Faculty Publications

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    Structure-property relationship of sol-gel electrospun ZnO nanofibers developed for ammonia gas sensing
    (Academic Press Inc. apjcs@harcourt.com, 2014) Senthil, T.; Anandhan, S.
    Zinc oxide (ZnO) based nanomaterials have been used in various gas sensors due to the wide band gap (3.37. eV), large exciton binding energy and high mobility of charge carriers of ZnO. In this work, nanocrystalline ZnO nanofiber mats were synthesized through combined sol-gel electrospinning techniques followed by calcination, in which poly(styrene- co-acrylonitrile) and zinc acetate were used as the binder and precursor, respectively. Average diameter of the ZnO nanofibers decreased from 400 to 60. nm, while their grain size and crystallinity were enhanced by increasing the calcination temperature. Morphology and structure of the ZnO nanofiber mats were characterized by high resolution transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. ZnO nanofiber mats were found to be superhydrophilic (contact angle was close to 0°) by contact angle measurements. The sensitivity of these ZnO nanofibers in detecting gaseous ammonia was tested using an indigenous set up. Due to their high surface area and superhydrophility, these ZnO nanofiber mats were highly sensitive in sensing gaseous ammonia and the sensitivity of these mats increased as a function of their calcination temperatures. © 2014 Elsevier Inc.
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    Properties of CdxZn1-xO thin films and their enhanced gas sensing performance
    (Elsevier Ltd, 2017) Bharath, S.P.; Bangera, K.V.; Shivakumar, G.K.
    CdxZn1-xO(0 ? x ? 0.20) thin films with different Cd concentrations were successfully deposited on glass substrate using spray pyrolysis technique. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDAX) were used for structural, surface morphological and compositional characterization. The XRD analysis revealed that the synthesized films were hexagonal in structure with (002) orientation. The SEM studies confirm the formation of homogeneous and uniform films. Optical transmittance and electrical conductivity of the films were evaluated using UV–Visible spectroscopy and two probe method respectively. The optical studies showed that the CdxZn1-xO thin films have optical transmittance in entire visible region. The resistivity of undoped films were very high and it decreases with addition of cadmium. The gas sensing properties were investigated at optimal temperature of 350 °C for various volatile organic compounds like acetone, ethanol and methanol. The CdxZn1-xO thin films with 10 at. % cadmium concentration showed the sensitivity of 50% for 1 ppm ethanol. © 2017 Elsevier B.V.
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    Sensitivity Study of Nanocrystalline Fe3BO6 Sensor for Methane Gas Detection
    (Institute of Electrical and Electronics Engineers Inc., 2018) Kumari, K.; Ram, S.
    The iron borate Fe3BO6 with functionalized properties in a nanostructure is an important material useful for electrodes, gas sensors, and biological probes. In this paper, we studied the X-ray diffraction pattern, field-emission electron microscopy, and methane (CH4) gas sensing properties of synthesized Fe3BO6 nanocrystallites in a shape of nanoplates and nanobars from an iron borate glass 40Fe2O3-60B2O3 by annealing it in microwave for 15 min at 823 and 1023 K, respectively, in air. The temperature dependent sensitivity for CH4 (1000 ppm) illustrates a maximum value of 43% at an operating temperature 525 K for the 1023 K annealed sample. The sensitivity is found to be varied from 9% to 39% when the CH4 gas concentration is increased from 50 to 1000 ppm. Thus, the sample has a reasonably good sensitivity for methane. Furthermore, the sensor exhibits fast response (1 min) and a good recovery time (1.6 min) as compared with other oxide materials. © 2001-2012 IEEE.
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    Enhanced gas sensing properties of indium doped ZnO thin films
    (Academic Press, 2018) Bharath, S.P.; Bangera, K.V.; Shivakumar, G.K.
    Indium doped ZnO (InxZn1-xO, 0 ? x ? 0.05) thin films were deposited on to soda lime glass substrate by employing spray pyrolysis as deposition technique. Effect of doping concentration on characteristics of thin films were examined by XRD, SEM, UV-Visible spectroscopy, electrical and gas sensing measurements. XRD analysis demonstrates polycrystalline nature of thin films and also shows the shift in orientation from (002) to (101) crystal plane with increase in indium doping concentration. Surface morphological analysis shows the formation of homogeneous particle like nanostructures. Optical transmittance determined from UV-Visible spectroscopy was in the range of 80–95%, which was decreasing with increase in indium doping concentration. Maximum electrical conductivity was achieved at an optimal indium doping concentration of 3 at.%. The gas sensing properties were examined for different concentration of volatile organic compounds like acetone, ethanol and methanol for different doping levels. In0.03Zn0.97O thin films showed good sensitivity towards ethanol, with sensitivity of 30% towards 25 ppm of ethanol. © 2018 Elsevier Ltd
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    Highly Sensitive and Stable NO2 Gas Sensors Based on SWNTs with Exceptional Recovery Time
    (Institute of Electrical and Electronics Engineers Inc., 2019) Chauhan, S.S.; Kumar, D.; Chaturvedi, P.; Rahman, M.R.
    Room temperature operable and highly sensitive NO2 gas sensors are fabricated based on (i) random and (ii) aligned networks of single-walled carbon nanotubes (SWNTs). The fabricated sensors are very sensitive, stable, and show shorter recovery time in the presence of UV light. Also, the variation of the response and recovery with network density is analyzed. The thin film resistor (TFR) of random network is fabricated by a reliable, cost-effective, and reproducible vacuum filtration method. The aligned network is fabricated using AC di-electrophoresis (DEP) technique. Electrodes spacing is optimized to avoid the chaining effect of aligned and bridged SWNTs between the gold electrode pair to enhance the stability and sensitivity of the sensor. Both the sensors based on random and aligned networks of SWNTs is tested with NO2 at room temperature. It is found that the sensor made of the aligned network shows 3.5 times more sensitivity as compared to the random networks gas sensor but recovery time increases. It is also observed that sensors fabricated by TFR and aligned network techniques are stable and having less than 0.02 % and 0.15 % change in resistance with baseline, respectively. The TFR gas sensors fabricated using as prepared (AP) and purified and low functionality (P2) SWNTs show higher stability but less sensitive compared to the aligned network. The measured complete recovery time of sensors based on random and aligned SWNTs are 50 sec and 124 sec, respectively, for 0.5 ppm NO2. It is also observed that as the network density decreases response improves but the recovery time increases. © 2001-2012 IEEE.
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    A scalable screen-printed high performance ZnO-UV and Gas Sensor: Effect of solution combustion
    (Elsevier Ltd, 2020) Manjunath, G.; Pujari, S.; Patil, D.R.; Mandal, S.
    In the present study, scalable screen-printed Zinc Oxide (ZnO) based sensor was demonstrated to sense ultra-violet irradiation and gases such as ammonia (NH3), ethanol (C2H5OH), liquefied petroleum gas (LPG), chlorine (Cl2) and hydrogen sulphide (H2S). A facile solution combustion synthesis (SCS) route was adopted to synthesize high purity, homogeneous, nanocrystalline and highly reactive ZnO with favourable morphologies, microstructural parameters for the sensing performance using low-cost and less-violent fuels such as urea, citric acid and glycine. Fuel impacts on uniform particle size distribution, bond length, grain size, lattice strain enhanced the gas sensing potential in the synthesized powders. Films were fabricated by depositing synthesized powders on the glass substrate via screen printing approach using Na-carboxy methyl cellulose as a binder, water as a solvent and annealed at 500 °C for 2 h in ambient. Non-stoichiometric, phase pure and adhered thick films with optical band gap (3.17-3.25 eV) imparted gas sensing properties because of recombination of an electron-hole pair and intrinsic defects. ZnO films obtained from glycine-fuel system exposed to 100 ppm of NH3, C2H5OH, Cl2 and 50 ppm of H2S, exhibited good gas sensitivity of ~8, 5, 3 and 10 at an operating temperature of 50, 100, 200 and 100 °C respectively with a faster response and recovery speed. But, high sensitivity ~6 to 100 ppm of LPG at 350 °C in ZnO films from citric acid fuel-system. ZnO films obtained from glycine fuel system showed a high response to UV irradiation for exposing time of 90s. Low cost, high-performance sensor can be fabricated for the dual applications - alarming to prolonged exposure to harmful UV radiation and detection of a series of toxic and damaging gases. © 2019 Elsevier Ltd
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    Room-temperature detection of ammonia and formaldehyde gases by La xBa1?xSnO3?? (x = 0 and 0.05) screen printed sensors: effect of ceria and ruthenate sensitization
    (Springer Science and Business Media Deutschland GmbH, 2021) Manjunath, G.; Vardhan, R.V.; Praveen, L.L.; Pothukanuri, P.; Mandal, S.
    In the present work, gas sensing properties of the screen printed ceria and ruthenate-sensitized BaSnO3 (BSO) with La doping heterostructure sensors towards the detection of ammonia and formaldehyde gases at room temperature were studied. Adhered, porous screen printed films with different morphologies were obtained by depositing the LaxBa1?xSnO3?? (x = 0 and 0.05) powder particles prepared by the polymerized complex method. Ceria and ruthenate sensitization for screen printed LaxBa1?xSnO3?? (x = 0.05) film was processed through dip-coating in the 0.03 M aqueous solution of CeCl3 and RuCl3, respectively. La-doped BaSnO3 (LBSO) sensor with smaller crystallites, needle-like morphology and high concentration of oxygen vacancies exhibited superior gas response of 65 and 29 towards 50 ppm of ammonia and formaldehyde gases, respectively. Superabundant sensitization of ceria and ruthenate reduced the oxygen vacancy and structural open porosity in the LBSO sensor; therefore, the ammonia gas response was decreased from 65 to 14 and 3, respectively, whereas the formaldehyde gas response was reduced to less than 1/6th times the LBSO sensor. Limit of detection of LBSO sensors was estimated to be ~ 1 and ~ 2 ppm against ammonia and formaldehyde, respectively. The presence of fluorite structured phase ceria with high oxygen atoms storage capacity facilitates the rapid oxidization of analyte gases and caused the expeditious response (75 s) and recovery (60 s) in CeOx-sensitized LBSO sensor. This study might give a new insight into the development of doped and sensitized BSO-based gas sensors operating at ambient conditions. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
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    Fast detection and discriminative analysis of volatile organic compounds using Al-doped ZnO thin films
    (Springer Science and Business Media Deutschland GmbH, 2021) Bharath, S.P.; Bangera, K.V.
    Abstract: Aluminum-doped zinc oxide (AZO) thin films with different doping concentrations have been synthesized by simple spray pyrolysis technique. Precursor solution concentration was maintained ~ 50 mM throughout the fabrication process and dopant concentration was varied from 0 to 5 at. %. Prepared solution was sprayed on top of pre-heated glass plate to get highly adhesive AZO thin films. Various characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Visible spectroscopy were adopted to get an insight into the material formation. Electrical and gas-sensing characteristics were also recorded in detail to evaluate its potential application as a transparent conductor and gas sensor. As determined from XRD analysis, continuous decrease in grain size was observed with increase in aluminum doping concentration. Further, extracting the interplanar distance and lattice parameters, it was noticed that there was a negligible random variation. Aluminum doping also plays a significant role in modifying the surface morphology of thin films. Randomly arranged plate-like structures in undoped ZnO thin films transform to granular morphology with aluminum doping. Minimum resistivity of 0.517?m with ~ 80% transmittance in visible region was achieved at an optimal aluminum doping concentration of 3 at.%. Aluminum doping helps in increasing the sensitivity of ZnO thin films toward various volatile organic compound vapors such as acetone and ethanol. 3 at.% Al-doped thin films were capable of detecting 100 ppm of ethanol and acetone with a highest sensitivity of ~ 60%. Al incorporation to ZnO lattice is also supportive in bringing down the response and recovery time of the sensing material. A very short response time of 3 s and recovery time of 28 s was achieved at 100 ppm of ethanol. Principal component analysis shows proper discrimination between acetone and ethanol. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
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    Highly sensitive and wearable NO2gas sensor based on PVDF nanofabric containing embedded polyaniline/g-C3N4nanosheet composites
    (IOP Publishing Ltd, 2021) Khalifa, M.; Anandhan, S.
    In this study, a highly flexible and wearable nitrogen dioxide (NO2) gas sensor was fabricated based on electrospun poly(vinylidene fluoride) (PVDF)/polyaniline (PANi)/graphitic-carbon nitride (g-C3N4) blend nanocomposite (EBNC). g-C3N4/PANi nanocomposite (GPC) was synthesized by in situ polymerization technique prior to its incorporation into PVDF nanofibers, which ensured uniformity of dispersion. For the comparison study, PVDF/GPC nanocomposite film was fabricated using doctor blade technique. EBNC sensor exhibited high sensitivity, selectivity, reproducibility along with quick response and complete recovery. Electrospinning and GPC synergistically improved the performance of the EBNC based gas sensor. The superior gas sensing ability along with its low cost and the use of scalable electrospinning technique could make this system a promising one for the detection of gaseous NO2. © 2021 IOP Publishing Ltd.
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    From fundamental to CO2 and COCl2 gas sensing properties of pristine and defective Si2BN monolayers
    (Royal Society of Chemistry, 2022) Thomas, S.; Madam, A.K.; Asle Zaeem, M.
    In this work, the capability of Si2BN monolayers (Si2BN-MLs) to sense CO2 and COCl2 molecules was investigated by analyzing the structural, electronic, mechanical and gas sensing properties of defect-free and defective Si2BN-ML structures. Electronic property analysis revealed that the Si2BN-ML retains its metallicity in the presence of vacancy defects. The computed vacancy formation energies of Si, B and N monovacancies are 3.25 eV, 2.27 eV and 2.55 eV, respectively, which indicate that the B monovacancy is thermodynamically more feasible. Besides, both pristine and defective Si2BN-ML structures show good mechanical stability. To validate the gas sensing properties, the adsorption energy and charge transfer were analysed, showing that both pristine and defective Si2BN-ML structures receive considerable charges from the CO2 and COCl2 molecules via a stable physisorption process. The work function analysis revealed that a minute increase <0.10 eV is responsible for the enhanced selectivity and sensitivity of Si2BN-ML structures in detecting CO2 and COCl2 molecules. The low adsorption energies of both CO2 and COCl2 gas molecules during the interaction with Si2BN-ML structures signify the possibility of a large number of adsorption-desorption cycles with an ultra-low recovery time, 0.174 ns for CO2 and 0.016 ns for COCl2, suitable for efficient gas sensing applications. © the Owner Societies.