http://mdpi.com/journal/sensors/special_issues/gas_sensors/ http://mdpi.com/1424-8220/9/9/6652/ Hydrogen sensing of thick films of nanoparticles of pristine, 0.2, 1.0 and 2.0 atomic percentage of Pt concentration doped ZnO were investigated. ZnO nanoparticles doped with 0.2–2.0 at.% Pt were successfully produced in a single step by flame spray pyrolysis (FSP) technique using zinc naphthenate and platinum(II) acetylacetonate as precursors dissolved in xylene. The particle properties were analyzed by XRD, BET, SEM and TEM. Under the 5/5 (precursor/oxygen) flame condition, ZnO nanoparticles and nanorods were observed. The crystallite sizes of ZnO spheroidal and hexagonal particles were found to be ranging from 5 to 20 nm while ZnO nanorods were seen to be 5–20 nm wide and 20–40 nm long. ZnO nanoparticles paste composed of ethyl cellulose and terpineol as binder and solvent respectively was coated on Al2O3 substrate interdigitated with gold electrodes to form thin films by spin coating technique. The thin film morphology was analyzed by SEM technique. The gas sensing properties toward hydrogen (H2) was found that the 0.2 at.% Pt/ZnO sensing film showed an optimum H2 sensitivity of ~164 at hydrogen concentration in air of 1 volume% at 300 °C and a low hydrogen detection limit of 50 ppm at 300 °C operating temperature. http://mdpi.com/1424-8220/9/9/6652/ Wed, 26 Aug 2009 00:00:00 CEST Sensors 2009-08-26 9 9 Article 6652 6669 1424-8220 Sensing Characteristics of Flame-Spray-Made Pt/ZnO Thick Films as H2 Gas Sensor 2009-08-26 doi: 10.3390/s90906652 Nittaya Tamaekong Chaikarn Liewhiran Anurat Wisitsoraat Sukon Phanichphant http://mdpi.com/1424-8220/7/3/319/ In this paper, the reliability of a micro-electro-mechanical system (MEMS)-based gas sensor has been investigated using Three Dimensional (3D) coupled multiphysics Finite Element (FE) analysis. The coupled field analysis involved a two-way sequential electro- thermal fields coupling and a one-way sequential thermal-structural fields coupling. An automated substructuring code was developed to reduce the computational cost involved in simulating this complicated coupled multiphysics FE analysis by up to 76 percent. The substructured multiphysics model was then used to conduct a parametric study of the MEMS-based gas sensor performance in response to the variations expected in the thermal and mechanical characteristics of thin films layers composing the sensing MEMS device generated at various stages of the microfabrication process. Whenever possible, the appropriate deposition variables were correlated in the current work to the design parameters, with good accuracy, for optimum operation conditions of the gas sensor. This is used to establish a set of design rules, using linear and nonlinear empirical relations, which can be utilized in real-time at the design and development decision-making stages of similar gas sensors to enable the microfabrication of these sensors with reliable operation. http://mdpi.com/1424-8220/7/3/319/ Wed, 14 Mar 2007 00:00:00 CET Sensors 2007-03-14 7 3 Review 319 340 1424-8220 Studying the Effect of Deposition Conditions on the Performance and Reliability of MEMS Gas Sensors 2007-03-14 doi: 10.3390/s7030319 Khaled Sadek Walied Moussa http://mdpi.com/1424-8220/7/3/267/ The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review. http://mdpi.com/1424-8220/7/3/267/ Wed, 07 Mar 2007 00:00:00 CET Sensors 2007-03-07 7 3 Review 267 307 1424-8220 Gas Sensors Based on Conducting Polymers 2007-03-07 doi: 10.3390/s7030267 Hua Bai Gaoquan Shi http://mdpi.com/1424-8220/6/12/1827/ The cataluminescence (CTL) of benzene and the benzene homologues tolueneand xylene on nanosized γ–Al2O3 doped with Eu2O3 (γ–Al2O3/Eu2O3) was studied and asensor of determining these gases was designed. The proposed sensor showed highsensitivity and selectivity at an optimal temperature of 432 ºC, a wavelength of 425 nm anda flow rate of 400 mL/min. Quantitative analysis was performed at the optimal conditions.The linear ranges of CTL intensity versus concentration of the benzene homologues were asfollows: benzene 2.4~5000 mL/m3, toluene 4.0~5000 mL/m3 and xylene 6.8~5000 mL/m3,with detection limits (3σ) of 1.8 mL/m3, 3.0 mL/m3 and 3.4 mL/m3 for each one,respectively. The response time of this system was less than 3 s. The coexistence of othergases, such as SO2, CO and NH3, caused interference at levels around 11.7%, 5.8% and8.9% respectively. The technique is a convenient and fast way of determining the vapors ofbenzene homologues in air. http://mdpi.com/1424-8220/6/12/1827/ Tue, 26 Dec 2006 00:00:00 CET Sensors 2006-12-26 6 12 Article 1827 1836 1424-8220 Studies of the Cataluminescence of Benzene Homologues onNanosized γ–Al2O3/Eu2O3 and the Development of a Gas Sensorfor Benzene Homologue Vapors 2006-12-26 doi: 10.3390/s6121827 Jieshan Lu Xiaoan Cao Canying Pan Lianfeng Yang Guangbo Lai Jianling Chen Cuiqin Wu http://mdpi.com/1424-8220/6/12/1751/ This review of 53 references deals with the uses of zeolites and zeolite-basedmaterials for developing gas sensors. The potential of these materials is highlighted andavenues for further research are suggested. http://mdpi.com/1424-8220/6/12/1751/ Wed, 13 Dec 2006 00:00:00 CET Sensors 2006-12-13 6 12 Review 1751 1764 1424-8220 Zeolite-based Materials for Gas Sensors 2006-12-13 doi: 10.3390/s6121751 Xiaowen Xu Jing Wang Yingcai Long http://mdpi.com/1424-8220/6/12/1721/ The performance of weak gaseous plume-detection methods in hyperspectral long-wave infrared imagery depends on scene-specific conditions such at the ability to properly estimate atmospheric transmission, the accuracy of estimated chemical signatures, and background clutter. This paper reviews commonly-applied physical models in the context of weak plume identification and quantification, identifies inherent error sources as well as those introduced by making simplifying assumptions, and indicates research areas. http://mdpi.com/1424-8220/6/12/1721/ Wed, 06 Dec 2006 00:00:00 CET Sensors 2006-12-06 6 12 Review 1721 1750 1424-8220 Overview of Physical Models and Statistical Approaches for Weak Gaseous Plume Detection using Passive Infrared Hyperspectral Imagery 2006-12-06 doi: 10.3390/s6121721 Tom Burr Nicolas Hengartner http://mdpi.com/1424-8220/6/11/1587/ Weak gaseous plume detection in hyperspectral imagery requires thatbackground clutter consisting of a mixture of components such as water, grass, and asphaltbe well characterized. The appropriate characterization depends on analysis goals.Although we almost never see clutter as a single-component multivariate Gaussian(SCMG), alternatives such as various mixture distributions that have been proposed mightnot be necessary for modeling clutter in the context of plume detection when the chemicaltargets that could be present are known at least approximately. Our goal is to show to whatextent the generalized least squares (GLS) approach applied to real data to look for evidenceof known chemical targets leads to chemical concentration estimates and to chemicalprobability estimates (arising from repeated application of the GLS approach) that aresimilar to corresponding estimates arising from simulated SCMG data. In some cases,approximations to decision thresholds or confidence estimates based on assuming the clutterhas a SCMG distribution will not be sufficiently accurate. Therefore, we also describe astrategy that uses a scene-specific reference distribution to estimate decision thresholds forplume detection and associated confidence measures. http://mdpi.com/1424-8220/6/11/1587/ Thu, 23 Nov 2006 00:00:00 CET Sensors 2006-11-23 6 11 Article 1587 1615 1424-8220 Characterizing Clutter in the Context of Detecting Weak Gaseous Plumes in Hyperspectral Imagery 2006-11-23 doi: 10.3390/s6111587 Tom Burr Bernie Foy Herb Fry Brian McVey http://mdpi.com/1424-8220/6/11/1616/ Airborne chemical sensing with mobile robots has been an active research areasince the beginning of the 1990s. This article presents a review of research work in this field,including gas distribution mapping, trail guidance, and the different subtasks of gas sourcelocalisation. Due to the difficulty of modelling gas distribution in a real world environmentwith currently available simulation techniques, we focus largely on experimental work and donot consider publications that are purely based on simulations. http://mdpi.com/1424-8220/6/11/1616/ Mon, 20 Nov 2006 00:00:00 CET Sensors 2006-11-20 6 11 Review 1616 1678 1424-8220 Airborne Chemical Sensing with Mobile Robots 2006-11-20 doi: 10.3390/s6111616 Achim J. Lilienthal Amy Loutfi Tom Duckett http://mdpi.com/1424-8220/6/11/1568/ A method of wet chemical synthesis suitable for high throughput and combinatorial applications has been developed for the synthesis of porous resistive thick-film gas sensors. This method is based on the robot-controlled application of unstable metal oxide suspensions on an array of 64 inter-digital electrodes positioned on an Al2O3 substrate. SnO2, WO3, ZrO2, TiO2, CeO2, In2O3 and Bi2O3 were chosen as base oxides, and were optimised by doping or mixed oxide formation. The parallel synthesis of mixed oxide sensors is illustrated by representative examples. The electrical characteristics and the sensor performance of the films were measured by high-throughput impedance spectroscopy while supplying various test gases (H2, CO, NO, NO2, propene). Data collection, data mining techniques applied and the best potential sensor materials discovered are presented. http://mdpi.com/1424-8220/6/11/1568/ Wed, 15 Nov 2006 00:00:00 CET Sensors 2006-11-15 6 11 Article 1568 1586 1424-8220 Wet Chemical Synthesis and Screening of Thick Porous Oxide Films for Resistive Gas Sensing Applications 2006-11-15 doi: 10.3390/s6111568 Gerald Frenzer Andreas Frantzen Daniel Sanders Ulrich Simon Wilhelm F. Maier http://mdpi.com/1424-8220/6/11/1440/ Volatile organic compound (VOC) detection is a topic of growing interest withapplications in diverse fields, ranging from environmental uses to the food or chemicalindustries. Optical fiber VOC sensors offering new and interesting properties whichovercame some of the inconveniences found on traditional gas sensors appeared over twodecades ago. Thanks to its minimum invasive nature and the advantages that optical fiberoffers such as light weight, passive nature, low attenuation and the possibility ofmultiplexing, among others, these sensors are a real alternative to electronic ones inelectrically noisy environments where electronic sensors cannot operate correctly. In thepresent work, a classification of these devices has been made according to the sensingmechanism and taking also into account the sensing materials or the different methods offabrication. In addition, some solutions already implemented for the detection of VOCsusing optical fiber sensors will be described with detail. http://mdpi.com/1424-8220/6/11/1440/ Wed, 01 Nov 2006 00:00:00 CET Sensors 2006-11-01 6 11 Review 1440 1465 1424-8220 Volatile Organic Compound Optical Fiber Sensors: A Review 2006-11-01 doi: 10.3390/s6111440 Cesar Elosua Ignacio R. Matias Candido Bariain Francisco J. Arregui http://mdpi.com/1424-8220/6/11/1428/ Over the last twenty years, newly developed chemical sensor systems (socalled“electronic noses") have odour analyses made possible. This paper describes theapplications of these systems for microbial detection in different fields such as medicineand the food industry, where fast detection methods are essential for appropriatemanagement of health care. Several groups have employed different electronic noses forclassification and quantification of bacteria and fungi to obtain accurate medicaldiagnosis and food quality control. So far, detection and identification of bacterial andfungal volatiles have been achieved by use of e-noses offering different correctclassification percentages. The present review includes examples of bacterial and fungalspecies producing volatile compounds and correlated to infectious diseases or fooddeterioration. The results suggest the possibility of using this new technology both inmedical diagnostics and in food control management. http://mdpi.com/1424-8220/6/11/1428/ Wed, 01 Nov 2006 00:00:00 CET Sensors 2006-11-01 6 11 Review 1428 1439 1424-8220 Application of Electronic Noses for Disease Diagnosis and Food Spoilage Detection 2006-11-01 doi: 10.3390/s6111428 Ida A. Casalinuovo Donato Di Pierro Massimiliano Coletta Paolo Di Francesco http://mdpi.com/1424-8220/6/10/1420/ The ZnO:Al thin films were prepared by RF magnetron sputtering on Si substrateusing Pt as interdigitated electrodes. The structure was characterized by XRD and SEManalyses, and the ethanol vapor gas sensing as well as electrical properties have beeninvestigated and discussed. The gas sensing results show that the sensitivity for detecting400 ppm ethanol vapor was ~20 at an operating temperature of 250°C. The high sensitivity,fast recovery, and reliability suggest that ZnO:Al thin film prepared by RF magnetronsputtering can be used for ethanol vapor gas sensing. http://mdpi.com/1424-8220/6/10/1420/ Mon, 30 Oct 2006 00:00:00 CET Sensors 2006-10-30 6 10 Article 1420 1427 1424-8220 ZnO:Al Thin Film Gas Sensor for Detection of Ethanol Vapor 2006-10-30 doi: 10.3390/s6101420 Shih Min Chou Lay Gaik Teoh Wei Hao Lai Yen Hsun Su Min Hsiung Hon http://mdpi.com/1424-8220/6/10/1411/ Various applications, such as pollution monitoring, toxic-gas detection, noninvasive medical diagnostics and industrial process control, require sensitive and selectivedetection of gas traces with concentrations in the parts in 109 (ppb) and sub-ppb range.The recent development of quantum-cascade lasers (QCLs) has given a new aspect toinfrared laser-based trace gas sensors. In particular, single mode distributed feedback QCLsare attractive spectroscopic sources because of their excellent properties in terms of narrowlinewidth, average power and room temperature operation. In combination with these lasersources, photoacoustic spectroscopy offers the advantage of high sensitivity and selectivity,compact sensor platform, fast time-response and user friendly operation. This paper reportsrecent developments on quantum cascade laser-based photoacoustic spectroscopy for tracegas detection. In particular, different applications of a photoacoustic trace gas sensoremploying a longitudinal resonant cell with a detection limit on the order of hundred ppb ofozone and ammonia are discussed. We also report two QC laser-based photoacousticsensors for the detection of nitric oxide, for environmental pollution monitoring andmedical diagnostics, and hexamethyldisilazane, for applications in semiconductormanufacturing process. http://mdpi.com/1424-8220/6/10/1411/ Fri, 27 Oct 2006 00:00:00 CEST Sensors 2006-10-27 6 10 Review 1411 1419 1424-8220 Photoacoustic Spectroscopy with Quantum Cascade Lasers for Trace Gas Detection 2006-10-27 doi: 10.3390/s6101411 Angela Elia Cinzia Di Franco Pietro Mario Lugarà Gaetano Scamarcio http://mdpi.com/1424-8220/6/10/1345/ This review is an attempt to give an overview on how surface science studies cancontribute to a fundamental understanding of metal oxide gas sensors. In here tin dioxide isused as a model system for metal oxide gas sensor materials and we review surface sciencestudies of single crystal SnO2. The composition, structure, electronic and chemicalproperties of the (110) and (101) surfaces is described. The influence of compositionalchanges as a function of the oxygen chemical potential on the electronic surface structureand the chemical properties is emphasized on the example of the (101) surface. The surfacechemical properties are discussed on the example of water adsorption. It is shown thechemical and gas sensing properties depend strongly on the surface composition. http://mdpi.com/1424-8220/6/10/1345/ Tue, 17 Oct 2006 00:00:00 CEST Sensors 2006-10-17 6 10 Review 1345 1366 1424-8220 Surface Science Studies of Gas Sensing Materials: SnO2 2006-10-17 doi: 10.3390/s6101345 Matthias Batzill http://mdpi.com/1424-8220/6/10/1308/ In this work, a new type of optical fiber based chemical sensor, the sub-nanolitersample cell (SNSC) based gas sensor, is described and compared to existing sensors designsin the literature. This novel SNSC gas sensor is shown to have the capability of gasdetection with a cell volume in the sub-nanoliter range. Experimental results for variousconfigurations of the sensor design are presented which demonstrate the capabilities of theminiature gas sensor. http://mdpi.com/1424-8220/6/10/1308/ Wed, 11 Oct 2006 00:00:00 CEST Sensors 2006-10-11 6 10 Article 1308 1320 1424-8220 Sub-Nanoliter Spectroscopic Gas Sensor 2006-10-11 doi: 10.3390/s6101308 Bassam Alfeeli Gary Pickrell Anbo Wang http://mdpi.com/1424-8220/6/9/1153/ Thin films of tin oxide were deposited by electron beam evaporation. The effectsof the sensor biasing voltage and film thickness on the CO-sensing of tin oxide thin filmswere investigated. The films were characterized using X-ray diffraction and X-rayphotoelectron spectroscopy All the films were found to be amorphous. The current-voltagecharacteristic of the sensor in air has shown that semiconductor-metal interface formsSchottky barrier. It was found that the CO-sensing properties depend on the sensor biasingvoltage and film thickness. For lower biasing voltages the sensitivity was much higher thanfor the higher voltages. It was found that the sensitivity of the films to CO increased withthe film thickness. http://mdpi.com/1424-8220/6/9/1153/ Tue, 26 Sep 2006 00:00:00 CEST Sensors 2006-09-26 6 9 Article 1153 1160 1424-8220 Biasing Voltage Dependence of Sensitivity of Electron Beam Evaporated SnO2 Thin Film CO Sensor 2006-09-26 doi: 10.3390/s6091153 Sardar M. Ayub Durrani http://mdpi.com/1424-8220/6/6/643/ In this review we discuss the advances in use of GaN and ZnO-based solid-statesensors for gas sensing applications. AlGaN/GaN high electron mobility transistors(HEMTs) show a strong dependence of source/drain current on the piezoelectricpolarization -induced two dimensional electron gas (2DEG). Furthermore, spontaneous andpiezoelectric polarization induced surface and interface charges can be used to develop verysensitive but robust sensors for the detection of gases. Pt-gated GaN Schottky diodes and Sc2O3/AlGaN/GaN metal-oxide semiconductor diodes also show large change in forwardcurrents upon exposure to H2 containing ambients. Of particular interest are methods fordetecting ethylene (C2H4), which offers problems because of its strong double bonds andhence the difficulty in dissociating it at modest temperatures. ZnO nanorods offer largesurface area, are bio-safe and offer excellent gas sensing characteristics. http://mdpi.com/1424-8220/6/6/643/ Sat, 24 Jun 2006 00:00:00 CEST Sensors 2006-06-24 6 6 Review 643 666 1424-8220 Wide Bandgap Semiconductor Nanorod and Thin Film Gas Sensors 2006-06-24 doi: 10.3390/s6060643 Byoung Sam Kang Hung-Ta Wang Li- Chia Tien Fan Ren Brent P. Gila David P. Norton Cammy R. Abernathy Jenshan Lin Stepehn J. Pearton http://mdpi.com/1424-8220/6/6/578/ A fiber optic sensor for Volatile Organic Compounds (VOCs) detection has beendeveloped and characterized for some organic gasses. The sensor is based on a novelvapochromic material, which is able to change its optical properties in presence of organicvapors in a reversely way. A nano Fabry Perot is constructed onto a cleaved ended opticalfiber pigtail by Electrostatic Self Assembly method (ESA), doping this structure with thevapochromic material. Employing a reflection scheme, a change in the intensity modulatedreflected signal at 850 nm have been registered. The response of the sensor has beenevaluated for five different VOCs, and a deeper study has been made for vapors of threedifferent alcohols. http://mdpi.com/1424-8220/6/6/578/ Fri, 16 Jun 2006 00:00:00 CEST Sensors 2006-06-16 6 6 Article 578 592 1424-8220 Development of an In-Fiber Nanocavity Towards Detection of Volatile Organic Gases 2006-06-16 doi: 10.3390/s6060578 Cesar Elosua Ignacio R. Matias Candido Bariain Francisco J. Arregui http://mdpi.com/1424-8220/6/5/526/ The precursors of SnO2 or In2O3/SnO2 nanocrystlline powders have been prepared bythe sol-precipitation method. The precursors were calcined at different temperatures to prepareSnO2 or In2O3/SnO2 nanocrystalline powders with different particle sizes. The nanocrystalliteswere examined by differential thermal analysis (DTA), X-ray diffraction (XRD) andtransmission electron microscopy (TEM). And then thick film CO sensors were fabricated usingprepared SnO2 or In2O3/SnO2 nanocrystlline powders loaded with PdOx. The composition thatgave the highest sensitivity for CO was in the weight% ratio of 5 wt.% In2O3/SnO2:PdOx as99:1(wt %). The composite material was found sensitive against CO at the working temperature200 °C. It was found that the sensors based on In2O3/SnO2 nanocrystalline system exhibitedvery short response time to CO at ppm level. These characteristics make the sensor to be apromising candidate for detecting low concentrations of CO. http://mdpi.com/1424-8220/6/5/526/ Wed, 10 May 2006 00:00:00 CEST Sensors 2006-05-10 6 5 Article 526 535 1424-8220 Micro Semiconductor CO Sensors Based on Indium-Doped Tin Dioxide Nanocrystalline Powders 2006-05-10 doi: 10.3390/s6050526 Il Jin Kim Sang Do Han Chi Hwan Han Jihye Gwak Hi Doek Lee Jin Suk Wang http://mdpi.com/1424-8220/6/5/492/ Effects of surface chemical modification with sodium silicate on the gas-sensingproperties of F-doped SnO2 gas sensor designed and fabricated employing micro-electromechanical system (MEMS) technology were investigated. Gas sensing properties of thesensor were checked against combustible gases like H2, CO, CH4 and C3H8 at a heatervoltage of 0.7 V. The H2 sensitivity of the surface modified F-doped SnO2 micro sensormarkedly increased and reached S = 175 which was found to be about 40 times more thanthat of unmodified sensor (S = ~ 4.2). The increase in the sensitivity is discussed in terms ofincreased resistivity and reduced permeation of gaseous oxygen into the underlying sensinglayer due to the surface modification of the sensor. The present micro-hydrogen sensor withenhanced sensitivity due to SiO2 incorporation is a low energy consuming portable sensormodule that can be mass-produced using MEMS technology at low cost. http://mdpi.com/1424-8220/6/5/492/ Tue, 09 May 2006 00:00:00 CEST Sensors 2006-05-09 6 5 Article 492 502 1424-8220 Enhancement of H2-sensing Properties of F-doped SnO2 Sensorby Surface Modification with SiO2 2006-05-09 doi: 10.3390/s6050492 Chi-Hwan Han Sang-Do Han S. P. Khatkar http://mdpi.com/1424-8220/6/5/503/ In case of typical chemical gas sensors reacted by gas adsorption on surface of anactive layer, it is difficult to detect some gases which have low chemical adsorption energylike inert gases. In this paper, we report a gas sensor using carbon nanotube(CNT) array aselectron emitters for the purpose of detecting these gases. Specifically, sensors werefabricated with applications of glass patterning by a sand-blast process and of anodicbonding between glass and silicon to improve the compactness of the structure and thereliability in process. The proposed sensor, based on an electrical discharge theory known asPaschen's law, worked by figuring the changes of dark discharge current and initialbreakdown voltage depending on the concentration and the identity of gases. In this work,air and Ar gases were examined and discussed. http://mdpi.com/1424-8220/6/5/503/ Fri, 05 May 2006 00:00:00 CEST Sensors 2006-05-05 6 5 Article 503 513 1424-8220 CNT Sensors for Detecting Gases with Low Adsorption Energy by Ionization 2006-05-05 doi: 10.3390/s6050503 Seongjeen Kim