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A novel method has been developed to cavitate aqueous solutions, which is called electrocavitation. An axial voltage is applied in a nanochannel containing an aqueous solution with a stepwise conductivity gradient. A combination of electrical and viscous forces then generates a tension in the solution which, at sufficiently low pressures, causes it to cavitate. Measurement of the current during the experiment as well as optical observation provides knowledge on the time and axial position of cavitation, after which the pressure at the cavitation position can be calculated from a theoretical model in which also the ζ-potential is inserted, which is separately determined from electroosmotic flow experiments. It is found that generally the cavitation position coincides with the position of the conductivity step. In several experiments the cavitation pressure in successive experiments on the same channel became increasingly lower, suggesting a gradual removal of cavitation nuclei from the system. We calculated that pressures as low as −1630 bar ±10 % have been reached, close to theoretically predicted pressures for homogeneous cavitation. The platform performs reliably and can be easily controlled.

This paper presents the realization of micrometer sized silicon nitride tetrahedra with well-defined angles that are folded out of a planar geometry using capillary forces. The required specific three-dimensional shape is achieved by a well-defined folding sequence. Using the favorable properties of the recently developed corner lithography technique, a programmable stop hinge is micro-machined by etching specifically defined intersection planes of the silicon mold. Tetrahedra were successfully folded by capillarity validating this new technique. The demand for such a microstructure has become very large since it can form the essential basic element for future three-dimensional data storage systems.

MicrochanneIs were created by fusion bonding of a Pyrex cover to a thermally oxidized silicon wafer, which contained anisotropically etched grooves. Such channels are frequently used in microfluidic handling systems, for example, in chemical analysis. Since in some of these labs-on-a-chip, in particular those used in liquid chromatography, the channels are subjected to high pressures of up to a few hundred bar, it is important to have information about the mechanical stability of the channel chip, in particular of the wafer bond involved in it. The latter is the subject of this paper. The maximum pressure that can be applied to several different channel chips was investigated experimentally. In order to find the relation among this maximum pressure, channel geometry, materials elasticity, and bond energy, an energy model was developed that is generally applicable to all types of wafer bonds. It was shown that the model is substantiated by the experimental pressure data, from which it could be calculated that the effective bond energy increased from 0.018 to 0.19 J/m/sup 2/ for an annealing temperature ranging from 310 to 470/spl deg/C.