Non-parabolic intergranular barriers in tin oxide and gas sensing

Chemoresistive properties of crystalline solids strongly depend on the concentration of stoichiometric defects. In the case of tin oxide, oxygen vacancies are a case in point of such kind of defects. We address the problem of band bending and Schottky barrier formation in tin oxide. We approached the problem of charged native defects, oxygen vacancies, in a metal oxide in equilibrium with an oxygen containing ambient under three equivalent points of view. We focused on the non-parabolic barriers character that form at intergrains. Implications in gas sensing are discussed.Fil: Aldao, Celso Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); ArgentinaFil: Malagù, C.. University of Ferrara; Itali

Sensing of gaseous malodors characteristic of landfills and waste treatment plants

Abstract. We approached the problem of sensing gaseous pollutants and malodors originating as a result of decomposition of organic compounds via chemoresistive sensors. A set of four screen-printed films based on two types of mixed tin and titanium oxides, mixed tungsten and tin oxides, and zinc oxide has been tested vs. the main gaseous components of malodors. N-butanol was also considered because of its importance as a reference gas in the odorimetric intensity scale. We found that, under proper working conditions, the films can sensitively detect such gases either in dry or in wet environments, within the range of concentrations of interest for their monitoring. We also demonstrated that the array is robust under solicitation by harmful interference gases such as CO, C6H6, NO2 and NO

Clinical validation results of an innovative non-invasive device for colorectal cancer preventive screening through fecal exhalation analysis

Screening is recommended to reduce both incidence and mortality of colorectal cancer. Currently, many countries employ fecal occult blood test (FOBT). In Emilia-Romagna (Italy), since 2005, FOBT immunochemical version (FIT) is performed every two years on people aged between 50 and 69 years. A colonoscopy is then carried out on those who are FIT positive. However, FIT shows approximately 65% false positives (non-tumoral bleedings), leading to many negative colonoscopies. The use of an economic and easy-to-use method to check FOBT-positives will improve screening effectiveness, reducing costs to the national health service. This work illustrates the results of a three-year clinical validation protocol (started in 2016) of a patented device composed of a core of nanostructured gas sensors. This device was designed to identify CRC presence by fecal volatile compounds, with a non-invasive, in vitro and low-cost analysis. Feces are, in fact, affected by tumor-volatile biomarkers, produced by cellular peroxidation and metabolic alterations. The protocol consisted in the analysis of fecal samples of FIT-positive subjects, using colonoscopy as a gold standard. A total of 398 samples were analyzed with machine learning techniques, leading to a sensitivity and specificity of 84.1% and 82.4%, respectively, and a positive predictive value of 72% (25–35% for FIT)

Devices for Screening and Monitoring of Tumors Based on Chemoresistive Sensors

Abstract In this work two devices are presented, named SCENT A1 (A1) and SCENT B1 (B1), composed of chemoresistive sensors. Such devices are capable of discriminating the different compositions of gas mixtures emitted by stools, for colorectal cancer screening (A1), and by blood, for tumors monitoring (B1), according to defined sampling protocols. Results have been acquired by a LabView® software and statistically treated (e.g. quadratic discriminant analysis, QDA) and show to be encouraging with an error of 5% for SCENT A1. Preliminary results of SCENT B1 proved to be promising. Further studies will be carried out for clinically validating the two devices

Thick-film gas sensors based on vanadium-titanium oxide powders prepared by sol-gel synthesis

Two titania powders modified by 10 at.% of vanadium were prepared by two different sol-gel routes. The powders fired at 650 °C had the rutile structure. These powders were used to produce prototype thick-film sensors. Four series of thick-film samples were fabricated by screen-printing, fired for 1 h at 650 and 850 °C. The morphology and gas-sensing properties were examined and compared with those of pure and Ta-added titania films, previously studied by the authors. Ta addition inhibited the anatase-to-rutile phase transformation during heating and was also effective in keeping the TiO2 grain size in the nanometre range. On the contrary, V addition facilitated the anatase-to-rutile phase transformation. Thick films obtained from the two powders had similar conductance behaviour vs. temperature. The gas response of the films was affected by both the grain size and firing temperature. © 2003 Elsevier Ltd. All rights reserved

Chemoresistive Gas Sensor based on SiC Thick Film: Possible Distinctive Sensing Properties Between H2S and SO2☆

Commercially available nanosized powder of silicon carbide (named SiC), was thermally, morphologically and structurally characterized. After that, it was screen-printed onto alumina substrates in order to obtain thick films to be tested as functional material for conductometric gas sensors. Samples were exposed to SO2 and H2S, gases with high importance in many application fields, with the aim of verifying its capability of distinguishing between them. The characterization highlighted that this semiconductor type is selective for sulphur dioxide (SO2), in concentrations within the ppm range. This interesting result was found at high temperatures (600-800°C), useful for harsh environmental, and the measurements proved to be completely free from humidity interference. Applications of such a sensor could span many fields, since SO2 plays an important role in air pollution, industrial processes and wine making monitoring

Introduction : translingual work.

This issue both reflects and builds on the efforts prompted by the 2011 College English essay “Language Difference in Writing: Toward a Translingual Approach,” by Bruce Horner, Min-Zhan Lu, Jacqueline Jones Royster, and John Trimbur. Contributions to this symposium contextualize the emergence of a translingual approach, explore the tension and interconnections between a translingual approach and a variety of fields, and explore the viability of a translingual approach in light of existing academic structures

nanograined anatase titania based optochemical gas detection

Optochemical sensing properties of thick films of titanium dioxide (titania) in anatase phase have been studied and compared with tin dioxide cassiterite. Anatase titania exhibits a large photoluminescence response to nitrogen dioxide, which acts as a luminescence enhancer. Intrinsic surface phenomena rather than bulk defectivity are proposed to account for the behaviour and the experimental results are fitted with the Langmuir model. Good operational performances working at room temperature are achieved

Effects of Vacuum Annealing on the Conduction Characteristics of ZnO Nanosheets

This paper is open acess and available in full at http://www.nanoscalereslett.com/content/10/1/368 .ZnO nanosheets are a relatively new form of nanostructure and have demonstrated potential as gas-sensing devices and dye sensitised solar cells. For integration into other devices, and when used as gas sensors, the nanosheets are often heated. Here we study the effect of vacuum annealing on the electrical transport properties of ZnO nanosheets in order to understand the role of heating in device fabrication. A low cost, mass production method has been used for synthesis and characterisation is achieved using scanning electron microscopy (SEM), photoluminescence (PL), auger electron spectroscopy (AES) and nanoscale two-point probe. Before annealing, the measured nanosheet resistance displayed a non-linear increase with probe separation, attributed to surface contamination. Annealing to 300 °C removed this contamination giving a resistance drop, linear probe spacing dependence, increased grain size and a reduction in the number of n-type defects. Further annealing to 500 °C caused the n-type defect concentration to reduce further with a corresponding increase in nanosheet resistance not compensated by any further sintering. At 700 °C, the nanosheets partially disintegrated and the resistance increased and became less linear with probe separation. These effects need to be taken into account when using ZnO nanosheets in devices that require an annealing stage during fabrication or heating during use

Experimental Study For The Feasibility Of A Crystalline Undulator

We present an idea for creation of a crystalline undulator and report its first realization. One face of a silicon crystal was given periodic micro-scratches (trenches) by means of a diamond blade. The X-ray tests of the crystal deformation due to given periodic pattern of surface scratches have shown that a sinusoidal shape is observed on both the scratched surface and the opposite (unscratched) face of the crystal, that is, a periodic sinusoidal deformation goes through the bulk of the crystal. This opens up the possibility for experiments with high-energy particles channeled in crystalline undulator, a novel compact source of radiation.Comment: 12 pages, 4 figure