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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    Synthesis and characterization of Cu 1-x Zn x O composite thin films for sensor application
    (Elsevier Ltd, 2019) Bharath, S.P.; Bangera, K.V.; Shivakumar, G.K.
    Cu 1-x Zn x O composite thin films were prepared using industrially applicable spray pyrolysis technique for volatile organic compound (VOCs)sensor application. Sensing properties for different concentration of VOCs such as acetone, ethanol and methanol were studied at different sensor operating temperature. XRD studies on prepared thin films confirmed formation of CuO[sbnd]ZnO composite thin films with presence of different peaks for monoclinic structured CuO and hexagonal structure ZnO, it was also observed that formation of composite material improves sensing property towards VOCs. Granular morphology observed from SEM images were also contributed to enhance sensitivity of Cu 1-x Zn x O thin films. Hot probe experiment reveals that all the thin films were p-type in conductivity nature. Maximum electrical conductivity was achieved for Cu 0.75 Zn 0.25 O composite thin films, which also showed highest sensing property for VOCs. Cu 0.75 Zn 0.25 O thin films were selective towards ethanol and were capable of detecting 1 ppm of ethanol at operating temperature of 290 °C. © 2019
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    Design optimization of a highly sensitive spiral photonic crystal fiber for liquid and chemical sensing applications
    (Academic Press Inc. apjcs@harcourt.com, 2019) Malavika, R.; Krishnan, P.
    In this paper, a spiral shaped photonic crystal fiber (PCF)is proposed for liquid sensing applications. The guiding properties of the proposed PCF are analysed. Sensitivity coefficient is analysed by varying different structural parameters for a wider wavelength range. In addition, confinement loss is also studied at the same wavelengths. The relative sensitivity achieved for the optimized parameters are 56.8%, 58.3% and 62.7% for water (n = 1.33), propane (n = 1.34)and propylene (n = 1.36)respectively. With its low confinement loss and high sensitivity the proposed PCF can be used for liquid and chemical sensing applications. © 2019 Elsevier Inc.
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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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    High sensitivity detection of chemicals based on sinusoidally apodized structured grating assisted liquid filled directional coupler
    (Springer, 2021) Raghuwanshi, S.K.; Singh, Y.; Singh, M.; Chack, D.; Kumar, R.; Prakash, O.
    The grating has a significant role in sensing applications. Similarly, the grating-assisted coupler has excellent potential in chemical sensing applications. The power coupling between two closely coupled waveguide couplers can be significantly tuned by incorporating grating between them. The grating has been taken of silica material with sinusoidal shape in variation. The grating layer is assumed to be embedded within the sensing layer while considering a changeable effective refractive index depending on the sensing layer substances. In the present paper, grating assisted directional coupler has been numerically analysed using its own developed MATLAB-based algorithm of finite difference method (FDM) scheme. FDM method has been applied to solve the Eigenvalue equation to obtain allowed Eigenvalues and corresponding Eigen vectors (TE and TM cases). In FDM, the analysis domain has been fine discretized into the mesh of 1-D equal spacing for reasonable accurate computation results. In experimental validation, Fibre Bragg grating (FBG) has been suspended between two high refractive index coupler regions, which act as a power coupling zone. Also, the coupling length has been changed from 5 to 20 ? m for tuning purposes and then optimized for grating parameters viz. length, period, etc. The whole structure is 2-Dimensional (x and y directions) with invariant in the y-direction. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, 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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    CO2 detection: using the polyethyleneimine–cerium oxide nanocomposite sensing film coated on interdigitated electrode prepared from copper clad
    (Taylor and Francis Ltd., 2022) Naveen Kumar, N.; Prasad, P.; Savitha, M.B.; Lokesh, L.; Shanmugam, B.K.; Navaneeth Gowda, N.; Rohith, H.V.
    In this effective work, Polyethyleneimine (PEI) and Cerium Oxide (CeO2) with disparate weight percentage were designated for sensing Carbon dioxide (CO2). Four heterogeneous varieties of sensors with a varied weight percentage of CeO2 in PEI were fabricated by drop-casting the sensitive films on prepared Interdigitated electrodes (IDE) from copper-clad. Morphological, compositional, absorbance and X-ray studies were led on the cerium oxide nanoparticles by field-emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX), UV-Visible spectrometer and X-ray diffractometer (XRD). Response capabilities of all the four sensors at room temperature were attentively scrutinized. Unique capabilities of Repeatability, sensitivity, error-free measurements of the response time and recovery time were carefully inspected. It was summarized that the appropriate weight ratio of CeO2 and PEI was critical for sensing response. A feasible comparison between sensing responses of the fabricated sensors to CO2 under nitrogen (N2) was typically done. Relevant sensing process was investigated too. © 2020 Informa UK Limited, trading as Taylor & Francis Group.
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    Photonic crystal fiber sensor for the detection of hazardous gases
    (Springer Science and Business Media Deutschland GmbH, 2022) Nizar, S.M.; Elizabeth Caroline, E.C.; Krishnan, P.
    Three different Photonic Crystal Fiber (PCF) gas sensors are designed to detect five different gases for a wide range of wavelengths. The three unique configurations are designed based on four outer Elliptical cores PCF (4E-PCF), four outer Circular cores (4C-PCF) PCF, and different Eight Elliptical cores PCF (8E-PCF) to analyze and sense the light interface with applied gases. For three proposed gas sensors, the sensing parameters for five different hazardous gases, such as relative sensitivity, effective area, birefringence and dispersion, are acquired. The five different gases considered in the sensor investigation are Sulfur trioxide [SO3] (20 °C), Tetracholorosilane [SiCl4], Tetracholoromethane [CCl4], Turpentine [C10H16], Tin Terra chloride [SnCl4]. Among the three designs, 8E-PCF yields a maximum sensitivity of 75.75%, an effective area of 2.45μm2, and a birefringence of 0.0421 for SnCl4 gas. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.