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Scaling effects on the optical properties of patterned nano-layered shape memory films
摘要： Nano-layered films of PVAc/PU systems were fabricated by forced assembly coextrusion method. The bulk shape memory properties of PVAc/PU systems were utilized to program nanoscale patterns such as diffraction grating which exhibit iridescence after patterning. A hot embossing process has been utilized to imprint diffraction grating patterns as nano-scale information onto the surface of the thin multilayer films. Three levels of hierarchy i.e. layer thickness, spacing and heights of patterns, governs the functionality of the patterned multilayer film. The time and temperature dependent viscoelastic shape memory behavior determines the opto-mechanical tunability of the film. Mechanical switching of the patterns also leads to optical switching of the films which corresponds to their efficiency of information retrieval. The recovery of patterns as well as the diffractive property depends on the layer thickness (l) of films and heights of patterns (h0). The results illustrate that the higher ratio of h0/l better is the recovery of the grating patterns and the corresponding diffractive properties. This scaling effect enables versatile applications in information security by tuning the layer structure of the multilayer shape memory films.
关键词： scaling effect,shape memory film,pattern programming,hot embossing,multilayer film,information security,diffractive optical element,thermal responsive optics
更新于2025-10-22 19:40:53
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Study on non-isothermal hot-embossing of polymer micro-prism array with efficiency and accuracy
摘要： 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.
关键词： micro-forming,die core,micro-grinding,hot-embossing,LGP,micro-prism array
更新于2025-09-23 15:21:21
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Laser-assisted surface processing for functionalization of polymers on micro- and nano-scale
摘要： Rapid manufacturing of functionalized polymers enable a cost-ef?cient method for many applications in the biological, and medical sector. Laser structuring techniques differ for fast fabrication processes of thermoplastics. Here we report on direct UV laser ablation of polystyrene and polydimethylsiloxane to control wettability and bio-compatibility. For this purpose contact angle measurements and L929 cell growth experiments were performed as function of laser and process parameters. This work also describes the potential of laser-assisted hot embossing which has been introduced to replicate pre-fabricated micro- and nano-sized structures onto polymers proving it to be a cost-ef?cient and ?exible method for surface functionalization. Therefore, pre-fabricated laser-induced periodic surface structures have been manufactured as mould inserts using ultrafast laser radiation near the ablation threshold. These mould inserts can also be made of nickel, silicon or glass proving laser-assisted hot embossing to be a versatile tool for the functionalization of thermoplastics and meet the requirements for modern manufacturing with regard to quality and production ?exibility.
关键词： Bio-compatibility,Functionalization of polymers,Wettability,Laser-assisted surface processing,Laser-assisted hot embossing,Micro- and nano-scale
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Low-Cost Fabrication of Polymer Based Micro-Optical Devices for Application in Illumination, Sensing, and Optical Interconnects
摘要： Fabrication of desired micro structures in polymers is always of keen interest for applications in illumination optics, sensors and optical interconnects. The challenge is to fabricate structures in the sub-micron range but at low cost. Among other fabrication methods as described in [1], maskless lithography tends to be cost effective and can create sub-micron structures. Here, we present a simple and low-cost fabrication process chain for fabricating desired micro structures in polymer, i.e. PMMA. The microstructures are, for example, grating structures and straight waveguides. The fabrication is done using a maskless lithography setup which employs a spatial light modulator and a UV LED. For recording the microstructure pattern a grayscale photoresist, i.e. OrmoComp, is used, which is coated on the silicon substrate. For writing waveguides, a translation stage is included in the setup to stitch the single exposure patterns together to form a continuous waveguide structure, as can be seen in Fig. 1(c). For replication an intermediate stamp, which is stable at high thermal loads, is obtained by casting Polydimethyl siloxane (PDMS) in an oven for 15 mins at 100 0C. The stamp is then used to replicate the microstructures onto the Polymethyl methacrylate (PMMA) using a hot embossing system, i.e. Jenoptik HEX03. A 500 μm thick PMMA (Plexiglas XT99524, Thyssen Krupp) foil is placed on the PDMS (ELASTOSIL RT 607A/B) stamp and an embossing pressure of 7 kPa is applied for 4 mins. After cooling to a release temperature of 40 0C, the PMMA foil is removed manually.
关键词： micro-optical devices,PDMS,optical interconnects,illumination,polymer,sensing,maskless lithography,PMMA,hot embossing
更新于2025-09-19 17:13:59
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Towards High Throughput Texturing of Polymer Foils for Enhanced Light Trapping in Flexible Perovskite Solar Cells using Roll‐to‐roll Hot Embossing
摘要： In this work, a high throughput method is presented to texture polymer foils by roll-to-roll hot embossing with the objective of increasing the substrate haze factor. Triple cation perovskite solar cells were deposited onto these structured substrate showing an efficiency increase up to 15 % (relative) compared to the reference flat device, due to an enhanced light absorption.
关键词： flexible optoelectronics,perovskite solar cells,roll-to-roll hot embossing,direct laser interference patterning,light trapping
更新于2025-09-12 10:27:22
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Picosecond Laser Interference Patterning of Periodical Micro-Architectures on Metallic Molds for Hot Embossing
摘要： In this work, it is demonstrated that direct laser interference patterning (DLIP) is a method capable of producing microtextured metallic molds for hot embossing processes. Three different metals (Cr, Ni, and Cu), relevant for the mold production used in nanoimprinting systems, are patterned by DLIP using a picosecond laser source emitting at a 532 nm wavelength. The results show that the quality and surface topography of the produced hole-like micropatterns are determined by the laser processing parameters, such as irradiated energy density and the number of pulses. Laser-induced periodic surface structures (LIPSS) are also observed on the treated surfaces, whose shapes, periodicities, and orientations are strongly dependent on the accumulated fluence. Finally, the three structured metals are used as embossing molds to imprint microlenses on polymethyl methacrylate (PMMA) foils using an electrohydraulic press. Topographical profiles demonstrate that the obtained structures are comparable to the masters showing a satisfactory reproduction of the texture. The polymeric microlens arrays that showed the best surface homogeneity and overall quality were those embossed with the Cr molds.
关键词： direct laser interference patterning,microstructures,hot embossing,polymethyl methacrylate,laser-induced periodic surface structures
更新于2025-09-11 14:15:04