Pillar Patterns Research Articles

Poly(ethylene glycol) dimethacrylate (PEGDMA) multi-functional pillar-patterned surface for osteogenic differentiation of pre-osteoblast and anti-bacterial effects to Escherichia coli and Staphylococcus aureus

Cells are sensitive to the surface topographical environment, which can subsequently induce changes in cell morphology, cytoskeleton, and differentiation. Therefore, the topological environment in bone implant devices is known to influence the cell behavior, adhesion, and differentiation of osteoblasts. Furthermore, bone implant devices with anti-bacterial properties could be necessary to prevent surgical site infections (SSIs). Consequently, there is a demand for research into multi-functional surfaces that can facilitate osteoblast differentiation while also possessing an anti-bacterial effect. In this study, we fabricated and assessed the poly(ethylene glycol) dimethacrylate (PEGDMA) nano/micro pillar-patterned surface to find the optimized dimensional characteristics of the pillar pattern for multi-functional effect. Results observed that the pillar pattern enhanced differentiation to osteoblast on the pillar-patterned surface (D1S0.5) having pillars with 0.5 μm height, 1 μm diameter, and 0.5 μm spacing between pillars and pillar-patterned surface (D1S1) having pillars with 0.5 μm height, 1 μm diameter, and 1 μm spacing between pillars. Subsequently, results of evaluating anti-bacterial effect revealed that the optimized pillar-patterned surface exhibited remarkable antibacterial effect, with the D1S0.5 pillar-patterned surface showing the highest antibacterial effect. Consequently, this study proposed and verified a multi-functional pillar-patterned surface capable of promoting osteoblast differentiation with anti-bacterial effects.

Robust Design of a Elastmeric Surface with Dimpled Pillar Pattern for Directional Friction of a Robot Gripper

Robust Design of a Elastmeric Surface with Dimpled Pillar Pattern for Directional Friction of a Robot Gripper

Aluminum Micropillar Surfaces with Hierarchical Micro- and Nanoscale Features for Enhancement of Boiling Heat Transfer Coefficient and Critical Heat Flux.

The rapid progress of electronic devices has necessitated efficient heat dissipation within boiling cooling systems, underscoring the need for improvements in boiling heat transfer coefficient (HTC) and critical heat flux (CHF). While different approaches for micropillar fabrication on copper or silicon substrates have been developed and have shown significant boiling performance improvements, such enhancement approaches on aluminum surfaces are not broadly investigated, despite their industrial applicability. This study introduces a scalable approach to engineering hierarchical micro-nano structures on aluminum surfaces, aiming to simultaneously increase HTC and CHF. One set of samples was produced using a combination of nanosecond laser texturing and chemical etching in hydrochloric acid, while another set underwent an additional laser texturing step. Three distinct micropillar patterns were tested under saturated pool boiling conditions using water at atmospheric pressure. Our findings reveal that microcavities created atop pillars successfully facilitate nucleation and micropillars representing nucleation site areas on a microscale, leading to an enhanced HTC up to 242 kW m-2 K-1. At the same time, the combination of the surrounding hydrophilic porous area enables increased wicking and pillar patterning, defining the vapor-liquid pathways on a macroscale, which leads to an increase in CHF of up to 2609 kW m-2.

Directed Self-Assembly of Cylinder-Forming Block Copolymers Using Pillar Topographic Patterns.

We conducted a computational study on the self-assembly behavior of cylinder-forming block copolymers, directed by a guide pattern of hexagonally or tetragonally arrayed pillars, using mesoscale density functional theory simulations. By adjusting the spacing (Lp) and diameter (D) of the pillars in relation to the intrinsic cylinder-to-cylinder distance (L2) of the cylinder-forming block copolymer, we investigated the efficiency of multiple-replicating cylinders, generated by the block copolymer, through the pillar-directed self-assembly process. The simulations demonstrated that at specific values of normalized parameters L˜2=L2/Lp and D˜=D/Lp coupled with suitable surface fields, triple and quadruple replications are achievable with a hexagonally arrayed pillar pattern, while only double replication is attainable with a tetragonally arrayed pillar pattern. This work, offering an extensive structure map encompassing a wide range of possible parameter spaces, including L˜2 and D˜, serves as a valuable guide for designing the contact hole patterning essential in nanoelectronics applications.

Integrating Micro-Patterned Flow Fields into Electrode Architecture Via Non-Solvent Induced Phase Separation for High Performance Redox Flow Batteries

To facilitate increasing penetration of intermittent renewables in the energy mix, there is a growing need for energy storage technologies. Redox flow batteries (RFBs) have attracted significant attention in recent years due to their suitable characteristics for long-duration stationary energy storage applications. However, the wider adoption of RFB systems is still limited by the capital cost, to which the reactor stack is a large contributor[1]. Further cost reduction can be achieved by reducing kinetic, mass-transfer, and ohmic losses to improve the stack performance. Porous electrodes are key components within the battery stack, providing active sites for electrochemical reactions, and transport pathways for active species. Commercially available carbon-fiber electrode architectures include carbon paper, carbon felt, and carbon cloth. They have a highly porous structure, but their relatively low surface area and low hierarchical fiber orientation increase both electrochemical and pumping losses[2]. There is still a need to develop a low-cost porous electrode that meets the requirements of high active surface area and facile electrolyte transport to enhance battery performance and system efficiency.Non-solvent induced phase separation (NIPS) is a manufacturing route in the field of membrane technology, which is widely used to fabricate asymmetric membranes[3]. Recently this route has also been used to fabricate non-fibrous porous electrodes[4]. The microstructure of NIPS electrodes is largely influenced and controlled by the solvent/non-solvent exchange rate at the interface between a polymer solution and a coagulation bath. When the phase exchange process is slow, segregation is delayed. This type of segregation generally results in a sponge-like, relatively dense structure[5]. This sponge-like structure has the advantage of small pore size and high surface area, but also has poor hydraulic permeability and high mass-transfer losses. The trade-off between surface area and permeability needs to be further optimized.In the present study, inspired by the flow field designs widely used in RFBs to guide the electrolyte flow paths for low pressure drop, uniform electrolyte distribution, and high electrochemical performance[6], we propose a strategy to imprint micro-patterned flow fields directly into the electrode architecture during NIPS processing to improve mass transfer properties. NIPS polymer films were cast onto molds with specific micro-patterns, and the resulting micro-channels can be preserved in the electrodes after carbonization. To verify the effectiveness of the micro-patterned electrodes, here, we investigate two selected micro-patterned designs. The groove-patterned electrodes were combined with flow-through flow fields (FT-FFs) for in-plane mass transport optimization, and the pillar-patterned electrodes were combined with interdigitated flow fields (IDFFs) for through-plane flow optimizations[7]. Two geometric sizes of the micro-patterns were considered in each design. The pore sizes and distributions of the micro-patterned electrodes were determined by mercury intrusion porosimetry. The hydraulic permeability of the electrodes was evaluated by half-cell pressure drop measurements, and the electrochemical specific surface area was determined through electrochemical impedance spectroscopy under non-faradaic conditions. In addition, we performed electrochemical battery tests with symmetric iron RFB (0.5 M Fe2+/Fe3+, 2 M HCl) cells and vanadium full-cells (1.6 M V active species at 50% state-of-charge). It was found that due to the small pore size (e.g., ~1 μm) and narrow pore size distribution of the sponge-like NIPS structure, the main contribution to the total losses in electrodes without micro-patterns in electrochemical performance comes from mass-transfer. Electrodes with groove and pillar patterns can help reduce the pressure drop and improve mass transfer properties. Pillar-patterned electrodes with the combination of IDFF show high overall electrochemical performance with greatly reduced mass transport resistances. At an electrolyte velocity of 10 cm/s, the total resistances for kinetic and mass transfer are less than 0.1 Ω·cm2 in symmetric iron cell tests. Compared to the activated commercial electrode (e.g., 2-layer Freudenberg H23 carbon paper, thermally treated at 450 oC for 12 h), the total resistances for kinetic and mass transfer are reduced by ~60%, which shows great potential for adoption in next generation high-performance RFB systems. References J. Noack, L. Wietschel, N. Roznyatovskaya, K. Pinkwart, J. Tübke, Energies, 9, 627 (2016).A. Forner-Cuenca, F.Brushett, Current Opinion in Electrochemistry, 18, 113-122 (2019).H. Wang, J. Jung, J. Kim, S. Kim, E. Drioli, Y. Lee, Journal of Membrane Science, 574, 44-54 (2019).C. Wan, R. Jacquemond, Y. Chiang, K. Nijmeijer, F. Brushett, A. Forner-Cuenca, Advanced Materials, 33, 2006716 (2021).D. Wang, J. Lai, Current Opinion in Chemical Engineering, 2, 229-237 (2013).X. Ke, J. Prahl, J. Alexander, J. Wainright, T. Zawodzinski, R. Savinell, Chemical Society Reviews, 23, 8721-8743 (2018).V. Muñoz-Perales, P. García-Salaberri, A. Mularczyk, S. Ibáñez, M. Vera, A. Forner-Cuenca, ChemRxiv, (2023).

Implementation of various colors in Cu(In,Ga)Se2 thin-film solar cells by diffractive nanostructures

With the increasing use of building-integrated photovoltaic technology, it has become necessary for solar panels to blend in with their surroundings. Diffractive nanostructures can be used to reduce optical losses and create colorful solar cells. To make colors on Cu(In,Ga)Se2 (CIGS) thin-film solar cells, we fabricated diffractive nanostructures by using nanoscale imprinting and transfer lithography methods. And we investigated how the material types and pattern shapes of the nanostructures influence the optical properties of solar cells, such as the short-circuit current density (JSC), coordination of color appearance, and color quality. We used two types of pillars and grating nanostructures of SiO2 and TiO2 layers on CIGS thin-film solar cells to produce various colors. The SiO2 demonstrated an increase in JSC without significant loss of color quality compared to TiO2. By utilizing a hexagonally arrayed pillar pattern, colors are observed at various angles on an axis different from the incident light, unlike colors observed only at a single angle in the grating structure. The nanoimprinting lithography process allowed us to produce high-quality nanostructures on both rigid glass and flexible stainless-steel substrates.

Protein ligand and nanotopography separately drive the phenotype of mouse embryonic stem cells

Biochemical and biomechanical signals regulate stem cell function in the niche environments in vivo. Current in vitro culture of mouse embryonic stem cells (mESC) uses laminin (LN-511) to provide mimetic biochemical signaling (LN-521 for human systems) to maintain stemness. Alternative approaches propose topographical cues to provide biomechanical cues, however combined biochemical and topographic cues may better mimic the in vivo environment, but are largely unexplored for in vitro stem cell expansion. In this study, we directly compare in vitro signals from LN-511 and/or topographic cues to maintain stemness, using systematically-varied submicron pillar patterns or flat surfaces with or without preadsorbed LN-511. The adhesion of cells, colony formation, expression of the pluripotency marker,octamer-binding transcription factor 4 (Oct4), and transcriptome profiling were characterized. We observed that either biochemical or topographic signals could maintain stemness of mESCs in feeder-free conditions, indicated by high-level Oct4 and gene profiling by RNAseq. The combination of LN-511 with nanotopography reduced colony growth, while maintaining stemness markers, shifted the cellular phenotype indicating that the integration of biochemical and topographic signals is antagonistic. Overall, significantly faster (up to 2.5 times) colony growth was observed at nanotopographies without LN-511, suggesting for improved ESC expansion.

Etched characteristics of nanoscale TiO2 using C4F8-based and BCl3-based gases

TiO2 is a material used in various fields such as electronics, optics, environment, etc. For the application to electronic and optical devices, TiO2 needs to be patterned using reactive ion etching using halogen-based gases. In this study, a TiO2 masked with ACL pillar pattern was etched using two types of gases namely C4F8-based (C4F8/SF6/Ar) and BCl3-based (BCl3/CF4/Ar), and the effect of etch gas and asynchronous pulsing (separated source power ON time and bias power ON time in a pulse period) on the etch properties such as the etch rates, etch selectivity, and aspect ratio dependent etching (ARDE) were investigated. The use of asynchronous pulsing with decreased bias pulsing ratio (high source power ON time and low bias ON time in a pulse period) improved the etch selectivity and ARDE possibly due to the lower sputter etching time after the removal of reacted species on the TiO2 surface and due to the more similar etch environment for different aspect ratio TiO2 features, respectively. The use of BCl3-based plasma showed higher etch selectivity over ACL compared to C4F8-based plasma, however, it showed the lower etch rate and more severe ARDE due to the stickiness of Cl compared to F to the sidewall during the etching of high aspect ratio TiO2.

Cooperative mining technology and strata control of close coal seams and overlying coal pillars

Mining of close coal seams envisages reservation of a large number of section coal pillars of a total width ranging from 30 to 40 m. This results in an enormous waste of coal resources and risks of spontaneous combustion, instability, and damage to the remaining coal pillars. This study attempts to mitigate the above problems via the proposed cooperative mining technical method for close seams and overlying coal pillars. It expounds on the technical principles, the required mining equipment, technology, and the system layout, and analyzes the key influencing factors of strata control. Using the numerical simulation via FLAC3D and PFC2D commercial software packages, the effect of horizontal distance between the lower coal seam roadway and the overlying coal pillar (i.e., spacing) on the surrounding rock control and rational layout of the roadway is studied. The mechanism of the overlying coal pillar width effect on the ground pressure of the stope and coal pillar recovery rate is clarified. The engineering case study shows that when the horizontal spacing was increased from 0 to 15 m, the surrounding rock deformation, surrounding rock stress peak value, and plastic zone area of the roadway decreased significantly. When the coal pillar width in the overlying section was increased from 25 to 40 m, the peak values of lateral and advance bearing stresses in the stope dropped by 21 and 12 MPa, respectively. Besides, the ground pressure driving strength of the stope was significantly reduced, and the recovery rates of the overlying coal pillar and rock between the close coal seams were increased by 7.45 and 4.29%, respectively. Combined with the top coal pillar drawing pattern, optimization concepts and their realization methods were proposed.

Hierarchically Patterned Self-Cleaning Polymer Composites for Daytime Radiative Cooling.

Passive daytime radiative cooling (PDRC) has the potential to reduce energy demand and mitigate global warming. However, surface contamination from dust and bacterial buildup limits practical PDRC applications. Here, we develop a hierarchically patterned nanoporous composite (HPNC) using a facile template-molding fabrication method to integrate PDRC materials with self-cleaning and antibacterial functions. The HPNC design decouples multifunctional control into different characteristic length scales that can be optimized simultaneously. The nanoporous polymer matrix embedded with tunable fillers enables 7.8 and 4.4 °C temperature reduction for outdoor personal and building cooling, respectively, under intense solar irradiance. Meanwhile, a microscale pillar array pattern integrated into the HPNC enables superhydrophobicity with self-cleaning and antisoiling functions to mitigate surface contamination. Moreover, the surface coating of photocatalytic agents can generate photoinduced antibacterial effects. The scalable fabrication and multifunctional capabilities of our HPNC design offer a promising solution for practical PDRC applications with minimal maintenance needs.

EUV Metal Oxide Resist Development Technology for Improved Sensitivity, Roughness and Pattern Collapse Margin for High Volume Manufacturing

One of the critical challenges for delivering next nodes or high-NA extreme ultraviolet (EUV) lithography to high volume manufacturing (HVM) in the semiconductor industry is to have a high-performance EUV resist process. The high-performance resist process needs to simultaneously meet multiple requirements, such as high resolution, high sensitivity, low roughness, a low defect level, and good global CD uniformity (CDU). In this paper, we will introduce a new wet development (DEV) method to improve the performance of metal oxide resists (MOR), which is named ESPERTTM** (Enhanced Sensitivity develoPER Technology). This newly invented method can meet multiple requirements together where it is not possible with the conventional development method. With 36 nm pitch pillar patterns, we have confirmed with after etch inspection (AEI) data that the new method produced 22% improvement in EUV dose and 7% improvement in LCDU, simultaneously. No pattern collapse was observed at least up to 15.4 nm pillar size. In the case of 30 nm pitch line/space (L/S) pattern, the improvements were 26% in EUV sensitivity and 12.3% in LWR also with AEI results. Furthermore, the new method could also shift the bridging cliff 0.5 nm to the larger line CD while its global CDU was improved 2.6 times. The new data achieved by the new wet development method make us believe that MOR are mostly ready for HVM and this new method is also aiming to be used in high NA EUV lithography in the near future.**) ESPERTTM is trademarks of Tokyo Electron Limited.

Experimental analysis and predictive modelling of Ti6Al4V laser surface texturing for biomedical applications

Laser surface texturing (LST) is a powerful technique for creating high quality micro-textured patterns with different shapes and sizes on metallic biomaterials. Textured surfaces may improve the interaction between bone and implant by increasing the surface contact area and thus promoting bone regeneration. The goal of this study was to explore Nd:YAG laser potential for texturing micro-scale pillars with pyramid geometry, with dimensions in a selected range, in a reproducible way. First, the design and texture of grooves were addressed, then proceeding to pillars. Two laser machining and marking strategies were investigated, and the consecutive laser processing strategy and continuous marking mode were selected due to the resultant smoother grooves. Then, a cross-hatched pattern was designed to texture a pillar pattern with targeted dimensions. Given the direct effect of the LST drawing and laser parameters on the texture dimensions, three mathematical models, one for each texture dimension (groove width, pillar width and pillar depth) were developed. These models are accurate tools for predicting the texture dimensions in the selected range and this LST approach was effective on creating well-defined, uniform and equally spaced surface textures on Ti6Al4V parts, in a reproducible way. A combination of drawing and laser parameters was selected for the target dimensions, also considering suitable wettability and roughness for biomedical applications.

Extendibility Study of Conventional IPA Drying Process From Dynamic Fluid Model for Pattern Collapse

1. IntroductionIPA (iso-Propyl alcohol) has been widely used in semiconductor manufacturing for drying silicon wafer to mitigate water mark and keep the surface clean after wet cleaning process. Then, IPA process has been extended by combining with the other engineering techniques such as surface modification treatment to dry fragile nano-sized Si patterns [1]. As the scaling of advanced semiconductor devices continues, however, the pattern collapse is one of the most challenging issues for IPA drying process today. Capillary force model explains the pattern collapse in the earlier studies, where Laplace pressure originated from meniscus between patterns is a critical factor [2]. And the model has been well referred to and extensively studied in semiconductor industry [3]. Although, the model does not take dynamics of fluid into account, our experimental result suggests that drying rate is also critical, i.e., pattern collapse rate decreases as drying rate increases. This result is not explained by the reported models since the drying rate is not considered as a variable. In this report, a new model is suggested and verified by unique experiments. Our proposed model assumed that osmosis of metastable liquid to nano-size structures occurs from the triple line which is the air-liquid-solid interface, and the region of osmosis is less favorable for pattern collapse. The width of osmosis region would be determined by the drying rate. Also, based on this study, extendibility of IPA drying process to smaller device feature size for advanced node is discussed.2. ExperimentalWafer processing was conducted in spin process chamber on HVM equipment for drying experiment. IPA was dispensed on rotating wafer then dried at 0 or 1500 rpm. Nano-structured wafer used was with 34 nm-diameter of Si pillars, and aspect ratio (AR) of the pillar was 12:1. Pattern collapse was observed by top-view SEM, and collapse rate was calculated by automated image analysis with obtained SEM pictures. For osmosis observation at the triple line, FPM was prepared by mixing 49% HF, 30% H2O2 and H2O at volume ratio of 1:2:100. A droplet of FPM was dropped on the surface of Si pillar pattern wafer and observed by optical microscopy while the drop was drying out. After drying, pattern collapse of the pillar pattern was observed by X-SEM. To study effect of drying rate and to maximize it, IPA was dispensed on 10×12 mm2 coupon, then vaporized at 0 rpm with flash lamp annealing. AR of the pillar was 16:1. Observation of pattern collapse by top-view SEM was also conducted.3. Results and DiscussionIPA drying at 0 and 1500 rpm resulted in collapse rate of 91.1% and 46.9%, respectively, on the pillar AR = 12:1 (Fig. 1). IPA was dried out faster when wafer rotation speed was 1500 rpm. Thus, collapse rate decreases as drying speed increases. On osmosis observation, FPM droplet was sucked into between the pillars, causing osmosis at around droplet, and generated colored interference according to liquid film thickness. X-SEM inspection after the droplet drying indicated the most pattern collapse seemed to occur at the osmosis region where liquid thickness nearly equals to the pillar height. We assumed by increasing drying rate the osmosis region would be minimized and the pattern collapse would be suppressed. To verify this model, the following evaluation was conducted. With extremely high drying rate of IPA by flash lamp annealing, we obtained 0% of collapse rate even in the pillar AR = 16:1 (Fig. 2). This result indicates that there is some more process margin for the pattern collapse on IPA drying process.4. ConclusionIn the IPA drying process, collapse rate decreases as drying rate increases. Our proposed model assumed that osmosis region of metastable liquid to nano-size structures occurs from the triple line, and the pattern collapse happens there. That explains reasoning for lower collapse rate at higher drying speed is that osmosis is minimized when drying rate is maximized. Test result from maximized IPA drying rate by flash lamp annealing indicates that there is some more process margin for the pattern collapse. In our view, by this method IPA drying process might be extended to two more device nodes.

Reduction of dislocation density in lattice-relaxed Al0.68Ga0.32N film grown on periodical 1 μm spacing AlN pillar concave-convex patterns and its effect on the performance of UV-B laser diodes

We report the results of crystal growth of thick AlGaN films on periodical 1 μm spacing AlN pillar concave-convex patterns and their impact on the performance of UV-B laser diodes. The formation of voids in the AlGaN film by increasing the AlN pillar height and the use of high-quality AlN templates were effective in improving the quality of AlGaN, and the dislocation density in the AlGaN film was reduced to approximately 3.4 × 108 cm−2. A UV-B laser diode was fabricated on the optimized AlGaN, demonstrating a threshold current density of ∼12 kA cm−2 and a high yield rate of over 90%.

Optically Rough and Physically Flat Transparent Conductive Substrates with Strong Far-Field Scattering

Optically rough and physically flat transparent conductive (OR-PF) substrates facilitate the performance improvement of optoelectronic devices and functional glasses via simultaneously enabling high-quality growth of functional layers and effective light management. This paper studies the effect of the interface morphology of the hole array pattern (HAP) and the pillar array pattern (PAP) on the far-field scattering properties of OR-PF substrates fabricated by spin-coating Al-doped ZnO (AZO) on nanoimprint-patterned glasses for improving the performance of superstrate-type thin-film solar cells. Theoretical calculation based on bidirectional scattering distribution function predicts that HAP with a period of 1.5 μm and a diameter of 1.3 μm [HAP(P1.5D1.3)] and the PAP(P1.0D0.5) interface morphology have a haze ratio in transmission (HT) of around 64% and a scatter angle of larger than 34°. The fabricated AZO/HAP(P1.5D1.3) and AZO/PAP(P1.0D0.5) show a flat surface with a σrms of less than 9 nm, a high visible light transmittance of over 86%, a sheet resistance of about 30 Ω/sq, and strong far-field scattering. In particular, AZO/PAP(P1.0D0.5) possesses an average HT of over 11% at the wavelength range of 600-850 nm and an angular intensity distribution of over 1.5% at an azimuthal angle of around 55°, indicating stronger far-field scattering than the conventional pyramid-textured B-doped ZnO (BZO/F). Compared to the flat substrate, AZO/PAP generates an implied Jsc gain of 16.2% in a CH3NH3PbI3 photoactive layer with a thickness of 300 nm under normal incidence at the wavelength range of 550-800 nm. For 60° incidence, AZO/PAP(P1.0D0.5) enables an implied Jsc gain of 2.3% with respect to BZO/F. As applied to the front electrode of CH3NH3PbI3 thin-film solar cells, compared to BZO/F, AZO/PAP(P1.0D0.5) would enable a gain of up to 16.7 and 11.2% in photoelectric conversion efficiency for the 0 and 60° incidence, respectively.

Surface topography effects on dynamic behavior of water droplet over a micro-structured surface using an improved-VOF based lattice Boltzmann method

A volume of fluid-based lattice Boltzmann method (VOF-LBM) is developed, using the open-source parallel lattice Boltzmann solver library (Palabos) to study the wettability of solid surfaces and include the droplets’ dynamic behavior. This improves the accuracy and diminishes limitations on the density and viscosity ratios and the outcoming spurious velocities. An experimental study is performed, and the numerical results are verified through comparison with experimental data. Next, to design novel hydrophobic surfaces with pillar structures, the effect of different pillar patterns and topographies on the contact angle of water droplets and the droplet motion over an inclined surface are investigated. Hydrophobic micro-pillar surfaces are designed to enhance the ease of droplets movement on the slope. The effect of contact angle, wetted area, and surface energy on the sliding behavior of droplets is examined and presented. Results indicate that the new VOF-LBM method can simulate high density and viscosity ratios (1000 and 1.81×10-2 respectively), allowing real-world problems to be analyzed with appropriate accuracy. This reduces the spurious velocities produced at the fluids interface by 19 times compared to the Shan and Chen method. Results demonstrate that the contact angle of the water droplet on the surface with a contact angle of 115° can reach 160° by changing the surface topography. Also, a hydrophobic micro-pillar surface is designed in which the droplet moves nearly 12% faster than the flat surface.

Design Rule for Constructing Buckling-Free Polymeric Stencil with Microdot Apertures.

A polymeric stencil with microdot apertures made by using polydimethylsiloxane (PDMS) molds with pillar patterns has many advantages, including conformal contact, easy processability, flexibility, and low cost compared to conventional silicon-based membranes. However, due to the inherent deformability of PDMS materials in response to external pressure, it is challenging to construct structurally stable stencils with high structural fidelity. Here, we propose a design rule on the buckling pressure for constructing polymeric stencils without process failure. To investigate the critical buckling pressure (Pcr), stencils are fabricated by using different PDMS molds with aspect ratio variations (AR: 1.6, 2.0, 4.0, and 5.3). By observing the buckled morphology of apertures, the structures can be classified into two groups: low (AR 1.6 and 2.0) and high (AR 4.0 and 5.3) AR groups, and Pcr decreases as AR increases in each group. To investigate the results theoretically, the analysis based on Euler’s buckling theory and slenderness ratio is conducted, indicating that the theory is only valid for the high-AR group herein. Besides, considering the correction factor, Pcr agrees well with the experimental results.

A Study on Fabrication Process of Gold Microdisk Arrays by the Direct Imprinting Method Using a PET Film Mold

In this study, an efficient nanofabrication process of metal microdisk arrays using direct imprinting was developed. This process was comprised of three steps; sputter etching on the quartz glass substrate, gold thin film deposition on an etched surface of a substrate, and transfer imprinting using a polyethylene terephthalate (PET) film mold on the Au thin film. A new idea to utilize a PET film mold for disk patterning by the nano transfer imprinting was examined. The PET film mold was prepared by thermally embossing the pillar pattern of a master mold on the PET film. The master mold was prepared from a silicon wafer. The PET film mold was used for transfer imprinting on a metal film deposited on a quartz substrate. The experimental results revealed that the PET film mold can effectively form gold micro-disk arrays on the Au film despite the PET film mold being softer than the Au film. This method can control the distribution and orientation of the nano-arrays on the disk. The plasmonic properties of the gold micro-disk arrays are studied and the absorbance spectrum exhibit depends on the distribution and orientation of gold micro-disk patterns. The nano-transfer imprinting technique is useful for fabricating metallic microdisk arrays on substrate as a plasmonic device.

Real-time capture of single particles in controlled flow by a rapidly generated foci array with adjustable intensity and pattern.

We propose a new, to the best of our knowledge, technique to capture single particles in real-time in a microfluidic system with controlled flow using micro-pillar traps fabricated by one-step. The micro pillars are fabricated in parallel by femtosecond multi-foci laser beams, which are generated by multiplexing gratings. As the generation process does not need integration loops, the pattern and the intensity distribution of the foci array can be controlled in real-time by changing the parameters of gratings. The real-time control of the foci array enables rapidly fabricating microtraps in the microchannel with adjustment of the pillar spaces and patterns according to the sizes and shapes of target particles. This technology provides an important step towards using platforms based on single-particle analysis, and it paves the way for the development of innovative microfluidic devices for single-cell analysis.

Influence of Surface Texture on the Variation of Electrokinetic Streaming Potentials.

The electrokinetic streaming potential (Vs) obtained through electrolyte flow in a microchannel is shown to be related to the underlying surface pattern. Pillar, mesh, and groove patterns were studied for comparing the relative magnitudes of the Vs with air-/liquid-filled surfaces. A record value of the related figure of merit, in terms of the developed Vs per-unit applied pressure, of ∼0.127 mV/Pa, was observed in a mesh texture liquid-filled surface (LFS) impregnated with an electrolyte-immiscible oil. The study indicated that increasing the solid fraction of the pattern surface decreases the effective slip length while enhancing the overall channel ζ potential. Consequently, maximizing the obtained Vs implies a balancing of the slip with the surface potential, with plausibly more significance of the latter. The work has implications for higher-efficiency electrical voltage sources.