessing and enhance the recognition accuracy. These results demonstrated the reliability of the model, which enhanced the flexibility for exploring the application of TaOx-based TS memristors. [ABSTRACT FROM AUTHOR]

Ge2Sb2Te5 (GST) alloy has the ability to quickly transform between the amorphous phase and the crystalline phase; therefore, it can be used in non-volatile phase change storage. First-principles molecular dynamics was used to simulate the reversible phase change process of GST alloy, namely, amorphization and crystallization. The amorphous state was obtained by melting (∼3000 K) and cooling, and the amorphization process was characterized by the pair correlation function and bond angle distribution. The bond angles of amorphous GST were mainly distributed around 60°, 90°, and 110°, indicating the existence of octahedral and tetrahedral bonding configurations. The crystalline state was obtained by annealing at a temperature of 600 K, and the crystallization process was characterized by the pair correlation function, component disordered number, bond angle distribution, and dynamic atomic structure change. The results show that the bond angle of GST in crystallization is mainly distributed around 90°, and the structure mainly contains four-membered rings formed by Ge–Te and Sb–Te. By analyzing the optical properties, with the growth of crystallization time, the absorption coefficient, reflectivity, and conductivity of GST were significantly improved. [ABSTRACT FROM AUTHOR]

In this work, Ti3C2/single-layer black phosphorus (BP)/Ti3C2 resistive random access memory (RRAM) was studied based on the first-principles theory. First, after determining the size of the material, the Ti3C2/BP(100) interface was built. By studying the electrostatic potential of the interface, it was found that there was a Schottky barrier at the interface, and the barrier height was obtained by calculating the work function and the band structure of the interface. Next, a Ti3C2/BP(100)/Ti3C2 RRAM device was designed based on the mechanism of the Schottky barrier at the interface. The bipolar switching characteristics were confirmed after calculating the I–V curve of the device, in which the turn-on threshold voltage is about 1.5 V, the turn-off threshold voltage is about 0.5 V, and the switch ratio is greater than 105. However, there are still shortcomings such as insufficient drive current. So, in the end, the optimization program is determined through a series of studies of device doping and vacancy, and it is found that after a certain concentration of Mg atoms are adsorbed, the conductivity of the resistive switching layer can be increased, the interface barrier can be adjusted, and the device performance such as the turn-on voltage, drive current, and switching ratio can be improved. This work may have guiding significance and value for the experimental research of manufacturing a new two-dimensional material RRAM. [ABSTRACT FROM AUTHOR]

Surgery represents the mainstream therapeutic modality in oncology. Aggressive radical surgery to achieve no residual tumor would improve survival, which is mainly affected by vascular involvement and accuracy of judging the negative margin of tumor resection. However, there is currently no intraoperative tool that can simultaneously perform microscopic analysis of the peritumoral vasculature in vivo and the surgical margin pathology of the tumor ex vivo, which leads to the randomness of one-time complete resection of the tumor, and the patient may have to undergo secondary surgery. To address this critical need, we developed a 532/266 nm dual-wavelength photoacoustic (PA) microscopy imaging (532/266-PAI) system that enables both in vivo tumor regional vascular involvement analysis and pathological margin assessment of fresh ex vivo tumor samples. A mammary tumor animal model was established to mimic the process of tumor resection, from in vivo imaging vascular involvement of tumor to intraoperative judgment of negative tumor margins. It is proved that the 532/266-PAI technology can identify the tumor vascular involvement through vascular visualization, determine the surgical plan, and then judge whether the tumor is completely removed through ultraviolet PA (UPA) tumor pathological imaging. Re-excision and secondary margin evaluation are performed when margin positive is diagnosed in the intraoperation UPA imaging. The 266/532-PAI technique has great potential for complete tumor resection in surgical navigation. [ABSTRACT FROM AUTHOR]

We systematically study the fatigue failure of the Ag/Poly (3-hexylthiophene-2,5-diyl)(P3HT)/WO3/ITO/PET flexible memristor under variable temperatures, which simulates essential synaptic learning functions. The theoretical calculations and finite element analysis results indicate that the P3HT/WO3 interface plays a key role in device fatigue failure at variable temperatures. As the temperature dropped from 100 to −30 °C, a significant decrease in the loosely adsorbed polymer chains and flattened chains occurs at the P3HT/WO3 interface and thus leads to the deterioration of the P3HT/WO3 interface. The weak P3HT/WO3 interfacial bonding substantially accelerates the crack propagation under low-temperature flexural cycles, which will ultimately cause the device to deteriorate. Our work may provide some useful information for future achievement of flexible memory synapses utilized in cryogenic environments. [ABSTRACT FROM AUTHOR]

This paper proposes a novel non-explosive and resettable release device driven by shape memory alloy (SMA), which can replace the commonly used pyrotechnic device. In the scheme, a flywheel nut with bidirectional thread is connected with two screws through the non-self-locking thread, and the target adapters are fixed with the two screws and then locked into a hole by the flywheel nut. When unlocking, the offset SMA actuator releases the flywheel nut by triggering the pulley assembly and multi-level levers. Under the pulling force of the pre-tightening load of the screws, the flywheel nut rotates at high speed to unlock the screws, thus releasing the target adapters. After separation, the device can be quickly reset with the reset tool without replacing any parts. The prototype of the release device is fabricated and tested; according to the performance test results, the device can bear the maximum bi-directional preload of 10 kN and the average unlocking force is 9.73 N. The unlocking time decreases with the increase in driving voltage, and the average unlocking response time is 342 ms under 9 V voltage. Furthermore, the actuator can function well with a lifetime of more than 50 cycles. It is concluded that this scheme has potential advantages to replace the traditional non-reusable explosive driving device. [ABSTRACT FROM AUTHOR]

The single Helmholtz resonator obtains only one absorption peak in the broad frequency range, which limits its application in reducing the noise with multiple spectra. This paper reports an acoustic multi-layer Helmholtz resonance metamaterial, which can achieve multiple absorption peaks at given low-frequency targets. Meanwhile, through adjusting structural parameters of the multi-layer Helmholtz resonator, its impedance can be altered correspondingly to realize the absorption of noise with the multi groups of specific frequencies. In this paper, in order to achieve fine absorption performance with the specific frequencies of 100 and 400 Hz for a substation noise source, the sound absorption principle of a classical Helmholtz resonator with the embedded aperture is introduced theoretically, and then two series of multi-layer Helmholtz resonance structures with different parameters are designed. Thickness of the multi-layer structure is only 1/30th of the working wavelength, and two groups of resonance peaks are generated at 100 and 400 Hz, respectively. A finite element model of the multi-layer Helmholtz resonator is constructed to simulate its absorption performance. The samples are fabricated through the 3D light-curing printing, and their sound absorption performances are detected by the standing wave method. The simulation results are in good agreement with the experimental data, and two peaks with near-perfect absorptions are achieved at the target frequencies. The multi-layer Helmholtz resonator for achievement of three groups of absorption peaks is proposed later. This work provides an effective method to design a sound absorber with multiple absorption peaks, which can promote the application of acoustic metamaterials. [ABSTRACT FROM AUTHOR]

Liquid-metal (LM) electrical switches have been desired for decades to overcome intrinsic shortcomings of traditional mechanical switches equipped with solid contacts. Existing LM electrical switches, functioning via solid-liquid wetting or liquid droplet actuation, mostly focus on low current and small signal switches. In this Letter, a LM switch aiming at a power-level current switch has been proposed. A proof-of-concept prototype was fabricated via encapsulating Galinstan droplets into a silicone matrix. The device switches on a circuit when LM droplets are squeezed into a capillary channel to coalesce. The switch-off process with arc burning is realized by capillary breakup of the LM bridge and high-speed contact separation driven by a pressure difference contributed by Laplace pressure, electrical arc pressure, and atmospheric pressure. Switching off 0.5 A–5 A current under DC 220 V within 0.13–1.69 ms, the device demonstrates a high-speed current interruption ability compared to two kinds of commercial push-button switches. A high-speed camera is utilized to visualize the LM switch's current interruption process. In such a situation, the LM contacts exhibit a separation speed up to 3.85 m/s. Apart from the pressure difference, a slip layer between the LM and capillary wall also plays an important role in driving LM contacts. The LM switch has potential for applications in communication and control equipment acquiring a fast switch of the electrical power signal. This paper offers a framework for designing the LM switch dealing with intense electrical discharge. [ABSTRACT FROM AUTHOR]

We have investigated the electrical properties of Ge1Sb2Te4 and Ge2Sb2Te5 thin films in the temperature range of 27 to 200 °C. The optical bandgap values obtained from the measured absorption spectra for amorphous Ge1Sb2Te4 and Ge2Sb2Te5 are 0.70 and 0.90 eV, respectively. The results of the in situ temperature dependence of the sheet resistance demonstrate that both Ge1Sb2Te4 and Ge2Sb2Te5 thin films in the amorphous phase exhibit a temperature-activated electrical conductivity with activation energy values of 0.42 and 0.45 eV, respectively. These results show that our experimental results agree well with the predictions of Mott's model. The temperature dependent carrier mobility was measured accurately using the surface acoustic wave method, which is an appropriate method for materials with low conductivities and low mobility. Typical values of drift mobility for amorphous Ge1Sb2Te4 and Ge2Sb2Te5 thin films at room temperature are round 10-3 cm2/(Vs) and 10-2 cm2/(Vs), respectively. The values of drift mobility remain small below 140 °C when the films are in an amorphous state. The drift mobility increases gradually as the temperature increases in the temperature range of 140-160 °C and shows dramatic changes above 160 °C. In general, the mobility of amorphous Ge2Sb2Te5 is 3 to 5 times higher than that of amorphous Ge1Sb2Te4. The smaller mobility for Ge1Sb2Te4 films might suggest that amorphous Ge1Sb2Te4 film has more vacancies, which results in more disordering as compared to that of Ge2Sb2Te5. [ABSTRACT FROM AUTHOR]

As-doped p-type ZnO films were grown on GaAs by sputtering and thermal diffusion process. Hall effect measurements showed that the as-grown films were of n-type conductivity and they were converted to p-type behavior after thermal annealing. Moreover, the hole concentration of As-doped p-type ZnO was very impressible to the oxygen ambient applied during the annealing process. In addition, the bonding state of As in the films was investigated by x-ray photoelectron spectroscopy. This study not only demonstrated an effective method for reliable and reproducible p-type ZnO fabrication but also helped to understand the doping mechanism of As-doped ZnO. [ABSTRACT FROM AUTHOR]

The present work is an investigation of the effects of metal vapour on the behavior of a fault arc in a closed, air-filled container. Experiments were performed to measure the pressure, temperature, and energy balance of the fault arc for different metal electrodes. Theoretical results are obtained using a magneto-hydrodynamic model for the fault arc and then compared with the experimental results. It is found that the effects of increased radiation and mass transfer caused by metal vapour considerably cool down the plasma in the central arc, whereas the influence of increased electrical conductivity is relatively small. The simulation of the energy balance suggests that the pressure rise is seriously affected by the metal vapour due to the similarity of heat transport processes of the fault arc. In the case of Cu and Al electrodes, the heating of surrounding gas dominates in the energy dissipation, while for Fe, the radiation does. Huge chemical energy released due to Al vapour results in the maximum pressure rise for Al electrodes, and the strong radiation in the case of Fe electrodes is responsible for its smallest pressure rise. [ABSTRACT FROM AUTHOR]

An experimental method for the air plasma composition based on two-color Mach–Zehnder interferometry was established. By applying two laser beams with different wavelengths, the distributions of the temperature and nonequilibrium parameter were obtained. In the arc center, the energy exchange between the electrons and heavy particles is sufficient enough to make the plasma reach the equilibrium state. In this case, by comparing the electron density and neutral particle density derived from the interferograms, the calculated species compositions of air plasma under local thermal equilibrium were validated. Additionally, the distribution of the nonequilibrium parameter indicates that departure from the equilibrium occurs at the edge of the plasma and that the nonequilibrium area gradually expands during the arc decay phase. This trend is in good agreement with the two-temperature arc simulation, indicating the validity of the two-temperature arc model in many previous works. [ABSTRACT FROM AUTHOR]

Ge2Sb2Te5 (GST) is a technologically important phase-change material for data storage, where the fast reversible phase transition between crystalline and amorphous states is used for recording information. The effects of vacancies on crystal GST were investigated by ab initio calculations. Based on analysis of the vacancy formation energy, the GST structure with Ge vacancy (VGe) was found to be the most stable. Thereafter, the influence of VGe defects on crystal GST structure was deliberated by analyzing the band structure, electron density difference, total density of states (TDOS) and partial density of states (PDOS) of GST structure. The results reveal that VGe can promote the Fermi level enter into the valence band, which makes the GST material exhibit more pronounced properties of P-type semiconductors. Nevertheless, VGe shows a slight effect on the chemical bond characters. When VGe concentration maintained at 20% in the GST structure, the band gap is the widest about 0.45eV. Moreover, VGe can result in the electrons in s orbital of Ge, Sb and p, d orbitals of Te make a contribution to the valence band, while electrons in p and d orbitals of Ge, Sb are more favorable to conduction band. [ABSTRACT FROM AUTHOR]

In this letter, light tunneling effect tuned by a meta-interface with electromagnetically-induced-transparency-like (EIT-like) properties is investigated. Both numerical and experimental results show that the Q-factor of tunneling mode can be well enhanced when an atomic-like three-level system with EIT-like properties is introduced at the interface of a pair structure constructed by epsilon-negative and mu-negative metamaterials. Further study reveals that the Q-factor can be tuned conveniently by altering the EIT-like meta-interface. Moreover, these advantages are not at costs of increase of volume and drastic reduction of transmittance. [ABSTRACT FROM AUTHOR]

Antennas in the ultra low frequency (ULF, 300 Hz to 3 kHz) and very low frequency (VLF, 3∼30 kHz) bands are usually very large. In this study, we developed a very small antenna, which can radiate electromagnetic waves in these frequency bands. The antenna consisted of two rotating charged plates (RCPs), which were charged by the voltage source. Numerical results of the radiated far field and its frequency spectrum are presented for three cases: (a) the antenna is charged with DC voltage, (b) the antenna is charged with AC voltage, and (c) the antenna rotates with variable speed and is fed with DC voltage. The predominant frequency component was equal to the rotating frequency of the RCPs fed with DC voltage. If the RCPs were fed with AC voltage two dominant frequencies were generated, which were determined by the difference in frequency between the RCP rotation frequency and the AC source frequency. When the RCPs rotated with variable speed and were fed with DC voltage, many frequency components were generated, which were determined by the initial rotational speed of the RCPs and their acceleration. [ABSTRACT FROM AUTHOR]

Rolling contact connector (RCC) is a new technology utilized in high performance electric power transfer systems with one or more rotating interfaces, such as radars, satellites, wind generators, and medical computed tomography machines. Rolling contact components are used in the RCC instead of traditional sliding contacts to transfer electrical power and/or signal. Since the requirement of the power transmission is increasing in these years, the rolling electrical contact characteristics become more and more important for the long-life design of RCC. In this paper, a typical form of RCC is presented. A series of experimental work are carried out to investigate the rolling electrical contact characteristics during its lifetime. The influence of a variety of factors on the electrical contact degradation behavior of RCC is analyzed under both vacuum and air environment. Based on the surface morphology and elemental composition changes in the contact zone, which are assessed by field emission scanning electron microscope and confocal laser scanning microscope, the mechanism of rolling electrical contact degradation is discussed.

A new design of DC hybrid circuit breaker based on high-speed switch (HSS) and arc generator (AG), which can drastically profit from low heat loss in normal state and fast current breaking under fault state, is presented and analyzed in this paper. AG is designed according to the magnetic pinch effect of liquid metal. By utilizing the arc voltage generated across AG, the fault current is rapidly commutated from HSS into parallel connected branch. As a consequence, the arcless open of HSS is achieved. The post-arc conducting resume time (Δ tc) of AG and the commutation original voltage (Uc), two key factors in the commutation process, are investigated experimentally. Particularly, influences of the liquid metal channel diameter (Φ) of AG, fault current rate of rise (di/dt) and Uc on Δ tc are focused on. Furthermore, a suitable Uc is determined during the current commutation process, aiming at the reliable arcless open of HSS and short breaking time. Finally, the fault current breaking test is carried out for the current peak value of 11.8 kA, and the validity of the design is confirmed by the experimental results.

The DC hybrid circuit breaker based on high-speed switch (HSS) and parallel connected capacitor has been widely applied in the fault current breaking of DC system. However, when the current is commutated from HSS to the capacitor according to single-stage operation, the capacitor has to absorb a large amount of energy stored in the system inductance within very short time. Meanwhile, a high over-voltage rate of rise is especially prone to be produced between the contacts of HSS, which will lead to a failed breaking. As a result, a novel DC hybrid circuit breaker based on the two-stage operation is proposed and analyzed in this paper. By controlling the thyristors in the commutation branches, the fault current is fast commutated into the capacitor, which can not only realize the arcless open of HSS, but also decrease the over-voltage rate of rise significantly in comparison to the traditional single-stage operation. The simulation model of fault current breaking under different conditions in 10 kV medium voltage DC system is constructed. The simulated over-voltages of single-stage and two-stage operations in the case of fault current breaking are compared and analyzed. Finally, the fault current breaking test in the two-stage operation is investigated experimentally, which validates the feasibility and effectiveness of the simulation model well.