Microstructure Array Research Articles

High-Throughput Two-Photon 3D Printing Enabled by Holographic Multi-Foci High-Speed Scanning.

The emerging two-photon polymerization (TPP) technique enables high-resolution printing of complex 3D structures, revolutionizing micro/nano additive manufacturing. Various fast scanning and parallel processing strategies have been proposed to promote its efficiency. However, obtaining large numbers of uniform focal spots for parallel high-speed scanning remains challenging, which hampers the realization of higher throughput. We report a TPP printing platform that combines galvanometric mirrors and liquid crystal on silicon spatial light modulator (LCoS-SLM). By setting the target light field at LCoS-SLM's diffraction center, sufficient energy is acquired to support simultaneous polymerization of over 400 foci. With fast scanning, the maximum printing speed achieves 1.49 × 108 voxels s-1, surpassing the existing scanning-based TPP methods while maintaining high printing resolution and flexibility. To demonstrate the processing capability, functional 3D microstructure arrays are rapidly fabricated and applied in micro-optics and micro-object manipulation. Our method may expand the prospects of TPP in large-scale micro/nanomanufacturing.

Optical Microlithography of Perovskite Quantum Dots/Organic Semiconductor Heterojunctions for Neuromorphic Photosensors

AbstractHeterojunctions of perovskite quantum dots (QDs) and organic semiconductors (OSCs) can synergistically leverage the unique optoelectronic properties of different functional components to fabricate advanced optoelectronic devices, such as neuromorphic photosensors, by low‐cost solution processes. However, a long‐lasting challenge remains in micropatterning high‐density perovskite QDs/polymer OSCs heterojunction array with high yield and reliability due to the fragility of functional layers to organic solvents. High‐density and micro‐structure patterned organic neuromorphic photosensor arrays based on OSCs and QDs are thus rarely reported. Here, an effective cross‐linking microlithography strategy is reported to fabricate perovskite QDs/OSCs microstructure arrays. The fabricated CsPbBr3 QDs/(poly(2,5‐(2‐octyldodecyl)−3,6‐diketopyrrolopyrrole‐alt‐5,5‐(2,5‐di(thien‐2‐yl) thieno [3,2‐b] thiophene) (DPPDTT) planer heterojunctions phototransistor array presents minor device‐to‐device variation, high density (6500 devices cm−2), and high yield (almost 100%). The device array exhibits impressive merits as a neuromorphic photosensor, including a photosensitivity of 3.02 × 107, a responsivity up to 1.92 × 104 A W−1, a detectivity exceeding 1014 Jones, and a persistent photoconductivity. Moreover, an energy consumption as low as 27.9 aJ is achieved at an operating voltage of −0.0001 V. The potential application of the heterojunction neuromorphic photosensor array in motion perception is demonstrated in conjunction with a neural network.

Superhydrophobic NiTi shape memory alloy arrays with switchable controlled anisotropic droplet sliding

Smart microstructured surfaces have attracted extensive attention in recent years, because the surface microstructure morphology can be tuned using an external field to change the wettability. Inspired by the surface microstructures of butterfly wings, a tilted array microstructure was fabricated on the surface of NiTi shape memory alloy (NiTi-SMA) using wire electrical discharge machining (WEDM). The modified surface with fluorosilane showed superhydrophobicity and anisotropic droplet sliding. As the shape of the tilted microarray structure could be repeatedly switched between the original shape and deformation under the action of force and heat, the contact angle of the surface was repeatedly switched between 155.9° ± 0.2° and 150.3° ± 0.3°, and the anisotropic sliding angle of the surface was repeatedly switched between 7.9° ± 1.6° and 22.9° ± 1.3°, and 19.6° ± 0.6° and 53.4° ± 2.9°. The range of switchable anisotropic sliding could be adjusted by changing the microstructure spacing L. In addition, the surface of the tilted microarray structure showed a directional water transport ability under the action of vibrations, and the directional transmission of water droplets could be selectively controlled by changing the morphology of the surface microstructure. Therefore, a smart surface with switchable wettability was realized on the NiTi-SMA surface, providing a new method to realize the smart control of droplets on smart microstructured surfaces.

A magnetically controlled microstructured surface for three-dimensional droplet manipulation

The smart manipulation of droplets has received widespread attention due to its potential applications in many fields. However, it is still challenging to realize robust multidimensional, versatile liquid manipulation using magnetically responsive surfaces. Here, a magnetically controlled surface with a dense array of cone-shaped microstructures is developed by the spray self-assembly method using soft nontoxic materials. The effects of the spray volume and material concentrations on the surface morphology and wettability are systematically investigated. The wettability and adhesion properties of the developed surface can be reversibly switched in the presence of an on/off magnetic field. In situ observation indicated that the driving force acted on the droplet is derived from localized deformation of the microstructures. Moreover, theoretical models of droplet manipulation are proposed to demonstrate the underlying mechanism. Under the actuation of the moving magnetic field, the surface can transport droplets of 1–14 μl in the vertical direction, and the modified superhydrophobic surface can transport droplets of 3–30 μl in the horizontal direction and achieve against-gravity droplet climbing with a volume of 10 μl at a climbing angle of 25°. The environmentally friendly and facilely manufacturable surface presents promising applications in liquid microreactors and the transportation of mixed fluids in biological and chemical research.

Effect of rapid thermal annealing on the surface properties of the microlens arrays machined on monocrystalline silicon

Microstructure arrays, such as microlens arrays, play a significant role in optical systems, biomedical imaging, and telecommunications. However, the machining-induced subsurface defects deteriorate their performance and functionality. To address this issue, this study proposes a rapid thermal annealing method to heal the subsurface defects using different temperatures ranging from 200 °C to 1000 °C in a vacuum. Firstly, the ultra-precision diamond sculpturing process is employed to machine the high-quality microlens array on the monocrystalline silicon surface. Then, the effects of the rapid thermal annealing on the microlens array surface, such as surface roughness and subsurface defect, are comprehensively investigated. Experimental results show that the annealing temperature of >600 °C contributes to the decrease in surface roughness and subsurface defect. Furthermore, to reveal the healing mechanism, a molecular dynamics simulation of rapid thermal annealing is performed by controlling the bulk temperature of machined monocrystalline silicon from 500 K to 1300 K. The simulation results show that recrystallization always occurred on the interface between the amorphous layer and monocrystalline silicon substrate and the healing mechanism should be solid phase epitaxy rather than random nucleation. The research findings would contribute to fabricating the defect-free optical lens in the industry.

Femtosecond Laser Additive Manufacturing of Dual-Responsive Microstructure Arrays on Flexible Substrates (Invited)

Femtosecond Laser Additive Manufacturing of Dual-Responsive Microstructure Arrays on Flexible Substrates (Invited)

Bio-inspired anti-slip and anti-adhesion surface with hemispherical microstructures for wafer handling

Natural climbers leverage strong friction and minimal adhesion for effective multidirectional movement. Toe pads of species like tree frogs display distinct microstructures with protrusions. Such insights have spurred the formulation of a biomimetic microstructure array for wafer handling applications. The curvature of these protrusions was meticulously analyzed to decipher contact mechanics. Moreover, the intricate balance between strong-friction and weak-adhesion mechanisms was evaluated, considering design variations across surface roughness levels. This culminated in a crafted microstructure array optimized for wafer-handling, highlighting the practicality of bioinspired friction enhancement in contemporary engineering domains.

Fabrication of Polymethyl Methacrylate (PMMA) Hydrophilic Surfaces Using Combined Offset-Tool-Servo Flycutting and Hot Embossing Methods.

Polymethyl methacrylate (PMMA) is a material with good surface wettability and has unique and widespread applications in industrial fields. However, fabricating this material in an environmentally friendly way while maintaining its mechanical robustness remains a challenging task. One effective way is through the rational design of microstructure surfaces. The current study fabricated a pyramid microstructure array on a mold surface using offset-tool-servo flycutting, which was then combined with hot embossing to replicate an inverted pyramid microstructure array on a PMMA surface. Firstly, a toolpath compensation algorithm was developed to linearize the arc toolpath and reduce the cost of ultra-precision lathe. Then, the algorithm was further developed to achieve automatic linear toolpath intersection, aiming to ensure the machining accuracy and improve machining efficiency. An experiment testing the linear toolpath intersecting at 90° was conducted, fabricating a pyramid microstructure array with nanoscale roughness on the mold surface. This surface was then employed for replicating an inverted pyramid microstructure array on the PMMA surface using hot embossing. Furthermore, the accuracy of replication was evaluated, and the experimental results demonstrated excellent replication fidelity, exceeding 98%. The microstructural surface of the PMMA exhibited a change in surface wettability. The wettability test showed a water-droplet contact angle reduction from 84.8° ± 0.1° to 56.2° ± 0.1°, demonstrating a good hydrophilic effect. This study introduces a novel, environmentally friendly and high-precision method to fabricate a functional PMMA surface with an inverted pyramid microstructure array. The results of this study also provide strong technical support and theoretical guidance for micro-nanostructure functional surface machining and replicating.

Recent trend in stretchable composite sensors for wearable robot applications

Conventional sensors can detect the various physical and chemical changes that occur during deformation and the states of materials with a high accuracy. However, almost all existing sensors are bulky and stiff, making them highly susceptible to failure when used in large deformation-compliant structures. By contrast, despite their relatively-low resolution and accuracy, the demand for flexible and stretchable sensors used in detecting human motion and vital signs has drastically increased. There are several types of stretchable sensors that contain functional materials such as carbon nanotubes (CNTs). These stretchable sensors have different working principles and applications based on the attributes of their core components. Several electrical signals are used in the measurement of the different physical parameters such as the electrical resistance and capacitance. Triboelectric nanogeneration or voltage signals that can be identified under contact or impact loading conditions are employed in some measurement methods. Additionally, an array of microstructures with a special shape that is directly related to movement and deformation detection, as well as conductive nano-particles that are elaborately aligned along a certain direction for specific sensor applications, are used in the other methods. In this study, a review of the recently-developed high-performance stretchable sensors made from functional materials using new sensing mechanisms for wearable robot applications is provided.

Topology optimization of differentiable microstructures

Recent years have seen a growing interest in topology optimization of functionally graded microstructures, characterized by an array of microstructures with varying volume fractions. However, microstructures optimized at slightly different volume fractions do not necessarily connect well when placed adjacently. Furthermore, optimization is commonly performed on a finite set of volume fractions, limiting the number of microstructure configurations.In this paper, we introduce the concept of differentiable microstructures, which are parameterized microstructures that exhibit continuous variations in both geometry and mechanical properties. To construct such microstructures, we propose a novel formulation for topology optimization. In this approach, a series of 2-dimensional microstructures is represented using a height field, and the objective is to maximize the bulk modulus of the entire series. Through this optimization process, an initial microstructure with a small volume fraction undergoes non-uniform transformations, generating a series of microstructures with progressively increasing volume fractions. Notably, when compared to traditional uniform morphing methods, our proposed optimization approach yields a series of microstructures with bulk moduli that closely approach the theoretical limit.

Molecular dynamics and experiment on ultraviolet-thermal curing abrasive tools for polishing microstructures

To achieve efficient polishing of the microstructure array, a preparation method of the UV-thermal curing abrasive tools with diamond was proposed. The properties of the UV-thermal curing system were studied using molecular dynamics (MD) and experiments. The time, frequency, and pressure parameters of the UV-thermal curing abrasive tool were optimized by polishing the copper plate. MD simulation results show that increasing the temperature to 340 K can improve the blending compatibility. With the increase of the bisphenol A acrylate, the tensile property enhances from 16.38 MPa to 42.98 MPa, and the size shrinkage and mass loss weaken. The addition of diamond particles improves the anti-friction coefficient. Finally, the microstructure is polished twice under the polishing pressure of 300 N and 200 N, resulting in a roughness of Ra61nm on the upper surface and Ra105nm on the lower surface. This study can be used to guide the preparation and application of UV-thermal curing abrasive tools for polishing microstructure.

Fast tool servo-based ultra-precision diamond sculpturing for fabricating micro-structured surfaces

To eliminate differences in surface quality and improve the machining flexibility of micro-structured surfaces, this paper proposes a novel ultra-precision diamond sculpturing method based on a triaxial fast tool servo (FTS). In this method, the diamond tool is directly driven by the FTS rather than the ultra-precision lathe to fabricate the micro-structure surfaces. The corresponding toolpath generation algorithm is established to take full advantage of the triaxial FTS. The toolpath is first generated through traditional calculating the shortest tool edge projection on the desired surface and the curve interpolation. The overshoot around the path corner is predicted by simulating the tracking path. Then an extended path is added to the original toolpath to stabilize the overshoot before removing the material. The simulation indicates that the hexagonal lens array can be favorably fabricated by the proposed ultra-precision diamond sculpturing method, and the developed toolpath reduces the form error from 20 to 5nm. The sculpturing experiments of sinusoidal micro-structure array and micro-lens array surfaces suggest that their actual peak-to-valley (PV) form errors are 70nm and 50nm, respectively. The single lens with the surface roughness Sa 3.44nm can be precisely fabricated in 0.1s, demonstrating the high machining efficiency and high machining quality of the proposed ultra-precision diamond sculpturing method.

Carbon Nanotube Network Topology-Enhanced Iontronic Capacitive Pressure Sensor with High Linearity and Ultrahigh Sensitivity.

Flexible capacitive pressure sensors with high sensitivity over a wide pressure range are highly anticipated in the fields of tactile perception and physiological signal monitoring. However, despite the introduction of microstructures on the electrolyte layer, the deformability is still limited due to the size limitation of the microstructures, making it difficult to significantly improve the sensitivity of iontronic capacitive pressure sensors (ICPSs). Here, we propose an innovative strategy of combining carbon nanotubes (CNTs) topological networks and ionic hydrogel micropyramid array microstructures that can significantly enhance the sensitivity of flexible ICPSs for ultrasensitive pressure detection. Compared with other previously reported ICPSs, the sensor developed in this work exhibits an unprecedented sensitivity (Smin > 1050 kPa-1) and a high linear response (R2 > 0.99) in a wide pressure range (0.03-28 kPa) enabled by CNT percolation networks inside the microstructred electrolyte layer. This ultrasensitive and flexible ICPS also can effectively detect pressure from a variety of sources, including sound waves, lightweight objects, and tiny physiological signals, such as pulse rate and heartbeat. This work provides a general strategy to achieve an ICPS with both broader pressure-response range and higher sensitivity, which provides a stable and efficient way for a low-cost, scalable sensor for sensitive tactile sensing in human-computer interaction applications.

In-situ laser-assisted ultraprecision cutting of WC-Co cemented carbide for creating microstructure arrays

Tungsten carbide-cobalt (WC–Co), as a typical cemented carbide, is widely used in the manufacturing field. However, creating high-quality microstructure arrays on its surfaces remains challenging due to its extraordinary hardness. To solve this problem, this study proposes an in-situ laser-assisted ultraprecision cutting (LAUC) process to machine different microstructure arrays on the WC-Co surfaces. Experimental results show two kinds of microstructure arrays, namely bi-sinusoidal microstructure array and micro-lens array, are successfully created on the WC-Co surfaces. The average error of feature sizes is less than 2%, showing the high cutting accuracy of the in-situ LAUC process. The average surface roughness of microstructure arrays is below 6 nm, showing the high cutting quality of the in-situ LAUC process. Furthermore, a comparison experiment with the traditional ultraprecision diamond turning process shows the proposed in-situ LAUC process improves the machinability of the WC-Co and decreases the tool wear, further demonstrating its superiority. Therefore, this work provides a new and effective method of creating microstructure arrays on WC-Co surfaces, which greatly enhances the machining quality and extends tool life.

Machinability improvement of titanium alloys in ultra-precision machining with micro-structured surface

Titanium alloys get wider applications in different areas due to its excellent mechanical properties. However, poor thermal conductivity and low elastic module of titanium alloy induce high tool wear and make it being one of hard-to-machine materials; especially the segmented chip formation accelerates the diamond tool wear in ultra-precision machining (UPM) of precision parts. This study applies micro-structured surface to improve machinability of titanium alloys in UPM by reducing the chip segmentation induced cutting forces fluctuations. Finite element (FE) model is built to study chip formation mechanism and characterize geometries of segmented chips in orthogonal diamond cutting of Ti6Al4V alloy with the aims at the design of micro-structures array. Turning experiments are conducted to compare cutting force, surface roughness, and tool wear for diamond turning of Ti6Al4V alloy on smooth surface and micro-structured surface. The results show that the FE simulated saw chips agree well with the measured ones. Moreover, the micro-structured surface helps to decrease cutting force, reduce diamond tool wear, and improve surface quality for UPM of titanium alloy. Especially, the new method fabricates micro-grooves array on the machined surface in half-finishing process of UPM without the need of any material pre-processing and extra manufacturing equipment, which can also provide the guidance for efficient and sustainable UPM of titanium alloys parts with high surface quality.

High-efficiency localized electrochemical deposition based on ultrafast laser surface modification

Localized electrochemical deposition is a promising technology that allows for additive manufacturing of micro-nano structures in designated areas with high precision and controllability. However, ultra-low printing speed of current localized electrochemical deposition hinders its practical applications, especially the manufacturing of large-scale and complex devices. Here we propose a strategy combining ultrafast laser surface modification with traditional electrochemical deposition to achieve high-efficiency and large-scale printing. With using a focused ultrafast laser, arbitrary large-scale patterned structure can be efficiently scratched on substrate surface. Since the laser scratched region has formed nano-sized surface relief structures which experience local field enhancement when subjected to a voltage, the electrochemical deposition rate in the laser scratched region can be significantly improved, resulting in equivalent localized electrochemical deposition under traditional electrochemical deposition conditions. Such parallel electrochemical deposition can significantly shorten the printing time for large-scale devices. As for the processing of microstructure arrays with a size of 16 mm2, the printing time is compressed within 10 min, among which the electrochemical deposition process is compressed to 10 s. The results demonstrate the potential for improving the efficiency and scalability of localized electrochemical deposition through this combined approach.

Design, fabrication, and characterization of picowell arrays on cyclic olefin copolymer surfaces generated with a 10.5 MeV N4+ ion microbeam

Handling of picoliter-to-nanoliter-scale volumes and objects has increasing importance in life sciences. This is the volume scale of cell extractions and individual living cells. Here, we introduce a method of generating a picoliter-scale device by direct writing of picowell arrays on a ZEONOR™ copolymer surface with high-energy medium-mass ion microbeam. Arrays of various microstructures were written in the sample using a microbeam of 10.5 MeV N4+ ions at various implanted ion fluences. The best array was obtained by implantation of annuli of 10 and 11 μm of inner and outer diameters with a fluence of 7.8 × 1012 ions/cm2.

Anisotropic Tensile and Compressive Strengths of Al-4wt.%Cu Alloy Powder: Part 2—Effect of Dendritic Arm Spacings

This investigation focuses on the effects of the compaction directions (i.e., transversal and longitudinal) and microstructural arrays (inside the powder utilized to constitute the specimens) on the anisotropic strengths. The initial powders are obtained from the as-cast Al-4 wt.% Cu alloys solidified in two distinct cooling rates, i.e., ~0.5 and 2.5 °C/s. The powder particles are compacted by using 300, 400 and 600 MPa and sintered at 540 °C for 1 h. The compressive and tensile strengths are carried out and the anisotropic strengths are determined. It is found that transverse samples exhibit higher UCS (ultimate compressive strength) and UTS (ultimate tensile strength) than the longitudinal samples. It is also found that the powder compacted in the transversal direction and utilizing powder with finer dendritic arm spacing provides better UCS and UTS results. The novelty in the study concerns the fact that is evidenced in the role of the dendrite spacings concatenated with the compaction pressure and direction upon the mechanical behavior. It is concluded that depending on the compaction level intended or demanded mechanical behavior, the planning in the compaction direction is preprogrammed. Since recycled powder particles from conventional machining, drilling and turning can potentially be utilized to constitute parts and components, the environmentally friendly aspects are associated, and hazardous stages in a manufacturing process are substantially reduced or eliminated.

Study of heat transfer performance of miniature heat sink for integrated circuit packaging field

The miniature heat sink is an essential component in integrated circuit packaging, playing a vital role in ensuring the stable and reliable performance of integrated circuits. In this paper, we establish a simulation model of the heat transfer performance of a miniature heat sink with a square columnar array microstructure and study the effect of the dimensional parameters of the miniature heat sink on the heat transfer performance. Then, the mathematical equations between the heat source temperature and the dimensional parameters of the miniature heat sink are obtained based on the response surface method, and the dimensional parameters are optimized. Finally, wire electrical discharge machining (WEDM) was used to prepare miniature heat sinks and to test the heat transfer performance. The experimental results show that both the simulation model and the mathematical equations have high accuracy, and the heat source temperature of the miniature heat sink with column width, column distance, and column height of 364 μm, 331 μm, and 1500 μm, respectively, can be reduced to 101.8 °C, which is 93.5 °C lower than the heat source temperature of 195.3 °C without heat sink, and the temperature reduction reaches 47.9%. The miniature heat sink has a simple manufacturing process, low manufacturing cost, small overall size, and good heat transfer performance, which has a broad application prospect in the field of integrated circuit packaging.

High-performance flexible pressure sensor based on ordered double-level nanopillar array films: Design, development, and modeling

To improve the sensitivity and broaden the range of flexible pressure sensors, we proposed a high-performance flexible pressure sensor based on ordered double-level nanopillar array films. In this work, polypyrrole/multi-walled carbon nanotube/polyurethane (PPy/MWCNT/PU) conductive films with double-level nanopillar array microstructures were prepared by continuously adjusting the oxidation and pore expansion parameters of a porous anodic alumina template (AAO), where the high pillar height was 1243.0 ± 7.0 nm, and the low pillar height was 868.0 ± 4.70 nm. We studied the influence of the structural characteristics of ordered double-level nanopillar array conductive films and a flexible pressure sensor on the sensing performance using finite element simulations, the establishment of sensing mechanism, and sensor performance measurements. The results showed that the pressure was positively correlated with the change rate of strain and the surface microstructure contact area of the ordered double-level nanopillar array films. The sensor sensitivity reached 208.353 kPa−1, and its range was extended by 267%. In addition, the sensor, which could monitor vocalization, drinking pulse and finger movements, could be used in a wide range of applications, including wearable medical monitoring and smart sign language textiles.