Microhole Array Research Articles

High-Performance Triboelectric Nanogenerator with Double-Side Patterned Surfaces Prepared by CO2 Laser for Human Motion Energy Harvesting

The triboelectric nanogenerator (TENG) has demonstrated exceptional efficiency in harvesting diverse forms of mechanical energy and converting it into electrical energy. This technology is particularly valuable for powering low-energy electronic devices and self-powered sensors. Most traditional TENGs use single-sided patterned friction pairs, which restrict their effective contact area and overall performance. Here, we propose a novel TENG that incorporates microwave patterned aluminum (MC-Al) foil and microcone structured polydimethylsiloxane (MC-PDMS). This innovative design utilizes two PMMA molds featuring identical micro-hole arrays ablated by a CO2 laser, making it both cost-effective and easy to fabricate. A novel room imprinting technique has been employed to create the micromorphology of aluminum (Al) foil using the PMMA mold with shallower micro-hole arrays. Compared to TENGs with flat friction layers and single-side-patterned friction layers, the double-side-patterned MW-MC-TENG demonstrates superior output performance due to increased cone deformation and contact area. The open-circuit voltage of the MW-MC-TENG can reach 141 V, while the short-circuit current can attain 71.5 μA, corresponding to a current density of 2.86 µA/cm2. The power density reaches 1.4 mW/cm2 when the resistance is 15 MΩ, and it can charge a 0.1 μF capacitor to 2.01 V in 2.28 s. In addition, the MW-MC-TENG can function as an insole device to harvest walking energy, power 11 LED bulbs, monitor step speed, and power a timer device. Therefore, the MW-MC-TENG has significant application potential in micro-wearable devices.

Rapid fabrication of gold microsphere arrays with stable deep-pressing anisotropic conductivity for advanced packaging

Smooth metal microspheres with uniform sizes are ideal for constructing particle-arrayed anisotropic conductive films (ACF), but synthesis is hindered by challenges in controlling anisotropic metal growth. Here, we present a positioned transient-emulsion self-assembly and laser-irradiation strategy to fabricate pure gold microsphere arrays with smooth surfaces and uniform sizes. The fabrication involves assembling gold nanoparticles into uniform colloidosomes within a pre-designed microhole array, followed by rapid transformation into well-defined microspheres through laser heating. The gold nanoparticles melt and merge in a layer-by-layer manner due to the finite skin depth of the laser, leading to a localized photothermal effect. This strategy circumvents anisotropic growth, enables tunable control of microsphere size and positioning, and is compatible with conventional lithography. Importantly, these pure gold microspheres exhibit stable conductivity under deep compression, offering promising applications in soldering micro-sized chips onto integrated circuits.

Microstructural Passivation of Patterned Al2O3 Back Contacts on CdS/CdTe Solar Cells

AbstractPatterned aluminum oxide (Al2O3) back contact on cadmium telluride (CdTe) solar cells can effectively mitigate the loss of the majority carriers while retaining the passivation benefits for minority carriers. This study investigates the impact of the point‐contact geometry on cell performance, where the spacing of the microholes is systematically varied at a constant microhole diameter (≈16 µm). Microhole arrays are created on an evaporated Al2O3 layer (≈30 nm) on CdTe using laser‐beam lithography and selective wet etching processes. Comparative analysis indicates a significant decrease in fill factor (FF) and short‐circuit current (ISC) when the contact fraction falls below 30%, likely due to the Al2O3 barrier impeding majority carriers. Above this fraction, FF and ISC are comparable to those of baseline CdTe cells without Al2O3. Open‐circuit voltage (VOC) shows a gradual decrease as Al2O3 coverage is reduced but exhibits a slight increase (<15 mV) when the contact fraction exceeds 30%. Cathodoluminescence (CL) characterization reveals that significantly improved radiative recombination occurs within the CdTe grain bulk with Al2O3, whereas this effect on grain boundaries is minimal. The findings imply complex local carrier dynamics in the patterned back‐contact region, closely tied to the microstructural properties of CdTe‐based solar cells.

Translucent Si Solar Cells Patterned with Pulsed Ultraviolet Laser Beam

We report an application of a pulsed ultraviolet (UV) laser (λ = 355 nm) in producing translucent Si solar cells. This process efficiently generates a densely packed microhole array on a fully fabricated Si P‐N junction solar cell in just a few minutes. Herein, prototype cells with a nominal microhole diameter of 23 μm with a spacing between 60 and 300 μm are fabricated. High‐resolution electron‐beam microscopy reveals that the UV laser beam introduces amorphized silicon oxide (SiOx) in proximity to the patterned microholes via localized heating in air. Quantitative photovoltaic (PV) analysis shows a decline in the open‐circuit voltage (Voc) and the fill factor (FF) of the cells with the increase in the microhole density, likely due to the P‐N junction damage during the laser beam irradiation. Despite the reduction in Voc and FF, the solar cells retain a short‐circuit current density (Jsc) above 90% without post‐processing. The inherent microhole geometry associated with the laser beam profile allows multiple light scattering within the confined microhole structure, enhancing the translucency of the cells. While further development is required for optimization, these findings support the potential use of UV laser beams for fast and scalable production of translucent solar cells.

Analysis of photothermal heating of microhole bowtie antennas on gold metal films

AbstractIn this work, we present a numerical and experimental study of the photothermal heating of microholes array (MHA) bowtie antennas on gold metal films. The article first shows how MHAs in gold metal films can absorb more heat depending on the geometry or placement of the MHA in each gold metal films. We show numerically and experimentally that the photothermal heating exhibits a maximum when the MHAs are patterned in a bowtie‐like geometry. Numerical studies were carried out by using COMSOL multiphysics and experimental results were obtained using thermal imaging microscopy for several different MHAs geometries, respectively. Our results showed a good agreement between experimental data and the numerical simulations, validating that MHAs bowtie antennas on gold metal films heat significantly more and make them ideal for use in photothermal applications.

Fabrication of RuO2-graphene/graphene thick-and-dense micro-hole array material by femtosecond laser for high volumetric rate performance

Nanostructured materials have a great application prospect in the next generation of electrochemical energy storage devices. However, there is a great obstacle for thick and dense electrodes with large tortuosity to simultaneously attain high areal and rate performance at the same time to meet the practical requirements. Herein, a simple electrostatic self-assembly method is adopted to anchor RuO2 onto graphene nanoflakes, the thick and dense film of RuO2-Graphene/Graphene(RuO2-G G-1) are prepared by filtration and mechanical compression, and then the micro-hole array structure was fabricated by femtosecond laser drilling, which shortened the diffusion path of hydrogen ion (H+). After etching, the pore diameter is 7 μm; the pore spacing is 40 μm and the array was regular. The mass loss of the electrode caused by etching was only 3 %, and the relative density of the electrode reached 79 %. Under the same thickness of the electrode, the pore electrode obviously reduces the ion resistance. The micro-hole array not only improves the areal and volumetric capacity of the RuO2-G G-1 electrode, but also improves the rate performance of the electrode., the rate capability increased from 65.6 % to 87.7 % at 20 A g-1. The study provides a powerful technique for the fabrication of dense and thick electrode in energy storage system.

Modeling and experiment of femtosecond laser processing of micro-holes arrays in quartz

Quartz material irradiated by femtosecond laser has increasingly attracted widespread attention for the micro-fabrication of photonic devices. Mechanism exploration is beneficial for accelerating the digital progress of laser processing. However, the mechanism between femtosecond laser and quartz is complicated and needs further theoretical investigation. This paper established the theoretical model based on the ionization model with the Drude equation to study the space–time evolution of free electron density and its influence on the absorption coefficient, reflectivity, and ablation depth. In addition, we achieved a 10 × 10 micro-holes array with a pore size less than 10 μm, cone angle less than 2° in a 0.25 mm thick quartz on the condition of a laser pulse energy Ep = 3 μJ, scanning velocity v = 0.1 mm/s, and defocusing distance Δf = −0.3 mm via the bottom-up femtosecond laser processing. The work gives a new insight into further understanding the ablation mechanism of transparent materials etching by the femtosecond laser. It provides a practical technical scheme for preparing commercial quartz photonic devices.

Laser Drilling of Micro-Hole Array on CFRP Using Nanosecond Pulsed Fiber Laser

Laser Drilling of Micro-Hole Array on CFRP Using Nanosecond Pulsed Fiber Laser

Polymeric microlens array formed on a discontinuous wetting surface using a self-assembly technique

In this paper, we demonstrate a facile way to prepare polymeric microlens arrays (MLAs) based on a discontinuous wetting surface using a self-assembly technique. A patterned hydrophobic-octadecyltrichlorosilane (OTS) surface was prepared by UV/O3 irradiation through a shadow mask. The area exposed to UV/O3 irradiation turned highly hydrophilic, whereas the area protected by the mask remained highly hydrophobic, generating the patterned OTS surface. The surface energy of the OTS/glass surface changed from 23 to 72.8 mN/m after 17 min of UV/O3 treatment. The scribing of the optical glue-NOA 81 onto the microhole array enabled one to obtain the MLAs due to the generation of the NOA 81 droplet array via the surface tension. After UV light curing, the cured NOA 81 droplet array with uniform dimensions within a large area exhibited excellent MLA characteristics. Moreover, the method developed in this study is simple in operation, low-cost, and requires neither a clean room nor expensive equipment.

Laser Patterning of Porous Support Membranes to Enhance the Effective Surface Area of Thin-Film Composite-Facilitated Transport Membranes for CO2 Separation.

Although thin-film composite membranes have achieved great success in CO2 separation, further improvements in the CO2 permeance are required to reduce the size and cost of the CO2 separation process. Herein, we report the fabrication of composite membranes with high CO2 permeability using a laser-patterned porous membrane as the support membrane. High-aspect-ratio micropatterns with well-defined micropores on their surface were carved on microporous polymer supports by a direct laser writing process using a short-pulsed laser. By using a Galvano scanner and optimizing the laser conditions and target materials, in-plane micropatterns, such as microhole arrays, microline grating, microlattices, and out-of-plane hierarchical micropatterns, were created on porous membranes. An aqueous suspension of hydrogel microparticles doped with an amine-based mobile carrier was sprayed onto the patterned surface to form a defect-free thin separation layer. The surface area of the separation layer on the patterned support is up to 80% larger than that of flat pristine membranes, resulting in a 52% higher CO2 permeance (1106 GPU) with a CO2/N2 selectivity of 172. The laser-patterned porous membranes allow the development of inexpensive and high-performance functional membranes not only for CO2 separation but also for other applications, such as water treatment, cell culture, micro-TAS, and membrane reactors.

Rapid Fabrication of Yttrium Aluminum Garnet Microhole Array Based on Femtosecond Bessel Beam

High-aspect-ratio microholes, the fundamental building blocks for microfluidics, optical waveguides, and other devices, find wide applications in aerospace, biomedical, and photonics fields. Yttrium aluminum garnet (YAG) crystals are commonly used in optical devices due to their low stress, hardness, and excellent chemical stability. Therefore, finding efficient fabrication methods to produce high-quality microholes within YAG crystals is crucial. The Bessel beam, characterized by a uniform energy distribution along its axis and an ultra-long depth of focus, is highly suitable for creating high-aspect-ratio structures. In this study, an axicon lens was used to shape the spatial profile of a femtosecond laser into a Bessel beam. Experimental verification showed a significant improvement in the high aspect ratio of the microholes produced in YAG crystals using the femtosecond Bessel beam. This study investigated the effects of the power and defocus parameters of single-pulse Bessel beams on microhole morphology and size, and microhole units with a maximum aspect ratio of more than 384:1 were obtained. Based on these findings, single-pulse femtosecond Bessel processing parameters were optimized, and an array of 181 × 181 microholes in a 400 μm thick YAG crystal was created in approximately 13.5 min. The microhole array had a periodicity of 5 μm and a unit aspect ratio of 315:1, with near-circular top and subface apertures and high repeatability.

Three-dimensional information measurement and reconstruction for micro-hole array based on the modified shape from focus

The geometrical characteristics of the micro-holes and the consistency of spatial distribution among the micro-holes in the micro-hole array fabricated by laser beam drilling (LBD) directly influence the cooling performance, reliability, and longevity of the workpiece. It is of great significance to establish the relationship between the LBD processing parameters and the characteristics of the micro-hole array through the three-dimensional (3D) information measurement and reconstruction of the micro-hole array, as well as to guide and improve the LBD processing technology. However, due to the small size and high aspect ratio of the micro-holes in the micro-hole array, the 3D information measurement and reconstruction of the micro-hole array face challenges. The conventional micro-hole measurement methods suffer from low efficiency, high measurement costs, and potentially destructive measurement processes. Furthermore, the conventional micro-hole measurement methods face challenges in simultaneously obtaining the geometrical characteristics of the micro-holes and the spatial distribution among the micro-holes in the micro-hole array. Therefore, a non-contact and non-destructive 3D information measurement and reconstruction method for the micro-hole array based on the modified shape from focus is proposed. A novel focus measure operator based on grayscale difference and adaptive neighborhood size is proposed to accurately evaluate the focus value and obtain the initial focus volume matrix. A novel image processing operator based on the gradient information of the image sequence is proposed to enhance the initial focus volume matrix. The experimental results indicate that the proposed focus measure operator, combined with the novel image processing operator, is more suitable and reliable for detecting the micro-holes due to its better unimodality, higher contrast, and narrower peak width than the conventional focus measure operator. The optimal focus position of each image point is obtained using the modified Gaussian curve fitting method. On this basis, the 3D information measurement and reconstruction of the micro-hole array are realized. By comparing the results with the conventional micro-hole measurement method, the feasibility and accuracy of the proposed method have been confirmed to be an effective measurement method for the micro-hole array.

Applying punching without die to micro-hole array processing

Aluminum alloy (Al6061) sheet micro-hole processing is extensively used in smartphones, tablet PC, and smart wearable devices. The micro-hole processing is commonly performed using laser, micro drilling, micropunching, micro discharge, and chemical etching technologies. Micro-punching technology is characterized by precision and rapid processing, but the precision positioning of the punch head and lower die is one of the major difficulties in micro-hole punching, especially in manufacturing array micro-holes. This study used punching without die technology. This technology uses an array punch head to punch the lower die holes on the base, then performs array micro-hole punching. The experimental results show that a micro-hole array with 37 micro-holes were successfully manufactured and can be reproduced many times. Tapered array micro-holes with a high aspect ratio can be manufactured using this punching without die technology; the micro-hole depth can be 260 μm, the inlet diameter is 116 μm, and the outlet diameter is 25 μm. This study has successfully developed the feasibility of array micro-hole punching technology.

Preparing microparticles on an elementary substrate using a micro-hole array sprayer to assist LIBS: a highly sensitive trace rare earth element detection method for aqueous solution analysis

Preparing solution samples on an Al substrate: an innovative approach for achieving ppb-level LIBS detection of rare earth elements.

A centrifugal-driven spiral microchannel microfiltration chip for emulsion and deformable particle sorting.

Droplet sorting and enrichment, as a prominent field within microfluidic technology, represent a pivotal stage in the manipulation of droplets and particles. In recent times, droplet sorting methods based on lab-on-disk (LOD) have garnered significant interest among researchers for their inherent merits, including high throughput, ease of operation, seamless device integration, and independence from supplementary driving forces. This study introduces a centrifugal force-driven microfluidic chip comprising spiral microchannels. The chip incorporates microhole arrays along the sidewall of the spiral channels, enabling size-based sorting and enrichment of microdroplets under the influence of multiple forces. Firstly, a comparative analysis was performed to assess the influence of the separation port structure and rotational speed on efficiency, and a mechanical modeling approach was employed to conduct kinetic analyses of droplet behavior during instantaneous separation. Those findings demonstrated a good agreement with the experimental results at ω < 100 rpm. Subsequently, sorting experiments on homogeneous droplets indicated that repetitive sorting could increase the recovery ratios, RT(α), of high-concentration droplets (20.7%) from 35.3% to over 80%. We also conducted a sorting experiment on three-component homogeneous-phase emulsions using a serially connected chip array, and the sorting throughput was 0.58 mL min-1. As a result, the RT(α) for 60 and 160 μm droplets were 99.4% and 88.9%, respectively. Lastly, we conducted elution experiments and dual-sample sorting on a single chip, and the fluorescence results demonstrated that this study provided an efficient and non-cross-contaminating sorting method for non-homogenous phase multi-sample microreactor units.

High-fidelity synthesis of microhole templates with low-surface-energy-enabled self-releasing photolithography.

Material patterning through templates has provided an efficient way to meet the critical requirement for surface function in various fields. Here, we develop a self-releasing photolithographic process to make large-area freestanding templates with precise patterns. The low surface energy of substrates by hydrophobic treatment with proper silane modification ensures the template self-releasing. This method eliminates the need of mechanical separation or any sacrificial layers. Major steps including UV exposure and baking are optimized to realize high-quality structures and the final release of templates. The negative photoresists of SU-8 and polyimide are chosen to confirm the feasibility of this process. Wafer-scale freestanding templates with uniform microhole arrays are obtained with high structural fidelity, smooth surfaces and excellent flexibility. The hole size ranges from several to several tens of micrometers with an extremely low variation (<1%). These advantages could promote the application of precisely structured templates for surface patterning in material and surface science.

Ultrasonic Vibration-assisted Electrochemical Discharge Machining of Quartz Wafer Micro-Hole Arrays

The micro-hole machining of quartz wafers depends on photolithography techniques akin to those used in semiconductor fabrication. These methods present challenges due to high equipment setup costs, large space requirements, and environmental pollution risks. This research applies ultrasonic vibration assistance in electrochemical discharge machining to create an array of micro-holes on quartz wafers. In the experiments, a self-prepared tungsten carbide micro-electrode array served as the tool electrode. This electrode was a 2 × 2 square array, with needles measuring 30 × 30 μm. A series of experiments was conducted to investigate the effects of various machining parameters, including working voltage, feed rate, duration time, duty factor, and ultrasonic power level, on the characteristics of the micro-hole array. The characteristics included average hole diameter and through-hole surface morphology. The experimental objective was to achieve a through-hole diameter of 80 μm with an accuracy of ±8 μm. During the electrochemical discharge machining, suitable ultrasonic vibrations can thin the insulating gas film coating on the electrode surface, resulting in a more uniform gas film. As the insulating gas film’s thickness decreased, so did the critical voltage needed for the electrochemical discharge machining, reducing the hole’s diameter expansion. The ultrasonic vibration assistance can enable the satisfaction of the dimensional accuracy requirement. The experimental results indicate that ultrasonic vibration assistance can effectively improve the processing capacity and reduce sample fragmentation. A working voltage of 44 V, feed rate of 1 μm/6 s, duration time of 30 μs, duty factor of 30%, and ultrasonic power level of 1 resulted in better inlet and outlet surface morphology without outlet fragmentation. Moreover, the average diameters of the inlet and outlet were roughly 80 μm while meeting the through-hole diameter of 80 μm with accuracy of ±8 μm.

Universal selective transfer printing via micro-vacuum force

Transfer printing of inorganic thin-film semiconductors has attracted considerable attention to realize high-performance soft electronics on unusual substrates. However, conventional transfer technologies including elastomeric transfer printing, laser-assisted transfer, and electrostatic transfer still have challenging issues such as stamp reusability, additional adhesives, and device damage. Here, a micro-vacuum assisted selective transfer is reported to assemble micro-sized inorganic semiconductors onto unconventional substrates. 20 μm-sized micro-hole arrays are formed via laser-induced etching technology on a glass substrate. The vacuum controllable module, consisting of a laser-drilled glass and hard-polydimethylsiloxane micro-channels, enables selective modulation of micro-vacuum suction force on microchip arrays. Ultrahigh adhesion switchability of 3.364 × 106, accomplished by pressure control during the micro-vacuum transfer procedure, facilitates the pick-up and release of thin-film semiconductors without additional adhesives and chip damage. Heterogeneous integration of III-V materials and silicon is demonstrated by assembling microchips with diverse shapes and sizes from different mother wafers on the same plane. Multiple selective transfers are implemented by independent pressure control of two separate vacuum channels with a high transfer yield of 98.06%. Finally, flexible micro light-emitting diodes and transistors with uniform electrical/optical properties are fabricated via micro-vacuum assisted selective transfer.

Highly sensitive flexible heat flux sensor based on a microhole array for ultralow to high temperatures

With the growing demand for thermal management of electronic devices, cooling of high-precision instruments, and biological cryopreservation, heat flux measurement of complex surfaces and at ultralow temperatures has become highly imperative. However, current heat flux sensors (HFSs) are commonly used in high-temperature scenarios and have problems when applied in low-temperature conditions, such as low sensitivity and embrittlement. In this study, we developed a flexible and highly sensitive HFS that can operate at ultralow to high temperatures, ranging from −196 °C to 273 °C. The sensitivities of HFSs with thicknesses of 0.2 mm and 0.3 mm, which are efficiently manufactured by the screen-printing method, reach 11.21 μV/(W/m2) and 13.43 μV/(W/m2), respectively. The experimental results show that there is a less than 3% resistance change from bending to stretching. Additionally, the HFS can measure heat flux in both exothermic and absorptive cases and can measure heat flux up to 25 kW/m2. Additionally, we demonstrate the application of the HFS to the measurement of minuscule heat flux, such as heat dissipation of human skin and cold water. This technology is expected to be used in heat flux measurements at ultralow temperatures or on complex surfaces, which has great importance in the superconductor and cryobiology field.

Electrolytic Characteristics of Microhole Array Manufacturing Using Polyacrylamide Electrolyte in 304 Stainless Steel.

Because of the ease with which oxide films form on its surfaces, stainless steel has strong corrosion resistance and excellent processing performance. Electrochemical machining (ECM) is a flexible process that can create microstructures on stainless steel (SS304); however, with traditional masked ECM, the efficiency and accuracy of microstructure machining are low. Proposed here is the use of a non-Newtonian fluid [polyacrylamide (PAM)] as the electrolyte. To date, there have been few papers on the electrochemical dissolution behavior of stainless-steel micromachining with a non-Newtonian fluid as the electrolyte. The aims of the study reported here were to investigate the electrochemical properties of SS304 with PAM and PAM-NaOH as electrolytes, and to explain their electrochemical corrosion mechanisms. The effects of different electrolytes were compared, and the polarization curves of SS304 in PAM and PAM-NaOH electrolyte solutions with different components were analyzed and compared with that in NaNO3 electrolyte. Then, the effects of the main processing parameters (pulse voltage, frequency, and duty ratio) on the machining performance were investigated in detail. A microhole array was obtained with a good quality comprising an average diameter of 330.11 µm, an average depth of 16.13 µm, and a depth-to-diameter ratio of 0.048. Using PAM to process microstructures on stainless-steel surfaces was shown to be feasible, and experiments indicated that the mixed electrolyte (PAM-NaOH) had not only the physical characteristics of a non-Newtonian fluid but also the advantages of a traditional electrolyte to dissolve processing products, and it effectively improved the processing accuracy of masked ECM for SS304.