The strong demand for renewable energy promotes research on novel methods and technologies for energy conversion. Microfluidic systems for energy conversion by streaming current are less known to the public, and the relatively low efficiencies previously obtained seemed to limit the further applications of such systems. Here we report a microdropletbased electrostatic generator operating by an acceleration-deceleration cycle ('ballistic' conversion), and show that this principle enables both high efficiency and compact simple design. Water is accelerated by pumping it through a micropore to form a microjet breaking up into fast-moving charged droplets. Droplet kinetic energy is converted to electrical energy when the charged droplets decelerate in the electrical field that forms between membrane and target. We demonstrate conversion efficiencies of up to 48%, a power density of 160 kW m À 2 and both high-(20 kV) and low-(500 V) voltage operation. Besides offering striking new insights, the device potentially opens up new perspectives for low-cost and robust renewable energy conversion.
We found that gold nanoparticles, when heated to close to their melting point on substrates of amorphous SiO2 or amorphous Si3N4, move perpendicularly into the substrate. Dependent on applied temperatures, particles can become buried or leave nanopores of extreme aspect ratio (diameter ≅ 25 nm, length up to 800 nm). The process can be understood as driven by gold evaporation and controlled by capillary forces and can be controlled by temperature programming and substrate choice.
In this contribution, we present for the first time the experimental results of energy conversion from the streaming current when a polymer is added to the working solution. We added polyacrylic acid (PAA) in concentrations of 200 ppm to 4000 ppm to a KCl solution. By introducing PAA, the input power, which is the product of volumetric flow rate and the applied pressure, reduced rapidly as compared to the case of using only a normal viscous electrolyte KCl solution. The output power at the same time remained largely constant, whereby an increase of the streaming current and a decrease of the streaming potential simultaneously occurred. These combined factors led to the massive increase of the energy conversion efficiency. Particularly, the results showed that when PAA was in a 0.01 mM KCl solution, the energy conversion efficiency of the system was enhanced by a factor of 447 (±2%), as compared to the case of the solution containing only 0.01 mM KCl. An enhancement factor of 249 (±4%) was also observed when PAA was added to the higher ionic strength background solution, 1 mM KCl. This finding can have practical use in microchannel-array energy conversion systems. When, instead of the negatively charged PAA, a non-ionic polymer polyethylene oxide (PEO) was added to the solution, no efficiency increase was observed, probably due to polymer wall adsorption.
Silicon pore optics are currently under development for missions such as the International X-ray Observatory (IXO) as an alternative to the glass or nickel shell mirrors that were used in previous generation X-ray telescopes. The unprecedented effective area requirement of the IXO requires a modular optics design suitable for mass production. In this paper we discuss the current state-of-the-art in plate manufacturing technology. We provide examples of process innovations that have directly impacted the cost per mirror plate and have reduced the manufacturing cost of a mirror module. We show how a switch from silicon to silica as the reflective surface results in a simplified process flow without a corresponding change in the optical performance. We demonstrate how standard photolithographic techniques, applied in the semiconductor industry, can be used to pattern a reflective layer. The 5 arc-second angular resolution requirement of the IXO has stimulated a theoretical analysis of engineering tolerances in relation to angular resolution. We prove that improved control of the wedge angle by means of etch rate monitoring results in improved angular resolution. The results of this investigation will be used as the basis for future development in design for mass production.
This paper presents a maskless method to manufacture fused silica chips for low-noise resistivepulse sensing. The fabrication includes wafer-scale density modification of fused silica with a femtosecond-pulsed laser, low-pressure chemical vapor deposition (LPVCD) of silicon nitride (SiN x ) and accelerated chemical wet etching of the laser-exposed regions. This procedure leads to a freestanding SiN x window, which is permanently attached to a fused silica support chip and the resulting chips are robust towards Piranha cleaning at ∼80°C. After parallel chip manufacturing, we created a single nanopore in each chip by focused helium-ion beam or by controlled breakdown. Compared to silicon chips, the resulting fused silica nanopore chips resulted in a four-fold improvement of both the signal-to-noise ratio and the capture rate for signals from the translocation of IgG 1 proteins at a recording bandwidth of 50 kHz. At a bandwidth of ∼1 MHz, the noise from the fused silica nanopore chips was three-to six-fold reduced compared to silicon chips. In contrast to silicon chips, fused silica chips showed no laser-induced current noise-a significant benefit for experiments that strive to combine nanopore-based electrical and optical measurements.
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