Conductive coatings on complex fibrous systems are attracting interest for new electronic and other functional systems. Obtaining a quantitative conductivity value for complex surface coatings is often difficult. This work describes a procedure to quantify the effective electrical conductivity of conductive coatings on non‐conductive fibrous networks. By applying a normal force orthogonal to the current and field direction, fiber/fiber contact is improved and consistent conductance values can be measured. Nylon fibers coated with an electroless silver plating shows effective conductivity up to 1950 S cm−1, and quartz fibers coated with tungsten by atomic layer deposition (ALD) show values up to ∼1150 S cm−1. Cotton fibers and paper coated with a range of ZnO film thicknesses by ALD show effective conductivity of up to 24 S cm−1 under applied normal force, and conductivity scaled as expected with film coating thickness. Furthermore, we use the conductive coatings to produce an “all‐fiber” metal–insulator–metal capacitor that functions as a liquid chemical sensor. The ability to reliably analyze the effective conductivity of coatings on complex fiber systems will be important to design and improve performance of similar devices and other electronic textiles structures.
Electrically conductive zinc oxide coatings are applied to polypropylene nonwoven fiber mats by atomic layer deposition (ALD) at 50–155 °C. A low temperature (50 °C) aluminum oxide ALD base layer on the polypropylene limits diffusion of diethyl zinc into the polypropylene, resulting in ZnO layers with properties similar to those on planar silicon. Effective conductivity of 63 S/cm is achieved for ZnO on Al2O3 coated polypropylene fibers, and the fibers remain conductive for months after coating. Without the Al2O3 precoating, the effective conductivity was much smaller, consistent with precursor diffusion into the polymer and sub-surface ZnO nucleation. Mechanical robustness tests showed that conductive samples bent around a 6 mm radius maintained up to 40% of the pre-bending conductivity. Linkages between electrical conductivity and mechanical performance will help inform materials choice for flexible and porous electronics including textile-based sensors and antennas.
Nitrogenase activities and the patterns of in vivo inhibition of nitrogenase by NW were compared in Rhodospiilum rubrum grown under several conditions of nitrogen availability. In cells grown on N2 or glutamate plus N2, nitrogenase activity was relatively low and was totally inhibited by added NH: in 15 to 20 min. In contrast, cells grown on glutamate alone displayed higher nitrogenase activity, and NH: had very little effect. Cells grown on limiting amounts of NH: had lower nitrogenase activity, but NH: produced little inhibitory effect. Uptake of NW could be demonstrated under all of these conditions, and this uptake was blocked by DL-methionine-dl-sulfoximine. The data indicated that cells not recently exposed to NHW had no mechanism for rapidly turning off nitrogenase activity in response to sudden additions of NW. In contrast, cells grown in the presence of N2, which form NW internally, inhibited nitrogenase activity relatively quickly in response to added NW.All species of purple nonsulfur photosynthetic bacteria that have been tested can reduce N2 to ammonia. The nitrogenase systems of these bacteria appear unique because the enzyme activity can be reversibly inhibited by ammonium ions. This effect has been observed only in vivo, and it is probably mediated by products of NW assimilation rather than by NW directly (see reference 13 for review). It also has been shown that cell-free extracts from Rhodospirillum rubrum (6,9), Rhodopseudomonas palustris (16), and Rhodopseudomonas capsulata (14) grown with glutamate or N2 as nitrogen sources have low nitrogenase activities, even though the activities of the intact cells were high at the time of harvest. In all cases, these low in vitro activities could be increased in the presence of Mn2+ and Mg-ATP by the addition of a component isolated from the respective chromatophores. This component, designated activating factor, appears to catalyze the release of a small, covalently bound molecule from the iron protein during the activation process (7). The in vitro activation phenomenon might be related to the regulation by ammonium salts observed in vivo, but no in vitro effect of NW on nitrogenase activity has been demonstrated.
Low-temperature vapor-phase tungsten atomic layer deposition (ALD) using WF6 and dilute silane (SiH4, 2% in Ar) can yield highly conductive coatings on nylon-6 microfiber mats, producing flexible and supple nonwovens with conductivity of ∼1000 S/cm. We find that an alumina nucleation layer, reactant exposure, and deposition temperature all influence the rate of W mass uptake on 3D fibers, and film growth rate is calibrated using high surface area anodic aluminum oxide. Transmission electron microscopy (TEM) reveals highly conformal tungsten coatings on nylon fibers with complex "winged" cross-section. Using reactant gas "hold" sequences during the ALD process, we conclude that reactant species can transport readily to reactive sites throughout the fiber mat, consistent with conformal uniform coverage observed by TEM. The conductivity of 1000 S/cm for the W-coated nylon is much larger than found in other conductive nonwovens. We also find that the nylon mats maintain 90% of their conductivity after being flexed around cylinders with radii as small as 0.3 cm. Metal ALD coatings on nonwovens make possible the solvent-free functionalization of textiles for electronic applications.
Articles you may be interested inInfluence of dosing sequence and film thickness on structure and resistivity of Al-ZnO films grown by atomic layer deposition J. Vac. Sci. Technol. A 32, 041516 (2014); 10.1116/1.4885063 New approach toward transparent and conductive ZnO by atomic layer deposition: Hydrogen plasma doping J. Vac. Sci. Technol. A 31, 01A130 (2013); 10.1116/1.4768172 Atomic layer deposition of Al-doped ZnO thin films J. Vac. Sci. Technol. A 31, 01A109 (2013); 10.1116/1.4757764Effective atomic layer deposition procedure for Al-dopant distribution in ZnO thin films Flexible electronics and wearable technology represent a novel and growing market for next generation devices. In this work, the authors deposit conductive zinc oxide films by atomic layer deposition onto nylon-6 nonwoven fiber mats and spun-cast films, and quantify the impact that deposition temperature, coating thickness, and aluminum doping have on the conductivity of the coated substrates. The authors produce aluminum doped zinc oxide (AZO) coated fibers with conductivity of 230 S/cm, which is $6Â more conductive than ZnO coated fibers. Furthermore, the authors demonstrate AZO coated fibers maintain 62% of their conductivity after being bent around a 3 mm radius cylinder. As an example application, the authors fabricate an "all-fiber" pressure sensor using AZO coated nylon-6 electrodes. The sensor signal scales exponentially under small applied force (<50 g/cm 2 ), yielding a $10 6 Â current change under 200 g/cm 2 . This lightweight, flexible, and breathable touch/force sensor could function, for example, as an electronically active nonwoven for personal or engineered system analysis and diagnostics.
Optical absorbance difference spectra of membrane vesicles prepared from aerobically grown Pseudomonas putida indicated that, when harvested in logarithmic phase, the cells contained one c-type cytochrome and two or three b-type cytochromes, one of which was cytochrome o. As the cells grew into stationary phase and the oxygen concentration of the medium dropped to essentially zero, an additional component believed to be cytochrome d was produced. Both the o-and d-type cytochromes might function as terminal oxidases. No a-type cytochromes could be detected at any stage of growth. Polarographic measurement of oxygen utilization revealed that cyanide and azide are effective inhibitors of the oxidation of ascorbate coupled with 2,6-dichlorophenolindo
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