Hot Imprinting Research Articles

Improving performance of AgNPs/PDA/TPU electrospun composite film based flexible pressure sensor by hot imprinted microstructure array

Highly sensitive sensors have attracted considerable attention in areas such as electronic skin, health monitoring and artificial intelligence. Herein, a simple and efficient approach was proposed to fabricate hierarchically structured flexible sensors. A common metal mesh was used as a template and its pattern was transferred to the surface of a composite film of silver nanoparticles (AgNPs) decorated polydopamine (PDA) and polyurethane (TPU) electrospun fibers by hot imprinting. The resulting film with a uniform convex microstructure array on the surface was used as the conductive sensing layer of the AgNPs/PDA/TPU sensor. The sensor exhibited a linear detection range increased from 15 kPa to 20 kPa compared to the control sensor without the microstructure. Furthermore, the sensitivity was improved from 8.13 kPa−1 to 10.44 kPa−1. The response time and recovery time of the sensor were determined to be 110 ms and 90 ms, respectively, and it maintained good stability at 10 kPa even after 1000 compression cycles. In addition, the sensor enabled real-time pressure signal detection for touch, joint movement and voice recognition, showing promising applications in health monitoring, pressure detection and human-machine interaction.

Micro-optical elements from optical-quality ZIF-62 hybrid glasses by hot imprinting

Hybrid glasses derived from meltable metal-organic frameworks (MOFs) promise to combine the intriguing properties of MOFs with the universal processing ability of glasses. However, the shaping of hybrid glasses in their liquid state – in analogy to conventional glass processing – has been elusive thus far. Here, we present optical-quality glasses derived from the zeolitic imidazole framework ZIF-62 in the form of cm-scale objects. These allow for in-depth studies of optical transparency and refraction across the ultraviolet to near-infrared spectral range. Fundamental viscosity data are reported using a ball penetration technique, and subsequently employed to demonstrate the fabrication of micro-optical devices by thermal imprinting. Using 3D-printed fused silica templates, we show that concave as well as convex lens structures can be obtained at high precision by remelting the glass without trading-off on material quality. This enables multifunctional micro-optical devices combining the gas uptake and permeation ability of MOFs with the optical functionality of glass. As an example, we demonstrate the reversible change of optical refraction upon the incorporation of volatile guest molecules.

Rapid fabrication of highly integrated and high numerical aperture chalcogenide glass microlens arrays

The fast growing of infrared imaging system for non-contact thermography, night surveillance and night driving assistance demands highly integrated optical lenses with miniaturization feature for performance improvement. Herein, we fabricated refractive type of microlens arrays (MLAs) with high numerical aperture (NA) and high integration on commercial chalcogenide glass (As2Se3) by combining photoresist thermal reflow and soft mold imprinting process. PDMS-type concave MLAs (PDMS-MLAs) soft mold is prepared by transfer printing process on photoresist (PR) MLAs fabricated by standard UV exposure and thermal reflow. The microlens on PDMS-MLAs could be further transferred to the surface of As2Se3 glass through the hot imprinting technique, forming chalcogenide glass-based MLAs (ChG-MLAs). Morphology detection reveals that microlens in the MLAs has an average aperture and sag height of approximately 13.4 and 1.7 μm. Moreover, the optical performance investigation demonstrated that the ChG-MLAs with 700 × 700 array size (10.5 × 10.5 mm) showed good structure uniformity and focusing capability, and through the FDTD simulation, it further evidenced that focal lengths of 6.3–8.1 µm with high numerical aperture of 0.64–0.73 (wavelength range: 3–5 μm) was achieved.

Patterning High-Resolution Microstructures on Thermoplastics by Ceramic Nanoparticles Filled Epoxy Coated Molds for Duplicating Nature-Derived Functional Surfaces.

Patterning high-resolution microstructures on thermoplastic substrates is of fundamental importance for the commercialization of microfluidics, advanced functional surfaces, and optical elements. Though many methods are developed to fabricate micropatterned plastic devices with 100 μm resolution, they suffer substantially higher cost or lower productivity when the resolution of the micropatterns is to be further improved. Here, we develop low-cost molds consisting of thin ceramic-filled-epoxy composite coatings on steel substrates. By virtue of the loaded ZrO2 nanoparticle fillers, the enhanced mechanical and thermal properties of the composite molds enable the epoxy microstructures to survive harsh conditions in conventional thermoplastic processing methods including hot embossing, imprinting, and mold injection. With the ceramic-filled-epoxy coated molds, we are able to improve the fabrication resolution of microstructures on plastics to 10 μm with unprecedented low-cost and excellent durability.

Façade elements for room illumination with integrated microstructures for daylight redirection and LED lighting

Lowering energy consumption of buildings is a common task, which is addressed in this presented research by the development and application of a micro structured system that successfully redirects daylight in order to light an office room instead of blocking it by shading systems. Designed as a common three-pane window compound and built utilizing manufacturing methods for mass production, namely hot embossing and UV imprinting, it can be handled as a common façade element. Measurements in the equipped office room prove a significant lowering of energy consumption for artificial lighting. This research is accompanied by the development of another façade element integrating an artificial luminaire to take care of situations in which no daylight is available, but without changing the location of the illumination source. The luminaire realized as micro structured surface emitter is incorporated as a window compound together with the LEDs used in a test façade, while offering a clear view to the outside. The view through the system is measured by a setup that partly mimics human perception. This transparent façade element emits light to the rooms ceiling for indirect illumination. Not yet being as efficient as standard lighting solutions, it offers new design options in reducing the use of common luminaires and in opening up new usable space at the ceiling and interior.

Fabrication of large-scale infrared diffractive lens arrays on chalcogenide glass by means of step-and-repeat hot imprinting and non-isothermal glass molding

In this study, a new cost-effective and high-precision process chain for the fabrication of large-scale infrared (IR) diffractive lens arrays on chalcogenide glass is proposed. First, a positive diffractive lens array is fabricated on a polymethylmethacrylate (PMMA) master substrate by employing a step-and-repeat hot imprinting process. The direct hot imprinting can transfer microstructures from a heated mold to the polymer substrate accurately. Repeating the hot imprinting process along a predetermined path, the desired diffractive lens array is obtained. Unlike photolithography and electron-beam writing, which are expensive technologies with sophisticated process steps, the hot imprinting is an easier, cheaper, and more eco-friendly method for fabricating diffractive features with continuous profile. Afterwards a casting process is applied to create a polydimethylsiloxane (PDMS) mold with negative features. The diffractive lens array is successfully transferred from the master substrate to the PDMS elastomer, which is used as a mold in subsequent precision glass molding. Finally, microstructures on the PDMS mold are replicated to the chalcogenide glass by non-isothermal glass molding. In this process, the PDMS mold and workpiece are set at different temperatures. Specifically the PDMS mold at low temperature maintains enough rigidity to press the features onto the softened chalcogenide glass, which is kept at a relatively higher temperature, resulting in a replica of high-fidelity diffractive lens array on the chalcogenide glass. Surface profiles and optical performance of the fabricated components are characterized quantitatively. Results showed that large-scale diffractive lens array can be successfully fabricated on chalcogenide glass by this proposed process chain with high quality and integrity.

Development of a roll-to-roll hot imprinting process for superhydrophobic polytetrafluoroethylene surfaces

Potential applications of superhydrophobic surfaces have attracted many researchers. Although numerous methods have been suggested to achieve superhydrophobic surfaces on various types of materials, only a few methods are suitable for process simplicity, productivity and large area applicability. In this study, we developed a roll-to-roll hot imprinting process for superhydrophobic surfaces to overcome such limitations. Hierarchical patterns were fabricated on the roll surface through wire electrical discharge machining. Through the roll-to-roll hot imprinting process using the pattern roll, the hierarchical patterns were transferred to the polytetrafluoroethylene surface. As a result, superhydrophobic surfaces with a water contact angle of 150° or more were obtained.

Superhydrophobic Polymer Surface with Hierarchical Patterns Fabricated in Hot Imprinting Process

Superhydrophobic surfaces have been widely applied to solve environmental issues using their many functions such as drag reduction, oil–water separation and self-cleaning. It is well known that superhydrophobicity of materials can be enhanced by imparting micro/nano hierarchical patterns on its surface. Although several techniques, such as MEMS, coating, and laser ablation, have been suggested to improve superhydrophobicity, they are unsuitable for mass production. To overcome this limitation, a facile fabrication method using hot imprinting process was developed in this study. Hierarchical patterns including micro sinusoidal patterns with discharge craters were formed on the die surface obtained using wire electrical discharge machining. Thermoplastic PTFE and PC polymer surfaces with hierarchical patterns were successfully replicated from the die surface after hot imprinting. In addition, an entangled micro fibril network was observed on the PTFE surface, whereas torn shapes were developed on the PC polymer surface. As a result, the polymer surfaces were found to exhibit superhydrophobicity with a water contact angle > 150°.

Characterization of microfibril development on PTFE surface during hot imprinting process and its application for oil–water separation

The importance of oil–water separator has increased due to environmental pollution caused by marine accidents. Many studies related to fabrication method of superhydrophobic surface have been conducted because those functional surfaces are an important component used in oil and water separators. However, processes that can be applied to large area and mass production still exist as limitations. In this paper, superhydrophobic surfaces were fabricated on polytetrafluoroethylene (PTFE) surface by hot imprinting. To impart rough surface morphology to PTFE surface, hot imprinting process using an electrical discharge textured (EDT) mold was conducted. It was found that undercut of a discharge crater on the EDT surface induced tensile deformation of PTFE surface during the hot imprinting process resulting in microfibril development. As a result, PTFE surface had rough morphology consisting of replicated EDT surface and microfibril network. Imprinted PTFE sheets showed high water contact angles about 154.3° with low contact angle hysteresis about 1.4°. Additionally, the effects of process temperature and roughness of the EDT mold on microfibril formation were investigated. It was found that microfibril formation is activated when the process temperature reaches glass transition temperature (115 °C) of PTFE. The PTFE sheets for oil–water separation were prepared by hot imprinting and followed by additional drilling process. The optimal hole diameter with respect to efficiency of oil–water separation was determined through experiments and separation of oil and water was effectively conducted.

Rapid and sensitive biomarker detection using molecular imprinting polymer hydrogel and surface-enhanced Raman scattering.

Biomarkers are important biochemical indicators, which could be used for identification, early diagnosis and monitoring of diseases during the course of treatment. However, biomarker diagnosis has some shortcomings such as requiring a large amount of samples, long test time and high cost, which seriously influences the correctness and timely treatment to patients. Here, a relatively fast and efficient plasmonic hot spot-localized surface imprinting of Ag spheres using biomarker template immobilization and hydrogel copolymerization is described. The technique takes a fine control of the imprinting process at the nanometre scale and provides a biosensor with high sensitivity. Proof of the opinion is established by detection of biomarker using surface-enhanced Raman scattering (SERS) spectroscopy. This work represents a valuable step towards SERS with biomarkers for cost-saving and time-saving diagnostic assay. It is expected that the new surface imprinted hydrogel plasmonic material can drive possibilities in advancing application of biomarkers in plasmonic biosensors.

Plasmonic Hot Printing in Gold Nanoprisms

The raster-scanned irradiation of ultrathin sub-micrometer crystalline gold colloidal prisms with the tightly focused spot of a femtosecond, near-infrared laser triggers the deterministic deformation and partial melting of nanometer-sized areas of the nanoprisms. The morphological modification of the Au nanoprisms evidences extremely localized sources of heat, the in-plane distribution of which varies with the particle shape and laser polarization. We demonstrate for the first time the direct relationship between heat source density and surface plasmon local density of states (SP-LDOS), which describes quantitatively the rich modal structure of the surface plasmons sustained by the 2D metallic platelets, independently of the knowledge of the illumination configuration. Green’s Dyadic numerical simulations confirm that the optical excitation of the 2D SP modes results in the subwavelength hot imprinting of the SP modal pattern onto the metal surface.

Chemical segregation in metallic glass nanowires.

Nanowires made of metallic glass have been actively pursued recently due to the superb and unique properties over those of the crystalline materials. The amorphous nanowires are synthesized either at high temperature or via mechanical disruption using focused ion beam. These processes have potential to cause significant changes in structure and chemical concentration, as well as formation of defect or imperfection, but little is known to date about the possibilities and mechanisms. Here, we report chemical segregation to surfaces and its mechanisms in metallic glass nanowires made of binary Cu and Zr elements from molecular dynamics simulation. Strong concentration deviation are found in the nanowires under the conditions similar to these in experiment via focused ion beam processing, hot imprinting, and casting by rapid cooling from liquid state. Our analysis indicates that non-uniform internal stress distribution is a major cause for the chemical segregation, especially at low temperatures. Extension is discussed for this observation to multicomponent metallic glass nanowires as well as the potential applications and side effects of the composition modulation. The finding also points to the possibility of the mechanical-chemical process that may occur in different settings such as fracture, cavitation, and foams where strong internal stress is present in small length scales.

Nanofeatured anti-reflective films manufactured using hot roller imprinting and self-assembly nanosphere lithography

This paper details the continuous fabrication of nanofeatured anti-reflective films for solar cells, using hot roller imprinting and self-assembly nanosphere lithography. Polystyrene nanospheres of different sizes (471, 628, and 1200nm) were first self-assembled onto Silicon substrates by a spin coater. A thin layer of aluminum was then deposited onto the surface of nanosphere-patterned substrates, using the plasma sputtering technique. After electroforming, nickel–cobalt membranes containing nano-arrays of different sizes were obtained. The membranes were then attached to the surface of the metallic roller in a hot roller imprinting facility. The imprinting facility was used to replicate the nanofeatures onto 60μm thick polyethylene terephthalate (PET) films. The imprinted films were characterized using water contact angle measurement, a UV–vis spectrophotometer, atomic force microscope (AFM), and scanning electron microscope (SEM); the enhancement efficiency of the nanofeatured films for the solar cells was also measured by a solar simulator. The measured results suggested that the imprinted films could effectively reduce the reflectance and increase the conversion efficiency of solar cells.

Hot Spot‐Localized Artificial Antibodies for Label‐Free Plasmonic Biosensing

The development of biomolecular imprinting over the last decade has raised promising perspectives in replacing natural antibodies with artificial antibodies. A significant number of reports have been dedicated to imprinting of organic and inorganic nanostructures, but very few were performed on nanomaterials with a transduction function. Herein we describe a relatively fast and efficient plasmonic hot spot-localized surface imprinting of gold nanorods using reversible template immobilization and siloxane co-polymerization. The technique enables a fine control of the imprinting process at the nanometer scale and provides a nanobiosensor with high selectivity and reusability. Proof of concept is established by the detection of neutrophil gelatinase-associated lipocalin (NGAL), a biomarker for acute kidney injury, using localized surface plasmon resonance spectroscopy. The work represents a valuable step towards plasmonic nanobiosensors with synthetic antibodies for label-free and cost-efficient diagnostic assays. We expect that this novel class of surface imprinted plasmonic nanomaterials will open up new possibilities in advancing biomedical applications of plasmonic nanostructures.

The integrated curved surface imprinting process technology aided by gas and gray-scale regulated electromagnetic force

Abstract This study proposes an integrated imprinting technology, of combining gas-aided imprinting technology and gray-scale, regulated, electromagnetic, force hot-imprinting technology, for the replication imprinting forming of the curved surface micro-nano structure. Based on the existing gas-aided hot imprinting forming technology, this study designed an electromagnetic disc that can regulate and control the imprinting force at different positions, and with features of even and precise control of gradual pressure. The electromagnetic disc was integrated with the gas and the electromagnetic force aided hot-imprinting technology to replicate micro-structure, to make the micro-nano imprinting technology and applications more mature. The experimental results showed that the proposed integrated imprinting technology can accurately replicate the curved surface micro-nano micro-structure.

Large area micro hot embossing of Pyrex glass with GC mold machined by dicing

Micro/Nano imprinting or hot embossing is currently a target of interest for industrial production of micro and Nano devices for the low cost aspect. In Fluidic MEMS (Micro Electromechanical Systems) applications, polymer materials have been widely employed for their low cost to fabricate the economical products (Becker and Heim in Sens Acuators A 83:120–135, 2000; Becker and Gaertner in Mol Biotechnol 82:89–99, 2001). However glasses are much more suitable for the higher temperature applications or under the stronger chemical environments. Moreover UV absorption of glass materials is much less than that of polymers, which is the advantage for bio-analysis. In Optical MEMS as well, glasses are good candidate materials for the better optical properties, such as high refractive index, low UV absorption and others. Although wet etching of glasses is widely employed for fabrication of fluidic MEMS devices, the wet etching is not satisfactory for the low machining resolution, the isotropic etched profile and poor roughness of the fabricated structures. Dry etching of glasses is then an alternative for Micro/Nano structuring, but the etching rate is extremely low (order of 0.1 μm/min) and the cost is too high because of the expensive RIE (Reactive Ion Etching) facility. Above mentioned is the reason why we are interested in hot embossing or imprinting of glasses of Micro/Nano scale. In our previous study, Micro/Nano imprinting was developed for Pyrex glasses using GC (Glassy Carbon) mold prepared by FIB machining (Takahashi et al. in Symposium on DTIP 2004 pp 441–446, 2004). The disadvantage of FIB machining is limited area of etching. The typical area of FIB is less than several hundreds micrometer square. This is the reason why we tried the large area of embossing using GC mold fabricated by dicing machine. Micro hot embossed test structures were successfully demonstrated with good fidelity. Fabricated micro structures can be applied for fabrication of microchamber array for PCR (Akagi et al. in Sci Techol Adv Mater 5:343–349, 2004; Nagai et al. in Anal Chem 73:1043–1047, 2001).

Control of electroosmotic flow in laser-ablated and chemically modified hot imprinted poly(ethylene terephthalate glycol) microchannels.

The fabrication of microchannels in poly(ethylene terephthalate glycol) (PETG) by laser ablation and the hot imprinting method is described. In addition, hot imprinted microchannels were hydrolyzed to yield additional charged organic functional groups on the imprinted surface. The charged groups are carboxylate moieties that were also used as a means for the further reaction of different chemical species on the surface of the PETG microchannels. The microchannels were characterized by fluorescence mapping and electroosmotic flow (EOF) measurements. Experimental results demonstrated that different fabrication and channel treatment protocols resulted in different EOF rates. Laser-ablated channels had similar EOF rates (5.3+/-0.3 x 10(-4) cm(2)/Vs and 5.6+/-0.4 x 10(-4) cm(2)/Vs) to hydrolyzed imprinted channels (5.1+/-0.4 x 10(-4) cm(2)/Vs), which in turn demonstrated a somewhat higher flow rate than imprinted PETG channels that were not hydrolyzed (3.5+/-0.3 x 10(-4) cm(2)/Vs). Laser-ablated channels that had been chemically modified to yield amines displayed an EOF rate of 3.38+/- 0.1 x 10(-4) cm(2)/Vs and hydrolyzed imprinted channels that had been chemically derivatized to yield amines showed an EOF rate of 2.67+/-0.6 cm(2)/Vs. These data demonstrate that surface-bound carboxylate species can be used as a template for further chemical reactions in addition to changing the EOF mobility within microchannels.