Elaboration and characterization of a 200 mm stretchable and flexible ultra-thin semi-conductor film.

We describe a process for transferring a 200 nm thick, 200 mm wide monocrystalline silicon (mono c-Si) thin film from a silicon-on-insulator onto a flexible polymer substrate. The result is a stretchable and flexible ultra-thin semi-conductor film that can be subjected to tensile stress experiments. The process uses off-the-shelf 200 mm wafers and standard polymer temporary bonding techniques. The backside substrate and buried oxide are removed using grinding and wet etching processes. No cracks or wrinkles are observed on the film prior to the tensile stress experiments. The stretching of the flexible structure results in up to 1.5% uniaxial tensile elastic strain on the thin mono c-Si film.

Optimization of hydrophilic/hydrophobic phase separation in sPEEK membranes by hydrothermal treatments.

Via SAXS, herein, we studied how a sPEEK microstructure evolves when it is immersed in water at a wide range of temperatures (20-100 °C) and time scales (from a few hours to dozens of days). In particular, we scrutinized the behavior of sPEEK at the temperature and time associated with the appearance of a well-defined nanosegregated morphology. At 80 °C, we observed nanoscale swelling along with smoothing of the water/polymer interface over a long period of time (several days). Herein, two of the main membrane properties, i.e., water uptake and proton conductivity, were studied for different immersion times and temperatures. It was found that the abovementioned properties were remarkably correlated with the evolution of the membrane microstructure, which was partly conserved after drying. The present findings helped us to understand that the thermally activated evolutions observed at both the nanoscale and macroscale were associated with the sPEEK ß-relaxation crossover. Therefore, the very different swelling behaviors of sPEEK and Nafion are correlated to the much higher ß-relaxation of sPEEK vs. Nafion (75 °C vs. -20 °C - dry state). From a practical viewpoint, this study emphasizes, for membranes alternative to Nafion, the importance and impact of the membrane pretreatment on their functional properties.

A new interpretation of SAXS peaks in sulfonated poly(ether ether ketone) (sPEEK) membranes for fuel cells.

The structure of a commercial sulfonated poly(ether ether ketone) (sPEEK) membrane was analyzed by Small-Angle X-Ray Scattering (SAXS) for different water uptakes obtained after immersion in liquid water at various temperatures. For low membrane swelling, the SAXS profile displays only a wide-angle peak in the 0.2-0.3 Å(-1) region. As the membrane swells, two supplementary correlation peaks arise and shift towards small angles, which are the signature of a structural evolution of the membrane, whereas the wide angle peak remains stable. The SAXS spectra of sPEEK membranes can thus display three correlation peaks simultaneously. Therefore we propose a new interpretation of these SAXS spectra which conclude that the two small angle peaks are attributed to the so-called matrix and ionomer peaks and the wide-angle peak is ascribed to the mean separation distance between sulfonic acid groups grafted onto the polymer backbone. This peak attribution implies that the sPEEK nano-phase separation is triggered by an immersion in hot water (ionomer peak apparition). Our new peak attribution was confirmed by studying the impact of temperature, electron density contrast and ionic exchange capacity.