This article demonstrates, through finite element analysis, the possibility to manufacture sub-30 nm polymeric channels using electrostatic induced lithography. Channels with a width of 25 nm, a depth of 50 nm and an inter-channel wall of 28 nm can be obtained by this patterning process. The influence of operational parameters such as the filling factor, the aspect ratio of the master electrode, the applied voltage and the gap between the two electrodes and initial film thickness has been studied in detail to define the fabrication limits of this process in the case of periodic nanostructures. Conclusions for such nanostructures can be generalised to other shapes manufactured from polymers.
Hollow microstructures serve many useful applications in the fields of microsystems, chemistry, photonics, biology and others. Current fabrication methods of artificial hollow microstructures require multiple fabrication steps and expensive manufacturing tools. The paper reports a unique one-step fabrication process for the growth of hollow polymeric microstructures based on electric fieldassisted capillary action. This method demonstrates the manufacturing of self-encapsulated microstructures such as hollow microchannels and microcapsules of around 100-lm height from an initial polymer thickness of 22 lm. Microstructure caps of several microns thickness have been shown to keep their shape under bending or delamination from the substrate. The inner surface of hollow microstructures is shown to be smooth, which is difficult to achieve with current methods. More complicated structures, such as a microcapsule array connected with hollow microchannels, have also been manufactured with this method. Numerical simulation of the resist growth process using COMSOL Multiphysics finite element analysis software has resulted in good agreement between simulated and experimental results on the overall shape of the resulting structures. These results are very positive and demonstrate the speed, versatility and cost-effectiveness of the method.
A high frequency tuned electromagnetic induction coil is used to induce ultrasonic pressure waves leading to cavitation in alloy melts. This presents an alternative ‘contactless’ approach to conventional immersed probe techniques. The method can potentially offer the same benefits of traditional ultrasonic treatment (UST) such as degassing, microstructure refinement and dispersion of particles, but avoids melt contamination due to probe erosion prevalent in immersed sonotrodes, and it can be used on higher temperature and reactive alloys. An added benefit is that the induction stirring produced by the coil, enables a larger melt treatment volume. Model simulations of the process are conducted using purpose-built software, coupling flow, heat transfer, sound and electromagnetic fields. Modelling results are compared against experiments carried out in a prototype installation. Results indicate strong melt stirring and evidence of cavitation accompanying acoustic resonance. Up to 63% of grain refinement was obtained in commercial purity (CP-Al) aluminium and a further 46% in CP-Al with added Al–5Ti–1B grain refiner.
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