On the temporal stability of analyte recognition with an e-nose based on a metal oxide sensor array in practical applications

The paper deals with a functional instability of electronic nose (e-nose) units which significantly limits their real-life applications. Here we demonstrate how to approach this issue with example of an e-nose based on a metal oxide sensor array developed at the Karlsruhe Institute of Technology (Germany). We consider the instability of e-nose operation at different time scales ranging from minutes to many years. To test the e-nose we employ open-air and headspace sampling of analyte odors. The multivariate recognition algorithm to process the multisensor array signals is based on the linear discriminant analysis method. Accounting for the received results, we argue that the stability of device operation is mostly affected by accidental changes in the ambient air composition. To overcome instabilities, we introduce the add-training procedure which is found to successfully manage both the temporal changes of ambient and the drift of multisensor array properties, even long-term. The method can be easily implemented in practical applications of e-noses and improve prospects for device marketing

Electronic Structure of Nitrogen- and Phosphorus-Doped Graphenes Grown by Chemical Vapor Deposition Method

Heteroatom doping is a widely used method for the modification of the electronic and chemical properties of graphene. A low-pressure chemical vapor deposition technique (CVD) is used here to grow pure, nitrogen-doped and phosphorous-doped few-layer graphene films from methane, acetonitrile and methane-phosphine mixture, respectively. The electronic structure of the films transferred onto SiO2/Si wafers by wet etching of copper substrates is studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy using a synchrotron radiation source. Annealing in an ultra-high vacuum at ca. 773 K allows for the removal of impurities formed on the surface of films during the synthesis and transfer procedure and changes the chemical state of nitrogen in nitrogen-doped graphene. Core level XPS spectra detect a low n-type doping of graphene film when nitrogen or phosphorous atoms are incorporated in the lattice. The electrical sheet resistance increases in the order: graphene < P-graphene < N-graphene. This tendency is related to the density of defects evaluated from the ratio of intensities of Raman peaks, valence band XPS and NEXAFS spectroscopy data. View Full-Tex

The Multisensor Array Based on Grown-On-Chip Zinc Oxide Nanorod Network for Selective Discrimination of Alcohol Vapors at Sub-ppm Range

We discuss the fabrication of gas-analytical multisensor arrays based on ZnO nanorods grown via a hydrothermal route directly on a multielectrode chip. The protocol to deposit the nanorods over the chip includes the primary formation of ZnO nano-clusters over the surface and secondly the oxide hydrothermal growth in a solution that facilitates the appearance of ZnO nanorods in the high aspect ratio which comprise a network. We have tested the proof-of-concept prototype of the ZnO nanorod network-based chip heated up to 400 °C versus three alcohol vapors, ethanol, isopropanol and butanol, at approx. 0.2–5 ppm concentrations when mixed with dry air. The results indicate that the developed chip is highly sensitive to these analytes with a detection limit down to the sub-ppm range. Due to the pristine differences in ZnO nanorod network density the chip yields a vector signal which enables the discrimination of various alcohols at a reasonable degree via processing by linear discriminant analysis even at a sub-ppm concentration range suitable for practical applications

Changes in somatosensory evoked potentials in rats following transient cerebral ischemia

Background. Cerebral ischemia induced by transient middle cerebral artery occlusion is one of the most popular ischemic stroke models used to evaluate drug candidates with neuroprotective properties. The possibilities of combining this model with neurophysiological techniques (e.g., electroencephalography, electrocorticography, evoked potential registration, etc.) to assess the effectiveness of novel pharmacotherapeutic strategies appear to be of great interest to current biomedical research.The aim. Identifying specific changes in somatosensory evoked potentials occurring after cerebral ischemia induced by middle cerebral artery occlusion in rats.Materials and methods. A total number of 18 white outbred male rats were randomized into 3 groups by 6 animals in each: 1) control (presumably healthy animals); 2) ischemia-30 (30-minute middle cerebral artery occlusion); 3) ischemia-45 (45-minute occlusion). At post-surgery day 7, cortical responses to sequential electrical stimulation of left and right n. ischiadicus were registered. N1, P2, N2, P3, and N3 peak latencies and amplitudes, peak-to-peak interval durations and amplitudes were calculated. Spearman’s rank correlation coefficients were used to assess the relationship between ischemia duration and evoked potential parameters, and the Chaddock scale was used to qualitatively evaluate the strength of correlations.Results. The rats subjected to cerebral ischemia demonstrated a decrease in some of the peak amplitudes of the ipsi- and contralateral somatosensory potentials evoked by n. ischiadicus stimulation. In the injured hemisphere, decreased P2 and N3 peak and P3–N3 interval amplitudes were registered ipsilaterally, and decreased P3 peak amplitudes and N2–P3 interval durations were observed contralaterally.Conclusions. The obtained data suggest that somatosensory evoked potential registration and analysis can be used to evaluate the functional state of central nerve tracts in rats subjected to cerebral ischemia

Self-activated ultrahigh chemosensitivity of oxide thin film nanostructures for transparent sensors

One of the top design priorities for semiconductor chemical sensors is developing simple, low-cost, sensitive and reliable sensors to be built in handheld devices. However, the need to implement heating elements in sensor devices, and the resulting high power consumption, remains a major obstacle for the realization of miniaturized and integrated chemoresistive thin film sensors based on metal oxides. Here we demonstrate structurally simple but extremely efficient all oxide chemoresistive sensors with similar to 90% transmittance at visible wavelengths. Highly effective self-activation in anisotropically self-assembled nanocolumnar tungsten oxide thin films on glass substrate with indium-tin oxide electrodes enables ultrahigh response to nitrogen dioxide and volatile organic compounds with detection limits down to parts per trillion levels and power consumption less than 0.2 microwatts. Beyond the sensing performance, high transparency at visible wavelengths creates opportunities for their use in transparent electronic circuitry and optoelectronic devices with avenues for further functional convergence.open181

PECULIARITIES OF INITIAL STAGES OF GROWTH OF HETEROEPITAXIAL FILMS GaP/SiAT PULSE LASER DEPOSITION

Heteroepitaxial thin GaP/Si films were obtained by pulsed laser sputtering, using the stage of the Osvoldovsky ripening of embryos at the initial stages of film growth. It was found that single-crystal GaP films were obtained during the passage of the stage of the Osvoldovsky maturation of nucleation

Physico-mechanical properties of the sinter of various chemical composition

The paper includes data on the physico-mechanical properties of sinter of various origins including density (bulk, average, and true), porosity (open and total), critical angle of repose, internal and external angles of repose measured on dropping the material down onto a horizontal surface from a steel sheet inclined by 40 , 60 , and 80 to the horizon, angle of external friction on the steel surface, the strength properties of the sinter in a cold state and after reduction at a temperature of 500 C. The investigated sinter had the following characteristics: an average density of 3.20-3.30 g/cm3; a true density of 4.43-4.57 g/cm3; an external angle of repose of 20.5-32.3 deg; a bulk porosity of 0.46-0.50 m3/m3; a degree of reduction by hydrogen at 500 C of 3.3-4.8%. It demonstrated the following strength characteristics in the cold state: IR+5 = 92.0%, D0.5-5 = 5.5%, A-0.5 = 2.5%. The strength characteristics after low-temperature reduction in hydrogen atmosphere were as follows: IR+5 = 29.80 %; D0.5-5 = 57.6 %; A-0.5 = 12.6 %. © Published under licence by IOP Publishing Ltd

Tuning Nitrogen-Doped Carbon Electrodes via Synthesis Temperature Adjustment to Improve Sodium- and Lithium-Ion Storage

Structural imperfections, heteroatom dopants, and the interconnected pore structure of carbon materials have a huge impact on their electrochemical performance in lithium-ion and sodium-ion batteries due to the specific ion transport and the dominant storage mechanism at surface defect sites. In this work, mesopore-enriched nitrogen-doped carbon (NC) materials were produced with template-assisted chemical vapor deposition using calcium tartrate as the template precursor and acetonitrile as the carbon and nitrogen source. The chemical states of nitrogen, the volume of mesopores, and the specific surface areas of the materials were regulated by adjusting the synthesis temperature. The electrochemical testing of NC materials synthesized at 650, 750, and 850 °C revealed the best performance of the NC-650 sample, which was able to deliver 182 mA·h·g−1 in sodium-ion batteries and 1158 mA·h·g−1 in lithium-ion batteries at a current density of 0.05 A·g−1. Our study shows the role of defect sites, including carbon monovacancies and nitrogen-terminated vacancies, in the binding and accumulation of sodium. The results provide a strategy for managing the carbon structure and nitrogen states to achieve a high alkali-metal-ion storage capacity and long cycling stability, thereby facilitating the electrochemical application of NC materials

PULSED LASER DEPOSITION OF GAPN THIN FILMS ON SI

Thin film GaP1-xNx were obtained by pulsed laser deposition It was found that a small mixing (1-2 cm-1) in the frequency positions LO phonon modes for films GaP1-xNx and a single-crystal GaP target was observed in the spectra obtained. The results obtained can be explained by a decrease in the crystal lattice parameter in the epitaxial layer GaP1-xNx

The potentiodynamic bottom-up growth of the tin oxide nanostructured layer for gas-analytical multisensor array chips

We report a deposition of the tin oxide/hydroxide nanostructured layer by the potentiodynamic method from acidic nitrate solutions directly over the substrate, equipped with multiple strip electrodes which is employed as a gas-analytical multisensor array chip. The electrochemical synthesis is set to favor the growth of the tin oxide/hydroxide phase, while the appearance of metallic Sn is suppressed by cycling. The as-synthesized tin oxide/hydroxide layer is characterized by mesoporous morphology with grains, 250–300 nm diameter, which are further crystallized into fine SnO2 poly-nanocrystals following heating to 300 °C for 24 h just on the chip. The fabricated layer exhibits chemiresistive properties under exposure to organic vapors, which allows the generation of a multisensor vector signal capable of selectively distinguishing various vapors