The one dimensional (1D) ZnSe nanostructures with controlled phase were prepared in organic solution by heating the selenium (Se) and zinc oleate with the Ag2Se seeds. The physicochemical state of Se could strongly influence the product phase, specifically, the soluble Se in oleylamine benefited the growth of wurtzite ZnSe nanowires, while the concentrated Se powder benefited the growth of zinc blende ZnSe nanowires. This study provided a novel route for the phase control of ZnSe nanowires by modulating the physicochemical state of Se.

A dribble of ferrofluids falls on a permanent magnet, inducing a ferrofluid buoyant force to form a liquid-soft bearing. Compared to conventional solid bearings used in the low frequency vibration shock absorbers and energy harvesters, these ferrofluid bearings exhibit a lower friction coefficient but pronounced temperature sensitivity. However, the influence of temperature on the load capacity remains insufficiently studied. Here, we investigate the load capacity variations with gap distance under different temperatures and standing times, analyzing hysteresis behavior under these conditions. Additionally, we examine the effect of alternating temperature conditions on the load capacity. We found that the temperature-induced aggregation of magnetic particles in high-gradient magnetic fields will enhance the load capacity at a small gap and weaken it at a large gap. This study clarifies the temperature range and performance of ferrofluid bearings for application.

Dehumidification and heating of electric vehicle heat pump systems are of significance in ensuring comfort and safety in winter. This study purposes to investigate the dehumidification and heating performances of a new-designed heat pump system. A numerical model is established and serves for analyzing the ventilation conditions for dew or fog removal of the windshield. Both ventilation conditions of the heat pump and the inner surface temperature of the windshield were investigated as per experimental measurements. Meanwhile, dehumidification rates, effective heating capacity, and coefficients of performance were analyzed under different operating conditions. It is shown that the heat-pump's air outlet conditions are within the range of suitable ventilation conditions meeting the needs of dew or fog removal. At the same compressor speed, the inlet air humidity of the evaporator inlet decreases, the dew or fog removal is more effective, and the coefficient of performance for heating increases but the coefficient of performance for dehumidification decreases. In the case of the same inlet air humidity, the dew or fog removal effect is better with increasing compressor speed; Meantime, the coefficient of performance for heating and dehumidification both decrease. The lower compressor speed and lower inlet air humidity for the evaporator enable the heat pump system to meet the demand for dew or fog removal of the windshield and ensure thermal comfort in the cabin. This study verifies the effectiveness of heat pump systems for dehumidification and heating and would be valuable to promote heat pump systems.

Fluid transportation is a critical element in the performance of fluid machinery devices. This paper proposes a ferrofluid linear pump in response to the demand for fluid control without mechanical moving parts inside tubes. The pump includes two rectangular permanent magnets, ferrofluid, tubes, four one-way valves, and a linear actuator. The ferrofluid is bound in the tube by a strong gradient magnetic field generated by two rectangular permanent magnets, forming a liquid plunger. Under the cooperation of four one-way valves on and off, the reciprocating motion of the permanent magnet makes the ferrofluid plunger drive fluid to flow directionally. The maximum backpressure of the ferrofluid plunger under static and dynamic conditions is thoroughly analyzed by theory and experiments. Experiments of the interface profile and backpressure are consistent with the theoretical results in the static condition. The maximum backpressure reaches 8.3kPa in the static condition when the volume of the ferrofluid plunger is 19ul. However, the dynamic test under a reciprocating speed of 10mm/s~50mm/s has a significant backflow phenomenon, and the theory for calculating the backpressure is no longer applicable. The mechanism of the backflow is explored. There is a layer of water film between the ferrofluid plunger and the tube wall. With the increase of the backpressure and reciprocating speed, the thickness of the water film and the velocity gradient may enlarge, which increases the backflow and reduces the volume flow rate. Ultimately, failure occurs when the backpressure exceeds the sealing threshold during the ferrofluid plunger reciprocating process. The critical pressure difference for the pump failure fluctuates around 7.4kPa.

For nano-magnetic fluid(NMF), the magnetic nano-particle(MNP) kinematic behavior in a magnetic field and the chain-like microstructure evolution are important to study the NMF properties at the microscopic level. However, the chain structure formation mechanism and the effects of multiple environmental factors on microstructural morphology remain unclear. In this paper, the interaction of a two-particle system, chain structure formation process, microstructure evolution and response time simulation of NMF is investigated by the discrete element simulation method. The results show that the magnetic dipole and repulsive forces dominate the chain structure formation and evolution under a uniform magnetic field. MNPs assemble into chain-like structures and various complex structures along the magnetic f ield direction. The volume fraction, magnetization intensity and particle size significantly affect the microstructure and the response time. The above study can obtain the specific morphology of the microstructure at different working conditions and broaden the application of NMF in practical engineering.

We demonstrate a novel edge-contact floating gate transistor (ECFGT) based on phase engineered MoS 2 for in-memory computing. The ECFGT performs ultra-high operation speed (10ns for programming and 100ns for erasing), low operation voltage (15V) and a significantly reduced power consumption (~11.5 fJ/per program, ~41.3 fJ/per erase). Besides, good endurance (>8×10 4 ) for multi-level conductance is demonstrated, and 5-bit distinguishable states in our device are utilized as synapses for neuromorphic computing. The ultra-small read currents (10 -12 ~10 -6 A) in the subthreshold mode of the individual devices illuminate the promise of constructing very large-scale neural network through device integration.

Using vibration energy harvester (VEH) to achieve self-power supply is an effectively way to ensure long-term use of electronic devices. In this paper, an electromagnetic VEH using magnetic fluid (MF) as lubricant and liquid spring is proposed, the VEH uses a hollow shell with variable internal diameter together with MF to form a liquid spring with variable stiffness coefficient to replace the traditional mechanical or magnetic spring, and planar coils and helical coils are used together to harvest the vibration energy, thereby broadening response frequency, improving energy harvest efficiency, and reducing VEH volume and damping. The influence of MF on the lubrication, liquid spring, and vibration state is studied theoretically, and the induced voltage is simulated. A crank-slider linkage has been built to test the performance of VEH, and the influence of vibration frequency, mass of MF, and coil type on the output performance has been studied during a 7.5 mm reciprocating linear motion of VEH. Results show that an appropriate amount MF can improve the output voltage by 173 % at 3.25 Hz, but too much MF will cause a rapid drop in output voltage. Helical coils generate higher voltage than planar coils, and the output power density of the helical coil is 0.92 mW/cm3 at 8.5 Hz. The energy management module can manage electric energy well, and half wave rectifier with low forward voltage drop may be more suitable for VEH with low output voltage. Besides, the VEH delivers a 1.36 mW/cm3 power density with a 10 omega load when it is swung by human at 6.4 Hz.

The self-levitation of a magnetized object composed of ring permanent magnet, soft magnetic pure iron core (Fe -core), and nonmagnetic aluminum core (Al-core) in ferrofluid (FF) is studied, and the focus is the influence of Fe -core (Al-core) on the magnetic fluid levitation force (MFLF) received by the immersed magnetized object. The formula for calculating MFLF is derived focusing on the gas-liquid and solid-liquid boundary interface between FF and surroundings, and experiments have been done to study the dependence between MFLF and the levitation height of the magnetized object and mass of FF. Researches show that Fe-core has a significant influence on MFLF, and the influence is determined by the magnetization of Fe-core and the distance between Fe-core and the boundary interface. In a word, the use of Fe-core is beneficial to obtain a smaller MFLF, the greater the magnetization of the Fe-core is and the closer it is to the boundary interface of FF, the smaller the MFLF is. The Fe-core near the bottom surface of the ring magnet tends to reduce the maximum MFLF corresponds to an approximate horizontal gas-liquid boundary interface when the levitation height is constant, and the Fe-core near the top surface of the ring magnet is more likely to reduce the change of MFLF caused by the disappear-ance of surface instability of FF. Or, in other words, the Fe-core near the top surface of the ring magnet tends to reduce the MFLF when magnetized object moves upward, and vice versa.

Abstract As the prevailing non-volatile memory (NVM), flash memory offers mass data storage at high integration density and low cost. However, due to the ‘speed-retention-endurance’ dilemma, their typical speed is limited to ~microseconds to milliseconds for program and erase operations, restricting their application in scenarios with high-speed data throughput. Here, by adopting metallic 1T-LixMoS2 as edge contact, we show that ultrafast (10–100 ns) and robust (endurance>106 cycles, retention>10 years) memory operation can be simultaneously achieved in a two-dimensional van der Waals heterostructure flash memory with 2H-MoS2 as semiconductor channel. We attribute the superior performance to the gate tunable Schottky barrier at the edge contact, which can facilitate hot carrier injection to the semiconductor channel and subsequent tunneling when compared to a conventional top contact with high density of defects at the metal interface. Our results suggest that contact engineering can become a strategy to further improve the performance of 2D flash memory devices and meet the increasing demands of high speed and reliable data storage.

In this paper, the self-levitation of cylindrical magnets wrapped by shells immersed in magnetic fluid (MF) is studied. The calculation formula of the magnetic fluid levitation force (MFLF) received by magnets and shells is derived, and the dependence between MFLF, mass of MF, and levitation height of magnets is studied. Attention is paid to the influence of magnetization direction of magnets and shells on MFLF, and experiments have been designed to study MFLF. Research shows that both the magnetization direction of magnets and shells can affect MFLF, and the use of soft magnetic shells and radial magnetized magnets is beneficial to obtain a smaller axial MFLF. In addition, the magnetization direction of magnets has a significant influence on the distribution and surface instability of MF, which is a key factor affecting MFLF. There are two intervals in which the MFLF changes drastically for the axial magnetized magnets, but only one for the magnets with radial magnetization. The reason is that the surface instability of MF caused by axial magnetized magnets plays a significant role in axial MFLF, while the surface instability caused by radial magnetized magnets has almost no influence on axial MFLF.

Two-dimensional (2D) semiconductors are promising channel materials for next-generation field-effect transistors (FETs). However, it remains challenging to integrate ultrathin and uniform high-κ dielectrics on 2D semiconductors to fabricate FETs with large gate capacitance. We report a versatile two-step approach to integrating high-quality dielectric film with sub-1 nm equivalent oxide thickness (EOT) on 2D semiconductors. Inorganic molecular crystal Sb2O3 is homogeneously deposited on 2D semiconductors as a buffer layer, which forms a high-quality oxide-to-semiconductor interface and offers a highly hydrophilic surface, enabling the integration of high-κ dielectrics via atomic layer deposition. Using this approach, we can fabricate monolayer molybdenum disulfide-based FETs with the thinnest EOT (0.67 nm). The transistors exhibit an on/off ratio of over 106 using an ultra-low operating voltage of 0.4 V, achieving unprecedently high gating efficiency. Our results may pave the way for the application of 2D materials in low-power ultrascaling electronics. A van der Waals buffer layer of Sb2O3 enables the integration of high-κ dielectric layer with sub-1 nm equivalent oxide thickness on two-dimensional semiconductors, resulting in high performance of two-dimensional field-effect transistors.

Using vibration energy harvesters (VEHs) to achieve self-power is an effective method to ensure long-term use of sensor networks. This paper proposes a nonlinear electromagnetic VEH lubricated by magnetic fluid (MF) for low-frequency vibration energy harvesting. The VEH uses fixed small magnets to reduce natural frequency and prevent moving a magnet stack from flipping, MF for lubrication to improve output voltage under weak vibration, and elastomers to prevent magnet damage under strong vibration. In addition, MF and elastomers can increase the nonlinearity of restoring force, broadening the response frequency of VEHs. The motion state of the VEH is analyzed, and a crank-slider mechanism is used to test the output performance of VEHs. The influence of shell conductivity, the number of fixed small magnets, and length of VEH on output voltage is studied, and the results show that the VEH with an insulated shell, fewer fixed small magnets, and suitable length generates higher output voltage. The MF mainly plays a damping role in strong vibration but mainly plays a lubricating role in weak vibration. For experiments with 15 mm amplitude at 7.9 Hz, the output power density of the VEH without MF and lubricated by MF are 2.436 and 1.862 mW/cm(3), respectively. MF damping reduces the output power density by 23.56%. However, for experiments with 7.5 mm amplitude at 3 Hz, the output power for VEHs without MF and lubricated by MF are 0.065 and 0.254 mW, respectively. The output power is increased by 291% with MF lubrication.

Phase engineering of two-dimensional transition metal dichalcogenides has received increasing attention in recent years due to its atomically thin nature and polymorphism. Here, we first realize an electric-field-induced controllable phase transition between semiconducting 2H and metallic 1T' phases in MoTe2 memristive devices. The device performs stable bipolar resistive switching with a cycling endurance of over 105, an excellent retention characteristic of over 105 s at an elevated temperature of 85 °C and an ultrafast switching of ∼5 ns for SET and ∼10 ns for RESET. More importantly, the device works in different atmospheres including air, vacuum and oxygen, and even works with no degradation after being placed in air for one year, indicating excellent surrounding and time stability. In situ Raman analysis reveals that the stable resistive switching originates from a controllable phase transition between 2H and 1T' phases. Density functional theory calculations reveal that the Te vacancy facilitates the phase transition in MoTe2 through decreasing the barrier between 2H and 1T' phases, and serving as nucleation sites due to the elimination of repulsive forces. This electric-field-induced controllable phase transition in MoTe2 devices offers new opportunities for developing reliable and ultrafast phase transition devices based on atomically thin membranes.

针对太阳能帆板等长直部件产生的复杂振动,结合磁性液体动力吸振器的运动与浮力方程,设计了一种衰减平面内任意方向直线与扭转振动的磁性液体动力吸振器.采用有限元仿真软件建立了吸振器仿真模型,研究吸振器充满磁性液体时顶板形状、永磁体直径和永磁体上通孔半径对吸振器悬浮力和刚度的影响.结果表明,永磁体直径增大或通孔减小会增大吸振器悬浮力和刚度,采用异形顶板时质量块直线行程更大且顶板形状不影响刚度.最后通过实验研究永磁体直径与磁性液体加入量对质量块所受悬浮力的影响.结果表明永磁体较大时质量块所受悬浮力随磁性液体添加而增大的速度更快,为避免"缓坡"的出现,应在质量块上下永磁体位置均匀添加磁性液体.

Heat pump systems for electric vehicles must assure the system's energy efficiency and the comfort and safety of the passenger cabin. This project aims to analyze the dehumidification and heat transfer characteristics of a heat exchanger through experiments and theoretical modeling. In this paper, a parallel flow minichannel heat exchanger was experimentally and theoretically studied under various operating conditions. A distributed parameter model considering heat and mass transfer was developed and utilized to predict the heat exchanger's dehumidification and heat transfer characteristics. The results reveal that, with a fixed inlet air relative humidity and a low refrigerant mass flow rate, the dehumidification rate (DHR) increases and subsequently declines with the increasing inlet airflow. When the inlet air relative humidity and inlet airflow are constant, the lower the refrigerant mass flow rate, the greater the enthalpy humidity ratio. As the inlet airflow increases, the refrigerant mass flow rate and inlet air relative humidity stay constant, and the enthalpy humidity ratio rises. The proposed model's predictions match the experimental data rather well. The predicted heat transfer rates (HTRs) and DHRs have absolute errors of less than 4% and 10%, respectively, compared with the experimental results. Under various airflows for the OM3 operating conditions, the distributions of HTR and DHR demonstrate that the HTR percentage is lowest in flow path IV, no dehumidification is conducted in flow path IV, and the DHR percentage is largest in flow path II. The proposed model may be employed to assess the dehumidification and heat transfer performance of heat exchangers and optimize the design of heat exchangers in similar heat pump systems.

The development of thermal management systems in electric vehicles challenges new understandings of outside heat exchangers. The increasing heat load of electric vehicles requires a corresponding improvement in their heat exchanger characteristics. The purpose of this work is to modify the classical Nusselt number correlation model through experiments to check and predict the heat transfer characteristics of such a heat exchanger. In this paper, a parallel flow microchannel outside heat exchanger was studied with experiments and numerical simulations. Heat transfer correlations on the air side were modified by experimental data obtained from a newly designed test bench. Experimental results show that the heat transfer rate increases with increasing inlet pressure and inlet airflow. Furthermore, a numerical model for predicting heat exchanger characteristics was also proposed with the modified Nusselt number correlations. The comparison between modeling and experimental heat transfer rate shows good agreement, in which the absolute errors of the corresponding heat transfer characteristics for the heat exchanger are within 25%. The typical heat transfer model with the j-factor was also applied to predict the heat transfer rate. Comparison between results of modeling and experiment shows that models with the modified Nusselt number correlations demonstrate advantages when predicting the outside heat exchanger characteristics in an air conditioning heat pump system. The Nusselt number correlation model has good applicability for various environmental conditions.

Utilizing the heat from air source with heat pump system in electric vehicles shows a significant advantage from thermoelectric heat source for heat supply in cold climate. It could improve the driving range of electric vehicles considerably in winter and replace the positive temperature coefficient (PTC) heater with an acceptable cost and reliability. In this work, a newly designed heat pump system was first introduced with less components and cost. Second, experiments were conducted to investigate its cooling performance, and subsequent heating performance from -10 to 10 degrees C. The typical heat transfer and flow characteristics of refrigerant were recorded, and the behavior of each component including compressor, evaporator, condenser, and outside heat exchanger were analyzed and interpreted. The results showed that the heating and cooling performance of the new heat pump system could almost remain the same with traditional air-conditioning system in automobile and surely satisfy with the heat requirement of electric vehicles. In the heating mode, the maximum heating capacity increases by 13% at 400 m(3)/h air volume from 300 m(3)/h at the ambient temperature -10 degrees C, while the outlet air temperature decreases by 4-6%. In addition, using a heat pump system showed an increase in the driving range of electric vehicles by 25-31% as compared to PTC heaters.

Recently, ferroelectric polarization coupling has been exploited for non-volatile p- and n-type doping of two-dimensional (2D) materials, which enables the design of 2D functional devices via a local polarization pattern. Here, we took advantage of this tool and study the effect of base width to the gain and photodetection performance of bipolar transistors made of few layer MoS2. We found that the space charge region in the base have typical width similar to 150-250 nm, and depends on the applied external bias. Such a characteristic causes the compromise between transistor gain and shunt resistance when changing the base width. For photodetection, this hinders the optimization of responsivity without increasing the dark current. As a result, an optimal device was made at the base width similar to 1040 nm, from which a responsivity of 160 A W-1, specific detectivity of similar to 1.3 x 10(12) cm root Hz W-1 and the response time similar to 9 mu s to 680 nm incident light was obtained. The results from the present study shed light on the further design of 2D functional devices that use lateral pn junctions as the basic building blocks.

Owing to their superior carrier mobility, strong light-matter interactions, and flexibility at the atomically thin thickness, two-dimensional (2D) materials are attracting wide interest for application in electronic and optoelectronic devices, including rectifying diodes, transistors, memory, photodetectors, and light-emitting diodes. At the heart of these devices, Schottky, PN, and tunneling junctions are playing an essential role in defining device function. Intriguingly, the ultrathin thickness and unique van der Waals (vdW) interlayer coupling in 2D materials has rendered enormous opportunities for the design and tailoring of various 2D junctions, e.g. using Lego-like hetero-stacking, surface decoration, and field-effect modulation methods. Such flexibility has led to marvelous breakthroughs during the exploration of 2D electronics and optoelectronic devices. To advance further, it is imperative to provide an overview of existing strategies for the engineering of various 2D junctions for their integration in the future. Thus, in this review, we provide a comprehensive survey of previous efforts toward 2D Schottky, PN, and tunneling junctions, and the functional devices built from them. Though these junctions exhibit similar configurations, distinct strategies have been developed for their optimal figures of merit based on their working principles and functional purposes.

In order to expand the range of applications of magnetic fluid, water-based magnetic fluid with different surfactants is synthesized and the property of fluidity has been intensively studied. Three kinds of surfactants (sodium dodecyl sulfate, oleic acid and polyethylene glycol) are used to synthesize three different magnetic fluids with the same magnetic nanoparticles and carrier liquid. Their microstructures and thermal stability of magnetic nanoparticles coated with different surfactants are characterized by transmission electron microscopy and thermogravimetric analysis. Results show that water-based magnetic fluid with sodium dodecyl sulfate agglomerates more obviously while magnetic fluid with polyethylene glycol keeps good dispersion. In addition, magnetic measurements reveal that all these magnetic fluids exhibit typical superparamagnetic behavior and the magnetic fluid using polyethylene glycol as surfactant maintains the specific saturation magnetization of similar to 60 emu g(-1). What is more, shear stress and viscosity of these three magnetic fluids are measured by the rotational rheometer. The shear stress increases with the increasing shear rate while the viscosity decreases with the increasing shear rate. This indicates that water-based magnetic fluid has the property of pseudoplastic fluid. What is more, the viscosity of the magnetic fluid with polyethylene glycol as surfactant is lower than other two magnetic fluids and is prone to reach a steady state at a low shear rate in a short time.