Encapsulated salts in velvet worm slime drive its hardening

Slime expelled by velvet worms entraps prey insects within seconds in a hardened biopolymer network that matches the mechanical strength of industrial polymers. While the mechanic stimuli-responsive nature and building blocks of the polymerization are known, it is still unclear how the velvet worms' slime hardens so fast. Here, we investigated the slime for the first time, not only after, but also before expulsion. Further, we investigated the slime's micro- and nanostructures in-depth. Besides the previously reported protein nanoglobules, carbohydrates, and lipids, we discovered abundant encapsulated phosphate and carbonate salts. We also detected CO₂ bubbles during the hardening of the slime. These findings, along with further observations, suggest that the encapsulated salts in expelled slime rapidly dissolve and neutralize in a baking-powder-like reaction, which seems to accelerate the drying of the slime. The proteins' conformation and aggregation are thus influenced by shear stress and the salts' neutralization reaction, increasing the slime's pH and ionic strength. These insights into the drying process of the velvet worm's slime demonstrate how naturally evolved polymerizations can unwind in seconds, and could inspire new polymers that are stimuli-responsive or fast-drying under ambient conditions.

Shaping Perovskites: In Situ Crystallization Mechanism of Rapid Thermally Annealed, Prepatterned Perovskite Films

Understanding and controlling the crystallization of organic-inorganic perovskite materials is important for their function in optoelectronic applications. This control is particularly delicate in scalable single-step thermal annealing methods. In this work, the crystallization mechanisms of flash infrared-annealed perovskite films, grown on substrates with lithographically patterned Au nucleation seeds, are investigated. The patterning enables the in situ observation to study the crystallization kinetics and the precise control of the perovskite nucleation and domain growth, while retaining the characteristic polycrystalline micromorphology with larger crystallites at the boundaries of the crystal domains, as shown by electron backscattering diffraction. Time-resolved photoluminescence measurements reveal longer charge carrier lifetimes in regions with large crystallites on the domain boundaries, relative to the domain interior. By increasing the nucleation site density, the proportion of larger crystallites is increased. This study shows that the combination of rapid thermal annealing with nucleation control is a promising approach to improve perovskite crystallinity and thereby ultimately the performance of optoelectronic devices.

Determination of a refractive index and an extinction coefficient of standard production of CVD-graphene

The refractive index and extinction coefficient of chemical vapour deposition grown graphene are determined by ellipsometry analysis. Graphene films were grown on copper substrates and transferred as both monolayers and bilayers onto SiO2/Si substrates by using standard manufacturing procedures. The chemical nature and thickness of residual debris formed after the transfer process were elucidated using photoelectron spectroscopy. The real layered structure so deduced has been used instead of the nominal one as the input in the ellipsometry analysis of monolayer and bilayer graphene, transferred onto both native and thermal silicon oxide. The effect of these contamination layers on the optical properties of the stacked structure is noticeable both in the visible and the ultraviolet spectral regions, thus masking the graphene optical response. Finally, the use of heat treatment under a nitrogen atmosphere of the graphene-based stacked structures, as a method to reduce the water content of the sample, and its effect on the optical response of both graphene and the residual debris layer are presented. The Lorentz-Drude model proposed for the optical response of graphene fits fairly well the experimental ellipsometric data for all the analysed graphene-based stacked structures.

Fabrication and characterization of thin silicon solar cells produced by in-line spray coating

Orthophosphoric acid spray-coating: a feasible method for pn junction formation on thin c-Si cells with lower cost and environmental impact.