Thermal Imprint Research Articles

Surface Plasmon Excited on Imprintable Thin-Film Metallic Glasses for Surface-Enhanced Raman Scattering Applications

Metallic glasses (MGs) are a class of amorphous alloys in contrast with crystalline metals and provide a challenge of engineering applications for unique structure and properties. However, plasmonic applications remain a virgin area for MGs. In this work, we discovered that certain compositions of gold-based MGs possessed negative dielectric constants and could be used as plasmonic materials. Furthermore, with a low glass-transition temperature of gold-based thin-film MGs (TFMGs), we were able to fabricate large dimensions of nanostructures using an inexpensive thermal imprint method in air instead of other costly lithography methods. We performed both measurements and simulations to demonstrate that our designed nanostructures were suitable for surface-enhanced Raman scattering (SERS) applications. In addition, in the absence of grain boundaries in amorphous TFMGs, damping due to increased scattering at grain boundaries does not occur, and SERS could be improved. Also, compared to regular SERS substrates of textured Si with deposited Au films, imprinted Au-based TFMGs provided complete coverage of Si underneath, and the vibrational signal of Si lattice would not show in Raman spectra to possibly overlap signals of analyte and decrease the accuracy of sensing. Our results suggested new avenues for applying a low-cost and high-throughput method on TFMGs to fabricate large dimensions of substrates for plasmonic applications.

Fabrication of Large-Area Flexible SERS Substrates by Nanoimprint Lithography

We demonstrate the nanofabrication of flexible plasmonic sensors comprising of gold nanocones achieved by nanoimprint lithography on polycarbonate (PC) sheets. Thermal imprinting was performed consistently over a large area (roughly the size of a 6 in. wafer) with a batch process; this can be extended to a continuous process using UV roll-to-roll nanoimprinting. This provides a process to scale up the fabrication of continuous imprinted rolls of PC sheets at an optimal rate of 3–5 m/min. The geometry of the peaks and the valleys of the nanocones in the as-imprinted PC is defined by the nickel mold used during imprinting; however, the gaps between the nanocones are tailored by varying the thickness of the gold deposited onto the substrate. Two different thicknesses of gold were deposited to study the effect of geometry on plasmonic sensing. The resulting PC sheet with gold coating enables highly sensitive detection of analytes by Surface Enhanced Raman Spectroscopy (SERS) by virtue of plasmonic hotspots ge...

Direct imprinting of indium–tin-oxide precursor gel and simultaneous formation of channel and source/drain in thin-film transistor

We report on a new fabrication process for thin-film transistors (TFTs) with a new structure and a new operation principle. In this process, both the channel and electrode (source/drain) are formed simultaneously, using the same oxide material, using a single nano-rheology printing (n-RP) process, without any conventional lithography process. N-RP is a direct thermal imprint technique and deforms oxide precursor gel. To reduce the source/drain resistance, the material common to the channel and electrode is conductive indium–tin-oxide (ITO). The gate insulator is made of a ferroelectric material, whose high charge density can deplete the channel of the thin ITO film, which realizes the proposed operation principle. First, we have examined the n-RP conditions required for the channel and source/drain patterning, and found that the patterning properties are strongly affected by the cooling rate before separating the mold. Second, we have fabricated the TFTs as proposed and confirmed their TFT operation.

Human Stress Research Using Facial Thermal Imaging

Thermal imaging is one of the most promising methods of probing the psychological status of human beings because of its non-invasiveness. The paper focuses mainly on the understanding of fundamental properties of physiological responses to emotional stress and how they can be captured by using thermal imaging techniques. We study the facial image of stressed participants for correlating the thermal imprint and estimated stress marker. While the correlations between the thermal ROI and stress marker (cortisol level & heart beat rate) is not directly significant, facial thermal imprints are sensitive to the emotional stress and have potential to detect stress in real time. Unlike the startle induced instantaneous temperature rise, our experimental results further demonstrate that the temperature in the periorbital region does not increase during the Trier social stress test, but increases after the onset of emotional stress. Overall, the experimental results suggest that facial thermal imaging is a valuable method for the estimation of emotional stress.

Mean of Correlation Method for Optimization of Affective States Detection in Children

At the moment, most of the studies on classification of affective states for children focus on visual observations and physiological cues, where all data collection for measuring physiological signals are contact-based and invasive. With the requirement of having the measuring device attached to the body approach, distraction of the subject normally masks the true affective states of the subject due to discomfort. In this paper, a non-invasive, contactless, and less distraction method is proposed to measure the physiological cues of the subjects using their thermal imprints from frontal face imaging. A thermal image camera is used to identify basic affective states, where it is a contactless and seamless device with ability to read the radiated thermal imprint of the subjects’ facial skin temperature. This paper proposes an effective algorithm of texture analysis based on novel technique using Gray Level Co-occurrence Matrix approach to be applied so as to identify blood-flow region. The cues from the first order statistics are computed in the identified blood flow region and concatenated along with second order statistics cues, in order to construct feature vectors to administer the vital and distinguishable characteristic pattern between affective states in thermal images. Result from the fine k-NN classifier obtained promises the efficacy of the proposed approach to be applied in our future work in human–robot interaction for autistic children learning and training.

Patterning thermoplastic polymers by fast room-temperature imprinting

To avoid the high-temperature process of thermal imprinting, the room-temperature imprint lithography was proposed to pattern thermoplastic polymers. However, the room-temperature imprint lithography is still limited by rigorous condition of high pressure and wasting time. In order to overcome the above-mentioned disadvantages, we have introduced a fast (5 s) imprint method, which is based on the difference of two interfacial forces, to pattern thermoplastic polymers under room-temperature without additional pressure. This method is appropriate for the flat substrate, the curved substrate and the flexible substrate. Furthermore, we also have successfully fabricated 3D hierarchical patterns with antireflection by this method.

Oldest lamproites from Peninsular India track the onset of Paleoproterozoic plume-induced rifting and the birth of Large Igneous Province

Potassic and ultrapotassic magmatism from deep lithospheric sources in intra-cratonic settings can be the signal of subsequent voluminous mafic magmatism and the formation of Large Igneous Provinces (LIPs) triggered by mantle plumes. Here we report for the first time, precise zircon U–Pb age data from a suite of lamproites in the Bastar Craton of central India that mark the onset of Paleoproterozoic rifting and culminating in the formation of extensive mafic dyke swarms as the bar codes of one of the major LIP events during the Precambrian evolution of the Indian shield. The lamproites from the Nuapada field occur as dismembered dykes and are composed of phenocrysts and microphenocrysts of altered olivine together with microphenocrysts of phlogopite and magnetite within a groundmass of chlorite and calcite with accessory rutile, apatite and zircon. The rocks compositionally correspond to olivine phlogopite lamproite and phlogopite lamproite. Geochemical features of the lamproites correlate with their counterparts in Peninsular India and other similar suites elsewhere in the world related to rift settings, and also indicate OIB-like magma source. The associated syenite shows subduction-related features, possibly generated in a post-collisional setting. Magmatic zircon grains with high Th/U ratios in the syenite from the Nuapada lamproite form a coherent group with an upper intercept age of 2473±8Ma representing the timing of emplacement of the magma. Zircon grains in three lamproite samples yield four distinct age groups at ca. 2.4Ga, 2.2Ga, 2.0Ga and 0.8Ga. The 2.4Ga group corresponds to xenocrysts entrained from the syenite whereas the 2.2Ga group is considered to represent the timing of emplacement of the lamproites. The ca. 2.0Ga zircon grains correlate with the major thermal imprint associated with mafic magmatism and dyke emplacement in southern Bastar and the adjacent Dharwar Cratons. A few young zircon grains in the syenite and lamproites show a range of early to middle Neoproterozoic ages from 879 to 651Ma corresponding to younger thermal event(s) as also represented by granitic veins cutting across these rocks and extensive silicification. Zircon Lu–Hf isotope data suggest magma derivation from a refertilized Paleo-Mesoarchean sub-continental lithospheric mantle, or OIB-type sources. The differences in Hf-isotope composition among the zircon grains from different age groups indicate that the mantle sources of the lamproite are heterogeneous at the regional scale. A combination of the features from geochemical and zircon Hf isotope data is consistent with asthenosphere-lithosphere interaction during the lamproite magma evolution.The timing of lamproite emplacement in central India correlates with the global 2.2Ga record of LIPs. We link the origin of the related mantle plume to the recycling of subducted slabs associated with the prolonged subduction-accretion history prior to the Neoarchean cratonization, as well as the thermal blanket effect of the Earth's oldest supercontinent. Pulsating plumes and continued rifting generated voluminous dyke swarms across the Bastar and Dharwar Cratons, forming part of a major global rifting and LIP event.

Low reflection Fresnel lenses via double imprint combined with vacuum-UV surface hardening

To improve the optical performance of Fresnel lenses, a technique for preparing them with antireflective structures of the moth-eye type is developed. Masters featuring such hierarchical structures are prepared in SU-8, a negative tone photoresist, by two consecutive thermal imprint steps. The moth-eye structures imprinted first are vacuum ultraviolet-treated at 172 nm to provide a surface-near the cross-linked layer that remains stable during the second imprint of the 100 μm sized Fresnel structures. A successful combination of both structure types is possible at an imprint temperature as low as 45 °C. This can be understood on the basis of the typical exposure and the crosslinking behavior of a chemically amplified negative tone resist like SU-8. The masters prepared in this way will be subjected to extrusion coating, the process of choice for future large area preparation of such structures in a single step.

Thermal nanoimprint to improve the morphology of MAPbX3 (MA = methylammonium, X = I or Br)

Perovskites have high potential for future electronic devices, in particular, in the field of opto-electronics. However, the electronic and optic properties of these materials highly depend on the morphology and thus on the preparation; in particular, highly crystalline layers with large crystals and without pinholes are required. Here, nanoimprint is used to improve the morphology of such layers in a thermal imprint step. Two types of material are investigated, MAPbI3 and MAPbBr3, with MA being methylammonium, CH3NH3+. The perovskite layers are prepared from solution, and the crystal size of the domains is substantially increased by imprinting them at temperatures of 100–150 °C. Although imprint is performed under atmospheric conditions which, in general, enhances the degradation, the stamp that covers the layer under elevated temperature is able to protect the perovskite largely from decomposition. Comparing imprinting experiments with pure annealing at a similar temperature and time proves this. Furthermore, imprint is capable of patterning the surface of the perovskite layers; lines and spaces of 150 nm width were reproducibly obtained under imprint at 150 °C. Moreover, a through-layer patterning is possible by using the partial cavity filling approach. Although not yet optimized, this simple way to define isolated perovskite patterns within a layer simply by thermal nanoimprint is of impact for the preparation of devices, as patterning of perovskite layers by conventional techniques is limited.

Wetting Behavior of Liquids on Micro-Patterned Polymer Surfaces Fabricated by Thermal Imprinting

Wetting Behavior of Liquids on Micro-Patterned Polymer Surfaces Fabricated by Thermal Imprinting

Micro-textured films for reducing microbial colonization in a clinical setting

Transmission of microbes in the hospital environment occurs frequently through human interactions with high-touch surfaces such as patient beds and over-bed tables. Although stringent cleaning routines are implemented as a preventive measure to minimize transmission of microbes, it is desirable to have high-touch surfaces made of antimicrobial materials. Physical texturing of solid surfaces offers a non-bactericidal approach to control the colonization of such surfaces by microbes. To investigate the efficacy of micro-textured polycarbonate films in reducing bacterial load on over-bed tables in a hospital ward. Two different micro-patterns were fabricated on polycarbonate film via a thermal imprinting method. Micro-textured films were then mounted on patient over-bed tables in a general hospital ward and the bacterial load monitored over 24h. Total colony counts, which represented on-specific bacterial loading, and meticillin-resistant Staphylococcus aureus counts were monitored at each time-point. Over a period of 24h, both micro-textured surfaces showed consistently lower bacterial load as compared to the unpatterned polycarbonate and the bare over-bed table laminate. This study supports the findings of earlier laboratory-scale studies that microscale physical texturing can reduce bacterial colonization on a solid surface. Results of the current study suggest that micro-textured surfaces could provide a viable method for reducing microbial contamination of high-touch surfaces in hospitals.

Optical Blood Glucose Sensor Based on Multimode Interference (MMI) Fabricated by Thermal Imprint Process

Optical Blood Glucose Sensor Based on Multimode Interference (MMI) Fabricated by Thermal Imprint Process

Genetic background and embryonic temperature affect DNA methylation and expression of myogenin and muscle development in Atlantic salmon (Salmo salar).

The development of ectothermic embryos is strongly affected by incubation temperature, and thermal imprinting of body growth and muscle phenotype has been reported in various teleost fishes. The complex epigenetic regulation of muscle development in vertebrates involves DNA methylation of the myogenin promoter. Body growth is a heritable and highly variable trait among fish populations that allows for local adaptations, but also for selective breeding. Here we studied the epigenetic effects of embryonic temperature and genetic background on body growth, muscle cellularity and myogenin expression in farmed Atlantic salmon (Salmo salar). Eggs from salmon families with either high or low estimated breeding values for body growth, referred to as Fast and Slow genotypes, were incubated at 8°C or 4°C until the embryonic ‘eyed-stage’ followed by rearing at the production temperature of 8°C. Rearing temperature strongly affected the growth rates, and the 8°C fish were about twice as heavy as the 4°C fish in the order Fast8>Slow8>Fast4>Slow4 prior to seawater transfer. Fast8 was the largest fish also at harvest despite strong growth compensation in the low temperature groups. Larval myogenin expression was approximately 4–6 fold higher in the Fast8 group than in the other groups and was associated with relative low DNA methylation levels, but was positively correlated with the expression levels of the DNA methyltransferase genes dnmt1, dnmt3a and dnmt3b. Juvenile Fast8 fish displayed thicker white muscle fibres than Fast4 fish, while Slow 8 and Slow 4 showed no difference in muscle cellularity. The impact of genetic background on the thermal imprinting of body growth and muscle development in Atlantic salmon suggests that epigenetic variation might play a significant role in the local adaptation to fluctuating temperatures over short evolutionary time.

Development of a roll-to-roll thermal imprinting system with seamless belt-type template

Compared to conventional thermal imprinting using a flat mold, roll-to-roll (R2R) thermal imprinting using a roller mold is a high-speed, high through-put process. In an R2R thermal imprinting process, however, the contact duration between a mold and a thermoplastic substrate is extremely short. This results in insufficient heating and pressing, leading to low fidelity of the imprinted microstructures. We have developed an R2R thermal imprinting system, which allows us to extend the contact duration between the mold and substrate. This system consists of two continuous, seamless belts that are made of metal foil. Each belt is driven by an individual hot roller; at least one belt is used as an imprinting mold, another as a carrier belt. A thermoplastic film to be imprinted is sandwiched between the two belts that provide preheating, heating and pressing, holding, and cooling for demolding during imprinting, leading to extended mold-substrate contact duration and enhanced heat transfer from the belt mold to the polymer film. R2R thermal imprinting has been performed successfully and promising results have been demonstrated.

A high-performance and low cost SERS substrate of plasmonic nanopillars on plastic film fabricated by nanoimprint lithography with AAO template

As a powerful spectroscopy technique, surface-enhanced Raman scattering (SERS) can provide non-destructive and sensitive characterization down to a single molecular level. Aiming to the main challenges of high-performance SERS-active substrates for their real-world applications involving the ultra-sensitive and reproducible signals detection and signal uniformity with large-area, herein, a facile and reliable strategy based on combination of thermal imprinting polycarbonate (PC) film with porous anodic aluminum oxide (AAO) mold and E-beam evaporation of gold is provided to fabricate a high-quality SERS-active substrate consisting of ultra-dense hot-spots with large-area uniformity. Two kinds of sub-10 nm gaps were obtained, including the nanogaps between the neighboring gold coated PC-nanopillars and those between gold on the top of the nanopillars and that on the base, which actually build up a three-dimensional (3D) hot-spot network for high-performance SERS detection. The effect of structural parameters on SERS enhancement was investigated numerically and experimentally, and by optimizing the structural parameters, a remarkable average SERS enhancement factor up to of 1.4×108 is achieved and it shows an excellent reproducibility with a relative standard deviation of 18%, which allows for enhanced practicability in the application of quantitative biochemical detection.

Three-dimensional photonic confinement in imprinted liquid crystalline pillar microcavities

We demonstrate the feasibility of a thermal imprint technology capable of structuring organic thin films with liquid crystalline properties forming feature sizes on a several micrometer scale. The imprint technique can directly be applied onto a variety of substrates including dielectric mirrors. The so fabricated three-dimensional microcavities have lateral extensions up to 20 μm and heights between 1 and 5 μm. Exemplarily, pillar microcavities were produced wherein three-dimensional photonic confinement is observed by the formation of 0D cavity mode patterns. The imprint technique further favors the formation of hemispherical pillar geometries rather than cylindrical pillars, resulting in equidistant mode spacings of transversal cavity modes.

Thermal and chemical variations of the Nigerian Benue trough lead-zinc-barite-fluorite deposits

The Benue trough is an intra-continental rift initiated in the Cretaceous during the opening of the South Atlantic Ocean. Lead-zinc-barite-fluorite mineralization occurs along the 600 km axis of the trough in three discrete sub-basins which coincide with the lower, middle and upper mineral districts of the Benue Valley. Lithologically these sub-basins are dominated by black carbonaceous shale in the Lower Benue, platform carbonates in the Middle Benue and sandstones in the Upper Benue. Micro-thermometric analysis of fluid inclusions in sphalerite, fluorite, barite and quartz have shown that each mineral district has its own unique thermal and chemical imprint. For example, the temperature can be bracketed between 109 °C and 160 °C for lower Benue, 89 °C–144 °C for the Middle Benue and 176 °C–254 °C for the Upper Benue. Chemical differentiation also exists between each mineral district with the Lower Benue having 22 wt % equivalent NaCl while the Middle and Upper Benue have 18 and 16 wt % equivalent NaCl respectively. This study shows that inter-district thermal and chemical variations exist between the ore-stage sulfide and post-sulfide gangue minerals of the entire Benue Valley. Similarly, intra-district thermal and chemical variations have also been observed among all the paragenetic minerals of each district.The thermal variations may be as a result of variations in the geothermal gradient accompanying continental rifting from one district to the other. The variations in the chemistry between the Lower Benue and the Upper Benue paragenic minerals may be as a result of the distinct lithological differences across the Benue Trough.

A rollable ultra-light polymer electrolyte membrane fuel cell

We have developed a highly flexible, ultra-light and thin polymer electrolyte membrane fuel cell that can be used as a portable power source for flexible electronics. To achieve such flexibility and ultra-lightness, we fabricated a thin flow-field plate using a thermal imprinting process and combined it with a laser-machined metal current collector. The air-breathing fuel cell, with a thickness of 0.992 mm and a weight of 2.23 g, demonstrated a total power of 508 mW and a performance degradation of <10% after severe bending fatigue (200 repeated bends). This high power per weight (0.228 W g−1) and robust bending durability have never been observed before. The highly flexible architecture enabled the operation of the fuel cell in an S-shape or even in a rolled-up state without any significant performance loss. We have fabricated a cylindrical planar stack of 10 fuel cells and successfully carried out its outdoor operation to demonstrate its practical applications in various fields.

Thermal imprinting modifies adult stress and innate immune responsiveness in the teleost sea bream.

The impact of thermal imprinting on the plasticity of the hypothalamic-pituitary-interrenal (HPI) axis and stress response in an adult ectotherm, the gilthead sea bream (Sparusaurata, L.), during its development was assessed. Fish were reared under 4 thermal regimes, and the resulting adults exposed to acute confinement stress and plasma cortisol levels and genes of the HPI axis were monitored. Changes in immune function, a common result of stress, were also evaluated using histomorphometric measurements of melanomacrophages centers (MMCs) in the head kidney and by monitoring macrophage-related transcripts. Thermal history significantly modified the HPI responsiveness in adult sea bream when eggs and larvae were reared at a higher than optimal temperature (HT, 22°C), and they had a reduced amplitude in their cortisol response and significantly upregulated pituitary pomc and head kidney star transcripts. Additionally, after an acute stress challenge, immune function was modified and the head kidney of adult fish reared during development at high temperatures (HT and LHT, 18-22°C) had a decreased number of MMCs and a significant downregulation of dopachrome tautomerase. Thermal imprinting during development influenced adult sea bream physiology and increased plasma levels of glucose and sodium even in the absence of an acute stress in fish reared under a high-low thermal regime (HLT, 22-18°C). Overall, the results demonstrate that temperature during early development influences the adult HPI axis and immune function in a teleost fish.

Patterning Polymer Electrolyte Membranes for Fuel Cell and Electrolysis Applications

Electrochemical processes have experienced a renaissance in recent years for the synthesis of commodity chemicals because their potential to integrate with electrified renewable energy sources and prospect to produce chemicals with a lower energy footprint under milder operating conditions. The heart of many electrochemical processes for electrolysis and energy storage and conversion, is the membrane electrode assembly (MEA) that intersects ions, electrons, and the products/reactants-percolating electrolyte. Optimizing the electrode-electrolyte interface in MEAs is vital for maximizing the thermodynamic efficiency of electrochemical processes. For example, the interface must foster facile mass transfer and charge-transfer to cater reaction kinetics. Patterning polymer electrolyte membranes’ (PEMs) surfaces is an attractive methodology capable of enlarging the electrode-electrolyte interfacial area, where reactants, catalysts, and PEMs coexist in MEAs. To date, there have been only a handful of micropatterned PEM demonstrations using 3D printing(1), plasma etching(2), mechanical abrasion(3), thermal imprint lithography(4, 5), multiplex lithography(6), photolithography(7), hot embossing(8), pulsed laser micromachining(9), or their combinations. It is more important to note that there exist even fewer demonstrations for their use in electrochemical technologies that provide electrical energy (e.g, fuel cells) and no demonstrations for electrolysis applications. This presentation reports our work on patterning PEM surfaces through photolithography and block copolymer lithography. Conventional photolithography methods enable micropatterning with feature sizes limited to above ~ 1 mm, whereas block copolymer lithography(10-12) allows nanopatterned features from sub-10nm to 100 nm over large areas without the need to directly write features (i.e., it is a low cost and scalable patterning technique). In this work, technical demonstrations of micro- and nano-patterned PEMs are given for alkaline anion-exchange membrane fuel cells, carbon dioxide electrolysis, and water electrolysis. Single-cell current-voltage relationships in addition to impedance spectra of the patterned PEMs used in MEAs for the aforementioned applications are provided. Connections between patterned feature sizes and MEA performance with individual resistance components will be discussed. Figure 1 below depicts a micropatterned PEM and self-assembled, nanostructured block copolymer templates.