Piezoelectric III-N semiconductor nanostructures are of increasing interest to be used for sensor technologies and energy harvesting. Within this group of materials, AlN is known for the largest bulk piezoelectric constant, but piezoelectric properties of AlN nanostructures are not well studied. In the current work, AlN nanostructures are fabricated by reactive magnetron sputter deposition at normal and glancing angle orientations on Si substrates covered by a conductive TiN film. Ag nanoparticles are used to facilitate nucleation of the nanostructures, which are found to have a bud-like shape consisting of individual pillars/lamellae. These pillars exhibit a wurtzite-like hexagonal lattice and preferential growth direction along the c-axis. Piezoresponse force microscopy is used to characterize the properties of the nanostructures. Giant values of the piezoresponse coefficient are measured, reaching up to 6 times higher values compared to AlN bulk and thin films. The obtained results create a basis for optimization of the fabrication parameters enabling tuning of the AlN piezoelectric properties and further development of the technology toward the formation of large-area nanoscale matrixes for energy generation.

Because of the large specific surface area, the properties of nanoporous metals and in particular their mechanical properties are sensitive to chemical modifications of their surfaces. Here, we exploit self-assembled monolayers (SAMs) to modify a surface of nanoporous gold and study their effect on plastic behavior. The SAMs investigated here (i) are made from alkanethiols, which consist of a sulfur headgroup that strongly binds to metal substrates, a hydrocarbon chain, and an end group, and (ii) are known to spontaneously self-organize into well-ordered, dense two-dimensional molecular films on the surface of coinage metals. Alkanethiols with various chain lengths and terminal groups were used to prepare SAMs on bulk nanoporous gold, and compression tests were performed on the SAM-modified and nonmodified macroscopic samples. Our experiments reveal a substantial, up to 50%, increase of the flow stress due to thiol adsorption. We attribute the strengthening to the adsorption locking of dislocation end points at the surface, which is mediated by the fairly strong metal-sulfur interaction. ©

In the present work, tannin-modified whey protein isolate (WPI/tannin) aerogels were synthesized, and their hydration properties were evaluated. The materials were prepared by introducing two different tannins (one hydrolyzable and one condensed) in the protein matrix via thermal-induced gelation of neutral or alkaline aqueous solutions (pH 7, 9, or 11) at 80 °C. WPI and WPI/tannin aerogels are nanostructured porous materials with high BET surface areas (216-353 m2 g-1). Subsequently, WPI and WPI/tannin aerogels were hydrophobized via silanization (with bis(trimethylsilyl)amine) in the gas phase (HWPI and HWPI/tannin aerogels). As a result of silanization, BET surface areas were reduced to 87-242 m2 g-1. The hydration properties of all aerogels were studied by measuring the water uptake and water contact angles. Pristine WPI aerogels absorbed high amounts of water (up to 4794% w/w in 24 h), swelled, and eventually disintegrated. WPI/tannin aerogels prepared with the condensed tannin absorbed more water (219-559% w/w) than those prepared with the hydrolyzable tannin (81-88% w/w). In any case, the water uptake was significantly lower compared with that of pristine WPI aerogels. After silanization, all aerogels absorbed much smaller amounts of water (39-84% w/w). The reduced water uptake was in agreement with the water contact angles, which were in the ranges 35-55° for WPI aerogels, 40-60° for WPI/tannin aerogels, 80-86° for HWPI aerogels, and 100-116° for HWPI/tannin aerogels. These results clearly indicate that both the introduction of tannin in the protein matrix and the silanization of the solid network are necessary to obtain water-stable WPI-based aerogels. There is an immense need for replacing the existing plastic-based food packaging with biobased and biodegradable materials. In this context, our results address the major disadvantage of most biobased materials (i.e., poor stability in aqueous environments) and render these new aerogels good candidates for food packaging applications.