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Raj V.B.,University of Delhi | Singh H.,Solid State Physics Laboratory DRDO | Nimal A.T.,Solid State Physics Laboratory DRDO | Sharma M.U.,Solid State Physics Laboratory DRDO | And 2 more authors.
Sensors and Actuators, B: Chemical | Year: 2017

ZnO/SAW sensor was reported to give distinct response towards liquor ammonia. To study the complete mechanism, ZnO thin films (40 nm) were deposited using rf sputtering in different reactive gas composition of argon and oxygen. The increase in oxygen content (30–100%) during film growth leads to decrease in the value of stress and bond energy. The individual contribution of different SAW sensing mechanisms such as mass loading, elastic effects and acousto-electric interaction, was evaluated and analyzed to understand the distinct response for liquor ammonia. It was found that mass loading seems to get affected by the presence of stress whereas elastic loading was affected by the crystallite size and bond energy (Zn[sbnd]O) in ZnO thin films. © 2016 Elsevier B.V.


Hasan P.M.Z.,Jamia Millia Islamia University | Islam S.S.,Jamia Millia Islamia University | Islam T.,Jamia Millia Islamia University | Azam A.,Aligarh Muslim University | Harsh,Solid State Physics Laboratory DRDO
Sensor Review | Year: 2010

Purpose - The purpose of this paper is to present the dependence of capacitive sensing of organic vapours by porous silicon (PS) on its molecular structure for the realization of a organic vapour sensor, compatible with existing silicon technology, with desired miniaturization and selectivity. Design/methodology/approach - The method introduces large surface area of PS obtained by electrochemically etching of silicon wafer for characterization of organic vapours through capacitive sensing. Findings - The method provides a comparative study of sensor response for organic vapour molecules of different structures and leads to an insight into the sensing mechanism. Research limitations/implications - The surface of PS has been stabilized by thermal oxidation process. Practical implications - The method is useful for the development of a simple, cost-effective sensor for selective gas analysis. Originality/value - The result is an outcome of regular experimental work carried out to observe the capacitive sensing behavior of PS for different organic vapours. © 2010 Emerald Group Publishing Limited. All rights reserved.


Sahu V.,University of Delhi | Shekhar S.,University of Delhi | Ahuja P.,University of Delhi | Gupta G.,National Physical Laboratory India | And 3 more authors.
RSC Advances | Year: 2013

We report the low-temperature (250 °C) synthesis of high-performance hydrophilic carbon black for application as a conducting filler in supercapacitor electrodes. Increased water content, due to the hydrophilicity, maintained the uniform hydration level of MnO2/carbon composite electrodes, with good protonic conduction. This results in an increase in the total specific capacitance by 24%. This journal is © 2013 The Royal Society of Chemistry.


Raj V.B.,University of Delhi | Nimal A.T.,Solid State Physics Laboratory DRDO | Tomar M.,University of Delhi | Sharma M.U.,Solid State Physics Laboratory DRDO | Gupta V.,University of Delhi
Sensors and Actuators, B: Chemical | Year: 2015

Abstract A new method has been devised for obtaining fast NO2 gas sensing characteristics by using detuned SnO2/SAW sensor oscillator. The deposited SnO2 thin films were polycrystalline showing XRD reflections corresponding to (1 0 1) and (2 1 1) planes of rutile structure. The frequency of the sensor remained tuned for SnO2 layer of small thickness (< 90 nm), and sensing response was moderate (< 140 kHz) with relatively slow response time and recovery time. However with increase in thickness (≥ 90 nm), the frequency of SAW sensor detuned resulting in enhanced sensing response (≥ 16 MHz) along with fast response time and recovery time. Independent experiments confirmed the change in elasticity of the sensing layer as the dominant sensing mechanism for SnO2/SAW sensor towards NO2 gas. © 2015 Elsevier B.V.


Raj V.B.,University of Delhi | Singh H.,Solid State Physics Laboratory DRDO | Nimal A.T.,Solid State Physics Laboratory DRDO | Tomar M.,University of Delhi | And 2 more authors.
Sensors and Actuators, B: Chemical | Year: 2015

ZnO/Quartz based surface acoustic wave (SAW) sensors have been fabricated for the detection of DMMP (di-methyl methyl phosphonate) at room temperature. The as-deposited ZnO thin films are c-axis oriented. The sensitivity of the sensor toward DMMP vapors increases with increase in the thickness of ZnO thin films. A change in elasticity of ZnO films with exposure to DMMP vapors is the dominant sensing mechanism. Various properties of ZnO thin films (roughness, porosity, crystallite size, bond strength etc.) responsible for elastic changes are analyzed by depositing the films under different processing conditions. The ZnO/SAW sensor is also highly selective toward DMMP vapors as compared to other interferants. The results throw light into the elasticity mechanism for SAW sensing along with the possibility of utilizing ZnO/SAW sensor for DMMP detection. © 2014 Elsevier B.V. All rights reserved.


Bhasker Raj V.,University of Delhi | Singh H.,Solid State Physics Laboratory DRDO | Nimal A.T.,Solid State Physics Laboratory DRDO | Tomar M.,University of Delhi | And 2 more authors.
Sensors and Actuators, B: Chemical | Year: 2013

In the present work, SAW sensors coated with various metal oxides as sensitive layer have been exploited for distinct detection of ammonia. Thin films of different metal oxides (ZnO, SnO2, TeO2 and TiO2) of same thickness (40 nm) were deposited under optimized parameters using rf sputtering technique for selective detection of liquor ammonia. As deposited ZnO thin film was highly c-axis oriented, whereas SnO 2 thin film was polycrystalline. However the coatings of TiO 2 and TeO2 thin films were amorphous. SAW sensor coated with ZnO film (ZnO/SAW) was found to be highly sensitive towards liquor ammonia as compared to other metal oxide coated SAW sensors. Effect of the thickness of ZnO sensing layer (20-80 nm) has been studied on the sensing response characteristics. Mass loading and elastic loading are identified as the major contributions towards the response of SAW sensor for ammonia and their contributions were evaluated by fitting with the theory. © 2013 Elsevier B.V. All rights reserved.


Raj V.B.,University of Delhi | Singh H.,Solid State Physics Laboratory DRDO | Nimal A.T.,Solid State Physics Laboratory DRDO | Sharma M.U.,Solid State Physics Laboratory DRDO | Gupta V.,University of Delhi
Sensors and Actuators, B: Chemical | Year: 2013

Chemical warfare agents (CWA) are deadly chemicals even at low levels of concentration. In the present work, an electronic-nose (E-nose) comprising of an array of four surface acoustic wave (SAW) sensors having different chemical sensitive coatings of ZnO, TeO2, SnO2 and TiO2 is prepared for the detection of CWA. The oxide thin films are coated on the surface of SAW devices by rf sputtering technique. ZnO and SnO2 thin films are poly-crystalline with fine surface morphology whereas TeO2 and TiO2 thin films are amorphous. The E-nose shows good sensitivity toward the four simulants (dimethyl methylphosphonate (DMMP), dibutyl sulfide (DBS), chloroethyl phenyl sulfide (CEPS) and diethyl chlorophosphate (DECP)) of CWA allowing sub ppm level detection possible. Different simulants give distinct characteristic pattern when passed through the surface of E-nose. Using principal component analysis (PCA), the four different simulants of CWA are well separated from each other. Even with the incorporation of interferants (petrol, diesel, kerosene, VOCs and water vapors) in the PCA study, all four simulants are well separated showing the capability of the prepared SAW E-nose to classify simulants of chemical warfare agents efficiently. © 2013 Elsevier B.V.


Singh H.,Solid State Physics Laboratory DRDO | Raj V.B.,University of Delhi | Kumar J.,Solid State Physics Laboratory DRDO | Mittal U.,Solid State Physics Laboratory DRDO | And 4 more authors.
Sensors and Actuators, B: Chemical | Year: 2014

An Electronic nose (E-nose) made up of an array of metal oxide thin film based SAW sensors is proposed as a detection system for the binary mixture of DMMP (simulant of nerve agent) and methanol at room temperature. The SAW devices are one port surface acoustic wave (SAW) resonators having center frequency of 433.9 MHz. The E-nose sensor array has SAW sensors coated with four different chemical sensitive coatings of ZnO, TeO2, SnO2 and TiO2 in order to recognize the individual components in a binary mixture of DMMP (in ppb levels) and methanol (in sub ppm levels). Principal Component Analysis (PCA) as a data pre-processing technique and Artificial Neural Network (ANN) as a pattern classification technique have been applied for obtaining a clear discrimination and correct classification. © 2014 Elsevier B.V.


Singh H.,Solid State Physics Laboratory DRDO | Raj V.B.,University of Delhi | Kumar J.,Solid State Physics Laboratory DRDO | Durani F.,Solid State Physics Laboratory DRDO | And 3 more authors.
Process Safety and Environmental Protection | Year: 2016

A functionalized polymer (SXFA: fluoroalcoholpolysiloxane) coated single surface acoustic wave (SAW) sensor E-Nose is proposed for the detection of harmful vapors by operating at different temperature. The polymer coated SAW sensor is used along with a reference SAW device in dual Colpitt's oscillator configuration. The sensor is tested with four different classes of vapors at different concentrations in an environmental chamber whose temperature can be varied in the range -20 to +70 °C. The sensor showed variation in response with exposure to benzene, methanol, diesel and DMMP vapors at different temperatures. The polymer coated SAW sensor was giving frequency shifts of 0.21-1.12 kHz for methanol (1000-4000 ppm), 0.3-2.69 kHz for benzene (400-1600 ppm), 0.81-7.39 kHz for diesel (12-48 ppm) and 4.27-8.07 kHz for DMMP (1-10 ppm) vapors at 30 °C operating temperature. Principal component analysis and artificial neural network algorithms are successfully implemented to classify and detect the target vapors. © 2016 Institution of Chemical Engineers.

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