A novel approach for the preparation of interconnected macroporous polymers with a controllable pore structure was reported. The method was based on the polymerization of water-in-oil Pickering high internal phase emulsion (HIPE) stabilized by polystyrene (PS)/silica composite particles. The composite Pickering stabilizers were facilely obtained by mixing positively charged PS microspheres and negatively charged silica nanoparticles, and their amphiphilicity could be delicately tailored by varying the ratio of PS and silica. The droplet size of Pickering HIPEs was characterized using an optical microscope. The pore structure of polymer foams was observed using a scanning electron microscope. The interconnectivity of macroporous polymers was evaluated upon their gas permeability, which was greatly improved after etching PS microspheres included in the Pickering stabilizers with tetrahydrofuran. As a result, fine tailoring of the pore structure of polymer foams could be realized by simply tuning the ratio of PS to silica particles in the composite stabilizer.
In dry plasma silicon etching, it is desired to have a high etching rate, a high etching selectivity to mask material, a vertical or controllable sidewall profile, and a smooth sidewall. Since the standard Bosch process (switching between SF6 and C4F8 gases) leads to a wavy/rough sidewall profile, the nonswitching pseudo-Bosch process is developed to give a smooth sidewall needed for nanostructure fabrication. In the process, SF6 and C4F8 gases are introduced to the chamber simultaneously. Here, the authors show that by introducing a periodic oxygen (O2) plasma cleaning step, that is, switching between SF6/C4F8 etching and O2 cleaning, the silicon etching rate can be significantly improved (by up to ∼55%, from 139 to 216 nm/min) without any adverse effect. This is mainly because O2 plasma can remove the fluorocarbon polymer passivation layer at the surface. The etching and cleaning step durations were varied from 5 s to 40 min and from 0 to 60 s, respectively. The fastest etching rates were obtained when the cleaning step takes roughly 10% of the total etching time.
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