Surface reconstruction of Se-doped NiS_(2) enables high-efficiency oxygen evolution reaction

Surface reconstruction of electrocatalysts has been widely witnessed during the electrochemical processes.Here,NiS_(2),NiSe_(2), and Se doped NiS_(2)(Se-NiS_(2)) are fabricated for oxygen evolution reaction(OER) through a mild sulfuration and/or selenylation process of Ni(OH)_(2) supported on carbon cloth(CC).Through careful in-situ Raman spectroscopy and ex-situ X-ray photoelectron spectroscopy,surface reconstruction of NiS_(2),NiSe_(2),and Se-NiS_(2) during the OER process has been revealed.A potentialdependent study shows that Se-NiS_(2) undergoes surface evolution at lower potentials and requires the lowest potential for conversion to NiOOH as a highly OER-active species,accompanied by the leaching of SO_(4)^(2-) and SeO_(4)^(2-) that can again be adsorbed on the catalyst surface to enhance the catalytic activity.Density functional theory(DFT) calculations confirm that Se-NiS_(2) is more susceptible to surface oxidation through the OER process.Therefore,Se-NiS_(2) exhibits outstanding OER activity and stability in alkaline conditions,requiring an overpotential of 343 mV at a current density of 50 mA cm^(-2).A novel insight is provided by our work in understanding the surface reconstruction and electrocatalytic mechanism of Ni-based chalcogenides.

Fabrication of Periodic Nanostructures Using AFM Tip-Based Nanomachining:Combining Groove and Material Pile-Up Topographies

This paper presents an atomic force microscopy(AFM)tip-based nanomachining method to fabricate periodic nanostructures.This method relies on combining the topography generated by machined grooves with the topography resulting from accumulated pile-up material on the side of these grooves.It is shown that controlling the distance between adjacent and parallel grooves is the key factor in ensuring the quality of the resulting nanostructures.The presented experimental data show that periodic patterns with good quality can be achieved when the feed value between adjacent scratching paths is equal to the width between the two peaks of material pile-up on the sides of a single groove.The quality of the periodicity of the obtained nanostructures is evaluated by applying one-and two-dimensional fast Fourier transform(FFT)algorithms.The ratio of the area of the peak part to the total area in the normalized amplitude–frequency characteristic diagram of the cross-section of the measured AFM image is employed to quantitatively analyze the periodic nanostructures.Finally,the optical effect induced by the use of machined periodic nanostructures for surface colorization is investigated for potential applications in the fields of anti-counterfeiting and metal sensing.

Micro Electrical Discharge Machining Deposition in Air for Fabrication of Micro Spiral Structures

Micro electrical discharge machining（EDM） deposition process is a new micro machining method for fabrication of metal micro structures. In this process, the high level of tool electrode wear is used to achieve the metal material deposition. Up to now, the studies of micro EDM deposition process focused mainly on the researches of deposition process, namely the effects of discharge parameters in deposition process on the deposition rate or deposition quality. The research of the formation of micro structures with different discharge energy density still lacks. With proper conditions and only by the z-axis feeding in vertical direction, a novel shape of micro spiral structure can be deposited, with 0.11 mm in wire diameter, 0.20 mm in outside diameter, and 3.78 mm in height. Then some new deposition strategies including angular deposition and against the gravity deposition were also successful. In order to find the forming mechanism of the spiral structures, the numerical simulation of the transient temperature distribution on the discharge point was conducted by using the finite-element method（FEM）. The results show that there are two major factors lead to the forming of the spiral structures. One is the different material removal form of tool electrode according with the discharge energy density, the other is the influenced degree of the movement of the removed material particles in the discharge gap. The more the energy density in single discharge is, the smaller the mass of the removed material particles is, and the easier the movements of which will be changed to form an order tendency. The fine texture characteristics of the deposited micro spiral structures were analyzed by the energy spectrum analysis and the metallographic analysis. It shows that the components of the deposited material are almost the same as those of the tool electrode. Moreover the deposited material has the brass metallic luster in the longitudinal profile and has compact bonding with the base material. This research is useful to understand the micro-process of micro EDM deposition better and helpful to increase the controllability of the new EDM method for fabrication of micro structures.

Diffractive Deep Neural Networks at Visible Wavelengths

Optical deep learning based on diffractive optical elements offers unique advantages for parallel processing,computational speed,and power efficiency.One landmark method is the diffractive deep neural network(D^(2) NN)based on three-dimensional printing technology operated in the terahertz spectral range.Since the terahertz bandwidth involves limited interparticle coupling and material losses,this paper extends D^(2) NN to visible wavelengths.A general theory including a revised formula is proposed to solve any contradictions between wavelength,neuron size,and fabrication limitations.A novel visible light D^(2) NN classifier is used to recognize unchanged targets(handwritten digits ranging from 0 to 9)and targets that have been changed(i.e.,targets that have been covered or altered)at a visible wavelength of 632.8 nm.The obtained experimental classification accuracy(84%)and numerical classification accuracy(91.57%)quantify the match between the theoretical design and fabricated system performance.The presented framework can be used to apply a D^(2) NN to various practical applications and design other new applications.

High-efficiency Approach for Fabricating MTE Rotor by Micro-EDM and Micro-extrusion

Micro-gas turbine engine（MTE） rotor is an important indicator of its property, therefore, the manufacturing technology of the microminiature rotor has become a hot area of research at home and abroad. At present, the main manufacturing technologies of the MTE rotor are directed forming fabrication technologies. However, these technologies have a series of problems, such as complex processing technology high manufacturing cost, and low processing efficiency, and so on. This paper takes advantage of micro electric discharge machining（micro-EDM） in the field of microminiature molds manufacturing, organizes many processing technologies of micro-EDM reasonably to improve processing accuracy, presents an integrated micro-EDM technology and its process flow to fabricate MTE rotor die, and conducts a series of experiments to verify efficiency of this integrated micro-EDM. The experiments results show that the MTE rotor die has sharp outline and ensure the good consistency of MTE rotor blades. Meanwhile, the MTE rotor die is applied to micro extrusion equipment, and technologies of micro-EDM and micro forming machining are combined based on the idea of the molds manufacturing, so the MTE rotor with higher aspect ratio and better consistency of blades can be manufactured efficiently. This research presents an integrated micro-EDM technology and its process flow, which promotes the practical process of MTE effectively.

Micro electrical discharge machining of small hole in TC4 alloy

Aiming at machining deeply small holes in TC4 alloy,a series of experiments were carried out on a self-developed multi-axis micro electrical discharge machining(micro-EDM)machine tool.To improve machining efficiency and decrease relative wear of electrode in machining deeply small hole in TC4 alloy,many factors in micro-EDM,such as polarity,electrical parameters and supplying ways of working fluid were studied.Experimental results show that positive polarity machining is far superior to negative polarity machining;it is more optimal when open-circuit voltage,pulse width and pulse interval are 130 V,5μs and 15μs respectively on the self developed multi-axis micro-EDM machine tool;when flushing method is applied in micro-EDM,the machining efficiency is higher and relative wear of electrode is smaller.

Micro precision casting based on investment casting for micro structures with high aspect ratio

Microcasting is one of the significant technologies for the production of metallic micro parts with high aspect ratio(ratio of flow length to diameter).A micro precision casting technology based on investment casting using centrifugal method was investigated.The micro parts of Zn-4%Al alloy with an aspect ratio up to 200 was produced at the centrifugal speed of 1 500 r/min and the mold temperature of 270℃.The investigations on the relationship between flow length and rotational speed were carried out. For microcasting,the flow length is not only dependent on the centrifugal speed under the constant centrifugal radius,but also on the preheating temperature of mold.The flow length increases as the rotational speed and the mold temperature increase,and is much higher at a mold temperature of 270 ℃thanat other mold temperatures.

Mechanism of size effects in microcylindrical compression of pure copper considering grain orientation distribution

In microscale deformation, the magnitudes of specimen and grain sizes are usually identical, and size- dependent phenomena of deformation behavior occur, namely, size effects. In this study, size effects in micro- cylindrical compression were investigated experimentally. It was found that, with the increase of grain size and decrease of specimen size, flow stress decreases and inhomogeneous material flow increases. These size effects tend to be more distinct with miniaturization. Thereafter, a modified model considering orientation distribution of surface grains and continuity between surface grains and inner grains is developed to model size effects in micro- forming. Through finite element simulation, the effects of specimen size, grain size, and orientation of surface grains on the flow stress and inhomogeneous deformation were analyzed. There is a good agreement between experimental and simulation results.

Hybrid Micro-forming Processes and Quality Evaluation of Micro-double Gear

Micro-gear is an important actuating component used widely in the micro electro mechanical systems(MEMS) devices.The technologies of micro-forming and precision assembly are urgently developed to manufacture the micro-double gear with central shaft.In the paper,a novel hy-brid-forming process with two kinds of piercing method have been proposed to manufacture the micro-double gear using micro forming technology.The tests of hybrid forming process were carried out with two steps and the micro-double gear was successfully manufactured with good surface quality.The results also show that the hybrid micro-forming process with central piercing method can improve the defects of inclining shaft generated by double-ended piercing method.The quality evaluation of micro-double gear was conducted with surface roughness,micro-hardness and impact tests.The results show that the micro-double gear with good mechanical properties can meet the requirements of application for milli-machines.

Surface finish of micro punch with ion beam irradiation

Ion beam irradiation was adopted for surface treatment of the micro punch manufactured by precision machining.Ar plasma was used for the ion irradiation process,which was generated by the electron cyclotron resonance(ECR)equipment.The surface finish processes of micro punch were carried out at irradiation angles of 45°and 10°,respectively.The surface roughness and topography were measured to estimate the quality of surface finish.The results show that the ion irradiation is very effective to reduce the surface roughness,which can be improved more significantly at irradiation angle of 10°than at 45°.The technology of surface finish with ion beam irradiation is suitable for the surface treatment of micro die.

Study of machining indentations over the entire surface of a target ball using the force modulation approach

A modified five-axis cutting system using a force control cutting strategy was to machine indentations in different annuli on the entire surface of a target ball.The relationship between the cutting depths and the applied load as well as the microsphere rotation speed were studied experimentally to reveal the micromachining mechanism.In particular,aligning the rotating center of the high precision spindle with the microsphere center is essential for guaranteeing the machining accuracy of indentations.The distance between adjacent indentations on the same annulus and the vertical distance between adjacent annuli were determined by the rotating speed of the micro-ball and the controllable movement of the high-precision stage,respectively.In order to verify the feasibility and effect of the proposed cutting strategy,indentations with constant and expected depths were conducted on the entire surface of a hollow thin-walled micro-ball with a diameter of 1 mm.The results imply that this machining methodology has the potential to provide the target ball with desired modulated defects for simulating the inertial confinement fusion implosion experiment.

Optimization of Uncertain Structures with Interval Parameters Considering Objective and Feasibility Robustness

For the purpose of improving the mechanical performance indices of uncertain structures with interval parameters and ensure their robustness when fluctuating under interval parameters, a constrained interval robust optimization model is constructed with both the center and halfwidth of the most important mechanical performance index described as objective functions and the other requirements on the mechanical performance indices described as constraint functions. To locate the optimal solution of objective and feasibility robustness, a new concept of interval violation vector and its calculation formulae corresponding to different constraint functions are proposed. The math?ematical formulae for calculating the feasibility and objective robustness indices and the robustness?based preferential guidelines are proposed for directly ranking various design vectors, which is realized by an algorithm integrating Kriging and nested genetic algorithm. The validity of the proposed method and its superiority to present interval optimization approaches are demonstrated by a numerical example. The robust optimization of the upper beam in a high?speed press with interval material properties demonstrated the applicability and effectiveness of the proposed method in engineering.

Flow stress and tribology size effects in scaled down cylinder compression

Microforming is an effective method to manufacture small metal parts.However,macro forming can not be transferred to microforming directly because of size effects.Flow stress and tribology size effects were studied.Scaled down copper T2 cylinder compression was carried out with the lubrication of castor oil and without lubrication.The results show that the flow stress decreases with decreasing the initial specimen diameter in both lubrication conditions,and the flow stress decreases by 30 MPa with the initial specimen diameter decreasing from 8 mm to 1 mm.The friction factor increases obviously with decreasing the initial specimen diameter in the case of lubricating with castor oil,and the friction factor increases by 0.11 with the initial specimen diameter decreasing from 8 mm to 1 mm.However,the tribology size effect is not found in the case without lubrication.The reasons of the flow stress and tribology size effects were also discussed.

Effect of die cavity dimension on micro U deep drawing behaviour with T2 foil

The strips U deep drawing experiments were carried out to study the effect of die cavity dimension with an extension machine manufactured by SANS company. The effects of parameters were analyzed in deep drawing process under different experimental conditions, such as punch load, reduction of thickness, angle of U part and surface quality. The experiment results show that the punch load increases with the decrease of female radius, and larger blank holder force enlarges the range of increasing. With the increasing of blank holder force, the angle of U part increases, and the reduction of foil thickness at the corner becomes larger. Obvious scratch and accumulation at the die cavity corner were observed by SEM. The investigation results indicate that micro U deep drawing of foil is affected by micro die cavity dimension.

Microwave Induced Ethanol Bath Bonding for PMMA Microfluidic Device

High bonding strength,low deformation and convenient procedure are all very important aspects in the microfluidic device fabrication process. In this paper,an improved microwave induced bonding technology is proposed to fabricate microfluidic device based on methyl methacrylate( PMMA). This method employs pure ethanol as the bonding assisted solvent. The ethanol not only acts as the microwave absorbing material,but also works as the organic solvent in bath. The presented research work has shown that the bonding process can be completed in less than 45 s. Furthermore,the convenient bonding only applies microwave oven,beakers and binder clips. Then,we discuss effects of microwave power,bonding time on bonding strength and deformation of microstructures on PMMA microfluidic device. Finally,a 4 layers micro-mixer has been fabricated using the proposed bonding technique which includes 15 trapezoid micro-channels,9 T-type mix units and an X-type mix unit. Experimental results show that the proposed bonding method have some advantages compared with several traditional bonding technologies,such as hot pressing bonding,ultrasonic bonding and solvent assisted bonding methods in respect of bonding strength,deformation and bonding process. The presented work would be helpful for low coat mass production of multilayer polymer microfluidic devices in lab.

Multiscale simulation and nanoindentation experimental study of initial plasticity of Fe single crystal

It is very important to understand the initial plastic behavior of metals at microscale.In order to research the initial plasticity of body centered cubic metals in micro-/nano-scale,the multiscale simulation method and experimental study were used to study the nanoindentation process of Fe single crystal.The results show that the first abruption of load-displacement curve in nanoindentation of Fe single crystal can be attributed to the first transition from elastic to plastic deformation characterized by the dislocation emission.

A Fully Differential Interface Circuit of Closed-loop Accelerometer with Force Feedback Linearization

In this paper,a fifth-order fully differential interface circuit( IC) is presented to improve the noise performance for micromechanical sigma-delta( Σ-Δ) accelerometer. A lead compensator is adopted to ensure the stability of the closed-loop high-order system. A low noise capacitance detection circuit is described with a correlated-double-sampling( CDS) technique to decrease 1 /f noise and offset of the operational amplifier. This paper also proposes a self-test technique for the interface circuit to test the harmonic distortion. An electrostatic force feedback linearization circuit is presented to reduce the harmonic distortion resulting in larger dynamic range( DR). The layout of the IC is implemented in a standard 0. 6 μm CMOS technology and operates at a sampling frequency of 250 kHz. The interface consumes 20 mW from a 5 V supply. The post-simulation results indicate that the noise floor of the digital accelerometer is about- 140 dBV /Hz1 /2at low frequency. The sensitivity is 2. 5 V /g and the nonlinearity is 0. 11%. The self-test function is achieved with 98. 2 dB thirdorder harmonic distortion detection based on the electrostatic force feedback linearization.

Noise analysis and characterization of a full differential CMOS interface circuit for capacitive closed-loop micro-accelerometer

To achieve a high precision capacitive closed-loop micro-accelerometer,a full differential CMOS based on switched-capacitor circuit was presented in this paper as the sensor interface circuit.This circuit consists of a balance-bridge module,a charge sensitive amplifier,a correlated-double-sampling module,and a logic timing control module.A special two-path feedback circuit configuration was given to improve the system linearity.The quantitative analysis of error voltage and noise shows that there is tradeoff around circuit's noise,speed and accuracy.A detailed design method was given for this tradeoff.The noise performance optimized circuit has a noise root spectral density of 1.0 μV/Hz,equivalent to rms noise root spectral density of 1.63 μg/Hz.Therefore,the sensor's Brown noise becomes the main noise source in this design.This circuit is designed with 0.5 μm n-well CMOS process.Under a ±5 V supply,the Hspice simulation shows that the system sensitivity achieves 0.616 V/g,the system offset is as low as 1.456 mV,the non-linearity is below 0.03%,and the system linear range achieves ±5 g.

Enhanced proton irradiation resistance in Cs-doped CH_(3)NH_(3)PbI_(3) films and solar cells

Mixed-cation perovskite solar cells have attracted tremendous attention in space applications due to their excellent power conversion efficiency (PCE) and stability to light and heat.Although the evolution of photovoltaic performance in different space environments has been investigated,the role of inorganic cesium ions (Cs^(+)) in the enhancement of irradiation resistance needs to be further clarified.Herein,the structure and performance evolution of Cs-doped CH_(3)NH_(3)PbI_(3)(MAPbI_(3)) films and planar heterojunction devices under proton irradiation up to 1×10^(16)p cm^(-2) were studied.5%of Cs^(+) doping can increase the cohesive energy of MAPbI_(3)and effectively alleviate the lattice strain induced by proton irradiation,thereby enhancing the crystallinity and stability of films.The bandgap changes of irradiated Cs_(0.05)MA_(0.95)PbI_(3) films under the identical fluence were only one third of that of MAPbI_(3) films.Upon irradiation under the fluence of 1×10^(14)p cm^(-2),the density of trap states in the undoped and 5%Cs-doped films increased by 71%and 9%,respectively,and the average PCE of 20 corresponding devices decreased only by 12%and 9%,respectively.This proves that the replacement of organic methylamine ion with inorganic cesium ion contributes to the improvement of MAPbI_(3) resistance to proton irradiation,thus confirming the application prospects of mixed-cation or all-inorganic perovskite solar cells in spacecraft.

A Novel Full Differential Feedforward Fourth-Order Bandpass Sigma-Delta Modulator

In this paper,in order to reduce power consumption and chip area,as well as to improve the performance of the bandpass sigma-delta modulator,a novel full differential feedforward fourth-order bandpass sigma-delta modulator was proposed. It used a resonator based on Salo architecture,which employed doublesampling and double-delay technique. The results show that the proposed modulator can achieve lower power consumption and a lower capacitive load than the conventional bandpass modulators on the platform of Simulink. The circuit is implemented with TSMC0. 18 μm CMOS process and operates at a sampling frequency of 20 MHz, 80 MHz effective sampling frequency. Furthermore,it consumes 21. 2 mW from a 1. 8 V supply. The simulated peak signal-to-noise ratio( SNR) is 85. 9 dB and the dynamic range( DR) is 91 dB with 200 kHz bandwidth.