The formation and growth of hydrogen bubbles on a Si(1 0 0) surface during its anisotropic etching in aqueous KOH has been investigated. Quantitative data on bubble size, lifetime and density on the etching surface was obtained and their dependence on KOH concentration, applied potential and temperature were measured. In situ FTIR measurements demonstrated a strong dependence of bubble attachment on surface termination and hence on the hydrophilicity of the Si(1 0 0) surface during etching. The formation of surface defects and the geometry of bubble imprints have been directly characterised with scanning probe microscopy. The analysis of hillock formation and statistical considerations show that the adhesion of hydrogen bubbles during anisotropic etching of silicon is a source of surface roughness and pyramid formation.

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We present the design, fabrication, testing and scaling characteristics of a silicone-based turning microvalve. Opening and closing are managed by turning a steel rod, with a diameter of 250 µm. The actuation energy for opening and closing the valve is 0.15 mJ, and when closed the valve withstands pressures higher than 0.7 MPa. The valve design in combination with studies of the scaling behavior of friction and sealing shows the feasibility of low-energy turning microvalves with a high-pressure seal. For an appropriate parameter range we show that the friction force scales linearly with the apparent contact area and with the relative radial displacement of the elastic channel walls. Finally, our results illustrate the necessity of parameter control in order to develop a robust valve with the benefits of down-scaling.