Search

Polishing is a main process in achieving high-quality surfaces of optical components. However, effective assessing technique for rough stage in the polishing process is sparse so that hinders the study on the mechanism and optimization of polishing. In this study, we propose an inspection method for polishing quality based on quasi Brewster angle technology (qBAT). An equivalent medium layer theory and its model are developed to accurately describe the optical reflection characteristics of a rough surface. Hence both rough- and fine-polishing qualities can be evaluated by the qBAT approach. To demonstrate the newly proposed method, laser crystal, gadolinium gallium garnets, is studied by computational simulation and experiments. A high consistence is achieved between theoretical simulation and experimental results, which proves the robustness of the method to the rough surfaces. To our knowledge, it is the first time that the qBAT is developed to evaluate the polishing quality covering rough- and fine-polishing stages. This capability shows great potential in fundamental research and process optimization of polishing brittle-hard materials.

van der Waals layered heterojunctions have a variety of band offsets that open up possibilities for a wide range of novel and multifunctional devices. However, due to their poor pristine carrier concentrations and limited band modulation methods, multifunctional p-n heterojunctions are very difficult to achieve. In this report, we developed a highly effective N2O plasma process to treat MoTe2/MoS2 heterojunctions. This allowed us to adjust the hole and electron concentrations in the two materials independently and simultaneously. More importantly, for the first time, we were able to create opposite doping on the two sides of the junction through a single-step treatment. With a very wide doping range from pristine to degenerate levels, a MoTe2/MoS2 heterojunction can be modulated to behave as a forward rectifying diode with enhanced rectifying ratio and as a tunneling transistor with negative differential resistance at room temperature. The new approach provides an effective and generic doping scheme for heterojunctions to construct versatile and multifunctional electronic devices.

The nano SiC coatings were prepared on the surface of graphite by laser irradiation under different laser energy densities (7.07–14.15 kJ/cm2). The influence of laser energy density on the structure and quality of coatings was systematically investigated. The results show that laser irradiation can transform the preset micron-SiC particle coating into nano-SiC particle coating. The nano-SiC coating prepared by laser irradiation can effectively enhance the high temperature oxidation resistance of the graphite substrate. When the laser energy density is 7.07 kJ/cm2, the prepared coating displays a single crystal structure and a good morphology without cracks and spheroidization. The coating prepared under the laser density of 10.61 kJ/cm2 shows a mixed crystal structure with obvious spheroidization. Further increase the laser energy density to 14.15 kJ/cm2, the main structure of prepared coating turns to polycrystalline and obvious cracks can be observed. The cross-section analysis of coating prepared under laser energy density of 7.07 kJ/cm2 indicates that there existed elemental diffusion between the coating and the substrate which increased the adhesion of coating. The calculations based on the Arrhenius formula present that this prepared coating has higher activation energy and therefore it has better high temperature oxidation resistance than the other prepared coatings.

Charge-trapping memory devices based on two-dimensional (2D) material heterostructures possess an atomically thin structure and excellent charge transport capability, making them promising candidates for next-generation flash memories to achieve miniaturized size, high storage capacity, fast switch speed, and low power consumption. Here, we report a nonvolatile floating-gate memory device based on an ReS2/boron nitride/graphene heterostructure. The implemented ReS2 memory device displays a large memory window exceeding 100 V, leading to an ultrahigh current ratio over 108 between programming and erasing states. The ReS2 memory device also exhibits an ultrafast switch speed of 1 μs. In addition, the device can endure hundreds of switching cycles and shows stable retention characteristics with ∼40% charge remaining after 10 years. More importantly, taking advantage of its anisotropic electrical properties, a single ReS2 flake can achieve direction-sensitive multi-level data storage to enhance the data storage density. On the basis of these characteristics, the proposed ReS2 memory device is potentially able to serve the entire memory device hierarchy, meeting the need for scalability, capacity, speed, retention, and endurance at each level.

Aims The present study aims to determine the effects of sodium-glucose cotransporter 2 (SGLT-2) inhibitors on the serum uric acid (SUA) levels of patients with type 2 diabetes mellitus (T2DM) in Asia. Methods PubMed, CENTRAL, Embase and Cochrane Library databases were searched for randomized controlled trials (RCTs) of SGLT-2 inhibitors in patients with T2DM up to July 15, 2021, without language or date restrictions. Results A total of 19 studies (4218 participants) with high quality were included in the present network meta-analysis. All of the included SGLT-2 inhibitors (empagliflozin, dapagliflozin, canagliflozin, ipragliflozin, luseogliflozin and tofogliflozin) significantly decreased SUA levels compared with those of the control (total standard mean difference [SMD] -0.965, 95% CI [-1.029, -0.901], P = 0.000, I2 = 98.7%) in patients with T2DM. Subgroup analysis and meta-regression showed that the combined analysis of different inhibitors may lead to heterogeneity of the results. Therefore, among the SGLT-2 inhibitors, the results of the subsequent network meta-analysis revealed that luseogliflozin and dapagliflozin ranked the highest in terms of lowering SUA level among the SGLT-2 inhibitors. Moreover, the network meta-analysis declared that luseogliflozin (1 mg and 10 mg) and dapagliflozin (5 mg) led to a superior reduction in SUA in patients with T2DM. Conclusions SGLT-2 inhibitors could significantly reduce SUA levels in patients with T2DM, especially luseogliflozin (1 mg and 10 mg) and dapagliflozin (5 mg) possess the best effects. Therefore, SGLT-2 inhibitors look extremely promising as an anti-diabetes treatment option in patients with T2DM with high SUA. This article is protected by copyright. All rights reserved.

Star wheel is a key component in the uniform speed universal joint of automobile steering structure. It is used for power transmission between any pair of rotating shafts whose axes intersect and their relative positions often change. With the popularization of intelligent manufacturing and automatic production line, the automatic detection of star wheel has important practical value. The correct placement of the star wheel directly affects the subsequent automatic measurement results, which is on the automatic detection line. The accurate and fast identification of the datum is the key factor to determine whether the star wheel can realize the automatic measurement and the measurement speed. This system takes Mitsubishi FX3GA-24MT-CM PLC as the core to design the star wheel datum recognition and correction device. Based on the machine vision image processing algorithm to accurately identify the datum level, the mechanical structure of transmission and correction is designed, as well as the PLC electrical control system to complete the automatic transmission, recognition and correction of the star wheel. The test results show that the recognition rate of the system is above 96%, and the detection time is 0.581s, which meets the technical requirements of the star wheel detection line.

The high pressure pump and injector of the direct injection engine in the cylinder are connected with the common rail pipe. The oil fluctuation of high pressure pump and the high frequency working cycle of engine lead to the large fluctuation of rail pressure, which makes the engine fuel injection pressure unstable. The control mathematical model of high pressure common rail system is established based on fluid mechanics. A linear active disturbance rejection controller is designed to estimate the uncertain state and disturbance information by means of extended state observation for the unmeasurable state and disturbance. The controller is verified by idle speed and acceleration condition. The simulation results show that the linear active disturbance rejection is effective and easier to implement in engineering.

Here, we prepared nano-SiO2-coated graphite films using a novel laser-assisted sol–gel method. The SiO2 sol–gel prepositioned on the graphite substrate was irradiated by the fiber laser at different energy densities. The growth mechanism of the coatings under laser irradiation was studied and the effects of processing parameters on the coating structure were systematically investigated. In addition, the high-temperature oxidation resistance of these samples was examined. Surface morphology and elemental composition were examined using scanning electron microscopy and energy-dispersive spectrometer. Phase constituents and microstructure were identified by x-ray diffraction and transmission electron microscopy. The oxidation resistance was analyzed by thermal gravimetric analysis. The results found that laser irradiation significantly modifies the sol–gel-deposited nano-SiO2 layer. A uniform and compact nano-SiO2 coating was obtained when irradiated by laser energy density of 14.4 kJ/cm2. Optimum high-temperature oxidation resistance was achieved for the two-layer SiO2-coated films.

Despite recent advances in the development of suitable electrode materials for sodium-ion batteries, it remains a daunting challenge to achieve better Na + storage performance without introducing new drawbacks. To improve the cycle stability and rate performance of Na₃V₂(PO₄)₃, most attention has been directed to improving the electronic conductivity by carbon compositing. However, excess carbon increases the difficulty of adhering the active materials. Besides, the ionic insulation of PVDF hinders the transfer of Na⁺, which severely limits the rate capability. Herein, we proposed a strategy of using biomass pectin polymer to build an electrode architecture with a sturdy construction and fast charge transfer structure. The rich carboxylic and hydroxyl groups endow pectin with a strong binding force that protects the integrity of the electrode and avoids exfoliation of the active materials. Thus, the sturdy construction enables Na₃V₂(PO₄)₃/C (NVP) to run for over 15 000 cycles. In addition, the construction of the conductive framework accelerates the fast transfer of the ion/electron, thereby giving rise to its enhanced rate capability. Thus NVP with even low carbon content of 1.15% could demonstrate superior rate capability at 100C rate. The rational design strategy in this study provides a new perspective for the optimizing electrode structure rather than material modification. Energy Market Authority (EMA) Ministry of Education (MOE) This work was financially supported by funding from Science and Technology Development Project, Jilin Province (Grant No. 20180101211JC) and the Joint Project between Jilin Province and Jilin University (SXGJQY2017-10). The authors also gratefully acknowledge Singapore MOE AcRF Tier 1 under grant no. RG113/ 15 and 2016-T1-002-065, Singapore EMA project EIRP 12/ NRF2015EWT-EIRP002-008.

Lu2O3 has attracted widespread attention in high-power lasers, scintillators, and semiconductors due to its high thermal conductivity, high stability, and large band gap. Due to the limitations of the growth process, high-precision characterization of polished quality and optical properties for large-size Lu2O3 single crystal is extremely scarce, which hinders the design and optimization of optics based on Lu2O3. In this study, we design a systematic machining scheme for large-size Lu2O3 single crystal thick chip to obtain polished crystal with virtually no surface and subsurface damage. The surface/subsurface quality was evaluated utilizing optical profilometer, scanning electron microscope, and transmission electron microscope. Variable-angle spectroscopic ellipsometer was employed to measure the optical constants over wide spectral region (210-1690 nm), removing the lack of optical constants of Lu2O3 single crystal in the ultraviolet region. The band gap is analyzed based on the optical constants results. The consistency of the measured data with the relevant literature verifies the reliability and accuracy of the measurement method along with the data. The surface/subsurface damage inspection method provides an effective approach for ultra-precision machining mechanism research and process optimization of Lu2O3 and other hard and brittle materials. The band gap and the optical constants in wide spectral region provide critical fundamental data for the design and performance optimization of related optics.

Transparent layers are critical for enhancing optical contrast of graphene on a substrate. However, once the substrate is fully covered by large-area graphene, there are no accurate transparent layer and reference for optical contrast calculations. The thickness uncertainty of the transparent layer reduces the analytical accuracy of graphene. Thus, in this Letter, we propose a reference-aided differential reflection (DR) method with a dual-light path. The accurate thickness of the transparent layer is obtained by improving the DR spectrum sensitivity using a designable reference. Hence, the analytical accuracy of graphene thickness is guaranteed. To demonstrate this concept, a centimeter-scale chemical-vapor-deposition-synthesized graphene was measured on a S i O 2 / S i substrate. The thickness of underlying S i O 2 was first identified with the 1 nm resolution by the DR spectrum. Then, the thickness distribution of graphene was directly deduced from a DR map with submonolayer resolution at a preferred wavelength. The results were also confirmed by ellipsometry and atomic force microscopy. As a result, this new method provides an extra degree of freedom for the DR method to accurately measure the thickness of large-area two-dimensional materials.

The repair reinforcement height is an important parameter of repair welding, which may have a great influence on structural integrity. In this paper, the effects of repair welding reinforcement height on the microstructure, microhardness, residual stresses and stress corrosion cracking (SCC) behavior of a 304 stainless steel-repaired joint were investigated by experimentation and simulation. With an increase of the repair weld reinforcement height, the &delta, ferrite content in weld and fusion zone is obviously reduced, and the ferrite shape is gradually changed from the skeleton to the worm shape. With the increase of repair welding reinforcement height, the microhardness and residual stresses decrease gradually. The tensile strength and elongation for higher repair weld reinforcement height are larger than those with lower repair weld reinforcement height. The higher the repair weld reinforcement height, the harder it is for SCC to occur. The repair welding in 304 stainless steel is recommended to be repaired no more than two times.

The atomic force microscopy (AFM) was proposed to characterize the surfaces of various materials with high sensitivity and resolution(sub-nanometer) since 1980s, but it intrinsically lacks amongst others chemical sensitivity. These limitations of AFM can be overcome by coupling with optical microscope, which allows to obtain more comprehensive characterization data by in-situ measurement. To integrate the AFM into the upright optical microscope easily, this paper proposed a novel design of AFM. The corresponding Raman-AFM system was developed which adopts the sample scanning structure with a self-developed ultra-thin AFM head. The AFM head employs an innovative multi-reflected laser beam to detect the deformation of the cantilever, which greatly reduces the Z-direction thickness of the head, making its Z-direction thickness smaller than the working distance of the objective lens. Therefore, the AFM probe can be directly mounted under the objective lens of the upright optical microscope without changing the existing optical path. To evaluate the performance of the proposed AFM system, a standard grid was imaged using the Raman-AFM system. Then, a sample of two-dimensional material, black phosphorus(BP)/molybdenum disulfide(MoS2) heterojunction, was characterized. The physicochemical information of the heterojunction was obtained by in-situ measurement of the surface topography and Raman spectra.

Packaging materials usable for DUV-LEDs are limited as most organic materials are affected by DUV radiation. Packages used are TO-packages or 3D-structured ceramic housings with quartz lid. Due to DUV-LEDs radiating up to 50% of their light to the sides a significant share is lost. This paper describes a hermetic SMD-compatible packaging approach that integrates reflectors into a quartz window to maximize the light extraction. Side emitted and otherwise wasted light is redirected towards the surface. It avoids costly 3D-structured ceramics and improves the overall thermal performance. Design choices of the reflector structures allow to tailor the radiation patterns of the LEDs.

A hydro-mechanical transmission (HMT) is a continuously variable transmission that transmits power both mechanically and hydraulically. Typically, a HMT consists of one or more planetary gear-sets and a pair of hydraulic pump/motors, making it bulky and expensive. A novel structure of HMT named the Hondamatic only consisted a two-shafted piston pump and a variable displacement piston motor, making it very compact. The two-shafted piston pump plays the role of a planetary gear and the piston barrels of the pump and motor are dual-used for mechanical transmission. This paper analyzes the operating principle of the Hondamatic and its performance through detailed modeling. The model considering the kinematics, inertial and compressibility dynamics as well as the mechanical and volumetric losses. Modeling concepts for axial piston pump/motors are adapted to the Hondamatic to result in a dynamic model with tunable parameters to analyze the operation, dynamics and efficiency. The friction between the pistons and piston bores, the throttling loss of the distributor valves and the leakage from the piston bores are the main power losses in the Hondamatic. The overall efficiency of the Hondamatic is above 80% under most working condition according to the simulation results, which makes the Hondamatic high efficient and very compact meanwhile.

An atomic force microscopy (AFM) scanning head is designed with the probe orthogonal scanning mode for metrological AFM to eliminate the curvature distortion. The AFM probe is driven by piezostage and the scanning trajectory of the probe in 3 directions are orthogonal to reduce the cross coupling. A new optical lever amplification optical path is developed to eliminate the coupling error. The tracing lens and probe tip are moved as an integrated part. The AFM is operated at contacting mode. The step approach process of the probe tip is tested to the sample surface and the noise of the AFM head is analyzed. The response of the probe demonstrates a 0.5 nm resolution of the probe head in the z direction. Finally, the planar scanning performance of the scanning head is demonstrated compared with tube scanning AFM.

A novel serpentine-channeled mask was introduced to Si substrate for low-dislocation GaN epitaxial growth and the fully coalesced GaN film on the masked Si substrate was achieved for the first time. Compared with the epitaxial lateral overgrowth (ELOG) growth method, this innovative mask only requires one-step epitaxial growth of GaN which has only one high-dislocation region per mask opening. This new growth method can effectively reduce dislocation density, thus improving the quality of GaN significantly. High-quality GaN with low dislocation density ∼2.4 × 107 cm−2 was obtained, which accounted for about eighty percent of the GaN film in area. This innovative technique is promising for the growth of high-quality GaN templates and the subsequent fabrication of high-performance GaN-based devices like transistors, laser diodes (LDs), and light-emitting diodes (LEDs) on Si substrate.

Electrical synaptic devices are the basic components for the hardware based neuromorphic computational systems, which are expected to break the bottleneck of current von Neumann architecture. So far, synaptic devices based on three-terminal transistors are considered to provide the most stable performance, which usually use gate pulses to modulate the channel conductance through a floating gate and/or charge trapping layer. Herein, we report a three-terminal synaptic device based on a two-dimensional molybdenum ditelluride (MoTe2)/hexagonal boron nitride (hBN) heterostructure. This structure enables stable and prominent conductance modulation of the MoTe2channel by the photo-induced doping method through electron migration between the MoTe2channel and ultraviolet (UV) light excited mid-gap defect states in hBN. Therefore, it is free of the floating gate and charge trapping layer to reduce the thickness and simplify the fabrication/design of the device. Moreover, since UV illumination is indispensable for stable doping in MoTe2channel, the device can realize both short- (without UV illumination) and long- (with UV illumination) term plasticity. Meanwhile, the introduction of UV light allows additional tunability on the MoTe2channel conductance through the wavelength and power intensity of incident UV, which may be important to mimic advanced synaptic functions. In addition, the photo-induced doping method can bidirectionally dope MoTe2channel, which not only leads to large high/low resistance ratio for potential multi-level storage, but also implement both potentiation (n-doping) and depression (p-doping) of synaptic weight. This work explores alternative three-terminal synaptic configuration without floating gate and charge trapping layer, which may inspire researches on novel electrical synapse mechanisms.

In this study, SiC nanocoatings were prepared on graphite substrates via a laser treatment process. Different laser energy densities were employed in the laser treatment. The surface morphology and elemental composition were systematically studied by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM) were used to characterize the phase composition and coating microstructure. A high-temperature oxidation test was also conducted to determine their anti-oxidation performance. The results show that laser irradiation triggers the transformation from micro SiC particles into SiC nanocoating consisting of numerous polycrystalline SiC nanoparticles. At the laser energy density of 10.42 kJ cm−2, the prepared SiC nanocoating reveals the best oxidation resistance at a high-temperature environment in tested samples. In addition to its dense and crack-free surface morphology, the formation of SiO2 in the SiC nanocoating also helped to enhance the high-temperature oxidation resistance as a self-healing agent. Laser preparation of SiC nanocoating enhances the high-temperature oxidation resistance and protects the underneath graphite substrate, which serves as an efficient and effective manufacturing method for SiC protective coatings.

Layered ReS2 with direct bandgap and strong in-plane anisotropy shows great potential to develop high-performance angle-resolved photodetectors and optoelectronic devices. However, systematic characterizations of the angle-dependent photoresponse of ReS2 are still very limited. Here, we studied the anisotropic photoresponse of layered ReS2 phototransistors in depth. Angel-resolved Raman spectrum and field-effect mobility are tested to confirm the inconsistency between its electrical and optical anisotropies, which are along 120° and 90°, respectively. We further measured the angle-resolved photoresponse of a ReS2 transistor with 6 diagonally paired electrodes. The maximum photoresponsivity exceeds 0.515 A⋅W−1 along b-axis, which is around 3.8 times larger than that along the direction perpendicular to b axis, which is consistent with the optical anisotropic directions. The incident wavelength- and power-dependent photoresponse measurement along two anisotropic axes further demonstrates that b axis has stronger light–ReS2 interaction, which explains the anisotropic photoresponse. We also observed angle-dependent photoresistive switching behavior of the ReS2 transistor, which leads to the formation of angle-resolved phototransistor memory. It has simplified structure to create dynamic optoelectronic resistive random access memory controlled spatially through polarized light. This capability has great potential for real-time pattern recognition and photoconfiguration of artificial neural networks (ANN) in a wide spectral range of sensitivity provided by polarized light.

In this study, a tracing method for a scanning electron microscope was developed based on a heterodyne interferometer, which can directly trace the measured values to the laser wavelength and then to the internationally defined meter length reference. In this method, a sample scanning motion is introduced, and the measuring mirror of the interferometer is fixed on the sample stage. The movement and displacement of the sample stage is recorded by the laser interferometer displacement measurement system, which synchronously collects the secondary electrons or backscattered electron signals excited on the sample surface. The feature size of the sample is measured, and the value can be traced directly to the international unit of length using the frequency-stabilized laser reference, which proves that the proposed method is an absolute measurement method. This study analyzed the specific technology implementation methods and experimental results, including positioning control of the displacement system and its measurement and control during the measurement process. Measurement uncertainty budgets are also discussed. Experimental measurements were carried out and their accuracy was verified. Results showed that this method could effectively obtain the performance parameters of the feature size intuitively and significantly improve the measurement accuracy.

The surface resistance to oil is very important for filtration efficiency, film cleaning and life span of ultrafiltration membranes. The atomic force microscope (AFM) has provided unprecedented opportunities to study interface interactions. In this paper, the probe with an oil droplet modified was used as a force sensor for evaluating the oil resistance of membrane surfaces. The adhesion forces between two types of modified tips and a serial of membrane surfaces in fluid was detected via force curves. On the one hand, the AFM probe with an oil droplet immobilized directly was used to study the adhesion forces between a series of PVF/F127 membranes and a hexadecane droplet. On the other hand, a tip attached polystyrene (PS) microsphere covered with a layer of oil was employed. It was found that the oil antifouling performance of membranes was improved effectively through blending F127 with PVF. As the F127 additive varied from 0% to 60%, adhesion force detected by the AFM probe with an hexadecane droplet immobilized showed a decreasing tendency from 2.84 nN to 0.73 nN. Meanwhile, the average interaction force detected by the second modified tip decreased from 3.39 nN to 0.54 nN. The measured force behavior was in agreement with experimental observations of contact angle measurement, which indicated that the blend membranes had better antifouling.

Core/shell shaped nanorod arrays with type-II band alignment heterojunction is a promising nanobuilding block for efficient charge transfer at the interface. Here in this work, we have fabricated Ag 2 S quantum dots decoration on surface of vertically aligned TiO 2 nanorod arrays. A modified two-step solution process is used to obtain uniform Ag 2 S quantum dots shell that promotes exciton dissociation at the organic/inorganic hybrid interface. Because of the enhanced charge transfer, the photovoltaic conversion efficiency shows a drastic improvement of up to 73% for the solar cell adopting TiO 2 /Ag 2 S core/shell nanorod arrays as the electron acceptor.

We experimentally study the electron overflow in InGaN/GaN blue light emitting diodes (LEDs) by measuring the electroluminescence (EL) emission spectra from p-type InGaN/GaN superlattices (SLs) adjacent to the quantum well (QW) active region. The integrated EL intensity ratio of the SL peak to quantum well peak was calculated to reveal the dependence of electron overflow from active region on current density. Our experimental results indicate that the electron overflow from the active region at both low and high current densities, and no saturation is observed even at the maximum current density (280 A/cm 2 ) applied. It is found that both direct electron leakage and Auger assisted leakage contribute to the electron overflow. Further analyses reveal that at low current densities (less than 150 A/cm 2 ) direct electron leakage dominates the mechanism for electron overflow, and simultaneously for efficiency droop, while electron overflow is mainly caused by Auger assisted leakage at high current density. These results identify the main mechanisms for efficiency droop of LEDs at different current density regimes.

In this study, the welding process of 304 stainless steel/Q345R low alloy steel composite plate is modeled by experimental and finite element methods to study the complex thermomechanical behavior. The residual stress and microstructure evolution of composite plate in the welding process are also investigated. The welding thermal cycle curve and residual stress distribution at the joint are obtained by using thermocouple and blind-hole methods. Optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to investigate the evolution of microstructure, morphology, and element diffusion of the joint. The results show that the maximum von Mises welding residual stress is 312 MPa, which is located in the bottom of the start point of the weld zone. The residual stress gradually decreases and tends to be stable along the direction from the weld to the base metal. In addition, a residual stress discontinuity is found at the interface between the bimetal. It is also found that the closer it is to the weld joint, the more uniform is the austenite distribution and the smaller are the grain sizes.

The controllable and wide-range modulation of the carrier type and mobility in atomically thin two-dimensional (2D) materials is one of the most critical issues to be addressed before 2D materials can be practically used for future electronic and optoelectronic devices. In this work, we propose using a novel surface charge transfer mechanism to accomplish the controllable and wide-range modulation of the carrier type and mobility in 2D materials. Our methodology uses a solution of triphenylboron (TPB) to physically coat 2D materials; the TPB molecule contains positive and negative charge centers that are spatially separable when induced by an electrical field. Consequently, the TPB can transfer either positive or negative charges to 2D materials depending on the direction of the applied electrical field and thus enhance the ambipolar behavior of the 2D-material FET. This method is so versatile that seven types of 2D materials including graphene, black phosphorus and five transition metal dichalcogenides (TMDCs) can be modulated to strong ambipolar behavior with significantly increased conduction. In addition, selectively suppressing or enhancing the negative charge center enables solely p-type and n-type doping. We also accomplish the precise tuning of carrier mobility in TMDCs from ambipolar to p-type by coating a mixture of TPB/BCF in certain concentration ratios.

Energy band engineering is of fundamental importance in nanoelectronics. Compared to chemical approaches such as doping and surface functionalization, electrical and optical methods provide greater flexibility that enables continuous, reversible, and in situ band tuning on electronic devices of various kinds. In this report, we demonstrate highly effective band modulation of MoTe2 field-effect transistors through the combination of electrostatic gating and ultraviolet light illumination. The scheme can achieve reversible doping modulation from deep n-type to deep p-type with ultrafast switching speed. The treatment also enables noticeable improvement in field-effect mobility by roughly 30 and 2 times for holes and electrons, respectively. The doping scheme also provides good spatial selectivity and allows the building of a photo diode on a single MoTe2 flake with excellent photo detection and photovoltaic performances. The findings provide an effective and generic doping approach for a wide variety of 2D materials.

We have demonstrated non-polar GaN power diodes (Schottky barrier diode and p–n junction diode) on foreign substrates featuring the true-lateral p–n and metal–semiconductor junctions. The diodes were fabricated on GaN islands laterally overgrown on the mask-patterned sapphire and Si substrates by metalorganic vapor phase epitaxy. The anode and cathode were formed on the opposed a-plane sidewalls of the island, making the device architecture essentially like the 90° rotation of the desired true-vertical power diodes. The ideality factor of the Schottky barrier diode remained 1.0 (from 1.00 to 1.05) over 7 decades in current. Specifically, a high critical electric field of 3.3 MV/cm was demonstrated on the p–n junction diode with avalanche capability. These performances reveal a strong potential of non-polar GaN with the true-lateral junctions for high power applications.

In order to clarify the role of different post-weld heat treatment processes in the manufacturing process, welding tests, post-weld heat treatment tests, and finite element analysis (FEA) are carried out for 12C1MoV steel pipes. The simulated temperature field and residual stress field agree well with the measured results, which indicates that the simulation method is available. The influence of post-weld heat treatment process parameters on residual stress reduction results is further analyzed. It is found that the post weld dehydrogenation treatment could not release residual stress obviously. However, the residual stress can be relieved by 65% with tempering treatment. The stress relief effect of &ldquo, post weld dehydrogenation treatment + temper heat treatment&rdquo, is same with that of &ldquo, temper heat treatment&rdquo, The higher the temperature, the greater the residual stress reduction, when the peak temperature is at 650&ndash, 750 &deg, C, especially for the stress concentration area. The longer holding time has no obvious positive effect on the reduction of residual stress.

The manufacture of metal electrode window on the ridge structure of laser diodes (LDs) is a confused issue in the LDs fabrication process. We show that the processing of the self-aligned step and negative photosensitive polyimide (NPP) thermal imidization which can achieve both accurate alignment of p-electrode window on the ridge structure and integrated dielectric layer at once time. This back word exposure technic can effectively simplify the process of accuracy of alignment and avoid etching of isolating layer. The optical and electrical performance of the LD chip measured at room temperature under a pulse current condition (the current duty ratio was 25%) were shown. The output optical power was greater than 20 mW, at 7.7 V operating voltage, and the reversed current is 3.9 × 10−5 mA when the bias voltage is −5 V. A lasing peak wavelength at around 442 nm became dominant at 320 mA. Our results provide an alternative effective approach to fabricate the well behavior LDs.

Measurements of the excitation power-dependence and temperature-dependence photoluminescence (PL) are performed to investigate the emission mechanisms of InGaN/GaN quantum wells (QWs) in laser diode structures. The PL spectral peak is blueshifted with increasing temperature over a certain temperature range. It is found that the blueshift range was larger when the PL excitation power is smaller. This particular behavior indicates that carriers are thermally activated from localized states and partially screen the piezoelectric field present in the QWs. The small blueshift range corresponds to a weak quantum-confined Stark effect (QCSE) and a relatively high internal quantum efficiency (IQE) of the QWs.

In-line digital holographic particle imaging is gifted with high axial resolution but axial displacement of nearly-in-focus or in-focus particle is unable to be measured because of twin-image problem. Both in-focus and out-of-focus particles can be measured by off-axis digital holographic particle imaging but with poor axial resolution. These two make particle tracking in three-dimensional more complicated. This paper proposes a compound method of in-line and off-axis digital holographic microscopy to measure the axial displacement of both the in-focus and out-of-focus particle with improved resolution up to nanometer scale collectively. In the proposed compound digital holographic microscopy (CDHM), the critical reconstruction distance (CRD) is calculated. The twin image effect can be resolved by ensuring the reconstruction distance is larger than the CRD, then in-line digital holographic particle imaging can be effectively applied. If the reconstruction distance is smaller than the CRD, the ring pixels of optical path length (RPOPL) method is applied to improve resolution. The axial displacement of silica particles 5 μ m and 10 μ m in diameter fixed on the piezoelectric stage were successfully measured using CDHM method at resolution up to 4 nm (in-focus particle) and 2 nm (out-of-focus particle).

Heterostructures formed by stacking atomically thin two-dimensional materials are promising candidates for flash memory devices to achieve premium performances, due to the capability of effective carrier modulation and unique charge trapping behavior at the interfaces with atomic flatness. Here, we report a nonvolatile floating-gate flash memory based on MoTe2/h-BN/graphene van der Waals heterostructure, which possesses increased data storage capacity per cell and versatile tunability. The decent memory behavior of the device is enabled by the carriers stored in the floating gate of graphene layer, which tunnel through the dielectric layer of h-BN from the channel layer of MoTe2 under static-electrical field. Consequently, the developed memory device is capable to store 2 bits per cell by applying varied gate bias to implement multi-distinctive current levels. The device also exhibits remarkable erase/program current ratio of ∼105 with 1 µs switch speed and stable retention with estimated ∼30% charge loss after 10 yr. Furthermore, the memory device can operate in both p- and n-type modes through contact engineering, offering wide adaptability for emerging applications in electronic technologies, such as neuromorphic computing, data-adaptive energy efficient memory, and complex digital circuits.

Developing angular trapping methods, which will enable optical tweezers to rotate a micronized bead, is of great importance for the studies of biomacromolecules during a wide range of torque-generation processes. Here we report a novel controlled angular trapping method based on composite Janus particles. We used a chemically synthesized Janus particle, which consists of two hemispheres made of polystyrene (PS) and poly(methyl methacrylate) (PMMA) respectively, as a model system to demonstrate this method. Through computational and experimental studies, we demonstrated the feasibility to control the rotation of a Janus particle in a linearly polarized laser trap. Our results showed that the Janus particle aligned its two hemisphere's interface parallel to the laser propagation direction as well as the laser polarization direction. In our experiments, the rotational state of the particle can be easily and directly visualized by using a CMOS camera, and does not require complex optical detection system. The rotation of the Janus particle in the laser trap can be fully controlled in real time by controlling the laser polarization direction. Our newly developed angular trapping technique has the great advantage of easy implementation and real time controllability. Considering the easy chemical synthesis of Janus particles and implementation of the angular trapping, this novel method has the potential of becoming a general angular trapping method. We anticipate that this new method will significantly broaden the availability of angular trapping in the biophysics community, and expand the scope of the research that can be enabled by the angular trapping approach., Comment: 16 pages, 5 figures

In the agricultural field, optical remote sensing technology plays an important role in crop monitoring or production estimation. However, the widespread distribution of clouds and rain limits the application of optical remote sensing. Synthetic aperture radar (SAR) has been widely used for studies of oceans, atmosphere, land, and space exploration, as well as by the military due to its all-weather nature, penetration to surface and cloud layers, and diversity of information carriers. However, it is difficult to classify ground objects with high accuracy based on SAR data. Considering the features of these two datasets, we proposed a framework to improve crop classifications in cloudy and rainy areas based on the optical-SAR response mechanism. Specifically, this method is designed to train a parametric analytic model in the area using both kinds of datasets and applied in the area with only SAR data to obtain the optical time-series features. Then crops from the second area were classified by the long-short-term memory network. As an example, the parametric analytic model in Lixian County was studied and was applied to Xifeng County to classify the crops with the OA of 61%, which had proved the robustness of the method.

The breakage of the lug pads and the barrel welds on the air preheater is a common problem. This paper analyzes the fracture failure during the operation of the air preheater. Through the investigation of the working environment of the air preheater, the fracture morphology detection and the microstructure observation, the finite element method is used to predict the welding residual stress and thermo-mechanical stress at the lug pad and the barrel weld. The results show that the microstructure degration at high temperature and high thermomechanical stress synergistic effect are the main factors leading to the fracture with mixed mode of ductile fracture with dimples and brittle fracture with fluvial cleavage pattern. Last, some suggestions were put forward to avoid fracture during hoisting.

Developing micro/nanoscale wire lasers with single-mode operation and lasing wavelength modulation is essential for realizing their practical applications such as optical communication and saturated spectroscopy. We demonstrated, to the best of our knowledge, the first tunable single-mode microrod laser without complicated micro/nano-manipulation and without additional environmental requirement. In this letter, we realized the wavelength modulation in a single semiconductor microrod simply and directly by changing the axial location of the active region, owing that the active region position plays a key role in determining the lasing mode of microrod lasers. Based on this feature, we proposed a pair of asymmetrical distributed Bragg reflectors (DBRs) with specific spectral selectivity to be induced in a GaN microrod to realize tunable single-mode lasing in a single semiconductor microrod. By using this method, lasing wavelength can be modulated from 369.5 to 375.7 nm flexibly and repeatedly in a 45 μm GaN microrod with the change of the excitation source position. This approach demonstrates a big application potential in numerous fields consisting of optical telecommunication and environmental monitoring.

Atomically thin two-dimensional (2D) materials are ideal gas sensing materials for achieving an ultra-low detection limit, due to the high surface-to-volume ratio, low electronic noise and sensitively tunable Fermi level. However, the sensitivity of 2D materials to their surrounding environment may also severely degrade the long-term stability of sensing devices, since most of them use the same 2D material flake as both the sensing and conduction material. In this work, we report a gas sensor based on a 2D material field effect transistor (FET) which uses few-layer black phosphorus (BP), boron nitride (BN) and molybdenum disulfide (MoS2) as the top-gate, dielectric layer and conduction channel, respectively. In this device configuration, the top-gate of BP with a superior gas adsorption capability serves as the sensing material, while the conduction channel of MoS2 is isolated from ambient environment by the coverage of the BN dielectric layer. The separation of the sensing and conduction materials not only improves the long-term stability of the device, but also enables us to use different materials for gas adsorption and conduction purposes to achieve optimum sensing performances. In addition, the adsorption kinetics of the gas molecules on the sensing channel can be sensitively detected by the current/resistance variation of the conduction channel, since the adsorbed gas molecules can effectively tune the Fermi level of sensing and conduction materials (BP and MoS2, respectively) through band alignment. We experimentally demonstrated that the proposed 2D material FET not only achieved a detection limit of 3.3 ppb to NO2, but was also capable to differentiate oxidizing and reducing gases.

A phase noise optimizing method was proposed in this paper to improve the imaging quality of digital microscopic holography (DHM). In this method, bidimensional empirical mode decomposition (BEMD) was utilized to decompose the digital hologram. According to the principle of decomposition, the characteristics of first order intrinsic mode function (IMF1) are close to the gray value of ideal interference fringes. Therefore, after using BEMD method the digital hologram was optimized with enhanced interference fringes, from which phase image with reduced noise can be retrieved. The validity of the proposed method on noise reduction was verified by experimental results on a nano-step.

In this paper, we present our work developing a family of silicon-on-insulator (SOI)–based high-g micro-electro-mechanical systems (MEMS) piezoresistive sensors for measurement of accelerations up to 60,000 g. This paper presents the design, simulation, and manufacturing stages. The high-acceleration sensor is realized with one double-clamped beam carrying one transversal and one longitudinal piezoresistor on each end of the beam. The four piezoresistors are connected to a Wheatstone bridge. The piezoresistors are defined to 4400 Ω, which results in a width-to-depth geometry of the pn-junction of 14 μm × 1.8 μm. A finite element method (FEM) simulation model is used to determine the beam length, which complies with the resonance frequency and sensitivity. The geometry of the realized high-g sensor element is 3 × 2 × 1 mm3. To demonstrate the performance of the sensor, a shock wave bar is used to test the sensor, and a Polytec vibrometer is used as an acceleration reference. The sensor wave form tracks the laser signal very well up to 60,000 g. The sensor can be utilized in aerospace applications or in the control and detection of impact levels.

A digital hologram-optimizing method was proposed to improve the imaging quality of dual-wavelength digital holographic microscopy (DDHM) by reducing the phase noise level. In our previous work, phase noise reduction was achieved by dual-wavelength digital image-plane holographic microscopy (DDIPHM). In the optimization method in this paper, the phase noise was further reduced by enhancing the real-image term and suppressing effects of the zero-order term in the frequency spectrum of a digital hologram. Practically, the carrier frequency of the real-image term has the correspondence with interference fringes in the hologram. Mathematically, the first order intrinsic mode function (IMF1) in bidimensional empirical mode decomposition (BEMD) has similar characteristics to the grayscale values of ideal interference fringes. Therefore, with the combination of DDIPHM and BEMD, by utilizing the characteristics of IMF1, the digital hologram was optimized with purified interference fringes, enhancing the real-image term simultaneously. Finally, the validity of the proposed method was verified by experimental results on a microstep.

Organic/inorganic hybrid perovskite solar cell has emerged as a very promising candidate for the next generation of near-commercial photovoltaic devices. Here in this work, we focus on the inverted perovskite solar cells and have found that remarkable photovoltaic performance could be obtained when using cadmium selenide (CdSe) quantum dots (QDs) as electron transporting layer (ETL) and lithium fluoride (LiF) as the buffer, with respect to the traditionally applied and high-cost [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The easily processed and low-cost CdSe QDs/LiF double layer could facilitate convenient electron-transfer and collection at the perovskite/cathode interface, promoting an optoelectric conversion efficiency of as high as 15.1%, very close to that with the traditional PCBM ETL. Our work provides another promising choice on the ETL materials for the highly efficient and low-cost perovskite solar cells. Electronic supplementary material The online version of this article (doi: 10.1186/s11671-017-2381-5) contains supplementary material, which is available to authorized users.

We utilize digital image-plane holographic microscopy (DIPHM) to achieve the real-time surface profile measurement of microstructure. The impulse response functions of DIPHM and traditional digital holographic microscopy (DHM) are both derived. The theoretical derivations indicate that the differences between the two techniques are caused by the diffraction effect of the recording plane with a finite size. The diffraction effect would introduce an unstable factor to the wavefront reconstruction. Therefore, the DIPHM has the characteristics of totally full field of view and low measuring noise compared to DHM. In addition, we take DIPHM and DHM in dual-wavelength mode as a special example to confirm the points above. From both experimental results and theoretical analysis, DIPHM is demonstrated to be an optimized technique with high-quality imaging, especially benefiting the situation where multi-wavelength measurement is required. This method is robust against environmental noise. SCANNING 38:288-296, 2016. © 2015 Wiley Periodicals, Inc.

We report the theoretical investigation of an electrically injected plasmonic nanolaser in visible regime. The green nanolaser is based on a hybrid waveguide which employs semiconductor nanowire gain medium to compensate the loss in metallic cavity. Two-dimensional sub-wavelength confinements (mode area about λ 2/100) and net modal gain are simultaneously achieved for quasi-one-dimensional surface plasmon mode supported in such waveguide. The device structure is further optimized for room temperature operation with achievable injected current density about several kilo ampere/square centimetres (kA/cm2). The approach is also beneficial to developing other nanophotonic devices on sub-wavelength scale.

We theoretically investigate the optical properties of conventional, normal (type A) parabolic and novel (type B) parabolic InGaN quantum well (QW) for blue light emitters. Two specially designed active layer structures by parabolic-shaped QW are proposed, and the optical characteristics of these two parabolic QW structures are calculated and compared to those of conventional QW structures. The electron–hole wavefunction overlap (Γe–hh) of type-B parabolic QWs is 2.8 times (69.6%) that in the conventional QW (24.8%), and the spontaneous emission rate is ninefold that of conventional QWs. The transparency carrier density of type-B parabolic QWs is much smaller than type-A parabolic or conventional QW. These results can be attributed to a higher indium index in the center of the type-B parabolic QWs, and that leads to better confinement of carriers wavefunctions.

Toward fabricating a novel multifunctional wound dressing material, we incorporated a series of contents of reduced graphene oxide (rGO) sheets into polydimethylsiloxane (PDMS) matrix to prepare the rGO-PDMS composite membrane and be used for wound dressing. The pore structure, dispersion of rGO, physical properties, water vapor transmission rate (WVTR), cytotoxicity and antibacterial activity were studied. Finally, the effect of the rGO-PDMS composite membrane on wound healing was investigated on a murine full-thickness skin wound model. The rGO-PDMS composite membrane exhibited bionic performance (ordered pore structure and suitable WVTR), improved mechanical properties, good compatibility and effective antibacterial activity. In vivo experiment indicated that the rGO-PDMS composite membrane could accelerate wound healing via enhancement of the re-epithelialization and granulation tissue formation. These findings suggest that rGO doping PDMS uniquely resulted in a multifunctional material for potential use in wound dressing.

For the miniaturization of two-dimensional autocollimator, a method of using embedded measurement system instead of special host computer is presented. This system integrates CMOS image sensor's driving circuit, frame processing, adaptive exposure control, centroid subdivision and localization of cross, misalignment angle calculation, display driver and other functions within a FPGA chip, and the sampling image and measurement results are displayed through the TFT-LCD mounted on the device body. The engineering prototype shows that the system has characters of high precision, high integration and high reliability.

In order to solve the problems of GaN heteroepitaxy on sapphire substrate, some techniques were explored. Freestanding GaN substrates have been made by hydride vapor phase epitaxy (HVPE), laser lift-off (LLO), and chemical mechanical polishing techniques. Wafer bending and cracking in the HVPE growth were partly settled by pulsed flow modulation method. High-crystal quality was established for 1.2 mm thick GaN substrate by X-ray diffraction measurement, in which the full width of half maximum values were 72, 110 arcsec for (102), (002) peaks. A novel micro-size patterned sapphire substrate (PSS) and a nano PSS were also fabricated. High-power vertical structure light emitting diodes (VSLEDs) have been developed by Au–Sn eutectic wafer bonding, homemade micro-area LLO, and light extraction structure preparation. The high-injection-level active region with low temperature GaN sandwiched layers was used for low-efficiency droop. The light output power of VSLED was achieved as 400 mW driven at 350 mA, and the dominant wavelength is about 460 nm. The structures and properties of strain modulated superlattices (SLs) and quantum wells as well as advanced simulation of carriers transport across the electron blocking layer were investigated in laser diodes. The hole concentration was achieved as high as 1.6 × 1018 cm−3 in AlGaN/GaN SLs:Mg by inserting an AlN layer. High-quality AlGaN epilayers and structures were grown by MOCVD. Some device structures of UV LEDs and detectors were demonstrated. The emission wavelength of 262 nm UV LED has been successfully fabricated. At last, high-quality InN and InGaN materials for solar cell were grown by boundary-temperature-controlled epitaxy and growth-temperature-controlled epitaxy. Hall-effect measurement showed a recorded electron mobility of 3,280 cm2/(V s) and a residual electron concentration of 1.47 × 1017 cm−3 at 300 K.