Engulfment control of platinum nanoparticles into oxidized silicon substrates for fabrication of dense solid-state nanopore arrays

We found that platinum (Pt) nanoparticles, upon annealing at high temperature of 1000 °C, are engulfed into amorphous fused-silica or thermal oxide silicon substrates. The same phenomenon was previously published for gold (Au) nanoparticles. Similar to the Au nanoparticles, the engulfed Pt nanoparticles connect to the surface of the substrates through conical nanopores, and the size of the Pt nanoparticles decreases with increasing depth of the nanopores. We explain the phenomena as driven by the formation of platinum oxide by reaction of the platinum with atmospheric oxygen, with platinum oxide evaporating to the environment. We found that the use of Pt provides much better controllability than the use of Au. Due to the high vapor pressure of platinum oxide, the engulfment of the Pt nanoparticles into oxidized silicon (SiO2) substrates is faster than of Au nanoparticles. At high temperature annealing we also find that the aggregation of Pt nanoparticles on the substrate surface is insignificant. As a result, the Pt nanoparticles are uniformly engulfed into the substrates, leading to an opportunity for patterning dense nanopore arrays. Moreover, the use of oxidized Si substrates enables us to precisely control the depth of the nanopores since the engulfment of Pt nanoparticles stops at a short distance above the SiO x /Si interface. After subsequent etching steps, a membrane with dense nanopore through-holes with diameters down to sub-30 nm is obtained. With its simple operation and high controllability, this fabrication method provides an alternative for rapid patterning of dense arrays of solid-state nanopores at low-cost.</p

Stability of an elongated thickness fluctuation in a horizontal soap film

International audienceEven though liquid foams are ubiquitous in everyday life and industrial processes, their ageing and eventual destruction remain a puzzling problem. Soap films are known to drain through marginal regeneration, which depends upon periodic patterns of film thickness along the rim of the film. The origin of these patterns in horizontal films (i.e. neglecting gravity) still resists theoretical modelling. In this work, we theoretically address the case of a flat horizontal film with a thickness perturbation, either positive (a bump) or negative (a groove), which is initially invariant under translation along one direction. This pattern relaxes towards a flat film by capillarity. By performing a linear stability analysis on this evolving pattern, we demonstrate that the invariance is spontaneously broken, causing the elongated thickness perturbation pattern to destabilise into a necklace of circular spots. The unstable and stable modes are derived analytically in well-defined limits, and the full evolution of the thickness profile is characterised. The original destabilisation process we identify may be relevant to explain the appearance of the marginal regeneration patterns near a meniscus and thus shed new light on soap-film drainage

Stability of a directional Marangoni flow

When a Marangoni flow of soluble surfactants is confined laterally, the flow forms an inertial surface jet which shows meander instabilities. The morphology and the destabilization of this surface jet are analyzed experimentally and theoretically.</p

Mitigating the influence of multivalent ions on power density performance in a single-membrane capacitive reverse electrodialysis cell

Abstract In recent years, the energy generated by the salinity gradient has become a subject of growing interest as a source of renewable energy. One of the most widely used processes is reverse electrodialysis (RED), based on the use of ion exchange membranes and Faradaic electrodes. However, the use of real salt solutions containing mixtures of divalent and monovalent ions in the RED process results in a significant loss of recovered power, compared with salt solutions containing only monovalent ions. From an original point of view, in this work we study and explain the influence of divalent ions and complex solutions in reverse electrodialysis devices equipped with capacitive electrodes with a single membrane (CREDSM). We show that CREDSM mitigates the impact of divalent ions. From a quantitative point of view, the power recovered in a Faradaic cell drops by more than 75 $$\%$$ % when the solutions contain 50 $$\%$$ % molar fraction of divalent ions and by 33 $$\%$$ % when the solutions contain 10 $$\%$$ % molar fraction of divalent ions. For similar low-cost membranes with fairly low selectivity, recovered power drops by only 34 $$\%$$ % when solutions contain 60 $$\%$$ % moles of divalent ions in CREDSM. We show that only the membrane potential, which makes up half of the cell’s open circuit potential, is affected. The potential of capacitive electrodes which counts for half of the potential cell does not decrease in the presence of divalents. For the same membrane under the same conditions, we estimate a loss of 62 $$\%$$ % in a RED device Furthermore, the membrane is not poisoned by divalent ions because we periodically change the electrical current direction, by means of switching the feed waters. CREDSM devices do not show any variation in membrane resistance or membrane selectivity. The techno-economic analysis suggests further valorization of salinity gradients in industrial operations

Functionality integration in stereolithography 3D printed microfluidics using a “print-pause-print” strategy

International audienceStereolithography 3D printing, although an increasingly used fabrication method for microfluidic chips, has the main disadvantage of producing monolithic chips in a single material. We propose to incorporate during printing various objects using a “print-pause-print” strategy. Here, we demonstrate that this novel approach can be used to incorporate glass slides, hydrosoluble films, paper pads, steel balls, elastic or nanoporous membranes and silicon-based microdevices, in order to add microfluidic functionalities as diverse as valves, fluidic diodes, shallow chambers, imaging windows for bacteria tracking, storage of reagents, blue energy harvesting or filters for cell capture and culture

Optical accessibility improvements for the characterization of the nanopede

Although microfluidic droplet production is a well-developed field, high-yield production of monodisperse nanoscale droplets is still in its infancy. Here, we present improvements made on the Nanopede chip, presented last year by Tregouet et al., which aims to fill this vacancy in the field. By improving both the chip and the chip holder, imaging at high magnification was achieved, allowing us to observe the droplet generation in order to elucidate the generation mechanism

Optical accessibility imporvements for the characterization of the nanopede

Although microfluidic droplet production is a well-developed field, high-yield production of monodisperse nanoscale droplets is still in its infancy. Here, we present improvements made on the Nanopede chip, presented last year by Tregouet et al., which aims to fill this vacancy in the field. By improving both the chip and the chip holder, imaging at high magnification was achieved, allowing us to observe the droplet generation in order to elucidate the generation mechanism