Drop size distribution is an important characteristic of emulsions, probably the most crucial one for their use in various applications. Here, a pilot‐scale apparatus with a cone‐shaped flow geometry is introduced. The plate contains a micro‐engineered membrane manufactured from silicon allowing for the production of emulsions with narrow drop size distributions. The process is characterized by producing model emulsions of the oil‐in‐water type under laminar rheometric flow conditions and by accessing the regime of drop detachment as a function of the wall shear stress applied, by means of high‐speed imaging in a separate flow cell. Furthermore, clear evidence is given of the crucial influence of the membrane wetting properties on the emulsification results, by comparing the performance of micro‐engineered membranes composed either of silicon, silicon nitride, or nickel, for pore diameters from 1 to 12 μm, in the flow cell.

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The top-down fabrication of high aspect ratio circular micro-and nanostructures in silicon nitride is presented. A new method is introduced to increase the aspect ratio of anisotropically etched holes by a factor of more than two with respect to the results obtained from an established dry-etching process. The method is based on the renewal of an etching mask after a first etching step has been completed. Mask renewal is done by line-of-sight deposition of a masking layer on the surface of the sample, which is mounted at an angle with respect to the deposition direction. No additional alignment step is required. The proof of principle is performed for silicon nitride etching through a mask of titanium, but the method has great potential to be applicable to a wide variety of substrate-mask combinations and to find entrance into various engineering fields. Two specific applications are highlighted. Firstly, a thick silicon nitride hardmask is used for the fabrication of deeply etched photonic crystal holes in indium phosphide (InP). For holes of 280 nm diameter, a record aspect ratio of 20 and an overall selectivity of 28.5 between a positive-tone resist layer and InP are reported. Secondly, the use of perforated silicon nitride membranes for droplet formation for applications in food engineering or pharmaceutics is addressed. Preliminary results show a potential for the self-aligned mask renewal method to exceed state-of-the-art membrane quality in terms of pore size, aspect ratio and membrane stability.

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