Fabrication Of Microstructures Research Articles

Photopolymerization of TiO2-based hybrid materials: effect of nanoparticles loading and photosensitive 1D microstructures fabrication

Photopolymerization of TiO2-based hybrid materials: effect of nanoparticles loading and photosensitive 1D microstructures fabrication

Fabrication of 3D graphene microstructures with uniform metal oxide nanoparticles via molecular self-assembly strategy and their supercapacitor performance

Metal oxide nanoparticles equipped graphene with outstanding performance display broad application. Compared with graphene sheets loaded nanoparticles, such 3D architecture not only has the intrinsic performance of 2D graphene and nanoparticles, but also provides advanced functionality in many aspects. Up to now, many strategies have been explored to construct 3D graphene hybrids. However, the application of extra agents and/or agglomeration nanoparticles has a detrimental impact on particle applications. Herein, we present a molecular self-assembly strategy for producing high-quality 3D graphene microstructures with uniform metal oxide (ZnO) nanoparticles by directly deriving 3D amphiphilic Zn(MAA)2 precursors with a well-layered structure into 3D graphene hybrid. Notably, the organic part of organized Zn(MAA)2 molecules play a structurally crucial function in the formation of the graphene layers. It not only guides the ordered self-assemblies, but also facilitates the rapid in-situ formation of graphene structures by generating lots of allyl radicals in the heating process. Meanwhile, during the formation of graphene layers, ZnO NPs generated from carboxylate groups of Zn(MAA)2 molecules penetrate into the graphene. The as-obtained ZG-500 HSs as supercapacitor electrode displays a specific capacitance of 272.1 F g−1 at 1 A g−1. In addition, an asymmetric supercapacitor based on ZG-500 HSs and activated carbon provides an energy density of 13.4 Wh kg−1 at the power density of 387.5 W kg−1. This novel strategy opens up a potential and green route to high quality 3D graphene hybrids for supercapacitor.

Benzylidene Cyclopentanone Derivative Photoinitiator for Two-Photon Photopolymerization-Photochemistry and 3D Structures Fabrication for X-ray Application.

Micron- and submicron-scale 3D structure realization nowadays is possible due to the two-photon photopolymerization (TPP) direct laser writing photolithography (DLW photolithography) method. However, the achievement of lithographic features with dimensions less than 100 nm is in demand for the fabrication of micro-optical elements with high curvature values, including X-ray microlenses. Spectroscopic and photochemical study of a photoinitiator (PI) based on a methyl methacrylate derivative of 2,5-bis(4-(dimethylamino)benzylidene) cyclopentanone was performed. Enhanced intersystem crossing in the methyl methacrylate derivative results in increased radical generation for the subsequent initiation of polymerization. A comprehensive study of the new photocompositions was performed, with particular emphasis on photochemical constants, the degree of photopolymerization, and topology. The optimal parameters for the fabrication of mechanically stable structures were determined in this research. The threshold dose parameters for lithography (radiation power of 5 mW at a speed of 180 µm/s) when trying to reach saturation values with a conversion degree of (35 ± 1) % were defined, as well as parameters for sub-100 nm feature fabrication. Moreover, the 45 nm feature size for elements was reached. Fabrication of X-ray lens microstructures was also demonstrated.

Manipulating propagation and evolution of polarization singularities in composite Bessel-like fields

Structured optical fields embedded with polarization singularities (PSs) have attracted extensive attention due to their capability to retain topological invariance during propagation. Many advances in PS research have been made over the past 20 years in the areas of mathematical description, generation and detection technologies, propagation dynamics, and applications. However, one of the most crucial and difficult tasks continues to be manipulating PSs with multiple degrees of freedom, especially in three-dimensional (3D) tailored optical fields. We propose and demonstrate the longitudinal PS lines obtained by superimposing Bessel-like modes with orthogonal polarization states on composite vector optical fields (VOFs). The embedded PSs in the fields can be manipulated to propagate robustly along arbitrary trajectories, or to annihilate, revive, and transform each other at on-demand positions in 3D space, allowing complex PS’ topological morphology and intensity patterns to be flexibly customized. Our findings could spur further research into singular optics and help with applications such as micromanipulation, microstructure fabrication, and optical encryption.

Large range nano autofocus method based on differential centroid technique

In this work, we propose a novel autofocus method with hundreds of microns detecting range and nanoscale precision based on differential centroid method for high-precision lithography. The sample defocus amount is obtained by extracting the spot shape information using two detectors. While improving the anti-noise performance of the system, the method ensures a large linear detection range and high detection accuracy. And corresponding theoretical analysis and simulation are carried out. The experimental results indicate that the differential signal curves present good linear characteristics. The autofocus range is up to 169.5 µm, the sensitivity is approximately 25 nm, and the amplitude of the noise fluctuation does not exceed 7.5 nm. The theoretical and experimental results show that, combining with high-precision lithography technology, this work can be widely used in the fabrication of various complex microstructures.

3D-printing textiles: multi-stage mechanical characterization of additively manufactured biaxial weaves

3D printing allows the fabrication of complex microstructures that would traditionally require specialized machinery. In the fabrication of textiles, 3D printing may enable unique yarn structures, greater manufacturing flexibility and facilitate the development of personalized and tunable devices. In literature, 3D printed textiles have not been subjected to a thorough mechanical characterization. In this paper, a generative model of 3D printed biaxial weaves is developed and a parametric study to effectively map the design parameters to the weaves’ mechanical properties is performed via a two-stage Design-of-Experiments methodology. The samples are printed with material jetting layer by layer in planar direction and destructively tested in tension to obtain the resulting stress–strain behavior. The stress–strain curves are approximated by a bilinear model characterized predominantly by a transition strain and the major modulus after transition. The transition strain is influenced by the load direction and the weave pattern, while the major modulus is impacted by the load direction, the yarn diameter, the weave pattern and the yarn spacing in descending order. Further evaluation of the fracture behavior shows a mitigation of layer-wise delamination. This result indicates that material jetting can enable the production of arbitrary, quasi-continuous textile structures. The characterization results presented here may pave the way towards the design of textiles with spatially varying mechanical properties.

Incremental rolling forming process to fabricate surface micro-grooves

The fabrication of functional micro-structures at sheet surface has a wide range of applications in noise reduction, friction reduction, heat and mass transfer, etc. By integrating the conventional rolling forming and the incremental sheet forming process, a flexible and widely applicable incremental rolling forming process was proposed in the present work to fabricate surface micro-grooves. First, a rolling tool which has hemispherical ring convex on the roller and the convex height is much higher than the height of forming groove was designed and manufactured. Then, a series of incremental rolling tests on titanium alloy (TA1) were carried out by using self-designed rolling tools, with varying roller size, rolling depth and feed rate. The results show that continuous micro-grooves with good dimensional consistency were prepared on the surface of the plate. Furthermore, by investigating rolling force and groove size after rolling, it was found that the rolling depth have significant effects on the micro-groove formation and only localized material flow is occurred at the grooved region. Compared with the traditional rolling process, the incremental rolling process has the advantages of low rolling force and adjustable groove spacing, which is conducive to the subsequent processing of the sheet.

Biotemplated Fabrication of ZnO Microstructures with Enhanced Photocatalytic Properties from Rape Pollen

Biotemplated Fabrication of ZnO Microstructures with Enhanced Photocatalytic Properties from Rape Pollen

Flexible capacitive pressure sensor array using acoustic-assisted fabrication of microstructures as surface and dielectric layers

Flexible pressure sensors have attracted considerable interests in the fields of intelligent robotics, human-machine interfaces and health monitoring for their portability, flexibility and real-time sensing performance. The microstructures of dielectric layer significantly affect the sensing performance of capacitive pressure sensors, but the common methods to fabricate microstructures always need physical and/or chemical molds, thus may not suit for low-cost fabrication of sensors. The wavy-shaped microstructures on the surface of fluid can be generated with the excitation of standing surface acoustic waves (SSAWs), which is suitable to be used as dielectric layers. Here, we developed a 6 × 6 flexible capacitive pressure sensor array with fingerprint-like surface cover layer and latticed dielectric layer. Both two layers were fabricated through the novel and rapid acoustic-assisted process. The fabricated capacitive sensor array exhibits high sensitivity of 28.8%/N for normal force loading, with spatial resolution of 1.5 mm. It has been successfully used to monitor the vibration of the Adam’s apple during swallowing and detecting the wrist activities in cycles. These studies demonstrate the great potential of the pressure sensor array with acoustically fabricated microstructures in wearable electronics for health monitoring. • A novel flexible pressure sensor array with spatial resolution of 1.5 mm for three-axis distributed force sensing is developed. • A novel and rapid acoustic-assisted process based on SSAWs is used to fabricate the surface layer and dielectric layer with microstructures. • The tactile sensor array features high flexibility and can be easily worn on neck or wrist for health monitoring. • Both Adam’s apple vibration sensing and wrist activity detection can be achieved by the developed tactile sensor array.

High Thermoelectric Performance of p-Type Bi0.4Sb1.6Te3+x Synthesized by Plasma-Assisted Ball Milling.

The exploration of new synthesis methods is important for the improvement of the thermoelectric property of a material for the different mechanisms of microstructure fabrication, surface activity modulation, and particle refinement. Herein, we prepared p-Bi2Te3 bulk materials by a simple synthesis method of the plasma-assisted ball milling, which yielded finer nanopowders, higher texture of in-plane direction, and higher efficiency compared to the traditional ball milling, favoring the simultaneous improvement of electrical and thermal properties. When combined with the Te liquid sintering, nano-/microscale hierarchical pores were fabricated and the carrier mobility was also increased, which together resulted in the low lattice thermal conductivity of 0.52 W·m-1·K-1 and the high power factor of 43.4 μW·cm-1·K-2 at 300 K, as well as the ranking ahead zT of 1.4@375 K. Thus, this work demonstrated the advantages of plasma-assisted ball milling in highly efficient synthesis of p-type Bi2Te3 with promising thermoelectric performance, which can also be utilized to prepare other thermoelectric materials.

Microstructure design and mechanical properties of grain-gradient graphene/aluminum composites

The metal matrix with mixed grain-gradient structure and the graphene with different characteristics could be designed and prepared to ameliorate the plasticity and toughness reduction of the metal matrix composites (MMCs) caused by graphene reinforcement. However, the relationship between the microstructure and the mechanical properties of composites needs to be investigated. In this paper, a self-developed structural modeling program is employed to design and establish a single-edge notch tensile finite element model of the graphene reinforced grain-gradient aluminum (Al) matrix composites, where the distribution and morphology of graphene and grains can be redistributed. Then, the grain size dependence of yield strength is introduced into the developed crystal plasticity finite element method (CPFEM) according to the classical Hall-Petch relationship, the damage mechanism of the graphene/Al composites with various designed novel microstructures is analyzed in combination with the cohesive zone model (CZM), and the microstructure of the graphene/Al composites with optimal mechanical properties is obtained. In addition, it is found that the failure mode, strength and toughness of the composites could be ameliorated by adjusting the bonding state of graphene-Al interface. This study provides a new insight into the microstructure design and fabrication of the graphene/Al composites with optimal comprehensive properties.

Material removal mechanism and microstructure fabrication of GDP during micro-milling

Glow discharge polymer (GDP) material is essential for target ball fabrication in inertial confinement fusion applications. Fine microstructures (∼several tens-hundreds of micros) machining on the GDP surface is required for directing the high-power laser. The machinability and material removal mechanism of the GDP are critical to achieve high surface quality, remaining an unsolved challenge. This study investigated cutting mechanisms of the GDP based on feed per tooth and inclination angle in micro ball-end milling. Chip formation modes and machined surface morphologies as well as their generation mechanism were studied. Three types of chips (i.e., chip clusters, bulk/node chips, banded chips) were formed when the forming force of compression shifts to shear. Thermal effect and plastic flow promote a smooth surface under the squeezing effect of the tool cutting edge. The different ratios of feed rate to tool line velocity caused the micro pits and feed marks on the machined surface with the viscoelasticity of polymer material. By analyzing the cutting force, specific cutting force and machined surface roughness, together with the chip modes and surface morphologies, a transition of cutting modes from ploughing to ploughing-shearing coexistence and then to shearing were revealed. Finally, micro-dimpled structures were machined for validating the influence of the reveled material removal mechanism for fabrication of microstructures. The presented findings are of great significance for the application of micro-cutting processes in future engineering fabrication of microstructures on the GDP target ball.

Fabrication of 3D microstructures in glass by direct writing electrochemical discharge machining

ABSTRACT The formation of 3D copper-filled microstructures in glass using direct writing electrochemical discharge machining (ECDM) and electrodeposition techniques is presented. Single-row stainless steel tool electrodes having tip sizes of 150 µm were made by wire electrodischarge machining (W-EDM). Tool wear mechanism and the tip size correction of the worn-out tools were investigated. Significant tool wear was observed after 5 ECDM repetitions of the tool electrodes involving drilling and milling operations. Due to the high temperature generated in the ECDM process, there is significant erosion in the tool electrodes, and the tip heights of the electrodes became non-uniform. Thus, the single-row tool electrode became non-reusable in the ECDM process. Therefore, the electrochemical dissolution (ECD) method was used to correct the tip dimension and make the tool reusable for the ECDM process. After the ECD correction, the obtained tip size was close to the original size of 150 µm with <5% inter-tip size variation. Up to two-cycle of ECDM and ECD size correction was performed; thus, enhanced reusability of the single-row tool electrodes was demonstrated. The 3D structures were metallized using the copper electroplating method. DC measurement of the microstructures showed good electrical connectivity with an ohmic nature.

Design and fabrication of micro and nano surface structures for enhancing metal–polymer adhesion using femtosecond laser treatment

This study investigated the effects of micro- and nanostructures on the adhesion strength between copper and an encapsulating mold compound (EMC). The shape of the microgrooves was designed based on fracture mechanics theory, and the effect of laser-induced periodic structure surface (LIPSS) formation on the microgroove was investigated using numerical simulations. The designed surface profiles were fabricated using femtosecond laser treatments, and the adhesion strength between copper and the EMC was evaluated. The results show that deep microgrooves improved the adhesion strength owing to the anchor effect. However, the aspect ratio between the pitch and depth of the microgroove had a limitation in enhancing the adhesion strength. The formation of LIPSSs on the mountaintop of the microgroove was very effective; however, an LIPSS on the valley of the microgroove was ineffective. Numerical analyses revealed that LIPSSs suppressed the shear deformation of the EMC and worked as resistance to interface delamination. Based on the findings obtained in this study, combining micro- and nano-scale surface structure formation with femtosecond laser treatments is an effective and eco-friendly method for improving adhesion strength.

Characterization of single crystal diamond damaged layer induced by ion implantation and restored by varying annealing conditions

Fabrication of single crystal diamond (SCD) micro-structure remains a challenge due to its unique chemical and mechanical stability. Fortunately, the stable diamond sp3 bonds can be changed by using ion implantation technology. Ion implantation induced defects present a gaussian-like distribution in the vertical area. The high-damaged area can be etched by chemical treatments, while the low-damaged area which is usually difficult to eliminate could degrade the performance of diamond devices. In this study, fabrication of SCD three-dimensional micro-structure on HPHT diamond substrate by using ion implantation and lift-off techniques has been carried out. A thermal annealing step is employed to remove residual damage induced by ion implantation process. Raman and photoluminescence spectroscopies are used to characterize the top side and back side of low-damaged layer induced by ion implantation and restored by varying thermal annealing conditions.

Fabrication of microstructures in the bulk and on the surface of sapphire by anisotropic selective wet etching of laser-affected volumes

In this paper a processing technique for sapphire is presented which combines laser-induced amorphization and subsequent selective wet etching of amorphized sapphire as well as anisotropic wet etching of single-crystalline sapphire (α-Al2O3). Using this technique, microstructures can be realized on the surface and in the bulk of sapphire substrates. By focusing ultra-short laser pulses inside sapphire, its structure can be transformed from crystalline into amorphous. The modified material can be selectively removed using etchants, such as hydrofluoric acid or potassium hydroxide (KOH), solely dissolving the amorphized part. In this work, however, an etchant consisting of a standard solution of sulphuric acid and phosphoric acid (96 vol% H2SO4: 85 vol% H3PO4, 3:1 vol%) at 180 °C is utilized. This method allows the realization of structures which are impossible to achieve when using conventional etchants which solely dissolve the amorphized sapphire. Ultrashort pulsed laser irradiation (230 fs) is used in this study as starting point for the subsequent anisotropic etching to form microstructures on the surface or in the bulk of sapphire that are terminated by characteristic crystal planes. In particular, the appearance of etching-induced patterns formed by stacks of rhombohedra is shown for structures below the surface, whereas triangular pits are achieved in surface processing.

Femtosecond Laser Direct Writing of Antireflection Microstructures on the Front and Back Sides of a GaSe Crystal

The development of antireflection coatings is crucially important to improve the performance of various photonic devices, for example, to increase the efficiency of harmonic generators based on high-refractive index crystals with significant Fresnel losses. A promising technique for the reducing of radiation reflection is to change the refractive index by fabrication of antireflection microstructures (ARM) on the surface. This paper presents the results of ARM direct writing on the surfaces of a nonlinear GaSe crystal (of ε modification, according to Raman and photoluminescence spectroscopy data) using fs laser radiation and a multiples approach. An increase in transmission from 65% to 80% for an ARM fabricated on one side of the crystal and up to 94% for ARMs fabricated on both sides is demonstrated. The increase in transmission with the increasing pulse energy, as well as with an increase in the number of pulses used for the formation of a single crater, is shown. The experimental results of ARM transmission of GaSe are in qualitative agreement with the simulation results based on the measured profiles and morphology of the ARM structures.

Fabrication of Chiral 3D Microstructure Using Tightly Focused Multiramp Helico-Conical Optical Beams.

Beams with optical vortices are widely used in various fields, including optical communication, optical manipulation and trapping, and, especially in recent years, in the processing of nanoscale structures. However, circular vortex beams are difficult to use for the processing of chiral micro and nanostructures. This paper introduces a multiramp helical–conical beam that can produce a three-dimensional spiral light field in a tightly focused system. Using this spiral light beam and the two-photon direct writing technique, micro–nano structures with chiral characteristics in space can be directly written under a single exposure. The fabrication efficiency is more than 20 times higher than the conventional point-by-point writing strategy. The tightly focused properties of the light field were utilized to analyze the field-dependent properties of the micro–nano structure, such as the number of multiramp mixed screw-edge dislocations. Our results enrich the means of two-photon polymerization technology and provide a simple and stable way for the micromachining of chiral microstructures, which may have a wide range of applications in optical tweezers, optical communications, and metasurfaces.

An embedded printed flexible strain resistance sensor via micro-structure design on graphene-filled conductive silicon rubber

Flexible strain sensors have been improved in sensing performance with the assistance of materials design, novel manufacturing, and microstructure fabrication. In this study, graphene was efficiently dispersed in ethanol and then re-dispersed into silicon rubber (SR) matrix, functioning as a flexible strain resistance sensor (FSRS) with functional macrostructure and modified microstructure to further improve the sensitivity. A stable dispersion of graphene was obtained in an ultrasound-aided ball milling process, where absolute ethanol was selected as the solvent and sodium dodecyl sulfonate as the surfactant. Graphene-filled conductive SR was embedded in the polydimethylsiloxane matrix as a conductive sensing layer, and the high sensing performance (GF = 25 ± 2) was achieved using a spiral printed. Micropores with an optimized interspacing of 10 mm were further introduced into the spiral CSM, and the results presented a significant improved sensitivity (GF = 51 ± 4) of the fabricated FSRS under a working strain (20%–30%) and cyclic test (>104 cycles). The FRSR was sensitive enough to monitor various movements of single and multi-joints of human body and identify the rhythm of music sound, which exhibited its potential application as a wearable flexible sensor.

Fabrication of 3D microstructures for flexible pressure sensors based on direct-writing printing

Microstructure plays an important role in improving the performance of flexible sensors. Changing the shape of the dielectric layer microstructure is an effective countermeasure to promote the sensitivity of capacitive sensors. Nevertheless, traditional microstructure fabrication methods have high manufacturing costs, cumbersome manufacturing processes, and single structure manufacturing, which restrict the development of flexible sensors. In this work, electro-hydro-dynamic (EHD) printing method and aerosol jet (AJ) printing method were applied to fabricate 3D microstructures, in a manner of printing the same pattern in multiple layers. The height and morphology of 3D microstructures, under different printing parameters, were compared by changing the number of printing layers and printing speed. Additionally, the printing effects of the two printing methods were compared. The results demonstrated that various shapes and highly controllable 3D microstructures could be fabricated by both methods. The EHD printing method had higher manufacturing precision, whereas the AJ printing method had higher stacking efficiency. The height and morphology of 3D microstructures could be effectively controlled by changing the number of printed layers and the printing speed of the microstructures. It is indicated that the EHD printing method and the AJ printing method both have great potential in the fabrication of 3D microstructures and that both methods had their own advantages.