3D Microcavities Research Articles

Polarization‐Sensitive Optoelectronic Synapse Based on 3D Graphene/MoS2 Heterostructure

AbstractOptoelectronic synapses with information sensing, processing, and memory function are promoting the development of artificial visual perception systems. However, optoelectronic synapses' relatively inferior optoelectronic performance impedes their application in complex neuromorphic computing. Herein, optoelectronic synapses based on 3D graphene/molybdenum disulfide (MoS2) heterostructure field‐effect transistors are developed by using the double stress layer self‐rolled‐up method. The graphene, with excellent electrical properties, enhances the carrier transport capacity of the device. The unique continuous photoconductivity of MoS2 is suitable for simulating various synaptic nerve morphological functions. Meanwhile, the 3D resonant microcavity is added to enhance the optical field and make the device polarization sensitive, which reveals more intangible features of objects. The device demonstrates room‐temperature photodetection at ultraviolet, visible, near‐infrared, and mid‐infrared regions, with photoresponsivity up to 105 A W−1 at 590 nm. Furthermore, multiple synaptic neuromorphic functions, such as inhibitory postsynaptic current, paired‐pulse facilitation, short‐term depression, and long‐term depression, are successfully emulated. Here a new concept is provided for designing high‐performance optoelectronic synapses with polarization sensitivity and excellent potential in artificial intelligence is shown.

High Sensitivity Multiple Microcavity Enhanced 3-D Printed Micro-Stud Array Ultrafast Response Detector at 6G Frequency

The next generation of communication 6G technology in the terahertz band is crucial for the development of the future high-speed information society. How to achieve a highly sensitive response to low power density terahertz signals at room temperature has been one of the frontier research hot issues within this field. In addition, the reproducible line height of the device and its availability for mass production are also urgent issues to be addressed. Here, We have proposed a 6G detector based on combining the advantages of sub-wavelength micro-structures, 3D micro-cavity, and Weyl-semimetallic films. The localized surface plasmon (LSP) effect by the micro-stud array is used for the enhancement of the light-matter interaction. Also, the 3D structure leads to a micro-cavity allowing for a near enhancement of the interaction on a small scale. Furthermore, the 0-band gap of the Weyl-semimetal and the enhanced response to low-energy photon displacement currents near makes the Weyl-semimetal more suitable for detecting terahertz waves. In addition, the use of projection micro stereolithography 3D print technology combined with magnetron sputtering of thin films makes this terahertz detection technology solution reproducible, low cost, simple processing, and promising for industrial production, contributing to the development and diffusion of 6G technology.

Three-dimensional surface-enhanced Raman scattering substrates constructed by integrating template-assisted electrodeposition and post-growth of silver nanoparticles

Three-dimensional (3D) plasmonic nano-arrays can provide high surface-enhanced Raman scattering (SERS) sensitivity, good spectral uniformity and excellent reproducibility. However, it is still a challenge to develop a simple and efficient method for fabrication of 3D plasmonic nano-arrays with high SERS performance. Here we report a facile approach to construct ordered arrays of silver (Ag) nanoparticles-assembled spherical micro-cavities using polystyrene (PS) sphere template-assisted electrodeposition and post-growth. The electrodeposited small Ag nanoparticles grow into bigger stable nanoparticles during the post-growth process, which could significantly improve the SERS sensitivity. The Ag nanoparticles-assembled 3D micro-cavity array provides much more hotspots in the excitation laser beam-covered volume than the two-dimensional counterpart. The relative standard deviation (RSD) of 612 cm−1 peak of rhodamine 6G (R6G) was calculated to be 8%, and the RSD of the characteristic peak taken from substrates of different batches was less than 10%. The detectable lower concentration as low as 1 fM was achieved for an aqueous solution of R6G. Such SERS substrate also showed high sensitivity to thiram (fungicide) and paraquat (herbicide) in water with limits of detection of 0.067 nM and 2.5 nM respectively. Furthermore, it also demonstrated that SERS detection of pesticide residues on fruits can be realized, showing a potential application in rapid monitoring food safety.

Micro electrical discharge milling of a monocrystalline silicon complex micro-cavity

ABSTRACT This paper develops a new method to restrain the fracture of monocrystalline silicon machining in EDM (Electrical discharge machining) through controlling the topography of single discharge crater. By this method, the complex 3D micro-cavity can be machined without obvious fracture. The fracture of monocrystalline silicon in EDM was revealed according to the EDM pits and the machining debris, then it is inferred that there are two ways to cause fractures, one is the breakages at the edge of the effective-removing crater, and the other way is the deformation accumulation caused by the superposition of the ineffective-removing crater. Then, it was found that if the morphology of single discharge crater can be controlled, the less fracture can be guaranteed during the manufacturing. Using narrow pulse width discharge, plenty of experimental tests were carried out focused on carters and surface of monocrystalline silicon with different machining parameters, with the assistance of characterization and analysis. Using these new results, the complex 3D structure is machined by layered compensation strategy and step-by-step milling strategy. It is found from the as-machined complex 3D cavity that it has no obvious defects at the edges, and the fracture is controlled.

Constructing Zn-P charge transfer bridge over ZnFe2O4-black phosphorus 3D microcavity structure: Efficient photocatalyst design in visible-near-infrared region

Black phosphorus (BP) is one of the most promising visible-near-infrared light-driven photocatalysts with favorite photoelectric properties and unique tunable direct band gap. Nevertheless, the further development of BP is hindered by the fast carrier recombination rate and high Gibbs free energy. Herein, an innovative strategy is developed for the controllable construction of Zn-P bonds induced zinc ferrite/black phosphorus (ZnFe2O4-BP) three dimensions (3D) microcavity structure. The Zn-P bonds serve as an efficient channel to optimize the carrier transport and Gibbs free energy of BP simultaneously. Besides, the unique 3D core-shell microcavity structure maintains the multiple reflections of sunlight inside the catalysts, which greatly improves the sunlight utilization upon photocatalysis. An optimized photocatalytic hydrogen production rate of 560 µmol h-1g-1 under near-infrared light (>820 nm) is achieved. A possible photocatalytic mechanism is proposed based on a series of experimental characterizations and theoretical calculations, this work provides a new sight to design high-quantity BP-based full-spectrum photocatalysts for solar energy conversion.

Experimental Study on the Fabrication of 3D Microelectrodes for Electrochemical Micromachining

The use of three-dimensional (3D) microelectrodes to machine micro-cavities in electrochemical micromachining (ECMM) can greatly improve processing efficiency. The 3D microelectrodes that are difficult to fabricate by traditional methods can be prepared by laminated object manufacturing and vacuum thermal diffusion bonding (VTDB). However, the VTDB process is very time-consuming, resulting in a long preparation cycle. To solve this problem, the present study proposed an approach combining wire electrochemical micromachining (WECMM) with micro-electric resistance slip welding to fabricate 3D microelectrodes. The machining surface quality and dimensional accuracy of 2D microstructures under different WECMM conditions were investigated. Moreover, the effects of the welding parameters on the bonding quality were studied. The experimental results show that with a 6 V machining voltage, 1.33 μm/s feed rate, and 30 μm movement amplitude for the wire electrode, the machining gap was approximately 10 μm and the machining surface was flat when using a tungsten wire 8 μm in diameter to machine 30 μm thick #304 stainless steel foils by WECMM. Under a 0.3 V welding voltage, 0.2 MPa welding pressure, 20 ms welding time and 160 times slip welding discharge, the error in 3D microelectrodes in lamination direction was smaller than 3 μm. Based on the proposed approach, two typical 3D microelectrodes were successfully fabricated and subsequently applied in ECMM to machine 3D micro-cavities in nickel plates.

Micro-EDM and micro-USM combined milling of ZrB2-SiC-graphite composite for 3D micro-cavities

The ZrB2-SiC-graphite composite is one of the most promising ceramics, which show significant potential in manufacturing parts served in ultra-high temperature. Micro-electrical discharge machining (micro-EDM) is an effective method in machining this conductive hard ceramic. However, the recast layer characterized by craters and micro-cracks is formed on the machined surface, resulting in poor surface quality. In this paper, micro-EDM and micro-ultrasonic machining (micro-USM) combined milling is proposed for manufacturing 3D micro-cavities in the ZrB2-SiC-graphite composite. The micro-cavity is firstly machined by micro-EDM milling, followed by micro-USM finish milling to remove the recast layer in the same system without changing the micro-tool. The machining performances are investigated with consideration of the surface topography and finishing depth. It is found that the more recast layer is removed when a higher ultrasonic amplitude, larger abrasive grain size, and lower tool feedrate are employed. Based on the preliminary experiments, the proper machining parameters are obtained and applied to the fabrication of micro-cavities. The machining results show that the surface quality is improved with the low surface roughness and absence of defect layer. Meanwhile, the high machining accuracy in the depth direction and processing efficiency are achieved. It is verified that the micro-EDM and micro-USM combined milling process is feasible for fabricating 3D micro-cavities in the ZrB2-SiC-graphite composite.

Elimination of 3D micro-electrode’s step effect and applying it in micro-EDM

3D micro-electrode is fitted out by multilayer 2D micro-structures, so the steps inevitably occur in the 3D micro-electrode. When the 3D micro-electrode is used in micro-EDM, steps are replicated onto the surface of the 3D micro-structure, which have an adverse impact on the shape precision of the 3D micro-structure. Focus on this problem, this paper proposed to eliminate the steps of the 3D micro-electrode based on skin effect and point discharge. Then, the paper detailedly researched the impact of machining voltage, machining depth, and processing numbers on the elimination of 3D micro-electrode’s step effect and its micro-EDM results. In order to verify the feasibility of this method, the paper designed a 3D micro-cavity structure which has slopes in the X and Y directions with slope angle of 45°. Finally, under workpiece of 304# stainless steel, pulse width of 800 ns, pulse interval of 4200 ns, machining voltage of 110 V, and machining depth of 650 μm (250 μm larger than the design depth), the step effect of the 3D micro-electrode was effectively eliminated and its micro-EDM result has a dimension error within 7 μm and slope error within 3°.

Vibration-assisted micro-ECM combined with polishing to machine 3D microcavities by using an electrolyte with suspended B4C particles

Three-dimensional (3D) microcavities can be machined by micro-electrochemical machining (micro-ECM) using a 3D microelectrode. However, with increasing machining depths, it becomes challenging to renew electrolyte and remove the electrolytic products from the machining gap. Therefore, 3D microcavities are usually shallow and the machined surfaces are of poor quality. To address these problems, this paper proposed performing 3D microelectrode vibration-assisted micro-ECM in combination with polishing to machine 3D microcavities by using an electrolyte containing suspended B4C particles. First, a 3D microelectrode with rectangular holes on both of its undersurfaces was fabricated by means of bending-and-avoiding mode wire electrical discharge machining in combination with vacuum thermal diffusion bonding. Second, the prefabricated microelectrode was applied in vibration-assisted micro-ECM to machine deep 3D microcavities using an electrolyte containing suspended B4C particles. Thereafter, the machined surfaces of the deep 3D microcavities were polished to improve the surface quality. Furthermore, the effects of vibration amplitude and frequency, polishing time, and B4C particle concentration on the microcavity surface quality were investigated in detail. The experimental results indicate that the electrochemical reaction attachments on the microelectrode surface were removed by polishing of the particles during processing, ensuring satisfactory processability of the microelectrode, as well as a highly efficient and stable micro-ECM process. Moreover, when the vibration amplitude was set to 10 μm, vibration frequency to 30 Hz, polishing time to 30 min, and B4C particle concentration to 5 g/L for the 300 μm deep microcavity machined by the proposed method, the microcavity bottom surface roughness was minimized (Ra = 0.223 ± 0.021 μm) and the sidewall roughness was improved. Finally, based on the proposed method and optimized polishing parameters, 3D microcavities of more than 800 μm deep with rectangular and semi-cylindrical islands were obtained.

Localized high-Q modes in conical microcavities

We carry out three-dimensional (3D) numerical simulation on a conical microcavity with a half-angle of 11 degree, where there exists high-Q modes by introducing a thin high refractive index film on a conical surface. Our study reveals that, rather than the surface profile of the microcavity, the effective radius plays crucial role in whether the cavity may support localized modes. Specifically, the change of high refractive index film thickness creates an additional angular momentum barrier, so that the conical microcavity may sustain localized high-Q modes. Our study offers a new degree of freedom to control the properties of 3D microcavities, which is useful for microlaser or sensor applications.

Three-Dimensional Microcavity Array Electrodes for High-Capacitance All-Solid-State Flexible Microsupercapacitors.

We report novel three-dimensional (3D) microcavity array electrodes for high-capacitance all-solid-state microsupercapactiors. The microcavity arrays are formed in a polymer substrate via a plasma-assisted reactive ion etching (RIE) process and provide extra sidewall surface areas on which the active materials are grown in the form of nanofibers. This 3D structure leads to an increase in the areal capacitance by a factor of 2.56 for a 15-μm-deep cavity etching, agreeing well with the prediction. The fabricated microsupercapactiors exhibit a maximum areal capacitance of 65.1 mF cm(-2) (a volumetric capacitance of 93.0 F cm(-3)) and an energy density of 0.011 mWh cm(-2) (a volumetric energy density of 16.4 mWh cm(-3)) which substantially surpass previously reported values for all-solid-state flexible microsupercapacitors. The devices show good electrochemical stability under extended voltammetry cycles and bending cycles. It is demonstrated that they can sustain a radio frequency (rf) microsystem in a temporary absence of a power supply. These results suggest the potential utility of our 3D microsupercapactiors as miniaturized power sources in wearable and implantable medical devices.

Fabrication of 3D Microelectrodes by Combining Wire Electrochemical Micromachining and Micro-electric Resistance Slip Welding

Micromachining, using microelectrodes, is a key technology for manufacturing three-dimensional (3D) microstructures. However, 3D microelectrodes are difficult to fabricate, 3D microstructures are fabricated mainly using simple-shaped tools microelectrode with a layer by layer scanning strategy. Based on micro double-staged laminated object manufacture (micro-DLOM), 3D microelectrodes can be obtained by combining closed loop middle-speed wire (Ø100∼180μm) electrical discharge machining (WEDM) and thermal diffusion welding. But it is difficult to obtain 3D microelectrodes with an edge length of end face less than 100μm, though by low speed wire electrical discharge machining (LS-WEDM) or femtosecond laser cutting, the dimension of 3D microelectrodes can be further miniaturized, they are both very expensive. To solve the problem above, this paper proposed a low-cost method combining wire (Ø8μm) electrochemical micromachining (WECMM) and micro-electric resistance slip welding to fabricate 3D microelectrodes. Firstly, with WECMM combining low frequency micro-vibration and travelling of wire electrode, 30-μm-thick 0Cr18Ni9 stainless steel foils were cut to obtain multi-layer two-dimensional (2D) microstructures. Secondly, through micro-electric resistance slip welding, the multi-layer 2D microstructures were laminated and bonded to fit 3D microelectrodes. Moreover, this paper investigated the influences of applied voltage, feed speed, wire electrode travelling and micro-vibration on machining surface quality and dimensional accuracy. Based on the studies above, two typical 3D microelectrodes with a dimension less than 100μm were successfully fabricated. Finally, applying the fabricated 3D microelectrodes to micro-electrochemical machining (micro-ECM), 3D micro-cavities were obtained.

Research on the Equivalent Plane Machining with Fix-length Compensation Method in Micro-EDM

Micro-EDM milling is an effective machining process for three-dimension (3D) micro-cavity of high hardness materials. Because of the sharp wear of the electrode, fix-length compensation method is proposed, thus results in a cone-shaped electrode. This compensation method can produce a slot with stable depth and conic cross-section. Because of layer by layer strategy in micro structure machining, the challenge for fix-length compensation method is to keep the whole process repeating continuously. This paper gives a double layers’ machining strategy in order to maintain the repeated machining for layer units. A concept of equivalent plane is proposed in order to construct a curved surface that can use fix-length compensation method. Then a simplified triangle model is presented in order to get corresponding algorithm for the compensation length of the second slot. Experiment results showed that the error of the compensation length was within 2μm. A simulation about the influence of the curved surface's fluctuation on the profile of the machined slot bottom of next layer was performed with Matlab. Simulation results showed that the influence was limited. An experiment of two layers’ machining with proposed strategy and algorithm was conducted. The evenness of the machined surface with depth of 66μm was within 4μm. Therefore, fix-length compensation method can be used to machining 3D cavity.

Laminated fitting fabrication of Cu–Sn composite 3D microelectrodes and elimination of ridges on the machined surface of 3D micro-cavities

Three-dimensional (3D) microelectrodes fitted by multi-layer Cu foil two-dimensional (2D) microstructures can be used in micro-electrical discharge machining (micro-EDM) to machine 3D micro-cavities. Due to the poor diffusion bonding between Cu foil 2D microstructures, the surfaces of micro-cavities often have ridges, which reduce the quality of the machined surface. To solve this problem, the paper proposed a method of using a Sn film as solder between Cu foils to fabricate Cu–Sn composite 3D microelectrodes. First, 50-μm-thick Cu foils coated with Sn on both sides were cut by femtosecond laser to obtain multi-layer 2D microstructures. Second, through transient liquid phase (TLP) bonding, the multi-layer 2D microstructures were laminated and bonded to fit composite 3D microelectrodes. In addition, the paper investigated the influence of the solder layer thickness, bonding time and temperature on the micro-EDM performance of composite 3D microelectrodes. The experimental results show that the composite 3D microelectrode has good micro-EDM performance when the solder layer thickness is 1μm, the bonding temperature is 800°C and the bonding time is 15h. Finally, applying this composite 3D microelectrode in micro-EDM, 3D micro-cavities were processed, and the processing results demonstrated that the ridges on the 3D micro-cavity surfaces were completely eliminated, thereby improving the quality of the machined surface.

Laminated fabrication of 3D queue micro-electrode and its application in micro-EDM

3D micro-electrode used in micro electrical discharge machining (micro-EDM) is difficult to be fabricated. Based on laminated object manufacturing (LOM) process, this paper superimposed multilayer 2D micro-structures together to fit out 3D micro-electrode and applied it in micro-EDM to process 3D micro-cavity mold. Firstly, 100-μm-thick Cu foils were cut by wire-electrical discharge machining (WEDM) to obtain multilayer 2D micro-structures, and then these 2D micro-structures were connected together to fit out 3D micro-electrode through vacuum pressure thermal diffusion welding. Secondly, under the effect of 80-V voltage, 0.2-MHz pulse frequency, 800-ns pulse width, and 4200-ns pulse interval, the 3D micro-electrode was applied in micro-EDM and 3D micro-cavity mold with high surface quality was obtained. Thirdly, in order to reduce the adverse impact of electrode wear on machining precision of 3D micro-cavity mold, 3D queue micro-electrode was used to process the same 3D micro-cavity mold, in which the first electrode is for rough machining and the others for fine machining. Finally, based on the above studies, two kinds of 3D queue micro-electrodes were fabricated, and the 3D micro-cavity molds with surface roughness Ra = 0.48 μm were obtained through micro-EDM. Compared with the scanning 3D micro-EDM process, the 3D micro-cavity mold can be obtained through up and down reciprocating method of the 3D queue micro-electrode, featuring simple machining process and high efficiency.

Algorithms and machining experiments to reduce depth errors in servo scanning 3D micro EDM

Abstract In servo-scanning 3D micro electro discharge machining (SS-3D MEDM), the depth errors of 3D micro cavities are accumulated layer by layer due to the contour scanning process with keeping discharge gap for compensating axial electrode wear in real time. In this research, the errors’ causes were analyzed, and then a layer depth constrained algorithm (LDCA) and an S-curve accelerating algorithm (SCAA) were proposed to reduce the depth errors. By LDCA, over-cutting errors can be avoided by controlling a tool-electrode feed maximum at every scanning spot. As a supplementary algorithm for LDCA, SCAA can compensate insufficient-machining errors at start and end of scanning paths. Implementation process and control strategy of the algorithms were also described. The purpose of this research is to efficiently machine complex 3D micro-cavities with high accuracies of shape and surface. By use of computer-aided manufacturing software of Pro/Engineer to plan complex 3D scanning paths, machining experiments were carried out to verify the proposed algorithms. The experimental results show: Typical 3D micro cavities 4 μm 3 /s with tool electrode of ∅ 80 μm and its rotational speed of 1000 r/min. In addition, the 3D micro cavities designed on unknown edge or hollow workpieces can be successfully formed.

Three-dimensional confinement of polaritons in ZnO microcylinder

High quality ZnO microcylinders (MCDs), which naturally form three-dimensional (3D) optical microcavities, were synthesized by a simple vapor transportation deposition method. The exciton-polariton effects in these 3D microcavities were investigated through the angle-resolved micro-photoluminescence (µ-PL) mappings. By using the coupled oscillator model, the 3D confinement effect of polaritons, i.e., two-dimensional (2D) whispering gallery (WG) type confinement in the cross section of the ZnO MCD, overlapping with the one-dimensional (1D) Fabry-Pérot (F-P) type confinement along the c-axis, was well interpreted.

Wear-resist Electrodes for Micro-EDM

This article proposes a new type of electrode for micro-electro-discharge machining (micro-EDM), which can produce ultra fine micro components from various kinds of materials including those that cannot be processed by the silicon or the Lithographie Galvanoformung Abformung (LIGA) processings. This electrode is made by way of the electrodeposition process on the basis of the difference between the discharging performance of the electrodeposited coating and that of the matrix to ensure uniform wear of electrode bottom faces. With this electrode, micro-holes on ANK80 steel can be successfully manufactured in a short period of time. Compared to the traditional electrodes, Cu-ZrB2 composite coating electrodes display better wear resistance on the same experimental conditions. The results disclose the prospects for this electrode to be used in producing micro components of high-aspect-ratio and 3D micro-cavities.

Progress in the control of the light–matter interaction in semiconductors

We discuss the influence of the relative dimensionalities of electron and photon states on the interaction of light and matter in semiconductors. A variety of effects are to be expected, such as the Purcell effect or the strong light–matter coupling, based on the nature of the electronic excitations (independent electron or excitons) and on the nature (planar or 3D microcavities and photonic crystals) and damping of the photonic states. Applications in the field of light-emitting diodes (LEDs) are detailed.

Study of 3D Micro-Ultrasonic Machining

Many manufacturing processes, such as lithography, etching, laser, electrical discharge machining (EDM), and electrochemical machining (ECM), are being applied to produce the meso- and microscale parts and products. Materials such as silicon, glass, quartz crystal, and ceramics are being increasingly used in microelectromechanical system (MEMS) devices. Ultrasonic machining (USM) offers an attractive alternative to machine some of the hard and brittle materials. However, the tool wear in micro-ultrasonic machining adversely affects the machining accuracy. Therefore, it is necessary to account for and to compensate the tool wear during machining. This paper reports the feasibility of applying the uniform wear method developed for micro electrical discharge machining and its integration with CAD/CAM to microultrasonic vibration process for generating accurate three-dimensional (3D) microcavities. Experimental results show that the tool shape remains unchanged and the tool wear has been compensated.