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Basic notions linked with concept theory can be accounted for by partial order relations. These orders translate the fact that, for an agent, an object may be seen as a better or a more typical exemplar of a concept than anyother. They adequately model notions linked with categorial membership, typicality and resemblance, without any of the drawbacks that are classically encountered in conjunction theory. An interesting consequence of such a concept representation is the possibility of using the tools of non-monotonic logic to address some well-known problems of cognitive psychology. Thus, conceptual entailment and concept induction can be reexamined in the framework of preferential inference relations. This leads to a rigorous definition of the basic notions used in the study of category-based induction.

Vapor-fed electrolysis of water has been performed using membrane-electrode assemblies (MEAs) incorporating earth-abundant catalysts and bipolar membranes (BPMs). Catalyst films containing CoP nanoparticles, carbon black, and Nafion were synthesized, characterized, and integrated into cathodes of MEAs. The CoP-containing MEAs exhibited stable (>16 h) vapor-fed electrolysis of water at room temperature at a current density of 10 mA cm⁻² with 350 mV of additional overvoltage relative to MEA's formed from Pt/C cathodic electrocatalysts due to slower hydrogen-evolution reaction kinetics under vapor-fed conditions and fewer available triple-phase boundaries in the catalyst film. Additionally, catalyst films containing a [NiFe]-layered double hydroxide ([NiFe]-LDH) as well as a hydroxide ion conductor, hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI), were synthesized, characterized, and integrated into the anodes of the MEAs. The [NiFe]-LDH-containing MEAs exhibited overvoltages at 10 mA cm⁻² that were similar to those of IrO_x-containing MEAs for vapor-fed electrolysis of water at room temperature. A BPM was formed by pairing Nafion with HMT-PMBI, resulting in a locally alkaline environment of HMT-PMBI to stabilize the [NiFe]-LDH and a locally acidic environment to stabilize the CoP. BPM-based MEAs were stable (>16 h) for vapor-fed electrolysis of water at room temperature at a current density of 10 mA cm⁻², with a change in the pH gradient of 1 unit over 16 h of electrolysis for IrOx-containing MEAs. The stability of [NiFe]-LDH-based MEAs under vapor-fed conditions was dependent on the catalyst film morphology and resulting BPM interface, with stable operation at 10 mA cm⁻² achieved for 16 h. All MEAs exhibited a drift in the operating voltage over time associated with dehydration. These results demonstrate that earth-abundant catalysts and BPMs can be incorporated into stable, room-temperature, vapor-fed water-splitting cells operated at 10 mA cm⁻².

In the presence of an electric field, bipolar membranes (BPMs) are capable of initiating water disassociation (WD) within the interfacial region, which can make water splitting for renewable energy in the presence of a pH gradient possible. In addition to WD catalytic efficiency, there is also the need for electronic conductivity in this region for membrane-integrated artificial photosynthesis (AP) systems. Graphene oxide (GO) was shown to catalyze WD and to be controllably reduced, which resulted in electronic conductivity. Layer-by-layer (LbL) film deposition was employed to improve GO film uniformity in the interfacial region to enhance WD catalysis and, through the addition of a conducting polymer in the process, add electronic conductivity in a hybrid film. Three different deposition methods were tested to optimize conducting polymer synthesis with the oxidant in a metastable solution and to yield the best film properties. It was found that an approach that included substrate dipping in a solution containing the expected final monomer/oxidant ratio provided the most predictable film growth and smoothest films (by UV/Vis spectroscopy and atomic force microscopy/scanning electron microscopy, respectively), whereas dipping in excess oxidant or co-spraying the oxidant and monomer produced heterogeneous films. Optimized films were found to be electronically conductive and produced a membrane ohmic drop that was acceptable for AP applications. Films were integrated into the interfacial region of BPMs and revealed superior WD efficiency (≥1.4 V at 10 mA cm⁻²) for thinner films (, National Science Foundation (Grant CHE‐1305124)

Machine sensing has progressed through innovative breakthroughs. Perhaps the most significant advancements have been in the field of machine vision through the advent of the charge-coupled-device (CCD) chip and the development of artificial neural networks. This is evident in the range of sophisticated behaviors that have been replicated including facial recognition and object tracking. Due to parallel processing of large amounts of temporally evolving data, these systems can rapidly learn, adapt and predict in changing environments. While there have been significant advances in chemically diverse sensor arrays that mimic the mammalian olfactory system under well-defined conditions, relatively little work has been done to understand the temporal response of these systems and to develop neural architectures that will enable machines to become chemically aware of their surroundings. In this work, the temporal response behavior for sensors is investigated, demonstrating that both the response evolution and steady-state provide useful information about the chemical environment under dynamic conditions and that neural networks are ideally suited to combine this information in unsupervised learning to perceive odors in a dynamic environment.

The development of chemically diverse arrays has gained the attention of researchers due to their anticipated capacity to mimic the function of olfactory receptors in the mammalian olfactory system. A major hurdle facing the field is the limited ability to generate large numbers of different sensing elements out of the relatively limited number of conducting polymers. In this work, chemically distinct electrocopolymerized sensors were created with pyrrole by using different substituted vinyl groups (e.g., styrene, m-styrene, 4-chlorostyrene, 4-chloromethylstyrene, 4-t-butylstyrene, 4-t-butoxystyrene, divinyl benzene and vinyl pyridine) as monomers. Copolymer films were grown at different potentials that created an additional level of sensor diversity by altering the relative amount of each of the components. By controlling the deposition conditions in this way, as well as setting different redox potentials to the films after growth changes the copolymer's composition and the amount of dopant anion that is incorporated into the sensing films respectively. The composition of the sensing films was also altered by changing the dopant-type during copolymer growth, thereby providing another mechanism for varying the chemical nature of the sensing materials. The chemical diversity among the 27 different sensing polymers used in this work is demonstrated with differential partitioning of 12 analytes, ranging from alcohols and solvents to fuels. This process of generating significant numbers of chemically distinct sensors represents a significant advancement in the efforts to approach the number of olfactory receptors in mammals. The fact that the sensing polymers can be electropolymerized onto very small conducting contacting electrodes shows that this approach is compatible with integrated circuit technology.

Methyl-terminated (110)-oriented silicon surfaces have been prepared from monohydride-terminated, H–Si(110) surfaces using a chlorination/alkylation procedure. Transmission infrared spectroscopy of the H–Si(110) surfaces showed absorption features indicating monohydride structures along the [−110] direction. X-ray photoelectron spectroscopy was used to characterize the methyl-terminated, CH3–Si(110), surfaces. Surface coverage calculations revealed 0.83 of an equivalent monolayer coverage for methyl-terminated Si(110) surfaces. No oxidation of silicon was observed in the high-resolution Si 2p spectra and the samples were stable against oxidation over time, with only 0.2 of a monolayer of surface oxide observed a month after the sample preparation. Thus, the chlorination/alkylation procedure can be used for the functionalization of monohydride Si(110) surfaces with improved long term stability.

Bifunctional films with higher electrochemical and bioactive properties have many promising applications including tissue engineering, drug delivery, nerve regeneration and bone healing. Since bone possesses natural bio-potential and electromechanical properties, the idea of utilizing small electrical pulses to induce bone-tissue growth has been explored in recent decades. Studies have revealed that electric stimulation (in the order of μV) has positive effects on the osteogenesis, and enhances the mineral formation in osteoblast-like cells. However, the mechanisms behind these effects are not well understood. Electric stimulation is generally performed through the implantation of metal electrodes that need to be removed after the treatment. This sometimes requires surgery that can lead to complications including infection and damaging newly formed bone-tissue. Therefore, in the search for new implant materials that are bioactive (allowing different cells to grow over it) and electrically conductive (to perform electrical stimulation), a composite material has been synthesized by integrating the electro-active properties of the conducting polymer (poly-3,4-ethylenedioxythiophene, doped with polystyrene sulfonate, PEDOT:PSS) with the biological properties of collagen (protein, which is present in the cornea) and collagen–calcium phosphate membranes (which mimics the composition of bone). It is shown that by varying the concentration of PEDOT:PSS, the composite (collagen–PEDOT:PSS) or the hybrid (collagen–hydroxyapatite–PEDOT:PSS) membrane could be altered to be highly biocompatible and highly electrically conductive.

A passive embeddable coupled coil sensor for remote bioprocess pH monitoring is described. The sensor is sterilizable, able to operate in a fluid medium, and small enough to fit inside a small bioreactor or test tube. It consists of a planar spiral inductor connected parallel to a varactor forming an LC resonant circuit. A pH combination electrode made of an iridium/iridium oxide sensing electrode and a silver/silver chloride reference electrode is connected parallel to the varactor. A potential difference change across the electrodes due to pH variation of the medium changes the voltage-dependent capacitance and shifts the resonant frequency of the sensor. An interrogator coil is inductively coupled to the sensor coil and remotely tracks the resonant frequency of the sensor. For in-fluid monitoring, the sensor is encapsulated in a manner that reduces the influence of the permittivity and conductivity of the medium. The sensor, calibrated over 2-12 pH range, exhibits a rapid response with 2.477-MHz/pH sensitivity. The sensor was used for remote pH monitoring of Yarrowia lipolytica and Saccharomyces cerevisiae fermentation in a shake flask over 63 and 25 h, respectively. The experiments demonstrate that the medium pH can be monitored repeatedly with an accuracy of 0.08 pH.

In this paper, the structural and electronic properties of polythiophene and polyprrrole-based systems have been investigated using first-principles calculations both in periodic and oligomer forms. Of particular interest is the band gap modulation through substitutions and bilayer formation. Specifically, S has been substituted by Se and Te in polythiophene, leading to polyseleophene and polytellurophene, respectively, and N has been substituted by P and As in polypyrrole. The values obtained of the binding energy suggest that all the systems studied can be realized experimentally. Stacking (bilayer formation) of pure polythiophene, polypyrrole and their derivatives leads to linear suppression of the band gap or HOMO-LUMO gap as a function of the stacking. Mixed bilayers, including one formed from polythiophene on top of polypyrrole, have also been considered. Overall, a wide range of band gaps can be achieved through substitutions and stacking. Hybrid (B3LYP) calculations also suggest the same trend in the band gap as PBE calculations. Trends in the binding energy are similar for both periodic and molecular calculations. In addition, the $\Gamma$-point phonon calculation are performed in order to check the stability of selected systems., Comment: 22 pages, 13 figures, and 4 Tables

Based on first-principles calculations, the materials properties (structural, electronic, vibrational, and optical properties) of out-of-plane heterostructures formed from the transiti on metal dichalcogenides, specifically MoS$_2$-WSe$_2$ and WS$_2$-MoSe$_2$ were investigated. The heterostructures of MoS$_2$-WSe$_2$ and WS$_2$-MoSe$_2$ are found to be direct and ind irect band gap semiconductors, respectively. However, a direct band gap in the WS$_2$-MoSe$_2$ heterostructure can be achieved by applying compressive strain. Furthermore, the excitoni c peaks in both monolayer and bilayer heterostructures are calculated to understand the optical behavior of these systems. The suppression of the optical spectrum with respect to the c orresponding monolayers is due to interlayer charge transfer. The stability of the systems under study is confirmed by performing phonon spectrum calculations.

Sensor arrays are currently used for classifying liquors, perfumes, and the quality of food products by mimicking the mammalian olfactory system. The use of this technology for the monitoring of stored grains and identifying the source of spoilage is a new application, which has the potential for broad economic impact. Carbon black polymer sensor array was fabricated and optimized for monitoring of incipient grain spoilage in a simulated stored grain bin. Various aspects of sensor array (flow rate, relative humidity, temperature, presence of background gas) were evaluated at stored grain conditions. Sensor response at low concentration (2% of vapour pressure) of 1-octanol, 1,4-benzoquinone, acetone was checked in presence of water vapour and 400 ppmv CO2 as background. Slightly variable sensor responses were observed compared to in absence of background gases. The responses were decreased by 6–15% on an average for poly(vinyl acetate), poly(bisphenol-A-carbonate) and poly(vinyl butaryl) sensor while exposed in presence of 50% water vapour. Polymers with high sensitive to background gases (H2O and CO2), such as PVP and P4VP were excluded from the array in this study. Co-polymers with styrene showed low sensitivity drop compared to non-styrene copolymers based on 9 months observation. Therefore, styrene copolymer sensors were best suited to build a stable sensor for the sensor array. Selected polymers for the sensor array retained their sensing properties despite being stored under a wide range of temperatures (−20 to 25°C). The sensor array could recognize pure wheat as well as was able to determine the presence of red flour beetle on it.

The electrical (DC) behavior of single silicon microwires has been determined by the use of tungsten probes to make ohmic contact to the silicon microwires. The basic electrical properties of the microwires, such as their DC resistivity and the doping distribution along the length of the microwires, were investigated using this approach. The technique was also used to characterize the junction between silicon microwires and conducting polymers to assess the suitability of such contacts for use in a proposed artificial photosynthesis system.

Polymer-based sensors have several advantages for gas detection. They can utilize different polymer composite films as their sensing materials, which results in their ability to respond to a wide range of volatiles. However, it is shown that polymer-based sensors suffer from a large temperature sensitivity that causes shift in their volatile response. To overcome this disadvantage, a new design of interdigitated electrodes on a micro-hotplate is proposed. This detector employs a micromachined sensor structure on silicon wafer that maintains a constant temperature throughout the device. Different micromachined sensor structures and substrates were investigated as candidates for constant temperature platforms. COMSOL simulations were performed to investigate the heat transfer profile. Sensor structure and dimensions together with the heater structure were optimized based on the simulation results.

First-principles calculations were performed to investigate the electronic structure of two-dimensional (2-D) Ge, Sn, and Pb without and with the presence of an external electric field in combination with spin-orbit coupling. Tight-binding calculations based on four orbitals per atom and an effective single orbital are presented to match with the results obtained from first-principles calculations. In particular, the electronic band structure and the band splitting are investigated with both models. Moreover, the simple $k\cdot p$ model is also considered in order to understand the band splitting in the presence of an external electric field and spin-orbit coupling. A large splitting is obtained, which is expected to be useful for spintronic devices. The fair agreement between the first-principle, $k\cdot p$ model, and tight-binding approaches leads to a table of parameters for future tight-binding studies on hexagonal 2-D nanostructures. By using the tight binding parameters, the transport properties of typical 0-D triangular quantum dots between two semi-infinite electrodes in the presence of spin-orbit coupling are addressed., 23 pages, 6 figures, and 3 tables

Exploration of the unusual properties of the two-dimensional materials silicene and germanene is a very active research field in recent years. This article therefore reviews the latest developments, focusing both on the fundamental materials properties and on possible applications., Comment: 9 pages, 9 figures, and 2 tables

Based on density functional theory calculations, the structural and electronic properties of polythiophene in periodic and oligomer forms have been investigated. In particular, the effects of Li or Cl adsorption onto a monolayer and Li or Cl-intercalation into bulk or bilayer polythiophene are addressed using periodic calculations. The binding energy of Li or Cl adsorbed bulk or bilayer polythiophene is significantly larger than for the monolayer. The trends in the binding energy as a function of adsorbent remain the same for both the periodic and molecular cases. The band gap or HOMO-LUMO gap and charge transfer are analysed. In addition, for the bulk or bilayer, different kinds of stacking have been considered. It is found that the parallel bulk or bilayer structure is energetically favorable compared to flipping the second layer by 180$^\circ$. This has been considered for both the periodic and oligomer forms. Moreover, for Li adsorption, polarons are found to be more stable than bipolarons, while the situation is opposite for Cl adsorption. The detailed analysis of the present study will be useful for understanding the structural properties and the tuneability of the electronic states, which is an important step to construct polythiophene based electronic devices., Comment: 29 pages, 9 figures, and 3 tables

The junction between n-type silicon microwires and p-type conducting polymer PEDOT:PSS (poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)) was investigated using a soft contact method. Dopant levels within the microwires were varied during growth to give a highly-doped region for improved contact and a low-doped region for light absorption. The low-doped region of the microwires had a dopant density of 5 X 10(17) cm(-3) while the highly-doped region had an increased dopant density of 5 X 10(18) cm(-3) over similar to 20 mu m. Uniform, highly-doped microwires, with a dopant density of 4 X 10(19) cm(3), were used as a comparison. Regions of highly-doped n-type Si microwires (N-D = 5 X 10(18) cm(-3) and 4 X 10(19) cm(-3)) contacted by PEDOT:PSS showed a significantly lower junction resistance compared to the low-doped (3 X 10(17) cm(-3)) regions of the microwire. Junctions incorporating the metal catalyst used during growth were also investigated. Microwires with copper at the interface had similar currentvoltage characteristics to those observed for the highly-doped microwire/conducting polymer junction; however, junctions that incorporated gold exhibited significantly lower resistances, decreasing the iR contribution of the junction by an order of magnitude with respect to the total voltage drop in the entire structure.

We have investigated various aspects of the geometric and spatiotemporal response properties of an array of sorption-based vapor detectors. The detectors of specific interest are composites of insulating organic polymers filled with electrical conductors, wherein the detector film provides a reversible dc electrical resistance change upon the sorption of an analyte vapor. An analytical expression derived for the signal/noise performance as a function of detector volume implies that there is an optimum detector film volume which will produce the highest signal/noise ratio for a given carbon black-polymer composite when exposed to a fixed volume of sampled analyte. This prediction has been verified experimentally by exploring the response behavior of detectors having a variety of different geometric form factors. We also demonstrate that useful information can be obtained from the spatiotemporal response profile of an analyte moving at a controlled flow velocity across an array of chemically identical, but spatially nonequivalent, detectors. Finally, we demonstrate the use of these design principles, incorporated with an analysis of the changes in detector signals in response to variations in analyte flow rate, to obtain useful information on the composition of analytes and analyte mixtures.

International audience; We investigate the family of concepts that an agent comes to knowthrough a set of defining features, and examine the role played by these features inthe process of categorization. In a qualitative framework, categorial membership isevaluated through an order relation among the objects at hand, which translates thefact that an object may fall more than another under a given concept. For conceptsdefined by their features, this global membership order depends on the degree withwhich each feature applies to the objects of the universe. The passage from theseindividual membership degrees to a global membership order poses a problemanalogous to vote aggregation in social choice theory. This similarity leads to anoriginal solution that is particularly well-adapted to the framework of cognitivepsychology. The resulting membership order extends to compound concepts, andprovides a good description of the guppy paradox and the conjunction effect.

Adsorption of eight organic molecules (acetone, acetonitrile, ammonia, benzene, methane, methanol, ethanol, and toluene) onto silicene has been investigated using van der Waals density functional theory calculations (DFT-D). The calculated values of the adsorption energies vary from $-0.11$ eV to $-0.95$ eV. Quantitatively, these values are higher than the corresponding adsorption energies of the molecules adsorbed on graphene. In addition, electronic structure calculations have been performed. The obtained values of the band gap range from 0.006 eV to 0.35 eV for acetonitrile to acetone, respectively. Furthermore, the effective mass of the electron is estimated and found to be comparatively small, which is expected to result in high electron mobility. In addition, we study the effect of Li atoms doped in pristine and acetone adsorbed silicene. In particular, we focus on the variation of the adsorption energy with respect to the number of Li atoms in the systems. Our results suggest new approaches for the use of silicene molecular-based energy storage and conversion as well as electronic devices., 17 pages, 5 Figures, and 2 Tables

International audience; It is well known that classical set theory is not expressive enough to adequately model categorization and prototype theory. Recent work on compositionality and concept determination showed that the quantitative solution initially offered by classical fuzzy logic also led to important drawbacks. Several qualitative approaches were thereafter tempted, that aimed at modelling membership through ordinal scales or lattice fuzzy sets. Most of the solutions obtained by these theoretical constructions however are of difficult use in categorization theory. We propose a simple qualitative model in which membership relative to a given concept f is represented by a function that takes its value in an abstract set Af equipped with a bounded total order. This function is recursively built through a stratification of the set of concepts at hand based on a notion of complexity. Similarly, the typicality associated with a concept f will be described using an ordering that takes into account the characteristic features of f. Once the basic notions of membership and typicality are set, the study of compound concepts is possible and leads to interesting results. In particular, we investigate the internal structure of concepts, and obtain the characterization of all smooth subconcepts of a given concept.

The emerging field of materials-based actuation continues to be the focus of considerable research because of its inherent scalability and its promise to drive micromechanical devices that cannot be realized with conventional mechanical actuator strategies. The electrolytic phase transformation actuator offers a new broad-spectrum solution to the problem of direct conversion of electrical to mechanical energy. Strains of 136,000% and unoptimized work cycle efficiencies near 50% are demonstrated in a prototype device. Conceivably capable of generating stress beyond 200 MPa, this new approach promises performance orders of magnitude beyond other novel actuation strategies.

We describe a method for generating a variety of chemically diverse, broadly responsive, low power vapor sensors. A key to our ability to fabricate chemically diverse sensing elements is the preparation of processable, air stable films of electrically conducting organic polymers. An array of such sensing elements produces a chemically reversible, diagnostic pattern of electrical resistance changes upon exposure to different odorants. Such conducting polymer elements are simply prepared and are readily modified chemically to respond to a broad range of analytes. In addition, these sensors yield a fairly rapid, low power, de electrical signal in response to the vapor of interest, and their signals are readily integrated with software or hardware-based neural networks for purposes of analyte identification. Principle component analysis has demonstrated that such sensors can identify and quantify different airborne organic solvents, and can yield information on the components of gas mixtures.

A novel strategy for preparing a wide range of substituted poly(aniline)s from a single precursor is described. This approach relies on a boron activation/electrophilic displacement reaction resulting in ipso-substitution. Specifically, we demonstrate this strategy to prepare a few of the many possible structures that can be generated from poly(aniline boronic acid), including poly(hydroxyaniline) and halogenated poly(aniline)s. The ability to tune the properties of poly(aniline) through the generation of these new structures will be useful in diverse fields where poly(aniline) is used ranging from polymer-based electronics to sensors.

Thin films of carbon black-organic polymer composites have been deposited across two metallic leads, with sorption of vapors producing swelling-induced resistance changes of the detector films. To identify and classify vapors, arrays of such vapor sensing elements have been constructed in which each element of the array contains a different polymer as the insulating phase and a common conductor, carbon black, as the conducting phase. The differing gas-solid partition coefficients for the various polymers of the detector array produce a pattern of differential resistance changes that is used to classify vapors and vapor mixtures. The performance of this detector array system towards 2,4-dinitrotoluene, the predominant signature in the vapor phase above land mines, in the presence high concentrations of water or of acetone has been evaluated.

The electron transfer dynamics in solar cells that utilize sensitized nanocrystalline titanium dioxide photoelectrodes and the iodide/triiodide redox couple have been studied on a nanosecond time scale. The ruthenium and osmium bipyridyl complexes Ru(H_2L‘)_2(CN)_2, Os(H_2L‘)_2(CN)_2, Ru(H_2L‘)_2(NCS)_2, and Os(H_2L‘)_2(NCS)_2, where H_2L‘ is 4,4‘-dicarboxylic acid 2,2‘-bipyridine, inject electrons into the semiconductor with a rate constant >10^8 s^(-1). The effects of excitation intensity, temperature, and applied potential on the recombination reaction were analyzed using a second-order kinetics model. The rates of charge recombination decrease with increasing driving force to the oxidized sensitizer, indicating that charge recombination occurs in the Marcus inverted region. The electronic coupling factors between the oxidized sensitizer and the injected electrons in TiO_2 and the reorganization energies for the recombination reaction vary significantly for the different metal complexes. The charge recombination rates are well described by semiclassical electron transfer theory with reorganization energies of 0.55−1.18 eV. Solar cells sensitized with Ru(H_2L‘)_2(CN)_2, Os(H_2L‘)_2(CN)_2, and Ru(H_2L‘)_2(NCS)_2 have favorable photoelectrochemical characteristics, and iodide is oxidized efficiently. In contrast, iodide oxidation limits the efficiency of cells based on sensitization of TiO_2 with Os(H_2L‘)_2(NCS)_2. The observation that charge recombination occurs in the Marcus inverted region has important implications for the design of molecular sensitizers in nanocrystalline solar cells operated under our experimental conditions.

Thin films of carbon black-organic polymer composites have been deposited across two metallic leads, with sorption of vapors producing swelling-induced resistance changes of the detector films. To identify and classify vapors, arrays of such vapor sensing elements have been constructed in which each element of the array contains a different polymer as the insulating phase and a common conductor, carbon black, as the conducting phase. The differing gas-solid partition coefficients for the various polymers of the detector array produce a pattern of differential resistance changes that is used to classify vapors and vapor mixtures. The performance of this detector array system towards 2,4-dinitrotoluene, the predominant signature in the vapor phase above land mines, in the presence high concentrations of water or of acetone (as a selected volatile organic carbon vapor), has been evaluated.

Thin films of carbon black-organic polymer composites have been deposited across two metallic leads, with swelling- induced resistance changes of the films signaling the presence of vapors. To identify and classify vapors, arrays of such vapor sensing elements have been constructed. Each element contained a different organic polymer as the insulating phase. The differing gas-solid partition coefficients for the various polymers of the detector array produced a pattern of resistance changes that was used to classify vapors and vapor mixtures. The performance of this system towards DNT, the predominant signature in the vapor phase above land miens, has been evaluated in detail, with robust detection demonstrated in the laboratory in less than 5 s in air at DNT levels in the low ppb range.

We describe a method for generating a variety of chemically diverse broadly responsive low-power vapor sensors. The chemical polymerization of pyrrole in the presence of plasticizers has yielded conducting organic polymer films whose resistivities are sensitive to the identity and concentration of various vapors in air. An array of such sensing elements produced a chemically reversible diagnostic pattern of electrical resistance changes upon exposure to different odorants. Principal component analysis has demonstrated that such sensors can identify and quantify different airborne organic solvents and can yield information on the components of gas mixtures.

The photoelectrical properties and stability of individual p-silicon (Si) microwire/polyethylenedioxythiophene/polystyrene sulfonate:Nafion/n-Si microwire structures, designed for use as arrays for solar fuel production, were investigated for both H-terminated and CH_3-terminated Si microwires. Using a tungsten probe method, the resistances of individual wires, as well as between individual wires and the conducting polymer, were measured vs. time. For the H-terminated samples, the n-Si/polymer contacts were initially rectifying, whereas p-Si microwire/polymer contacts were initially ohmic, but the resistance of both the n-Si and p-Si microwire/polymer contacts increased over time. In contrast, relatively stable, ohmic behavior was observed at the junctions between CH_3-terminated p-Si microwires and conducting polymers. CH_3-terminated n-Si microwire/polymer junctions demonstrated strongly rectifying behavior, attributable to the work function mismatch between the Si and polymer. Hence, a balance must be found between the improved stability of the junction electrical properties achieved by passivation, and the detrimental impact on the effective resistance associated with the additional rectification at CH_3-terminated n-Si microwire/polymer junctions. Nevertheless, the current system under study would produce a resistance drop of ~20 mV during operation under 100 mW cm^(−2) of Air Mass 1.5 illumination with high quantum yields for photocurrent production in a water-splitting device.

We discuss the figures of merit for conducting membranes in artificial photosynthetic systems and describe an electronically and ionically conducting polymer composite with attractive performance characteristics.

The use of conjugated polymers for sensor applications continues to be the subject of intense research. In addition to their use as electronic conductors, they have been exploited as active sensing elements by coupling ligands to the backbone. In this approach, binding of an analyte results in physical distortions or changes in electron density, thereby altering conductivity. Poly(aniline), in particular, has received a great deal of attention due to its proton coupled redox chemistry and its resulting pH-dependent properties. For example, poly(aniline) has been used as a pH electrode and has been coupled to reactions that generate or consume protons to create sensors. Herein, we report a new strategy that exploits the inductive effect of reactive substituents on the pK_a of poly(aniline) to produce active sensing elements.

We describe herein the construction of simple, low-power, broadly responsive vapor sensors. Insulating polymer-conductor composites have been shown to swell reversibly upon exposure to vapors. Thin films of polymer composites have been deposited across two metallic leads, with swelling-induced resistance changes of the films signaling the presence of vapors. To identify and classify vapors, arrays of such vapor-sensing elements have been constructed, with each element containing either carbon black or poly(pyrrole) as the conducting phase mixed with one of several different organic polymers as the insulating phase. A convenient chemical polymerization of poly(pyrrole) which allows a high degree of processibility is also described. The differing gas-solid partition coefficients for the various polymers of the sensor array produce a pattern of resistance changes that can be used to classify vapors and vapor mixtures. This type of sensor array has been shown to resolve common organic solvents, including molecules of different classes (such as aromatics from alcohols) as well as those within a particular class (such as benzene from toluene and methanol from ethanol). The response of an individual composite to varying concentrations of solvent is shown to be consistent with the predictions of percolation theory. Accordingly, significant increases in the signals of array elements have been observed for carbon black-polymer composites that were operated near their percolation thresholds.

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