UV-visible diffuse reflectance spectroscopy was used to probe the electronic structure and domain size of tungsten oxide species in crystalline isopolytungstates, monoclinic WO 3 , and dispersed WO x species on ZrO 2 surfaces. UV-visible absorption edge analysis, CO 2 chemisorption, and Raman spectroscopic results show that three distinct regions of WO x coverage on ZrO 2 supports appear with increasing WO x surface density: submonolayer region (0-4 W nm -2 ), polytungstate growth region (4-8 W nm -2 ), and polytungstate/crystalline WO 3 coexistence region (>8 W nm -2 ). The structure and catalytic activity of WO x species on ZrO 2 is controlled only by WO x surface density (W nm -2 ), irrespective of the WO x concentration, oxidation temperature, and ZrO 2 surface area used to obtain a particular density. The submonolayer region is characterized by distorted octahedral WO x species that are well dispersed on the ZrO 2 surface. These species show a constant absorption edge energy, they are difficult to reduce, and contain few acid sites where o-xylene isomerization can occur at 523 K. At intermediate WO x surface densities, the absorption edge energy decreases, WO x domain size increases, WO x species become easier to reduce, and o-xylene isomerization turnover rates (per W atom) increase with increasing WO x surface density. At high WO x surface densities, a polytungstate monolayer coexists with monoclinic WO 3 crystallites. The growth of monoclinic WO 3 crystallites results in lower o-xylene isomerization turnover rates because WO x species become inaccessible to reactants. In the presence of H 2 at typical catalytic reaction temperatures (∼523 K), strong acid sites form on WO x -ZrO 2 catalysts with polytungstate domains by a slight reduction of the cluster and delocalization of an electron from an H atom resulting in H +δ (Brønsted acid site).
Efforts to impart elasticity and multifunctionality in nanocomposites focus mainly on integrating polymeric and nanoscale components. Yet owing to the stochastic emergence and distribution of strain-concentrating defects and to the stiffening of nanoscale components at high strains, such composites often possess unpredictable strain-property relationships. Here, by taking inspiration from kirigami—the Japanese art of paper cutting—we show that a network of notches made in rigid nanocomposite and other composite sheets by top-down patterning techniques prevents unpredictable local failure and increases the ultimate strain of the sheets from 4 to 370%. We also show that the sheets' tensile behaviour can be accurately predicted through finite-element modelling. Moreover, in marked contrast to other stretchable conductors, the electrical conductance of the stretchable kirigami sheets is maintained over the entire strain regime, and we demonstrate their use to tune plasma-discharge phenomena. The unique properties of kirigami nanocomposites as plasma electrodes open up a wide range of novel technological solutions for stretchable electronics and optoelectronic devices, among other application possibilities.
Organic vapor phase deposition was used to grow polycrystalline pentacene channel thin-film transistors. Substrate temperature, chamber pressure during film deposition, and growth rate were used to vary the crystalline grain size of pentacene films on O2-plasma treated SiO2 from 0.2 to 5 μm, leading to room-temperature saturation regime field-effect hole mobilities (μeff) from 0.05±0.02 to 0.5±0.1 cm2/V s, respectively. Surface treatment of SiO2 with octadecyltrichlorosilane (OTS) prior to pentacene deposition resulted in μeff⩽1.6 cm2/V s, and drain current on/off ratios of ⩽108 at room temperature, while dramatically reducing the average grain size. X-ray diffraction studies indicate that the OTS treatment decreases the order of the molecular stacks. This suggests an increased density of flat-lying molecules, accompanying the improvement of the hole mobility at the pentacene/OTS interface.
Progress towards the integration of technology into living organisms requires electrical power sources that are biocompatible, mechanically flexible, and able to harness the chemical energy available inside biological systems. Conventional batteries were not designed with these criteria in mind. The electric organ of the knifefish Electrophorus electricus (commonly known as the electric eel) is, however, an example of an electrical power source that operates within biological constraints while featuring power characteristics that include peak potential differences of 600 volts and currents of 1 ampere. Here we introduce an electric-eel-inspired power concept that uses gradients of ions between miniature polyacrylamide hydrogel compartments bounded by a repeating sequence of cation- and anion-selective hydrogel membranes. The system uses a scalable stacking or folding geometry that generates 110 volts at open circuit or 27 milliwatts per square metre per gel cell upon simultaneous, self-registered mechanical contact activation of thousands of gel compartments in series while circumventing power dissipation before contact. Unlike typical batteries, these systems are soft, flexible, transparent, and potentially biocompatible. These characteristics suggest that artificial electric organs could be used to power next-generation implant materials such as pacemakers, implantable sensors, or prosthetic devices in hybrids of living and non-living systems.
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