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Register a new userHot embossing of Au- and Pb- based alloys for X ray grating fabrication
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Grating-based X-ray phase-contrast interferometry has a high application impact in material science and medicine for imaging of weakly absorbing (low Z) materials and soft tissues. For the absorbing gratings, casting of highly x-ray absorbing metals, such as Au and Pb alloys, has proven to be a viable way to generate large area periodic high aspect ratio microstructures. In this paper, we review the grating fabrication strategy with a special focus on a novel approach of casting low temperature melting alloys (Au-Sn and Pbbased alloy) into Si grating templates using hot embossing. The process, similar to nanoimprint lithography, requires particular adjusting efforts of process parameters as a function of the metal alloy and the grating feature size. The transition between solid and liquid state depends on the alloy phase diagram, the applied pressure can damage the high aspect ratio Si lamellas and the microstructure of the solid metal can affect the grating structure. We demonstrate that metal casting by hot embossing can be used to fabricate gratings on large area (up to 70x70 mm2) with aspect ratio up to 50:1 and pitch in the range of 1-20 {mu}m.
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Today, hot embossing and injection molding belong to the established plastic molding processes in microengineering. Based on experimental findings, a variety of microstructures have been replicated so far using the processes. However, with increasing requirements regarding the embossing surface and the simultaneous decrease of the structure size down into the nanorange, increasing know-how is needed to adapt hot embossing to industrial standards. To reach this objective, a German-Canadian cooperation project has been launched to study hot embossing theoretically by a process simulation and experimentally. The present publication shall report about the first results of the simulation - the modeling and simulation of large area replication based on an eight inch microstructured mold.
We reported the usage of grating-based X-ray phase-contrast imaging in nondestructive testing of grating imperfections. It was found that electroplating flaws could be easily detected by conventional absorption signal, and in particular, we observed that the grating defects resulting from uneven ultraviolet exposure could be clearly discriminated with phase-contrast signal. The experimental results demonstrate that grating-based X-ray phase-contrast imaging, with a conventional low-brilliance X-ray source, a large field of view and a reasonable compact setup, which simultaneously yields phase- and attenuation-contrast signal of the sample, can be ready-to-use in fast nondestructive testing of various imperfections in gratings and other similar photoetching products.
In large area micro hot embossing, the process temperature plays a critical role to both the local fidelity of microstructure formation and global uniformity. The significance of low temperature hot embossing is to improve global flatness of embossed devices. This paper reports on experimental studies of polymer deformation and relaxation in micro embossing when the process temperatures are below or near its glass transition temperature (Tg). In this investigation, an indentation system and a micro embosser were used to investigate the relationship of microstructure formation versus process temperature and load pressure. The depth of indentation was controlled and the load force at a certain indentation depth was measured. Experiments were carried out using 1 mm thick PMMA films with the process temperature ranging from Tg-55 degrees C to Tg +20 degrees C. The embossed structures included a single micro cavity and groups of micro cavity arrays. It was found that at temperature of Tg-55 degrees C, elastic deformation dominated the formation of microstructures and significant relaxation happened after embossing. From Tg-20 degrees C to Tg, plastic deformation dominated polymer deformation, and permanent cavities could be formed on PMMA substrates without obvious relaxation. However, the formation of protrusive structures as micro pillars was not complete since there was little polymer flow. With an increase in process temperature, microstructure could be formed under lower loading pressure. Considering the fidelity of a single microstructure and global flatness of embossed substrates, micro hot embossing at a low process temperature, but with good fidelity, should be preferred.
The paper presents a comprehensive analysis of elastic properties of polystyrene-based nanocomposites filled with different types of inclusions: small spherical particles (SiO2 and Al2O3), alumosilicates (montmorillonite, halloysite natural tubules and Mica) and carbon nanofillers (carbon black and multi-walled carbon nanotubes). Composites were fabricated by melt technology. The analysis of composite melts showed that the introduction of Montmorillonite, Multi-walled carbon nanotubes, and Al2O3 particles provided an increase in melt viscosity by an average of 2 to 5 orders of magnitude over the pure polystyrene. Block samples of composites with different filler concentrations were prepared, and their linear and nonlinear elastic properties were studied. The introduction of more rigid particles led to a more profound increase in the elastic modulus of the composite, with the highest rise of about 80% obtained with carbon fillers. Carbon black particles provided also an enhanced strength at break of about 20% higher than that of pure polystyrene. The nonlinear elastic moduli of composites were shown to be more sensitive to addition of filler particles to the polymer matrix than the linear ones. The nonlinearity coefficient $beta$ comprising the combination of linear and nonlinear elastic moduli of a material demonstrated considerable changes correlating with changes of the Youngs modulus. The absolute value of $beta$ showed rise in 1.5-1.6 times in the CB- and HNT-containing composites as compared to that of pure PS. The changes in nonlinear elasticity of fabricated composites were compared with measurements of the parameters of bulk nonlinear strain waves in them. Variations of wave velocity and decay decrement correlated with observed enhancement of materials nonlinearity.
Improving lithium-ion batteries (LIBs) safety remains in a challenging task when compared with the tremendous progress made in their performance in recent years. Embedding thermo-responsive polymer switching materials (TRPS) into LIB cells has been proved to be a promising strategy to provide consistent thermal abuse protections at coin-cell level. However, it is unrealistic to achieve large-scale applications without further demonstration in high-capacity pouch cells. Here, we employed tungsten carbide (WC) as a novel conductive filler, and successfully overcame the intrinsic processing difficulty of polyethylene (PE) matrix in a scalable solvent-based method to obtain ultra-thin, uniform, highly conductive TRPS. Moreover, by integrating TRPS directly into LIB electrodes, no extra fabrication facilities or processes are required for making the cells. As a result, multi-layer pouch cells with consistent electrochemical performance and thermal abuse protection function were fabricated using industry relevant manufacturing techniques, which brings TRPS one step further to the real application scenarios.
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