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The development of hydrophobicity on polymer surfaces in mass production is one of the most critical challenges in the plastic industry. This paper deals with a novel combined hot embossing process in which femtosecond laser ablation is utilized to texture the embossing stamps. By controlling the process temperature and axial forces, the laser textures were transferred to polymer surfaces, successfully resulting in hydrophobicity. Four different polymers, including ABS, PP, PA, and PC, along with two different laser textures, namely ball and pyramid, were tested. The laser and hot embossing parameters under which the textures were transferred to the polymers are introduced. The critical micro- and nano-features of the transferred textures that resulted in high hydrophobic contact angles are also discussed. The results indicate that PP and ABS have higher contact angles, respectively, while under the given parameters, PA and PC did not exhibit hydrophobic surfaces. [ABSTRACT FROM AUTHOR]

The development of hydrophobicity on polymer surfaces in mass production is one of the most critical challenges in the plastic industry. This paper deals with a novel combined hot embossing process in which femtosecond laser ablation is utilized to texture the embossing stamps. By controlling the process temperature and axial forces, the laser textures were transferred to polymer surfaces, successfully resulting in hydrophobicity. Four different polymers, including ABS, PP, PA, and PC, along with two different laser textures, namely ball and pyramid, were tested. The laser and hot embossing parameters under which the textures were transferred to the polymers are introduced. The critical micro- and nano-features of the transferred textures that resulted in high hydrophobic contact angles are also discussed. The results indicate that PP and ABS have higher contact angles, respectively, while under the given parameters, PA and PC did not exhibit hydrophobic surfaces.

Molding in thermoplastic polymers using ultrasonic hot embossing technology is promising due to its high precision reproducibility. To understand, analyze and apply the formation of polymer microstructures by the ultrasonic hot embossing method, it is necessary to understand dynamic loading conditions. The Standard Linear Solid model (SLS) is a method that allows analyzing the viscoelastic properties of materials by representing them as a combination of springs and dashpots. However, this model is general, and it is challenging to represent a viscoelastic material with multiple relaxations. Therefore, this article aims to use the data obtained from dynamic mechanical analysis for extrapolation in a wide range of cyclic deformations and to use the obtained data in microstructure formation simulations. The formation was replicated using a novel magnetostrictor design that sets a specific temperature and vibration frequency. The changes were analyzed on a diffractometer. After the diffraction efficiency measurement, it was found that the highest quality structures were formed at a temperature of 68 °C, a frequency of 10 kHz, a frequency amplitude of 1.5 µm and a force of 1 kN force. Moreover, the structures could be molded on any thickness of plastic. [ABSTRACT FROM AUTHOR]

Increasingly compact and powerful light emitting diodes require the development of efficient optical diffusers to manage their lighting capability according to the required application. In this study, a cost‐effective strategy is demonstrated for fabricating micro‐structured polymethylmethacrylate (PMMA) diffusers for white light sources. By combining different laser‐based processes, namely direct laser engraving (DLE), direct laser writing (DLW), and direct laser interference patterning (DLIP), periodic patterns are fabricated in stainless steel surfaces with line‐ and dot‐like geometries with feature sizes ranging from 1.7 to 900 µm. The fabricated hierarchical geometries are transferred to PMMA surfaces by plate‐to‐plate hot embossing. The relationship between the surface topography and the white light scattering behavior is investigated by confocal and scanning electron microscopy combined with photospectroscopy and image processing of photographs. The triple‐scaled hierarchical structures can increase the haze up to 76% in the visible spectrum, while keeping the total transmittance over 90%, as the flat surface. [ABSTRACT FROM AUTHOR]

Molding in thermoplastic polymers using ultrasonic hot embossing technology is promising due to its high precision reproducibility. To understand, analyze and apply the formation of polymer microstructures by the ultrasonic hot embossing method, it is necessary to understand dynamic loading conditions. The Standard Linear Solid model (SLS) is a method that allows analyzing the viscoelastic properties of materials by representing them as a combination of springs and dashpots. However, this model is general, and it is challenging to represent a viscoelastic material with multiple relaxations. Therefore, this article aims to use the data obtained from dynamic mechanical analysis for extrapolation in a wide range of cyclic deformations and to use the obtained data in microstructure formation simulations. The formation was replicated using a novel magnetostrictor design that sets a specific temperature and vibration frequency. The changes were analyzed on a diffractometer. After the diffraction efficiency measurement, it was found that the highest quality structures were formed at a temperature of 68 °C, a frequency of 10 kHz, a frequency amplitude of 1.5 µm and a force of 1 kN force. Moreover, the structures could be molded on any thickness of plastic.

This work aims at developing polymer surfaces with enhanced hydrophobicity by controlling both the surface chemistry and the surface structure. As a first step, a chemical surface modification is achieved by the incorporation of a synthetized tailored fluorinated copolymer, named POISE-a (Polymer prOcessing Interface StabilizEr), in a commercial polystyrene matrix. Then, a complementary physical approach based on micro-structuration of a polymer surface is used. Polystyrene films containing various contents of POISE-a were elaborated by a solvent casting method. The structuration of the films was conducted by replicating a texture from a nickel insert using a hot-embossing technique with optimized processing conditions. The beneficial effect of POISE-a on both the wettability properties and the replication efficiency was evaluated by the water/polymer static contact angle and the quantification of the replication rate, respectively. The use of this tailored additive, even at low percentages (i.e., 1 wt.%), associated with the structuration of the PS surface, improves both the hydrophobicity of polystyrene and the robustness of the replication process. [ABSTRACT FROM AUTHOR]

Abstract Soft thermoplastic elastomers (sTPE) and specifically styrenic block copolymers (SBC) are making rapid progress in the prototyping and mass production of microfluidic chips. However, these new materials lack guidelines and protocols for chips fabrication, curbing their widespread applications compared to polydimethylsiloxane. In this work, the prototyping potential of a commercially available SBC material, Flexdym, for continuous flow applications is explored. This SBC material exhibits both reversible and permanent self‐adhesion depending on the time and bonding temperature, allowing for rapid and adaptive chip fabrication. Replicates are embossed in 2 min, assembled and sealed in 10 min. Under continuous flow, stud interfaces fabricated with this method can withstand 1 bar with reversible bonding and up to 3 bar after permanent bonding. The integration of an acoustic transducer in an SBC chip to induce acoustic streaming enables rapid mixing and local enrichment of polystyrene microparticles up to 8× the injected concentration. The reversible bonding feature of SBC chips allows to culture endothelial cells in open channels and then close and perfuse through channel to stain the cell. Our finding suggests that TPE‐based materials offer numerous possibilities for prototyping microfluidic chips for analytical and biomedical applications when working with continuous flow at high pressure is required.

Soft thermoplastic elastomers (sTPE) and specifically styrenic block copolymers (SBC) are making rapid progress in the prototyping and mass production of microfluidic chips. However, these new materials lack guidelines and protocols for chips fabrication, curbing their widespread applications compared to polydimethylsiloxane. In this work, the prototyping potential of a commercially available SBC material, Flexdym, for continuous flow applications is explored. This SBC material exhibits both reversible and permanent self‐adhesion depending on the time and bonding temperature, allowing for rapid and adaptive chip fabrication. Replicates are embossed in 2 min, assembled and sealed in 10 min. Under continuous flow, stud interfaces fabricated with this method can withstand 1 bar with reversible bonding and up to 3 bar after permanent bonding. The integration of an acoustic transducer in an SBC chip to induce acoustic streaming enables rapid mixing and local enrichment of polystyrene microparticles up to 8× the injected concentration. The reversible bonding feature of SBC chips allows to culture endothelial cells in open channels and then close and perfuse through channel to stain the cell. Our finding suggests that TPE‐based materials offer numerous possibilities for prototyping microfluidic chips for analytical and biomedical applications when working with continuous flow at high pressure is required. [ABSTRACT FROM AUTHOR]

This work aims at developing polymer surfaces with enhanced hydrophobicity by controlling both the surface chemistry and the surface structure. As a first step, a chemical surface modification is achieved by the incorporation of a synthetized tailored fluorinated copolymer, named POISE-a (Polymer prOcessing Interface StabilizEr), in a commercial polystyrene matrix. Then, a complementary physical approach based on micro-structuration of a polymer surface is used. Polystyrene films containing various contents of POISE-a were elaborated by a solvent casting method. The structuration of the films was conducted by replicating a texture from a nickel insert using a hot-embossing technique with optimized processing conditions. The beneficial effect of POISE-a on both the wettability properties and the replication efficiency was evaluated by the water/polymer static contact angle and the quantification of the replication rate, respectively. The use of this tailored additive, even at low percentages (i.e., 1 wt.%), associated with the structuration of the PS surface, improves both the hydrophobicity of polystyrene and the robustness of the replication process.

Proton exchange membrane fuel cells (PEMFCs) have been identified as one of the most promising renewable energy system for use in automotive applications. However, due to the wide range of weather conditions around the world, the PEMFCs must be stable for operating under these variable conditions. One of the inefficiencies of PEMFCs in automotive applications is during vehicle warm-up, where the low hydration level within the PEMFC can lead to a low performance of the fuel cell. In this study, a proton exchange membrane (PEM) was prepared with regular, microstructured features tuned over a range of aspect ratios. These microstructured membranes were incorporated into MEAs and analyzed for their membrane, proton, and oxygen transport resistances. These fuel cells were tested under different conditions to simulate vehicle start-up, normal operating conditions, and hot operating conditions. It was determined that microstructured PEMs improved performance over planar PEMs under both the start-up and hot conditions. Despite the improved performance of the microstructured PEMs, a high hydrogen cross-over and short-circuit current were also observed for these samples. Adjusting the preparation techniques and tuning the dimensions of the microstructures may provide avenues for further optimization of PEMFC performance. Image 1 • Proton exchange membranes (PEMs) were prepared with regular arrays of recessed features. • Aspect ratio of the microstructures was controlled by tuning the hot-embossing method. • Structured membranes were coated with catalysts and evaluated for fuel cell performance. • Analyses included assessing the electron, proton, and oxygen transport resistances. • Microstructured PEMs improved performance under both the start-up and hot conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The isothermal hot-embossing leads to inefficiency because of heating and cooling whole polymer workpiece for precision micro-forming. Hence, a non-isothermal hot-embossing is proposed by compressing and melting a micron-scale surface layer into heated core microgrooves without changing the solid-state workpiece. The objective is to understand how the upper layer micro-prism array is formed on large-size polymer surface with regard to core microgroove parameters and hot-embossing variables. First, the micro-prism shape and sizes were in-process modeled through a hybrid of mechanical compression and hot-melt flowing inside core microgrooves; then the micro-grinding with the trued wheel micro-tip was employed to fabricate various microgrooves on macro-size die cores; finally, the micro-forming accuracy and efficiency were experimentally investigated in hot-embossing. It is shown that the integrated micro-prism array with nanometer-scale surface roughness is rapidly generated inside accurate and smooth core microgrooves with 1–3 seconds. The micro-forming accuracy is dominated by the hot-embossing variables under the limitations of core microgroove parameters. Moreover, the hot-embossed surface roughness reaches 10–30 nm through the hot-melt layer flowing even if the core surface roughness is larger. It is confirmed that the rapid micro-forming sizes and surface roughness may be predicted by the micro-nano core topographies and the hot-embossing variables. [ABSTRACT FROM AUTHOR]

Optical glass-microprism arrays are generally embossed at high temperatures, so an online cooling process is needed to remove thermal stress, but this make the cycle long and its equipment expensive. Therefore, the hot-embossing of a glass-microprism array at a low strain rate with reasonable embossing parameters was studied, aiming at reducing thermal stress and realizing its rapid microforming without online cooling process. First, the flow-field, strain-rate, and deformation behavior of glass microforming were simulated. Then, the low-cost microforming control device was designed, and the silicon carbide (SiC) die-core microgroove array was microground by the grinding-wheel microtip. Lastly, the effect of the process parameters on forming rate was studied. Results showed that the appropriate embossing parameters led to a low strain rate; then, the trapezoidal glass-microprism array could be formed without an online cooling process. The standard deviation of the theoretical and experimental forming rates was only 7%, and forming rate increased with increasing embossing temperature, embossing force, and holding duration, but cracks and adhesion occurred at a high embossing temperature and embossing force. The highest experimental forming rate reached 66.56% with embossing temperature of 630 °C, embossing force of 0.335 N, and holding duration of 12 min.

Abstract A gradient porous microneedle array (GPMA) is developed for transdermal drug delivery. A modified hot embossing approach is proposed to fabricate the GPMA from poly (lactic- co -glycolic acid) powders within a cavity array mold under the coupling combination of gradient thermal and pressure multi-fields. The porosity of the microneedles is a gradient, and the pores are mainly distributed in the tip region. The liquid drug formulation can directly be loaded in the pores of the microneedle tips by dipping. GPMA could penetrate into the rabbit skin without breakage and the penetration force per microneedle is approximately 22 mN. The GPMA can diffuse a dry model drug, namely Rhodamine B, in vitro in the rabbit skin dermis. The GPMA can also effectively deliver an insulin solution in vivo in diabetes rats, lowering the blood glucose levels. Above all, as a dry or liquid drug carrier and a minimally invasive injector, the GPMA offers an effective alternative for transdermal drug delivery. Graphical abstract Unlabelled Image Highlights • A gradient porous microneedle array (GPMA) was developed for transdermal drug delivery. • A modified hot embossing approach was proposed to fabricate the GPMA. • GPMA can deliver an insulin solution in diabetes rats, lowering the blood glucose level. [ABSTRACT FROM AUTHOR]

Abstract The soiling of photovoltaic (PV) modules can significantly reduce their energy yield unless a mitigation strategy is employed. One solution investigated in this work involves the implementation of a passive self-cleaning superhydrophobic top cover. To this end, superhydrophobicity was induced by hot-embossing random microtextures on a highly transmissive and photostable fluorinated ethylene propylene (FEP) film. The impact of fabrication parameters (hot-embossing force and temperature) on achieving high contact angles (> 150°) and low roll-off angles (< 10°), which characterizes a surface as superhydrophobic, were investigated. It was found that a minimum threshold force of at least 15 kN and 5 kN must be used to achieve superhydrophobicity for processing temperatures of 270 °C and 280 °C respectively. Meanwhile at the highest investigated temperature of 290 °C, any force within the investigated range of 500 N to 50 kN suffices. The best fabrication parameters were identified (5 kN at 280 °C), resulting in a contact angle of 156 ± 1° and a roll-off angle of 8 ± 3°. When incorporated into a silicon PV mini-module, the addition of the textured FEP film enhances the short circuit current density (J SC) by 1.1%. Moreover, the self-cleaning properties of the textured FEP films result in a recovery ratio of 93.6% (in terms of J SC), which is significantly greater than that of the reference glass encapsulated PV mini-module (61.1%). Graphical abstract fx1 Highlights • Random microtextures produce highly transmissive and superhydrophobic FEP surface. • Minimum threshold force to achieve superhydrophobicity identified (5 kN). • Easier to obtain superhydrophobicity at higher fabrication temperatures. • Relative 1.1% enhancement of power conversion efficiency of PV modules. • Self-cleaning recovery of 93.6% in terms of J SC achieved with best case sample. [ABSTRACT FROM AUTHOR]

We propose two approaches—hot-embossing and dielectric-heating nanoimprinting methods—for low-cost and rapid fabrication of periodic nanostructures. Each nanofabrication process for the imprinted plastic nanostructures is completed within several seconds without the use of release agents and epoxy. Low-cost, large-area, and highly sensitive aluminum nanostructures on A4 size plastic films are fabricated by evaporating aluminum film on hot-embossing nanostructures. The narrowest bandwidth of the Fano resonance is only 2.7 nm in the visible light region. The periodic aluminum nanostructure achieves a figure of merit of 150, and an intensity sensitivity of 29,345%/RIU (refractive index unit). The rapid fabrication is also achieved by using radio-frequency (RF) sensitive plastic films and a commercial RF welding machine. The dielectric-heating, using RF power, takes advantage of the rapid heating/cooling process and lower electric power consumption. The fabricated capped aluminum nanoslit array has a 5 nm Fano linewidth and 490.46 nm/RIU wavelength sensitivity. The biosensing capabilities of the metallic nanostructures are further verified by measuring antigen–antibody interactions using bovine serum albumin (BSA) and anti-BSA. These rapid and high-throughput fabrication methods can benefit low-cost, highly sensitive biosensors and other sensing applications. [ABSTRACT FROM AUTHOR]

The nanostructures found in nature sometimes have elaborate, three-dimensional structures that consist of soft and flexible constituents, and which exhibit diverse mechanical and optical functions. Here, we introduce a facile, low-cost and scalable nanofabrication approach based on a hot embossing process that can replicate sub-micron to nanoscale features on elastomeric substrates. We have further developed this technique to achieve polymer/metal heterostructure nanopillar arrays via conformal coating of Au films on polymeric templates. Each nanopillar displays a smooth surface and a constant diameter along the vertical direction. Raman spectroscopy studies revealed that the metallic nanostructures decorated with methylene blue exhibited a dominant Raman peak at 1624 cm −1 that was enhanced more than 3000 times and seven times relative to bare planar Si and Au-coated planar polystyrene substrates, respectively. These results indicate that our nanopillar array can be exploited as a flexible, large area platform for surface-enhanced Raman spectroscopy. [ABSTRACT FROM AUTHOR]

We report here a simple and efficient hot embossing process capable of mass fabricating superhydrophobic and self-cleaning polytetrafluoroethylene (PTFE) film surfaces. Adding superhydrophobicity to hydrophobic polytetrafluoroethylene (PTFE) significantly enhances their application potential in industry as well as in daily life. We applied a picosecond laser to fabricate regular array of micro-holes companied with submicron structures on high strength steel substrate to form a lotus-leaf-like template. Then the hot embossing process was performed on flat PTFE films to introduce a dual-scale structure composed of the micro-scale protrusions and nano-scale fibril structures on the top of protrusions. The hot embossing parameters such as the embossing pressure and time were optimized to achieve required micro- and nano-scale dual structure on PTFE film very closed to the similar dual structure of the lotus leaf surface. The PTFE films then exhibited superhydrophobicity with contact angle up to 154.6° and sliding angle of as low as 5.5°. The thermal stability of the superhydrophobic PTFE films was investigated from room temperature up to 430 °C. We demonstrate that the micro–nano dual structure on PTFE films and their superhydrophobicity is thermally stable up to 340 °C. The micro-scale protrusions will collapse and the superhydrophobicity will lose when the temperate is over 370 °C. [ABSTRACT FROM AUTHOR]

We report low-loss, single-mode rib optical waveguides on-chip, fabricated using hot-embossing for the first time of radio-frequency sputtered $$\hbox {As}_{2}\hbox {Se}_{3}$$ chalcogenide-glass thin films on a chalcogenide-glass substrate. Waveguides 4-6 $$\upmu \hbox {m}$$ wide and $$1.9 \pm 0.1~\upmu \hbox {m}$$ high are fabricated. Waveguide optical loss, using the Fabry-Perot technique, which is known to over-estimate loss, is found to be $$<$$ 0.78 $$\hbox { dB cm}^{-1}$$ for the TE mode, and $$<$$ 0.81 $$\hbox {dB cm}^{-1}$$ for the TM mode, at 1,550 nm wavelength. Glass stability of the chalcogenide rib waveguides is excellent and is discussed in relation to the results of others. [ABSTRACT FROM AUTHOR]

In this paper, the results of exploiting self-organized sub-micron polystyrene (PS) wrinkle patterns possessing random orientation, in preparation of a nickel stamp for hot embossing purposes, are presented. Self-organized patterns were prepared employing a method in which a stiff cross-linked capping layer on the topmost part of the soft polystyrene layer was created by using reactive ion etching (RIE) device with mild conditions and argon as a process gas, and the wrinkle formation was initiated thermally. Different surface patternings were obtained using silicon and stainless steel (SST) wafers as substrates. Prepared Ni-stamps were employed in hot embossing of polycarbonate (PC) and cyclo-olefin polymer (COP) films, using a nano-imprinting process. The replication quality of the self-organized wrinkle structures in PC and COP films was monitored by comparing the shape and dimensions of the original and final surface structures. The hot embossed sub-micron scale features, originally formed on stainless steel substrate, were found to have influence on the optical properties of the PC and COP films by lowering their reflectances. [ABSTRACT FROM AUTHOR]

Abstract: Hot embossing is an attractive alternative to other micro-replication methods, since its cost effectiveness makes it suitable for mass-fabrication of wide range of elements. In this work, hot embossing is presented in context of fabrication of micro-optical elements made of soft glasses for near and mid infrared spectral region. Particular attention is given to the selection of suitable materials from which the mold is prepared, in order to minimize sticking and degradation of the embossing stamps. Refractive lens and diffractive gratings are successfully developed with the proposed approach. [Copyright &y& Elsevier]

The use of bottom-up approaches in tissue engineering applications is advantageous since they enable the combination of various layers that could be made from different materials and/or incorporate different biochemical cues. Regarding the complex structure and the vascular system of the bone tissue, the aim of this study was to develop an innovative bottom-up approach that allows the construction of 3D biodegradable scaffolds from 2D microfabricated membranes with precise shape, pore size and porosity. For that purpose, poly (caprolactone) (PCL) and starch - poly (caprolactone) (SPCL (30 % starch)) blended sheets were used as substrates to produce the microfabricated membranes using micro hot-embossing. The use of this micro fabrication process allowed accurately imprinting micropillars and microholes in reproducible way. The assembling of the microfabricated membranes was performed using an easy, highly reproducible and inexpensive approach based on its successive stacking. Additionaly, the suitability of the microfabricated membranes to support the attachment and the cytoskeletal organization of human bone marrow stem cells (hBMSCs), macrovascular endothelial cells and osteoblasts derived from hBMSCs was demonstrated. Furthermore, hBMSCs proliferated and maintained the expression of the stromal progenitor marker STRO-1 when cultured on both PCL and SPCL microfabricated membranes. The proposed methodology constitutes a promising alternative to the traditional processing methods used to prepare tissue engineering scaffolds. [ABSTRACT FROM AUTHOR]

ABSTRACT A moth-eye anti-reflective structure was fabricated by hot-embossing and UV nanoimprint lithography on a solar cell protective film to suppress the reflection of incident light. Moreover, a superhydrophobic surface was developed by reducing the surface energy by forming a hydrophobic self-assembled monolayer coating on an anti-reflective structured resin surface. Therefore, the transmittance of incident light was increased by the anti-reflective structure. As a result, the solar cell efficiency was enhanced and the total accumulated electrical energy generated by a solar cell with a nano-patterned polymeric film was increased. The efficiency of each solar cell was evaluated by an analysis of its I-V characteristics using a solar simulator, and the external quantum efficiency according to the wavelength of incident light was analyzed by using an incident photon-to-current conversion efficiency system. Finally, the enhancement of the generated power was confirmed by a field test and a power charging experiment. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: An alternative strategy to integrate electrochemical cells composed of two and three electrodes into total COC polymeric microsystems is presented. Results based on in-situ amperometric and potentiometric measurements are shown. [Copyright &y& Elsevier]

Abstract: Stainless steel micromold is an alternative of silicon (Si) micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti–Al–PTFE coatings, which affected the bonding structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti–Al–PTFE coatings were a mixture of carbide, PTFE-like material and amorphous carbon. The surface roughness of coated micromolds decreased with the increase in the PTFE concentration. The Ti–Al–PTFE coating deposited with 50W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1×10−3 N/m, respectively. The coated stainless steel micromolds showed a better replication performance compared to the bare stainless steel micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the micromold channels and the limitations of the Ti–Al–PTFE coatings for application in hot-embossing. [Copyright &y& Elsevier]

Abstract: Self-assembled monolayer (SAM) coatings of n-octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] were deposited on Si micromolds for micro hot-embossing by dipping the Si molds into an anhydrous toluene solvent containing OTS. The coated samples were designated as OTS20, OTS40, OTS60 and OTS80 with respect to deposition time of 20, 40, 60 and 80min to study the effect of deposition time on the coating quality. The composition, surface roughness, friction coefficient, thermal stability and surface energy were measured using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), nanotribological test and contact angle test, respectively. The thermal stability of the OTS coatings was determined by measuring water contact angle after heating at various temperatures. The XPS and AFM results showed that a prolonged deposition induced a denser and thicker coating structure and more aggregation of OTS, which also increased the surface roughness. A comparative study of the uncoated and OTS60 coated Si micromolds depicted that the OTS coatings had a good potential to improve the surface quality and efficiency of the molds. The OTS60 coating was evaluated after heat treatment at embossing temperature of 130°C for a better understanding of the failure mechanism of the micromolds, which showed that the surface properties of the molds remained unchanged at the embossing temperature. Further characterization of the damaged Si micromolds showed that the peel-off of the coatings after a number of replications was the main reason for the failure of the molds. It was found that periodic re-cleaning of the micromolds and re-deposition of the OTS coatings on the coated Si micromolds could extend the lifetime of the molds up to about 112 embossing operations per mold. [Copyright &y& Elsevier]

Abstract: The development of a one-step process for producing high fidelity hot-embossed cyclic-olefin co-polymer (COC) based microfluidic devices without the need for pre-annealing the base polymer substrate/film is outlined. This was achieved through proper selection of the hot-embossing conditions that was based on an in-depth understanding of the fundamental factors which affect the replication accuracy of microchannels during the hot-embossing process. An important factor that is commonly overlooked in the hot-embossing of films (typically with thicknesses less than 1mm) is the existence of polymer chain orientation. Generally, polymer films used for hot-embossing are not pre-annealed to minimize residual stresses and remove any chain orientation that may be present, and this affects the replication accuracy. In contrast, polymer substrates (typically with thicknesses more than 1mm) that are used for hot-embossing to produce microfluidic devices need to be pre-annealed to minimize residual stresses and remove any chain orientation. Processing of the latter thus required an additional step. The avoidance of such pre-annealing may affect the replication accuracy. In the present work, it was demonstrated that microfluidic devices with high fidelity microchannels could be produced using a single-step hot-embossing process based on knowledge of the influence of embossing temperature, embossing pressure, embossing time and polymer chain orientation in the film/substrate on micro-replication. [Copyright &y& Elsevier]

Abstract: The light-emitting diode (LED) has been the subject of much interest in the role of a backlight module for liquid crystal displays (LCDs). However, a traditional LED lamp is a point-light source, and so is not suitable for use in large LCD panels. This study presents a new packaging method for LEDs, which uses a gapless dual-curvature microlens array (GDMLA) to improve its ability to illuminate a panel. GDMLAs of different dimensions were simulated and fabricated in order to examine their light luminance and uniformity. Commercial optical simulation software, “Tracepro”, was used to obtain a GDMLA of optimized geometry and dimensions. Based on the simulated data, a GDMLA mold was first fabricated using a LIGA-like process (Lithographie Galvanoformung Abformung, LIGA); this was known as the first mold. In this study, the first mold was obtained using a nickel cobalt (Ni–Co) electroplating process. In order to obtain a highly accurate and strong mold, a bulk metallic glass (BMG) alloy, Mg58Cu31Y11, was chosen as the material for the second mold, which exhibits excellent forming ability and high hardness. The pattern of the first mold was replicated onto BMG by hot-embossing, and the shrinkage between the first and the second mold was less than 0.2%. Next, the pattern of the GDMLA on the second mold was replicated onto ultraviolet (UV)-curable resin, producing the final optical film for a LED package. The shrinkage between the second mold and the UV-cured optical film was less than 0.4%; this means that the process exhibits a high replication ability. The fabricated GDMLA had the characteristics of dual curvatures and a high fill-factor of 100%. The light uniformity of the LED package with the GDMLA optical film was measured, and the results demonstrated that the GDMLA is a good optical device for use in LED packages. In addition, the relationship between the simulation and experimental results is assessed and discussed. [Copyright &y& Elsevier]

Abstract: The need for a flexible and high-throughput process for the fabrication of a polymer-based micro-fluidic device is becoming increasingly important as bio-device industry is expanding very fast. The present work investigated the fabrication of a polymer-based micro-fluidic device by using the combination of the focused ion beam (FIB) milling and the hot-emboss process. The milled depth-ion dose curve for Si was investigated, and some silicon molds were prepared by a repetitive-pass milling with FIB. A Si mold was then used for the hot-emboss of poly-methyl-methacrylate (PMMA) to replicate micro-fluidic parts. Prior to hot-embossing, a FIB milled silicon mold was heat-treated at 500°C for 10min in vacuum (0.07Pa). The FIB milled fields in the Si mold could be replicated on the PMMA with the dimensional deviation less than 1% under the temperature of 150°C, the force of 50kgf, the loading force velocity of 50μm/min and the press hold time of 300s. [Copyright &y& Elsevier]

Abstract: This study describes the fabrication of Si molds by using electron beam lithography (EBL) combined with inductively coupled plasma (ICP) etching and its application to the hot-emboss of polyimide (PI) microfluidic platform. The dynamic mechanical thermal properties and the formability of a polyimide film were investigated as a function of temperature by dynamic mechanical thermal analysis (DMTA) and hot-embossing tests. Based on the results, the microfluidic channel could be replicated on PI surface with good fidelity by hot-embossing with the Si mold structured by using EBL combined with ICP etching. [Copyright &y& Elsevier]

Abstract: This study demonstrated a replication process for metallic micro-mold that combines the parylene-C (poly-chloro-p-xylylene C) hot-embossing and electroplating techniques. A nickel original master was fabricated using the deep RIE silicon etching followed by the electroplating process. Then, the patterned fields composed of arrays of 25μm-high, 10μm-wide and 1mm-long lines with 10μm spacing in nickel molds were successfully replicated on the 60μm-thick parylene-C films by the hot-emboss process. Under complete filling conditions, the deviation of the replicated micropattern was less than 2.4%. The electroplated copper successfully filled parylene-C replica master patterns with the aspect ratio of 2.5 without the void formation by both adding organic addictives and controlling the seed layer thickness. After electroplating, the copper micro-mold could be successfully separated from the parylene-C replica master. [Copyright &y& Elsevier]

Abstract: Various nano-/micro-structuring methods, including focused ion beam (FIB), femto-second laser, KrF eximer laser and dicing techniques, were used to fabricate glassy carbon (GC) micro-molds and were characterized in terms of the process rate, the roughness and the shape of machined structure. The combination of femto-second laser ablation with subsequent FIB milling provided a possibility for the rapid fabrication of high quality micro-structures on a wide surface area. Obtained molds were applied to the hot-emboss process of glasses to investigate process conditions needed for the replication of structures with various geometries and dimensions. [Copyright &y& Elsevier]

Hot embossing allows the high precision replication of features from a mould insert into thermoplastic materials. The technique has been developed mainly for microsystem applications, in particular, the manufacture of micro-optical and micro-fluidic components and systems. It can also be applied to packaging applications. We developed a specific process based on a two-step replication process utilizing hot embossing and a rigid polymeric intermediate mould, which allows the manufacture of complex three-dimensional shapes to realize a functional optical package for optical microsystems. [ABSTRACT FROM AUTHOR]

High-precision micromilling was assessed as a tool for the rapid fabrication of mold masters for replicating microchip devices in thermoplastics. As an example, microchip electrophoresis devices were hot embossed in poly(methylmethacrylate) (PMMA) from brass masters fabricated via micromilling. Specifically, sidewall roughness and milling topology limitations were investigated. Numerical simulations were performed to determine the effects of additional volumes present on injection plugs (i.e., shape, size, concentration profiles) due to curvature of the corners produced by micromilling. Elongation of the plug was not dramatic (< 20%) for injection crosses with radii of curvatures to channel width ratios less than 0.5. Use of stronger pinching potentials, as compared to sharp-corner injectors, were necessary in order to obtain short sample plugs. The sidewalls of the polymer microstructures were characterized by a maximum average roughness of 115 nm and mean peak height of 290 nm. Sidewall roughness had insignificant effects on the bulk EOF as it was statistically the same for PMMA microchannels with different aspect ratios compared to LiGA-prepared devices with a value of ca. 3.7 × 10−4 cm2/(V s). PMMA microchip electrophoresis devices were used for the separation of pUC19 Sau3AI double-stranded DNA. The plate numbers achieved in the micromilled-based chips exceeded 1 million/m and were comparable to the plate numbers obtained for the LiGA-prepared devices of similar geometry. [ABSTRACT FROM AUTHOR]

Abstract: Various methods, including focused ion beam (FIB), femto-second laser, KrF eximer laser and dicing techniques, were employed for preparing glassy carbon (GC) micro-molds, and those methods were characterized in terms of the process rate, the roughness and the shape of machined structure. FIB milling using a repetitive pass method produced nano/microstructures with flat channel bottom and nearly vertical sidewalls. Although FIB milling was slowest process, it provided the best quality of machined surface (R a =4–30nm depended on milled depth). Femtosecond-pulsed laser machining also allowed fabricating flat bottom and nearly vertical sidewalls on an area of 1.2×1.2mm2 at a scanning speed of 20mm/s, but lead to an increase of the surface roughness (R a =80nm). Femto-second laser in combination with FIB milling provided a possibility for the rapid fabrication of high quality microstructures on wide surface area. The roughness of machined surface decreased to 45nm by the subsequent FIB milling. Microstructuring with a nanosecond-pulsed KrF eximer laser at an irradiation wavelength of 248nm with a fluence of 13.2J/cm2 also allowed the fast fabrication of master structure for micro-gear, resulted in slanted sidewalls and not ideally flat bottoms. The surface roughness (R a) of the bottom and the side wall was about 45 and 70nm, respectively. Dicing technique allowed machining micro-channels with a rectangular and pyramidal cross-section on an area of 15×15mm2 under the feed speed of 50mm/min. By reducing the feeding speed from 100mm/min to 50mm/min, surface roughness (R a) of the structure side wall decreased from 150nm to 70nm. Achieved glassy carbon molds were then applied to the hot-emboss process of Pyrex and quartz glasses to investigate embossing conditions (emboss temperature, pressure and hold time) needed for the replication of Pyrex and quartz glass structures with various geometries and dimensions in glass plates with thickness of 1mm. Replication results showed good replication at the nanoscale, resulted in the almost the same dimensions and surface roughness with that of cavities. Thicker plate provided faster filling in the emboss process of glass. [Copyright &y& Elsevier]

Abstract We have demonstrated simultaneous fabrication of designed defects within a periodic structure. For rapid fabrication of periodic structures incorporating nanoscale line-defects at large area, topographically assisted holographic lithography (TAHL) technique, combining the strength of hologram lithography and phase-shift interference, was proposed. Hot-embossing method generated the photoresist patterns with vertical side walls which enabled phase-shift mask effect at the edge of patterns. Embossing temperature and relief height were crucial parameters for the successful TAHL process. Periodic holes with a diameter of 600 nm at a 1 μm-pitch incorporating 250 nm wide line-defects were obtained simultaneously.