Micro-sized Patterns Research Articles

Dislocation Evolution in Cyclic-Loaded Cu Nanopillars with Different Configurations.

Small-sized metals generally exhibit unusual deformation responses subjected to cyclic loading, since their limited volume cannot effectively accommodate micro-sized dislocation patterns typically found in their bulk counterparts. Here, the cyclic behaviors in Cu nanopillars with different configurations are investigated using in situ transmission electron microscopy fatigue test. Dislocation tangles formed in single- and twinned-crystal nanopillars as a result of cycling-induced operations of multiple slip systems and further unpinning and absorption of pinned dislocations. While, nanopillars configured with low-angle grain boundary (LAGB) underwent the degradation and eventual decomposition of the LAGB due to the cycling-induced emission of grain boundarydislocations, which resulted in high-density mobile dislocations to withstand the cyclic loading. These findings contribute to a systematic and comprehensive understanding of the micro-mechanics of dislocation-related phenomena in the cyclic response of nanoscale metals.

Raman-based mapping and depth-profiling of the relaxation state in amorphous silicon

We show that the micro-scale variations in the relaxation state of amorphous silicon (a-Si) can be well-identified by Raman mapping over hundreds or thousands of μm2 in 1–2 h. Pure and relaxed a-Si is obtained by self-implantation in crystalline silicon (c-Si) followed by anneal at 500 °C. It is then locally re-implanted over micro-sized patterns to produce unrelaxed a-Si zones. Raman mappings are obtained by pointwise confocal μ-Raman and hyperspectral Raman imaging. We also measure the depth profiles of the relaxation state in re-implanted a-Si by scanning the edge of a re-implanted sample. We infer from the depth profiles that the minimal damage dose to fully de-relax a-Si is 0.04 displacements per atoms, which is an order of magnitude smaller than the fluence needed to fully amorphize c-Si.

Nano-sized graphene oxide coated nanopillars on microgroove polymer arrays that enhance skeletal muscle cell differentiation

The degeneration or loss of skeletal muscles, which can be caused by traumatic injury or disease, impacts most aspects of human activity. Among various techniques reported to regenerate skeletal muscle tissue, controlling the external cellular environment has been proven effective in guiding muscle differentiation. In this study, we report a nano-sized graphene oxide (sGO)-modified nanopillars on microgroove hybrid polymer array (NMPA) that effectively controls skeletal muscle cell differentiation. sGO-coated NMPA (sG-NMPA) were first fabricated by sequential laser interference lithography and microcontact printing methods. To compensate for the low adhesion property of polydimethylsiloxane (PDMS) used in this study, graphene oxide (GO), a proven cytophilic nanomaterial, was further modified. Among various sizes of GO, sGO (< 10 nm) was found to be the most effective not only for coating the surface of the NM structure but also for enhancing the cell adhesion and spreading on the fabricated substrates. Remarkably, owing to the micro-sized line patterns that guide cellular morphology to an elongated shape and because of the presence of sGO-modified nanostructures, mouse myoblast cells (C2C12) were efficiently differentiated into skeletal muscle cells on the hybrid patterns, based on the myosin heavy chain expression levels. Therefore, the developed sGO coated polymeric hybrid pattern arrays can serve as a potential platform for rapid and highly efficient in vitro muscle cell generation.

Photo-Patternable, High-Speed Electrospun Ultrafine Fibers Fabricated by Intrinsically Negative Photosensitive Polyimide.

This work describes polyimide (PI) ultrafine fibrous membranes (UFMs) with aligned fibrous structures, fabricated via the high-speed electrospinning procedure. Organo-soluble intrinsically photosensitive PI is utilized as the fiber-forming agent. The effects of different rotating speeds on the fiber morphology and properties are studied. The aligned UFMs possess hydrophobicity, favorable optical properties, and improved deformation durability. The extension strength of the UFMs reinforces obviously with the increased rotating speed and reaches the maximum of 9.18 MPa at 2500 rpm. In addition, due to the photo-cross-link nature of the PI resin, the UFMs present lithography capability, which can obtain micro-sized patterns on aluminum substrates, and even part of the fibrous structure was retained after development. This work shows promise in manufacturing fiber-based photolithographic hierarchical structures on flexible substrates, which exhibit potential in achieving multiple functions on fiber-based electronic devices.

Fully Auto-calibrated Active-stereo-based 3D Endoscopic System using Correspondence Estimation with Graph Convolutional Network.

We have developed a series of 3D endoscopic systems where a micro-sized pattern projector is inserted through the instrument channel of the endoscope and shapes are reconstructed by a structured light technique using captured images of the endoscopic camera. One problem of the previous works is that the accuracy of shape reconstruction is low, because the projector cannot be fixed to the endoscope, and thus, the pose of the pattern projector w.r.t. the camera cannot be pre-calibrated. In this paper, we propose a method to auto-calibrate the pose of the projector without using any special devices nor manual process. Since the technique is one-shot, multiple shapes can be reconstructed from an image sequence and a large 3D scene can be recovered by merging them. Experiments are conducted using the real system.

Droplet delivery and nebulization system using surface acoustic wave for mass spectrometry.

We present a piezoelectric transducer for standing wave surface acoustic wave nebulization (SW-SAWN). The transducer nebulizes nonvolatile analytes present in bulk fluid into ambient air after which the aerosolized drops are sampled by mass spectrometry (MS) for detection. Furthermore, we report for the first time integration of anisotropic ratchet conveyors (ARCs) on the SAWN transducer surfaces to automate the sample preparation and droplet delivery process. The ARCs employ micro-sized hydrophilic patterns on hydrophobic Cytop coatings. Moving, positioning, merging, and mixing of droplets at a designated nebulization location are demonstrated. To create the ARCs, we adopt parylene C as a stencil mask so that the hydrophobicity of the Cytop does not degrade during the microfabrication process. MS measurements with the SAWN chip are performed under different input frequencies. The SAWN transducer can provide a controllable nebulization rate by varying the input nebulization frequency while maintaining a reasonable signal to noise ratio for MS detection.

Flexible Micro-Supercapacitors Based on Interdigitated Electrodes of Flash Lamp Annealed Graphene and Carbon Nanotube Composites

We fabricate graphene-carbon nanotube based flexible micro-supercapacitor, using flash lamp annealing. Flash lamp annealing enables the rapid reduction of graphene oxide to graphene in a millisecond time scale and also favors the formation of highly ordered open network of graphene. Interdigitated micro-sized patterns were designed on graphene oxide-carbon nanotube hybrid thin film via laser ablation. Then, flash lamp annealing process converts the insulating graphene oxide to reduced graphene oxide that is conducting at accurate locations. The resulting interdigitated flash lamp annealed graphene-carbon nanotube was then tested as electrode materials for electrochemical capacitors. The electrochemical performance of the electrodes will be presented in terms of volumetric capacitance, energy density and power density.

Flexible Micro-Supercapacitors Based on Interdigitated Electrodes of Flash Lamp Annealed Graphene and Carbon Nanotube Composites

We fabricate graphene-carbon nanotube based flexible micro-supercapacitor, using flash lamp annealing. Flash lamp annealing enables the rapid reduction of graphene oxide to graphene in a millisecond time scale and also favors the formation of highly ordered open network of graphene. Interdigitated micro-sized patterns were designed on graphene oxide and carbon nanotube hybrid thin film via laser ablation. Then, flash lamp annealing process converts the insulating graphene oxide to reduced graphene oxide that is conducting at accurate locations. The resulting interdigitated flash lamp annealed graphene and carbon nanotube was then tested as electrode materials for electrochemical capacitors. The electrochemical performance of the electrodes will be presented in terms of volumetric capacitance, energy density and power density.

Photovoltaic module active self-cleaning surface using anisotropic ratchet conveyors fabricated with parylene-C stencil

This paper describes an active self-cleaning surface using an anisotropic ratchet conveyor (ARC) to move a water droplet under orthogonal vibrations. Two different ARC systems were designed and fabricated with self-assembled monolayers and hydrophobic Cytop thin films. A novel way to create micro-sized patterns on Cytop was developed without degrading the original Cytop hydrophobicity. Droplet transport speed is 20.5 mm/s at frequency 52 Hz and acceleration 3.3 g (g = 9.8 m/s2). Optical transmission measurements show Cytop can improve optical transmittance by 2.5∼3.5% over the entire visible wavelength range. Solar cell module power output is measured to verify the output power efficiency gain. The self-cleaning function is demonstrated with ARC patterns.

Preparing of Interdigitated Microelectrode Arrays for AC Electrokinetic Devices Using Inkjet Printing of Silver Nanoparticles Ink

The surge in popularity of lab-on-chip applications has set a new challenge for the fabrication of prototyping devices, such as electrokinetic devices. In such devices, a micro-electrode is the key component. Currently, microelectromechanical systems (MEMS) processes such as lift-off and etching techniques are employed to prepare the micro-sized conductive patterns. These processes are time-consuming, require a material removal step, clean-room facilities, and the utilisation of harmful chemicals. On the other hand, rapid fabrication is required by researchers designing such devices to test their functionality. Additive manufacturing technology such as the inkjet printing of conductive material is one potential solution to achieve that objective. In this study, we report the utilisation of inkjet printing for the rapid prototyping of alternating current (AC) electrokinetic devices on a rigid glass substrate. The non-lithographical and vacuum-free process for the fabrication of a microfluidic device was demonstrated. The smallest feature size of 60 μm was successfully printed. The crystalline structure of the printed material under different curing temperatures was characterised. It was found that these treatment conditions affect electrical conductivity. Although a low-temperature sintering process was applied, low resistivity was obtained. An AC electrokinetics device for the manipulation of microparticles has been prepared to illustrate such printed silver micro-patterns. The results strongly support the idea that inkjet printing is a powerful and cost-effective prototyping tool for researchers who work with electrokinetic devices.

Janus Nanoparticles for T Cell Activation: Clustering Ligands to Enhance Stimulation.

The in vitro activation of T cells by synthetic particles is a promising technique for adoptive cancer immunotherapy. While it is known that cell-surface receptors form clusters during T cell activation, the use of clustered ligands on synthetic particles to modulate T cell response is a largely unexplored concept. Building upon our previous finding that T cells respond differently to various micro-sized patterns of ligands, we here investigate the effect of nano-sized ligand clusters on T cell activation. Two-faced Janus nanoparticles were fabricated to display ligands of different functions in spatially segregated clusters on single nanoparticles. Going beyond our earlier qualitative study, here we precisely quantified and controlled the surface density and the total amount of ligands on single nanoparticles. We show that nanoparticles with clustered ligands activate T cells to a greater level than ones uniformly coated with the same number of ligands. The enhanced effect is due to increased local surface density of ligands. The results demonstrate that the spatial arrangement of ligands on particles influences activation response of T cells and may be used as a new strategy to increase T cell stimulation in the presence of insufficient amount of stimuli. This fundamental study also represents an initial step in using nanoscale Janus particles for manipulating immune cell responses.

Copper Micro-Labyrinth with Graphene Skin: New Transparent Flexible Electrodes with Ultimate Low Sheet Resistivity and Superior Stability.

We have developed self-assembled copper (Cu) micro-labyrinth (ML) with graphene skin for transparent flexible electrodes of optoelectronic devices. The Cu ML is simply formed by heating a thin Cu film with a 100-nm thickness on a SiO2/Si substrate at 950 °C under hydrogen ambient to block the oxidation. Moreover, the Cu ML can have graphene skin at the surface by inserting carbo-hydroxyl molecules (CxHy) during heating due to the catalytic decomposition of C–H bonds on the Cu surface. The Cu ML with graphene skin (Cu ML-G) has superior sheet resistivity below 5 Ω/sq and mechanical flexibility without cracks at the bending radius of 0.1 cm. Although the transmittance of Cu ML-G is a little lower (70%~80%) than that of conventional metallic nanowires electrodes (such as Ag, ~90% at the visible wavelength), it has good thermal stability in conductivity without any damage at 200 °C due to a micro-sized pattern and graphene skin which prohibits the surface migration of Cu atoms.

Photoluminescent Dye Doped Cholesteric Liquid Crystal Reflector with Micro-Sized Patterns Using Reactive Mesogens

Photoluminescent Dye Doped Cholesteric Liquid Crystal Reflector with Micro-Sized Patterns Using Reactive Mesogens

Micro-patterning technique using a rotating cutting tool controlled by an electromagnetic actuator

This work describes a micro-patterning or surface texturing technique on the fixed work surface using a proposed new spindle system with a rotating cutting tool controlled in real time. The proposed spindle system creates micro-sized patterns using rotating tools such as a micro-milling tool and a micro-grinding wheel. The shaft of the spindle is suspended by air bearings, and an electromagnetic actuator controls the radial motion of the spindle housing instead of the shaft. This generates a micro-pattern array on the electro-less Ni-coated workpiece in the micro-milling process. A PID controller is adopted to make the system stable, and adaptive feedforward cancellation is used to effectively compensate for the run-out of the spindle system during machining. The machining results show that this compensation improves the pattern accuracy. It is expected that micro-patterning using the proposed spindle system can be applied over a large surface area.

Carbon nanotube field emitters on KOVAR substrate modified by random pattern

We investigated the field emission characteristics of patterned carbon nanotubes (CNTs) on KOVAR substrates with different surface morphologies. The substrate with a micro-sized random pattern was fabricated through chemical wet etching, whereas the substrate with a nano-sized random pattern was formed by surface roughening process of polymer and chemical wet etching. The field emission characteristics of these substrates were the compared with those of non-treated substrates. It was clearly revealed that the field emission characteristics of CNTs were influenced by the surface morphology of the cathode substrate. When the surface of cathode was modified by random pattern, the modified substrate provided a large surface area and a wider print area. Also, the modified surface morphology of the cathode provided strong adhesion between the CNT paste and the cathode. Particularly, the substrate with the nano-sized random pattern showed that the turn-on field value decreases and the field enhancement factor value improves as compared with non-treated substrate.

Particle deposition on the patterned membrane surface: Simulation and experiments

Mitigation of membrane fouling is important for the sustainable operation of waste-water treatment. A wide range of physical, chemical and biological anti-fouling techniques has been proposed to reduce membrane fouling. Through these efforts, patterned membranes on which micro-sized surface patterns are engraved are known to exhibit effective anti-fouling performance without any chemical or biological treatment. To optimize anti-fouling properties of patterned membranes, particle deposition on the patterned membrane surface needs to be understood. In this study, both Brownian dynamics simulation and particle deposition experiments were conducted to understand the mechanism of particle deposition on the patterned membrane surface. A model experimental system was developed, in which poly(methyl methacrylate) (PMMA) colloidal suspension was pumped into a microfiltration module containing a patterned membrane. Stagnant flow zone was formed in the valley region of the surface pattern, in which more particles were deposited. High shear stress was distributed near the apex region, where few particles were deposited. Both the simulation and the experimental results confirmed these observations. Flow characteristics near the patterned membrane surface were found to be strongly correlated with the particle deposition. This study will provide a useful insight for the design of efficient micro-structured membranes.

Interfaces of Molecular Recognition Sites and Biosensors; Novel Bio-Sensing Materials

ABSTRACTWe introduce a sensing element, “Molecularly Imprinted Polymer (MIP),” which created by “Molecular Imprinted Technique.” However, the sensitivity of MIP’s based bio-sensors limits for practical applications due to the low sensitivity. To achieve a high sensitivity of MIP’s based sensors, the synthesis of “high affinity receptor or binding sites,” such as “monoclonal particles” is a key objective. In previous studies, affinity distribution plots indicated that “high affinity binding sites” were obtained when the number of binding sites per particle decreased. It means that smaller particles are expected to have higher affinity binding sites compared to larger particles. The result motivated us to produce small-sized MIP’s particles for the achievement of higher sensitivity. Microfluidic Synthesis has taken a great attention to synthesize small particles. However, the microfluidic synthesis gave us a difficulty, especially collections of MIP’s particles from the surface of PDMS-based microchannels due to a sticking problem. Thus, we employed a new approach, which can collect MIP’s particles without any sticking problem from the surface of the reactor. It is a photopatterned MIP’s system generated on the glass surface. We prepared a photomask with micro-sized patterns and then fabricate MIP’s particles on a glass surface by photopolymerization. Uniform MIP’s patterns were printed on the glass surface. The interface between the glass surface and the MIP’s pattern was observed by SEM. Micro-sized MIP’s particles were collected from the glass surface by scratching off the photocured MIP’s patterns.

Design of a Patterned Diamond Substrate for Ordered Neural Cell Adhesion

Diamond has recently attracted lots of interest as a potential candidate for neural interface due to many of its advantages such as biocompatibility, superior hardness and chemical inertness. Here we present a method for designing and fabricating a diamond platform for ordered neural cell adhesion. Microcontact printing was used for selective nanodiamond seeding and chemical vapor deposition was conducted subsequently to form diamond patterns. We compared different printing methods and precise microsized patterns were finally fabricated for the formation of ordered neural cell network.

Fabrication of Viewing Angle Direction Brightness-Enhancement Optical Films using Surface Textured Silicon Wafers

We demonstrate a low-cost, superbly efficient way of etching for the nano-, and micro-sized pyramid patterns on (100)-oriented Si wafer surfaces for use as a patterned master. We show a way of producing functional optical films for the viewing angle direction brightness-enhancement of Lambertian LED (light emitting diode)/OLED (organic light emitting diode) planar lighting applications. An optimally formulated KOH (Potassium hydroxide) wet etching process enabled random-positioned, and random size-distributed (within a certain size range) pyramid patterns to be developed over the entire (100) silicon wafer substrates up to 8" and a simple replication process of master patterns onto the PC (poly-carbonate) and PMMA (poly-methyl methacrylate) films were performed. Haze ratio values were measured for several film samples exhibiting excellent values over 90% suitable for LED/OLED lighting purposes. Brightness was also improved by 13~14% toward the viewing angle direction. Computational simulations using LightTools<TEX>$^{TM}$</TEX> were also carried out and turned out to be in strong agreement with experimental data. Finally, we could check the feasibility of fabricating low-cost, large area, high performance optical films for commercialization.

진동 마이크로 밀링을 이용한 미세 반복 패턴 가공 기술 연구

This paper introduces a system to machine micro-sized patterns effectively on surface based on micro-milling process using tools with simultaneous rotation and oscillation, oscillation micro milling. To review the effectiveness of proposed concept, we integrated a micro-spindle supported by active magnetic bearings with a precision 3-axis air bearing stage using double-wedge mechanism, and tested this oscillation milling. Two types of oscillation milling were tested, which are linear oscillation milling with a flat end mill and elliptical oscillation milling with a ball end mill with 0.3 mm of diameter. The spindle was rotating 110 krpm and workpiece was moving constant speed of 2~8 mm/sec during the oscillation milling. As the results, multiple oval shape dimples were generated in regular spacing, and the variation of elliptical motion made different shapes of patterns. The results showed that proposed oscillation milling can be successfully used for machining repeated micro-patterns.