Micropore Arrays Research Articles

Two-dimensional metamaterials as meta-foams for optimized surface-enhanced solar steam generation

We report on a new class of metamaterials, which consists of meta-foams, optimized for high performance in enhanced solar steam generation. The design of these meta-foams involves precise dimensional control of a periodic two-dimensional micro-pore array. Proof-of-concept of meta-foams efficiency is demonstrated using two fabrication technologies. The first one involves microscale plasma etching onto a nanostructured black silicon substrate. As an alternative low-cost technique, we also use 3D printing of a graphene-containing polymer material. The experimental validation shows that the best evaporation rate reaches 1.34 kg/(h·m2) under 1 sun illumination, in open-air conditions under normal temperature and relative humidity conditions of 20 °C and 58%, an unmatched value so far under similar conditions, while the theoretical limit is estimated at 1.5 kg/(h·m2). This corresponding to a 89% conversion efficiency. Experimental data concur well with the predicted performance obtained by numerical simulations. The proposed model simultaneously accounts for both heat and mass transfer, including photothermal conversion and water phase change, to guide the optimization towards the maximization of the evaporation rate, an important figure of merit in many applications, including solar heat harvesting and solar water purification.

Influence of the thickness of a SiO2 reflective layer on the performance of a structured CsI(Tl) scintillation screen based on an oxidized Si micropore array template in X-ray imaging.

To obtain better light guidance and optical isolation effects under a limited microcolumn wall thickness, the influence of the thickness of a SiO2 reflective layer on the performance of a structured CsI(Tl) scintillation screen based on an oxidized Si micropore array template in X-ray imaging was simulated. The results show that the SiO2 reflective layer should maintain a certain thickness to achieve good light-guide performance. However, if the template is entirely composed of SiO2, the light isolation performance of the microcolumn wall will be slightly worse. The results provide a basis for optimizing the thickness of SiO2 reflective layer.

Influence of Si wall thickness of CsI(Tl) micro-square-frustums on the performance of the structured CsI(Tl) scintillation screen in X-ray imaging

To improve the detection efficiency of the structured scintillation screen with CsI(Tl) micro-square-frustums based on oxidized Si micropore array template in the case of a period as small as microns, the influence of Si wall thickness of the CsI(Tl) micro-square-frustums on the performance of the structured screen in X-ray imaging was investigated. The results show that when CsI(Tl) at the bottom of the screen is structured, the detective quantum efficiency (DQE) improves at almost all spatial frequency as the top thickness of the Si wall tSi decreases. However, when CsI (Tl) at the bottom of the screen is not structured, the DQE becomes better at low-frequency and worse at high-frequency as tSi decreases. The results can provide guidance for optimizing tSi according to the comprehensive requirements of detection efficiency and spatial resolution in X-ray imaging.

Platinum Nanocatalysts Supported on Defective Hollow Carbon Spheres: Oxygen Reduction Reaction Durability Studies.

The durability and long-term applicability of catalysts are critical parameters for the commercialization and adoption of fuel cells. Even though a few studies have been conducted on hollow carbon spheres (HCSs) as supports for Pt in oxygen reduction reactions (ORR) catalysis, in-depth durability studies have not been conducted thus far. In this study, Pt/HCSs and Pt/nitrogen-doped HCSs (Pt/NHCSs) were prepared using a reflux deposition technique. Small Pt particles were formed with deposition on the outside of the shell and inside the pores of the shell. The new catalysts demonstrated high activity (>380 μA cm−2 and 240 mA g−1) surpassing the commercial Pt/C by more than 10%. The catalysts demonstrated excellent durability compared to a commercial Pt/C in load cycling, experiencing less than 50% changes in the mass-specific activity (MA) and surface area-specific activity (SA). In stop-start durability cycling, the new materials demonstrated high stability with more than 50% retention of electrochemical active surface areas (ECSAs). The results can be rationalised by the high BET surface areas coupled with an array of meso and micropores that led to Pt confinement. Further, pair distribution function (PDF) analysis of the catalysts confirmed that the nitrogen and oxygen functional groups, as well as the shell curvature/roughness provided defects and nucleation sites for the deposition of the small Pt nanoparticles. The balance between graphitic and diamond-like carbon was critical for the electronic conductivity and to provide strong Pt-support anchoring.

Modulation Mechanism of Vortex Beam by Helical Microporous Array

Modulation Mechanism of Vortex Beam by Helical Microporous Array

Multi-physics simulation and experimental study of the reaction kinetics process of oxygen inhibition zone formation in constrained-surface stereolithography process

In this paper, based on the mechanism of oxygen inhibiting the curing of acrylate-based monomers, the reaction kinetics model for the formation of the oxygen inhibition zone is established. This model is applied to study the variation of the thickness of the oxygen inhibition zone with the process parameters and the microscopic characteristics of the constrained substrate with the PDMS film as the oxygen permeation window. Experiments are performed on substrates with different micropore area ratios, and the experimental results are in good agreement with the simulation. The research results show that the thickness of the oxygen inhibition zone can be up to 28 µm while the thickness of cured layer can be over 140 µm. The thickness of the oxygen inhibition zone increases with the increasing PDMS film diffusion coefficient, oxygen concentration, constrained substrate area ratio, and micropore size, but decreases with the increasing light intensity, photoinitiator concentration, and PDMS film thickness. When the micropore area ratio are too small, or the micropore diameter is too large under the same area ratio, an obvious periodic microstructure will appear on the surface of the cured layer, affecting the quality of the cured layer surface. The reaction kinetics multi-physics model for the formation of inhibition zone in constrained-surface stereolithography process has been established, considering the photopolymerization reaction kinetics and the effect of oxygen polymerization inhibition, as well as the influence of the substrate’s micropore array and PDMS film’s characteristics on oxygen mass transfer during polymerization. The effects of factors such as the microscopic characteristics of the substrate and the oxygen diffusion coefficient of the PDMS film on the inhibition zone have been investigated. Photopolymerization experiments are performed on substrates with different micropore area ratios, and the experimental results are in good agreement with the simulation. The research results show that the thickness of the oxygen inhibition zone can be maintained at 28 µm under reasonable control parameters, while the thickness of cured layer can be over 140 µm, meeting the requirement of achieving the minimum oxygen inhibition zone for continuous printing. • The reaction kinetics multi-physics model for the formation of inhibition zone has been established. • The effects of factors on the inhibition zone have been investigated. • Photopolymerization experiments are performed and the experimental results are in agreement with the simulation. • The optimized parameters meet the requirement of achieving the minimum oxygen inhibition zone for continuous printing.

UV laser-produced copper micro-mesh with superhydrophobic-oleophilic surface for oil-water separation

We report a method to fabricate micro-pore arrays on a copper sheet by a 355 nm UV nanosecond pulse laser, and investigate the effects of surface microstructures and micro-pore spacing on the wettability of the formed copper micro-mesh. We found that the surface was initially hydrophilic, but changed to superhydrophobic-oleophilic with water contact angle 151° and oil contact angle about 10° after exposed to ambient environment for 14 days. We analysed the surface morphologies of the processed samples with a three-dimensional profilometer, measured the water and oil contact angles, and characterized the surface by a field emission environmental scanning electron microscope (FESEM) and energy dispersive X-ray spectrometer (EDS). The surface chemistry changes were confirmed by X-ray photographic spectroscopy (XPS). Effective oil-water separation performance of the fabricated copper mesh was demonstrated. Learning from the natural change, we designed a coating material containing C8 long C–C (H) chain and coated onto the freshly prepared copper mesh to convert the surface property into a preferred superhydrophobic-oleophilic nature. This study provides a controllable methodology consisting laser processing and surface modification for making micro-pore copper mesh as a simple and effective method for oil-water separation.

Temperature and humidity sensor based on MEMS technology

This work presents a monolithically integrated temperature and humidity sensor based on microelectromechanical systems technology. The temperature sensor working on the “bi-metallic” effect has the advantages of wide temperature range, high sensitivity, and fast detection. The humidity sensor has a polyimide parallel plate capacitive structure with the microporous array on the upper electrode designed for high sensitivity and fast response. Numerical analysis and COMSOL simulation showed that the temperature detection sensitivity is 0.2 mV/°C in the range of 193–393 K and humidity sensitivity is 0.405 pF/% relative humidity (RH) with the response time of 34 s in the humidity range of 0%–100% RH. The integrated temperature and humidity sensor has the advantages of small dimension, wide detection range, high precision, and fast response.

Performance of a CsI(Tl) scintillation screen with a dual-periodic structure based on an oxidized silicon micropore array template in X-ray imaging.

To address the reduction in the detection efficiency of a structured CsI(Tl) scintillation screen when its structure period reaches the order of microns, a dual-periodic structure of the screen is proposed. The special feature of the dual structure is that each unit of the primary structure is divided equally into either four or nine square column-shaped scintillation sub-units. The sub-units are separated only by SiO2 layers to form a secondary structure. The results show that the performance of a dual-structure CsI(Tl) screen in X-ray imaging is much better than that of a corresponding single-structure screen.

Innovative Systems to Deliver Allergen Powder for Epicutaneous Immunotherapy.

Allergy is a disorder owing to hyperimmune responses to a particular kind of substance like food and the disease remains a serious healthcare burden worldwide. This unpleasant and sometimes fatal allergic disease has been tackled vigorously by allergen-specific immunotherapy over a century, but the progress made so far is far from satisfactory for some allergies. Herein, we introduce innovative, allergen powder-based epicutaneous immunotherapies (EPIT), which could potentially serve to generate a new stream of technological possibilities that embrace the features of super safety and efficacious immunotherapy by manipulating the plasticity of the skin immune system via sufficient delivery of not only allergens but also tolerogenic adjuvants. We attempt to lay a framework to help understand immune physiology of the skin, epicutaneous delivery of powdered allergy, and potentials for tolerogenic adjuvants. Preclinical and clinical data are reviewed showing that deposition of allergen powder into an array of micropores in the epidermis can confer significant advantages over intradermal or subcutaneous injection of aqueous allergens or other epicutaneous delivery systems to induce immunological responses toward tolerance at little risk of anaphylaxis. Finally, the safety, cost-effectiveness, and acceptability of these novel EPITs are discussed, which offers the perspective of future immunotherapies with all desirable features.

A structural polymer for highly efficient all-day passive radiative cooling

All-day passive radiative cooling has recently attracted tremendous interest by reflecting sunlight and radiating heat to the ultracold outer space. While some progress has been made, it still remains big challenge in fabricating highly efficient and low-cost radiative coolers for all-day and all-climates. Herein, we report a hierarchically structured polymethyl methacrylate (PMMA) film with a micropore array combined with random nanopores for highly efficient day- and nighttime passive radiative cooling. This hierarchically porous array PMMA film exhibits sufficiently high solar reflectance (0.95) and superior longwave infrared thermal emittance (0.98) and realizes subambient cooling of ~8.2 °C during the night and ~6.0 °C to ~8.9 °C during midday with an average cooling power of ~85 W/m2 under solar intensity of ~900 W/m2, and promisingly ~5.5 °C even under solar intensity of ~930 W/m2 and relative humidity of ~64% in hot and moist climate. The micropores and nanopores in the polymer film play crucial roles in enhancing the solar reflectance and thermal emittance.

A method for detecting IL-6 in serum of patients with uremia

As the gold standard of protein detection, enzyme-linked immunosorbent assay (ELISA) is widely used in medical treatment and biology. Here, we report a digital ELISA method that combines fluorescence-coded magnetic beads with micropore arrays to effectively improve the accuracy of the detection. Fluorescence coded magnetic beads were used as solid support of ELISA, which were modified to specifically capture IL-6 in serum, and then combined with galactosidase to form a sandwich structure. These beads are then mixed with a fluorescent substrate and passed into a microfluidic chip. Under the action of gravity, the beads are trapped and isolated by an array of micropores in the chip. Combined with image recognition technology, the fluorescence intensity of micropores containing enzymes will increase rapidly. By mining image information, the IL-6 content in uremia patients can be detected with high precision.

Tribological properties of suspended hexagonal boron nitride under electric field

Hexagonal boron nitride (h-BN) has huge potential applications in micro-nano electromechanical system due to its good lubricity and insulation. In this paper, a microporous array is prepared on a SiO<sub>2</sub>/Si substrate by the substrate etching process, and then the h-BN is transferred to the microporous substrate to form a suspension structure. The effect of electric field on tribological properties of suspended h-BN is studied by atomic force microscopy. The results show that the friction of the suspended h-BN is smaller than the friction on the h-BN supported by the substrate, because the greater in-plane stretch weakens the puckering effect. The electric field increases the friction of the suspended h-BN, and the influence of positive bias is greater than that of negative bias. The application of the electric field increases the electrostatic force on the tip, thereby increasing the additional load and the interface barrier in the friction process. The electric field causes the stick-slip behavior to change from single-slip to multi-slip. Compared with the h-BN supported by the substrate, h-BN in the suspended state is strongly affected by the electric field. The reduction of the interface distance and the absence of the substrate oxide layer lead the electrostatic force to increase. This paper proposes a method to adjust h-BN’s friction by electric field, which provides theoretical guidance for studying the friction characteristics of two-dimensional materials.

Friction properties of suspended graphene

Minimizing friction is a goal that has long been pursued in history. The role of micro-electromechanical system and nano-electromechanical system (MEMS/NEMS) in electronic devices is becoming more and more important. Due to the increasingly small size of the device, large surface-to-volume ratio leads to severe friction and wear problems of the device, thus limiting its performance. Graphene is considered as a good lubricating material in MEMS/NEMS due to its extremely thin size and excellent anti-friction effect. The study of nano-friction properties of graphene is of great significance in further developing the MEMS/NEMS. In this work, microporous arrays are prepared on a SiO<sub>2</sub>/Si substrate, and graphene is stripped on the micropores to form a suspension structure. The friction properties of suspended graphene and supported graphene are measured by using atomic force microscope. The results show that the nanofriction on suspended graphene is significantly reduced compared with that on supported graphene. The supported graphene experiences a frictional enhancement effect because of the puckering effect, while the friction enhancing effect disappears in the suspended graphene. With the increase of graphene thickness, the out-of-plane stiffness increases gradually, and the friction difference between suspended graphene and supported graphene decreases gradually. In addition, the nanofriction properties of suspended graphene under new tip and pretreated tip are also different. The friction between the pretreated tip and graphene is significantly higher than that between the new tip and graphene. The surface friction difference between the suspended graphene and the supported graphene decreases when the pretreated tip is used compared with the new tip. This work demonstrates that the deformability of atomic-scale structures can provide an additional channel of regulating the friction of contact interfaces. By comparing the changes of surface friction between the suspended graphene and the supported graphene with different thickness and tip sizes, the influence of out-of-surface deformation on the friction of graphene is revealed, thus providing theoretical guidance for effectively improving the friction performance of graphene solid lubricant.

Fabrication and Characteristics of MgZnO Ultraviolet Detector Based on Ag Microporous Array Structure Electrode

Fabrication and Characteristics of MgZnO Ultraviolet Detector Based on Ag Microporous Array Structure Electrode

Influence of preparation process on the transparency of CsI microcolumns in the structured CsI scintillation screen based on oxidized silicon micropore array template

The structured CsI scintillation screens based on oxidized silicon micropore array templates can maintain high spatial resolution in X-ray imaging while increasing their thickness. However, the detection efficiency of the screens is not only related to their thickness, but also related to the transparency of the CsI scintillation microcolumns in the screens, because it affects the output of the scintillation light. In this work, the hexagonal array arranged structured CsI scintillation screens based on oxidized silicon micropore templates with pore pitch about 4.3μm and diameter about 3.0μm were fabricated by vacuum melting and pressure injection method. In order to improve the transparency of the CsI microcolumns, the effects of filling temperature and pressure on the morphology, crystallinity, X-ray excited optical luminescence (XEOL) and transparency of the CsI scintillation microcolumns were studied after a preliminary research on TG-DSC, melt viscosity and bulk preparation of CsI material. The results show that with the increase of filling temperature, the cracks and microbubbles in the filled CsI microcolumns become less or even disappear under the filling pressure of 6 MPa, and the crystallinity of the microcolumns becomes better. Meanwhile, the intensity of the XEOL becomes stronger. The light attenuation coefficients of the CsI scintillation microcolumns prepared at different filling temperature were derived by Geant4 Monte Carlo simulation toolkit according to the results of XEOL. The light attenuation coefficient decreases significantly as the filling temperature increases. When the filling temperature reaches 660 °C, the light attenuation coefficient of the CsI microcolumns has dropped below 0.002μm−1. Such a low light attenuation coefficient is completely suitable for X-ray imaging of the structured high-resolution CsI scintillation screens based on oxidized silicon micropore array templates that have been developed.

Bioactive Self‐Pumping Composite Wound Dressings with Micropore Array Modified Janus Membrane for Enhanced Diabetic Wound Healing

AbstractTreatment of chronic wounds such as diabetic wounds with large volumes of biofluids is a significant clinical challenge due to ischemia caused by localized edema. To alleviate edema and stimulate angiogenesis, a four‐layer composite dressing is designed with a micropore array modified Janus membrane for self‐pumping and bioactive ion backflow, a superabsorbent layer for high capacity water absorption, and a bioactive layer containing bioglass for stimulating angiogenesis. The modified Janus membrane not only allows wound exudates transport from wound bed to the dressing, but also enables controlled backflow of bioactive ion containing fluid to the wound bed for stimulating angiogenesis. The in vivo experiment confirms the function of composite dressing in reducing wound edema, stimulating blood vessel formation and promoting diabetic wound healing. These results demonstrate that the novel composite dressing is a promising wound healing biomaterial for promoting chronic wound healing, and the unique characteristics of the micropore arrayed Janus membrane may extend its applications in biomedicine.

A micropore array-based solid lift-off method for highly efficient and controllable cell alignment and spreading

Interpretation of cell–cell and cell-microenvironment interactions is critical for both advancing knowledge of basic biology and promoting applications of regenerative medicine. Cell patterning has been widely investigated in previous studies. However, the reported methods cannot simultaneously realize precise control of cell alignment and adhesion/spreading with a high efficiency at a high throughput. Here, a novel solid lift-off method with a micropore array as a shadow mask was proposed. Efficient and precise control of cell alignment and adhesion/spreading are simultaneously achieved via an ingeniously designed shadow mask, which contains large micropores (capture pores) in central areas and small micropores (spreading pores) in surrounding areas contributing to capture/alignment and adhesion/spreading control, respectively. The solid lift-off functions as follows: (1) protein micropattern generates through both the capture and spreading pores, (2) cell capture/alignment control is realized through the capture pores, and (3) cell adhesion/spreading is controlled through previously generated protein micropatterns after lift-off of the shadow mask. High-throughput (2.4–3.2 × 104 cells/cm2) cell alignments were achieved with high efficiencies (86.2 ± 3.2%, 56.7 ± 9.4% and 51.1 ± 4.0% for single-cell, double-cell, and triple-cell alignments, respectively). Precise control of cell spreading and applications for regulating cell skeletons and cell–cell junctions were investigated and verified using murine skeletal muscle myoblasts. To the best of our knowledge, this is the first report to demonstrate highly efficient and controllable multicell alignment and adhesion/spreading simultaneously via a simple solid lift-off operation. This study successfully fills a gap in literatures and promotes the effective and reproducible application of cell patterning in the fields of both basic mechanism studies and applied medicine.

Effective metal mold method for the production of bionic adhesives based on electrochemical modifications

Bionic adhesives with tip-expanded microstructural arrays have attracted considerable interest owing to their high adhesive performance at low preloads. Their mainstream manufacturing method is molding. Due to most molds are made of silicon or silicon-based soft templates, and have poor wear resistant or vulnerability to high temperature, limiting their use in large-scale manufacturing. Nickel is widely used as an embossing mold in the micro/nano-imprint industrial process owing to its good mechanical properties. However, the processing of metal molds for the fabrication of tip-expanded microstructural arrays is extremely challenging. In this study, using electrodeposition techniques, the shape of the micropores is modified to obtain end-controlled pores. The effect of the non-uniformity of the electric field on the microporous morphology in the electrodeposition process is systematically investigated. Furthermore, the mechanism of non-uniformity evolution of the microporous morphology is revealed. The optimized microporous metal array is used as a mold to investigate the cavity evolution laws of the elastic cushions under pre-load during the manufacturing process. As a result, typical bionic adhesives with tip-expansion are obtained. Moreover, corresponding adhesion mechanics are analyzed. The results show that electrochemical modifications have broad application prospects in the fabrication of tip-expanded microstructures, providing a new method for the large-scale fabrication of bionic adhesives based on metal molds.

Angular dependence of secondary electron yield from microporous gold surfaces

We report exhaustive measurements of the secondary electron yield (SEY) from a gold film containing an array of micropores as a function of the angle of incidence of the primary electrons. The SEY measurements are in good agreement with Monte-Carlo (MC) simulations. A highly accurate empirical fit to the SEY data as a function of the incident electron impact angle is also proposed. In this study, the micropores have aspect ratios (ratio of pore height over pore diameter) ranging from about 1.5 to 3.5. The effect of the pore array density (porosity) and pore aspect ratio is analyzed in greater detail. It is found that increasing the pore aspect ratio and porosity leads to a sharp reduction in the total SEY in agreement with MC simulations.