Multilayer Microstructures Research Articles

Flexible Sensors with Enhanced Sensitivity and Broadened Detection Range Through Conformal Printing and Space-Confined Design.

Enhancing the sensitivity and extending the linear sensing range of flexible pressure sensors are crucial for their development and incorporation in wearable electronics. Conventional sensors face a trade-off between sensitivity and linear sensing range, which is often limited by the monotonicity of materials and structural design. To address this challenge, a new piezoresistive flexible sensor is developed in this work, drawing inspiration from the intricate microstructure and pressure-sensing capabilities of human skin. This advanced sensor is constructed with a dual-layer resistive sensing design, which includes an external conductive layer comprising of MXene/Ag composite and an internal carbon nanomaterial conductive network. The design incorporated bionic micro-spines and multilayer porous microstructures with microcapsules to optimize the overall performance. This scalable and economical approach yielded a sensor that surpassed human tactile resolution, and the sensor can adeptly monitor comprehensive human motions and respiratory rhythms and recognize spoken language. In addition, it exhibited reliable photothermal sterilization performance, making it suitable for long-term health diagnostics and treatment. The proposed sensor demonstrated immense potential for applications in physical health monitoring, motion detection, electronic skin, and human-computer interactions.

Customized flexible iontronic pressure sensors: Multilevel microstructures by 3D-Printing for enhanced sensitivity and broad pressure range

Flexible capacitive pressure sensors stand out for their energy efficiency, rapid responsiveness, and exceptional durability, with their performance hinging on the intricate design of microstructures and the strategic selection of dielectric materials. However, creating cost-effective and practical fabrication methods for these components continues to pose a significant challenge. This study unveils an innovative iontronic flexible pressure sensor that integrates an ionic layer with sophisticated multilayer microstructures, setting new benchmarks in pressure sensing technology. The sensor operates within an expansive pressure range, achieving sensitivities as high as 92.14 kPa−1 at pressures from 0 to 50 kPa, and 22.96 kPa−1 at pressures ranging from 50 to 800 kPa, demonstrating extraordinary sensitivity. It also achieves an exceptionally low detection limit of 6.67 Pa and features swift response times of 56 ms to activate and 18 ms to deactivate. Enhanced by the addition of CuSO4, the sensor not only withstands freezing conditions but also significantly boosts sensitivity. Moreover, this sensor is capable of detecting human joint movements and subtle pressure fluctuations under high-pressure conditions, suggesting a breakthrough in the field. This research presents a simple, reliable, and cost-efficient method for developing flexible iontronic pressure sensors, poised to revolutionize applications in wide-ranging pressures and adverse temperature environments.

Electrospun Sulfonated Poly(ether ether ketone) and Chitosan/Poly(vinyl alcohol) Bifunctional Nanofibers to Accelerate Proton Conduction at Subzero Temperature.

Multilayered microstructures can accelerate the proton conduction process in proton exchange membranes (PEMs). Herein, we design and construct PEMs with microstructures based on bifunctional nanofibers and sulfonated poly(ether ether ketone) (SPEEK) nanofibers. Specifically, the bifunctional nanofibers composed of poly(vinyl alcohol) and chitosan are prepared and then combined with the electrospun SPEEK nanofibers. The stable microstructure is derived from the compatible interfacial property of nanofibers and the formed hydrogen bonds. The multilayered microstructure consisting of nanofibers accelerates the proton conduction even at subzero temperature because of regulating the proton conduction pathways. Specifically, the (SKNF/CPNF/SKNF)/PA membrane exhibits the proton conductivities of (0.951 ± 0.138) × 10-2 S/cm at -30 °C and (7.32 ± 0.37) × 10-2 S/cm at 160 °C. Additionally, the fine proton conductivity stability is demonstrated by the proton conductivity in the long-term test and the cooling/heating cycle test, such as 1.67 × 10-2 S/cm at -30 °C (after 1000 h), 4.52 × 10-2 S/cm at 30 °C (after 810 h), 1.12 × 10-2 S/cm at -30 °C, and 1.01 × 10-1 S/cm at 30 °C in the cooling/heating process (5 cycles). The single fuel cell possesses an open-circuit voltage of 0.886 V and a peak power density of 0.508 W/cm2 at 130 °C.

Graphene oxide nanosheets reinforced quaternized poly(2,6-dimethyl-1,4-phenylene oxide) composite membranes with enhanced hydroxide ions conduction at subzero temperature

The realization of high hydroxide ion conductivity on the premise of enough alkaline stability is basic of the practical application of anion exchange membranes (AEMs). In this research, we propose a facile way to enhance the hydroxide ion conductivity at subzero temperature through constructing multilayered microstructures of AEMs. Graphene oxide (GO) nanosheets and 3,6-diazaspiro[5.5]undecane bromide (DSUBr) are alternately deposited on the surface of a quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO) membrane with the layer by layer self-assembly process. Multilayered and compact microstructures are retained even if the prepared QPPO/(GO/DSUOH)5 membranes are immersed in 2 M KOH solution for 300 h. The hydroxide ions conduction resistance is reduced, deriving from the well-ordered dispersion of components. For example, the QPPO/2-(GO/DSUOH)5 membrane exhibits the hydroxide ion conductivities of 0.922 mS/cm at −25 °C and 58.5 mS/cm at 80 °C. Furthermore, the prepared AEMs possess the enhanced hydroxide ion conductivity owing to the fine dimension and component stabilities. After the ten-cycle hydroxide ion conductivity stability test, the retention rates of hydroxide ion conductivity are 99.4 % at −25 °C and 105 % at 30 °C. Additionally, the residual hydroxide ion conductivity reaches 61.6 mS/cm at 80 °C in 2 M KOH solution for 624 h. A single fuel cell equipped with the QPPO/2-(GO/DSUOH)5 membrane exhibits the maximum power densities of 80.8 mW/cm2 at 30 °C and 351.6 mW/cm2 at 60 °C.

One-pot approach for acoustic directed assembly of metallic and composite microstructures by metal ion reduction

Acoustic-directed assembly is a modular and flexible bottom-up technique with the potential to pattern a wide range of materials. Standing acoustic waves have been previously employed for patterning preformed metal particles, however, direct patterning of metallic structures from precursors remains unexplored. Here, we investigate utilization of standing waves to exert control over chemical reaction products, while also exploring their potential in the formation of multi-layered and composite micro-structures. Concentric micro-structures of gold and silver were obtained by introducing a metal precursor salt and a reducing agent into a cylindrical piezoelectric resonator that also served as a reservoir. In addition, we introduce an innovative approach to directly fabricate metallic multi-layer and composite structures by reducing different metal ions or adding nanoparticles during the reduction step. We showcased our method through the fabrication of layered structures, incorporating a combination of gold and silver, as well as structures composed of silver and hematite nanoparticles. The produced structures were characterized through both surface and cross-sectional analyses, revealing the influence of the acoustic field on the mesostructure as well. This innovative approach is promising for production of complex microstructures with enhanced functionality and controlled properties.

Strong enhancement of third harmonic generation from a Tamm plasmon multilayer structure with WS2.

Improving the conversion efficiency is particularly important for the generation and applications of harmonic waves in optical microstructures. Herein, we propose to enhance the efficiency of third harmonic generation by integrating a monolayer WS2 with the metal/dielectric/photonic crystal multilayer structure. The numerical simulations show that the multilayer structure enables to generate the Tamm plasmon mode between the metal film and photonic crystal around the telecommunication wavelength, which is consistent with the experimental result. By measuring with a self-built nonlinear optical micro-spectroscopy system, we find that the third harmonic signal can be reinforced by 16-fold through inserting the monolayer WS2 in the dielectric spacer. This work will provide a new way for improving nonlinear optical response, especially THG in multilayer photonic microstructures.

High-performance flexible piezoresistive pressure sensor based on multi-layer interlocking microstructures

PDMS/CNT films with microdome arrays and porous TPU/MXene nanofibre films are assembled into high-performance piezoresistive pressure sensors, which greatly improve the sensitivity and stability of piezoresistive pressure sensors.

Microstructural Analysis of Solid Oxide Electrochemical Cells via 3D Reconstruction Using a FIB-SEM Dual Beam System

The 3D reconstruction based on tomography technology enables quantitative and qualitative microstructural analysis of complex multiphase oxide structures. This powerful approach is widely investigated in diverse areas, in particular, gaining more importance in solid oxide electrochemical cells (SOCs) fields. SOCs are promising energy conversion devices with high efficiency, however, they have complex and porous/dense multilayered microstructures, which are closely related to the electrochemical reaction in the electrodes, thus, one of the major factors determining overall output performance of SOCs. Therefore, it is necessary to quantify the microstructural parameters of the cell. A focused ion beam-scanning electron microscope (FIB-SEM) dual beam system is one well-established method to obtain tomographic images to reconstruct 3D microstructures. It has an appropriate scale of tenth of nm to μm-level with high spatial resolution to represent the microstructural characteristics of the SOC electrodes. This presentation is intended to introduce our progress on 3D reconstruction techniques to quantitatively analyse SOCs, obtaining microstructural features such as particle size, connectivity, tortuosity, contact area, and triple phase boundary density. These in-depth analyses are helpful in extensively understanding electrochemical behavior in SOC electrodes.

Enhancing proton conduction of high temperature proton exchange membranes based on carbon dots doped polyvinyl chloride nanofibers

Carbon dots (CDs) as the easy-to-get and cheap carbon nanomaterials exhibited the great potential in various high-performance electrolytes. In this research, we constructed high temperature proton exchange membranes with multilayered microstructures through a couple of polyvinyl chloride (PVC) nanofibers layers wrapping a thin CDs layer. In the prepared (PVC/CDs/PVC)es membrane, the CDs provided a mount of sites to anchor phosphoric acid (PA) molecules with the formation of the (PVC/CDs/PVC)es/PA membrane. The proton conduction was accelerated by the continuous proton conduction channels consisting of the CDs layer and PA molecular chains. Notably, the proton conduction behavior was guided by the PVC nanofibers in the (PVC/CDs/PVC)es/PA membrane. Furthermore, a large number of hydrophilic oxygenated functional groups surrounding CDs facilitated the proton conduction process owing to the reduced proton conduction resistance in the hydrophilic membrane. For the PVC/ImCDs/PA membrane, the imidazolium groups could enhance proton conductivity. From our perspective, the imidazolium groups grafted CDs (ImCDs) participated into the proton conduction process through providing imidazolium groups for ameliorating proton conduction network. The enhanced proton conduction was achieved through constructing multilayered structure. Specifically, the (PVC/CDs/PVC)es/PA membrane exhibited the proton conductivity of 5.61 × 10-3 S/cm at 150 °C, which was higher than 7.73 × 10-4 S/cm of the PVC/CDs/PA membrane. Notably, the PA doped membrane could retain the mechanical strength without microstructure expansion.

A Review of Advances in Fabrication Methods and Assistive Technologies of Micro-Structured Surfaces

Micro-structured surfaces possess excellent properties of friction, lubrication, drag reduction, antibacterial, and self-cleaning, which have been widely applied in optical, medical, national defense, aerospace fields, etc. Therefore, it is requisite to study the fabrication methods of micro-structures to improve the accuracy and enhance the performance of micro-structures. At present, there are plenty of studies focusing on the preparation of micro-structures; therefore, systematic review of the technologies and developing trend on the fabrication of micro-structures are needed. In present review, the fabrication methods of various micro-structures are compared and summarized. Specially, the characteristics and applications of ultra-precision machining (UPM) technology in the fabrication of micro-structures are mainly discussed. Additionally, the assistive technologies applied into UPM, such as fast tool servo (FTS) technology and slow tool servo (STS) technology to fabricate micro-structures with different characteristics are summarized. Finally, the principal characteristics and applications of fly cutting technology in manufacturing special micro-structures are presented. From the review, it is found that by combining different machining methods to prepare the base layer surface first and then fabricate the sublayer surface, the advantages of different machining technologies can be greatly exerted, which is of great significance for the preparation of multi-layer and multi-scale micro-structures. Furthermore, the combination of ultra-precision fly cutting and FTS/STS possess advantages in realizing complex micro-structures with high aspect ratio and high resolution. However, residual tool marks and material recovery are still the key factors affecting the form accuracy of machined micro-structures. This review provides advances in fabrication methods and assistive technologies of micro-structured surfaces, which serves as the guidance for both fabrication and application of multi-layer and multi-scale micro-structures.

Non-integral depth measurement of high-aspect-ratio multi-layer microstructures using numerical-aperture shaped beams

This work presents a new optical metrology technique for accurate depth measurement of individual high-aspect-ratio (HAR) multi-layer microstructures with high spatial resolution and signal-to-noise ratio (SNR). To resolve the limitations of existing optical metrology techniques, light shaping with high light efficiency is optimized using numerical-aperture controlled laser beams. Experimental tests evidenced a 28-fold improvement in SNR for measuring large-depth structures when compared with measurements obtained using traditional broadband incoherent illumination. More importantly, instead of integral measurement characteristics currently limited by conventional spectral reflectometry or scatterometry, non-integral depth measurement of an individual microstructure from densely spaced microstructures such as through-silicon vias (TSV) and redistribution layers (RDL) can be realized using the developed optical measuring system with desired numerical aperture and field of view achieved simultaneously. As demonstrated by the measurement of a single submicron structure with linewidth as small as 0.6 µm and an aspect ratio of 5, the precision of depth measurement can be kept within a few nanometers.

Epitaxy of multilayer-stacking MoS2 crystal microstructures by chemical vapor deposition

Stacking structures show great potential for the modulation of physical properties of two-dimensional materials. However, most studies have focused on bilayer (BL) stacking MoS2 with same morphology. Here, we report a simple but effective process for manufacturing multilayer stacking MoS2 crystal microstructures. The epitaxial growth mechanism is investigated by studying a typical trilayer (TL) stacking MoS2 with different shapes. Raman and photoluminescence (PL) mapping exhibit high homogeneity and obvious boundary contrast between the different structures. The TL-MoS2 microstructure field-effect transistor (FET) shows high carrier mobility and on/off ratio, which is related to stacking configuration. It is note that type I junction can form between the different structures and the obvious photocurrent observed are in the junction region. The 15.3° twisted BL-AB stacking MoS2 Moiré superlattices with a period of 1.39 ± 0.05 nm. This work provides a reference for the development and application of multilayer-stacking MoS2.

Fabrication and Testing of Bioinspired Composites with Curved Multilayer Microstructures

Fabrication and Testing of Bioinspired Composites with Curved Multilayer Microstructures

Recent progress in flexible pressure sensors based on multiple microstructures: from design to application.

Flexible pressure sensors (FPSs) have been widely studied in the fields of wearable medical monitoring and human-machine interaction due to their high flexibility, light weight, sensitivity, and easy integration. To better meet these application requirements, key sensing properties such as sensitivity, linear sensing range, pressure detection limits, response/recovery time, and durability need to be effectively improved. Therefore, researchers have extensively and profoundly researched and innovated on the structure of sensors, and various microstructures have been designed and applied to effectively improve the sensing performance of sensors. Compared with single microstructures, multiple microstructures (MMSs) (including hierarchical, multi-layered and hybrid microstructures) can improve the sensing performance of sensors to a greater extent. This paper reviews the recent research progress in the design and application of FPSs with MMSs and systematically summarizes the types, sensing mechanisms, and preparation methods of MMSs. In addition, we summarize the applications of FPSs with MMSs in the fields of human motion detection, health monitoring, and human-computer interaction. Finally, we provide an outlook on the prospects and challenges for the development of FPSs.

Calibrating uncertain parameters in melt pool simulations of additive manufacturing

Melt pool scale numerical modeling of additive manufacturing (AM) processes can provide predictive capabilities and theoretical insight into the process-property-structure-performance relationships for AM parts. Despite capabilities of numerical models to solve complex multi-physics problems, it is often important to consider a tradeoff between detailed physics and computational cost. Therefore, sources of uncertainty in both experimental conditions and the parameters needed for modeling require models to be validated against empirical evidence. Here, a method is proposed to calibrate uncertain parameters used in continuum-scale melt pool models for powder bed fusion (PBF) AM. Both a simplified heat transfer model and a heat transfer and fluid flow model were investigated. A surrogate model and Markov chain-based optimization algorithm calibrated melt pool geometry for models within experimental variation of the target melt pool width and depth from the NIST AM-Bench 2018-02 dataset. The melt pool temperature distributions, solidification parameters, and simulated multi-layer solidification microstructures were compared between the two models. Similar results from both models indicate that calibrated, lower fidelity numerical models may be used in place of higher fidelity models to generate melt pool solidification data. These calibrated models therefore enable lower computational cost melt pool simulations without a noticeable decrease in simulation accuracy for grain-scale microstructure simulations.

Multi-layered heterostructured CoCrFeMnNi high-entropy alloy processed using direct energy deposition and ultrasonic nanocrystalline surface modification

The advantages of heterostructured materials as structural materials include superior mechanical properties and the ability to tailor the strength-ductility combination via microstructure customization. To maximize heterostructure effects, this study combined direct energy deposition and ultrasonic nanocrystalline surface modification processes to create a CoCrFeMnNi equiatomic high-entropy alloy with multi-layered microstructures. The fabricated CoCrFeMnNi high-entropy alloy has a novel microstructure composed of multiple layers of repetitive microstructures with heterogeneity and demonstrates a remarkable synergetic strengthening effect in comparison to conventional heterogeneous materials. The outstanding mechanical properties derived from various hard and soft layer interfaces, as well as the effects of each layer and interface, were quantitatively analyzed using grain-scale digital image correlation technology. By combining the direct energy deposition and ultrasonic nanocrystalline surface modification processes, this study presents a method for fabricating a new class of heterostructured materials with multi-layered microstructure that exhibit deformation heterogeneity and grain size heterogeneity. The multi-layered microstructure with multiple heterogeneous boundaries breaks the conventional wisdom regarding heterostructured materials having only one or two heterogeneous interfaces.

Offset-tool-servo diamond end flycutting multi-layer hierarchical microstructures

Microstructural functional surfaces inspired by nature have been widely applied in the fields of optics, aerospace, electronics and communication. There function not only originates from a single layer of surface microstructures, but also depends largely on the combined effect of hierarchical structures. Hierarchical microstructures are generally overlapped by two or more layers to generate a functional complementary and combined surface. Fast/slow tool servo technology is usually employed to fabricate micro/nanostructures. However, it is challenging to fabricate multi-layer hierarchical microstructures with sharp edges using only a commercial three-axis ultra-precision lathe. In the present study, a novel ultra-precision offset-tool-servo end flycutting (OTSEF) system was developed. Considering the geometry and installation pose of the diamond tool, a tool path based on the OTSEF system was planned, and different hierarchical microstructures could be fabricated using a compensated linear tool trajectory. Furthermore, a mathematical modeling for tool path generation for complex multi-layer hierarchical microstructures, overlapping micro-lens units with secondary pyramid structures, was established. After determining and compensating for the misalignment between the center of the diamond tool and workpiece, hierarchical microstructures with high precision and quality were successfully fabricated. The theoretical and experimental results demonstrate that the OTSEF system has unique advantages in the fabrication of multi-layer hierarchical microstructures. The present research not only provides a deep insight into tool path modeling but also a machining method for multi-layer hierarchical microstructures.

Bioinspired drag reduction surfaces via triple lithography method based on three-layer hybrid masks

Drag reduction is a significant challenge for many industries, such as ships, pipelines, aircraft, energy, and transportation. Multilayer hierarchical microstructures can inhibit the development of vortices near the wall, which is beneficial to drag reduction. However, existing methods have difficulty performing the controlled fabrication of complex multilayer hierarchical microstructure arrays. Here, a novel triple lithography method based on three-layer hybrid masks is proposed for the controlled fabrication of three-dimensional multilayer hierarchical microstructure surfaces. The capability of the proposed process is verified by the multilayer hierarchical microstructures. In the fabrication process, a special lithography sequence is designed based on the hybrid mask materials. The drag reduction ability of the multilayer hierarchical microstructures is investigated in a closed air channel measurement system. The experimental results demonstrate that the fabricated multilayer hierarchical microstructures exhibit significant drag reduction ability under certain conditions. Conceptual models based on the fluid-solid coupling interface interaction are proposed to explain the drag reduction mechanism of multilayer hierarchical microstructures. The proposed fabrication method provides a powerful means for practical engineering applications of various bioinspired functional surfaces, such as drag reduction, anti-icing, antifouling, self-cleaning, and superhydrophobic surfaces.

Terahertz Chiral Metamaterials Enabled by Textile Manufacturing.

Easy-to-fabricate, large-area, and inexpensive microstructures that realize control of the polarization of terahertz (THz) radiation are of fundamental importance to the development of the field of THz wave photonics. However, due to the lack of natural materials that can facilitate strong THz radiation-matter interactions, THz polarization components remain an undeveloped technology. Strong resonance-based responses offered by THz metamaterials have led to the recent development of THz metadevices, whereas, for polarization control devices, micrometer-scale fabrication techniques including aligned photolithography are generally required to create multilayer microstructures. In this work, leveraging a two-step textile manufacturing approach, a chiral metamaterial capable of exhibiting strong chiroptical responses at THz frequencies is demonstrated. Chiral-selective transmission and pronounced optical activity are experimentally observed. In sharp contrast to smart-clothing-related devices (e.g., textile antennas), the investigated chiral metamaterials gain their THz properties directly from the yarn-twisting enabled microhelical strings. It is envisioned that the interplay between meta-atom designs and textile manufacturing technology will lead to a new family of metadevices for complete control over the phase, amplitude, and polarization of THz radiation.

The interactions between integrin α5β1 of liver cancer cells and fibronectin of fibroblasts promote tumor growth and angiogenesis.

Hepatocellular carcinoma (HCC) progression is closely related to pathological fibrosis, which involves heterotypic intercellular interactions (HIIs) between liver cancer cells and fibroblasts. Here, we studied them in a direct coculture model, and identified fibronectin from fibroblasts and integrin-α5β1 from liver cancer cells as the primary responsible molecules utilizing CRISPR/Cas9 gene-editing technology. Coculture led to the formation of 3D multilayer microstructures, and obvious fibronectin remodeling was caused by upregulated integrin-α5β1, which greatly promoted cell growth in 3D microstructures. Integrin-α5 was more sensitive and specific than integrin-β1 in this process. Subsequent mechanistic exploration revealed the activation of integrin-Src-FAK, AKT and ERK signaling pathways. Importantly, the growth-promoting effect of HIIs was verified in a xenograft tumor model, in which more blood vessels were observed in bigger tumors derived from the coculture group than that derived from monocultured groups. Hence, we conducted triculture by introducing human umbilical vein endothelial cells, which aligned to and differentiated along multilayer microstructures in an integrin-α5β1 dependent manner. Furthermore, fibronectin, integrin-α5, and integrin-β1 were upregulated in 52 HCC tumors, and fibronectin was related to microvascular invasion. Our findings identify fibronectin, integrin-α5, and integrin-β1 as tumor microenvironment-related targets and provide a basis for combination targeted therapeutic strategies for future HCC treatment.