Composite materials of organically stabilized or cross-linked metal nanoparticles represent a versatile material class with manifold potential applications. Numerous studies explored their tunable optical and charge transport properties. However, due to challenging experimental requirements, only a few studies addressed their mechanical properties. Here, we report the first investigation on the tunability of the elastic properties of cross-linked gold nanoparticle (GNP) composites. Thin films consisting of GNPs (diameter 3–4 nm) cross-linked with α,ω-alkanedithiols of different chain length, as well as 1,4-benzenedithiol, were fabricated by spin-coating and transferred onto circular apertures with diameters of ∼100 μm. The mechanical properties of thus-prepared freestanding membranes with thicknesses between 21 and 51 nm were probed using bulge tests with atomic force microscopy (AFM) based deflection readout. We demonstrate that, along with their optical and charge transport characteristics, the elastic modulus of these GNP composites can be adjusted in a range from ∼3.6 to ∼10 GPa by shortening the α,ω-alkanedithiol chain length from 10 to 3 methylene units. These variations in elasticity are attributed to the varying fraction of soft organic matter and to structural differences within the composites. Our results provide a basis for further experimental and theoretical studies, as well as for applications of cross-linked nanoparticle composites in future micro- and nanoelectromechanical (MEMS/NEMS) devices, their design, and modeling.

In this communication the application of gold nanoparticle membranes as ambient pressure sensors with electromechanical signal transduction is demonstrated. The devices were fabricated by sealing microstructured cavities with membranes of 1,6-hexanedithiol cross-linked gold nanoparticles, which were electrically contacted by metal electrodes deposited on both sides of the cavities. Variations of the external pressure resulted in a deflection of the membranes and, thus, increased the average interparticle distances. Therefore, the pressure change could easily be detected by simply monitoring the resistance of the membranes.

Their tunable electrical, optical, and mechanical properties make freestanding membranes of organically cross-linked gold nanoparticles (GNPs) interesting materials for applications in micro- and nanoelectromechanical systems. Here, we demonstrate the application of α,ω-alkanedithiol-cross-linked GNP membranes as electrostatically driven actuators. The devices were fabricated by depositing these membranes (thickness 29-45 nm) onto cylindrical cavities (diameter ∼200 μm; depth ∼8-15 μm), which were lithographically patterned in a SU-8 resist. Applying voltages of up to ±40 V across the membrane and the silicon substrate deflected the membranes by several hundreds of nanometers, as measured by atomic force microscopy, confocal microscopy, and interferometry. A simple electrostatic model, which takes into account the membranes' mechanical properties, was used to interpret the experimental data.

In this article, highly sensitive differential pressure sensors based on freestanding membranes of cross-linked gold nanoparticles are demonstrated. The nanoparticle membranes are employed as both diaphragms and resistive transducers. The elasticity and the pronounced resistive strain sensitivity of these nanometer-thin composites enable the fabrication of sensors achieving high sensitivities exceeding 10 −3 mbar −1 while maintaining an overall small membrane area. Furthermore, by combining micro-bulge tests with atomic force microscopy and in situ resistance measurements the membranes' electromechanical responses are studied through precise observation of the concomitant changes of the membranes' topography. The study demonstrates the high potential of free-standing nanoparticle composites for the fabrication of highly sensitive force and pressure sensors and introduces a unique and powerful method for the electromechanical investigation of these materials.

Questions In pasture‐dominated landscapes, endozoochory by large herbivores is an important vector of plant dispersal. Conditions influencing the potential for endozoochorous dispersal of plant species by grazers are, however, still poorly known. Here, we assess the impact of feeding habits and functional traits on the likelihood of endozoochorous dispersal by cattle (ruminants) and horses (non‐ruminants). Location Pasture of 27 ha in NW Germany, year‐round grazed by free‐ranging cattle and horses. Methods Vegetation relevés were established in 45 plots, from which dung samples of cattle and horses were collected. The number and composition of seedlings emerging from dung samples were compared with the vegetation of the study site in terms of plant functional trait composition. For the first time, feeding habits were included in the analysis. GLMs were used to identify traits that increased the potential for endozoochorous dispersal. Results A total of 65 species germinated from the dung samples. These species had higher average fodder and nutrient indicator values than the species composition of the vegetation. In particular, species found in horse dung were more tolerant of grazing and had more elongated seeds. The likelihood of endozoochorous dispersal was higher for common than for rare species and was influenced by feeding habits. Conclusions The likelihood of plant species being dispersed endozoochorously can be linked to different functional traits and is dependent on the type of grazer and the population size of target species in the vegetation. Differences between cattle and horses in seed dispersal may result from species‐specific grazing habits and different digestion modes.

In article number 2003381, Hendrik Schlicke, Tobias Vossmeyer, and co‐workers present a pressure sensor based on a free‐standing gold nanoparticle membrane acting as a diaphragm and resistive transducer. The elastic membrane features strain‐sensitive conductivity that is governed by tunneling through the interparticle gaps. While measuring the resistance of the bulged membrane, the topography is scanned using an atomic force microscope to explore its electromechanical properties.