Journal Articles
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Item 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.Item A Highly Sensitive Photonic Crystal Fiber Gas Sensor for the Detection of Sulfur Dioxide(Springer Science and Business Media B.V., 2022) Elizabeth Caroline, E.C.; Nizar, S.M.; Krishnan, P.Sulfur dioxide (SO2) is one of the most prevalent contaminants in the atmosphere. It is mostly generated as a byproduct of the burning of sulfur-containing coal and oils, as well as the smelting of various ores. SO2 contributes to the development of major diseases such as asthma and chronic bronchitis. In this paper, we proposed a Wheel Structured circular air hole Photonic Crystal Fiber (WS-PCF) based gas sensor to detect SO2 gas. The proposed WS-PCF gas sensor consists of a four-layer-thick circular cladding air hole. The diameter of the first layer varies throughout the optimization procedure, while the diameters of the succeeding three layers remain constant. The numerical investigation on the sensor parameters such as numerical aperture, effective area, non-linearity, confinement, loss and the relative sensitivity of the proposed sensor are extensively analyzed in a wavelength range of 0.9 µm to 1.2 µm. The proposed WS-PCF gas sensor offers the highest relative sensitivity of 83.64% and a lower confinement loss of 6.34 × 10 - 9dB/ km. The proposed sensor is simple and offers 14% high sensitivity and very low confinement loss (10-3reportedinliterature) compared with the exist literature. © 2022, The Author(s), under exclusive licence to Springer Nature B.V.Item Improvement in Performance of InAs Surface Quantum Dot Heterostructure-Based H2S Gas Sensor by Introducing Buried Quantum Dot Layer(Institute of Electrical and Electronics Engineers Inc., 2023) Mantri, M.R.; Panda, D.P.; Punetha, D.; Pandey, S.K.; Singh, V.P.; Pandey, S.K.; Chakrabarti, S.In this work, we have demonstrated InAs surface quantum dot (SQD)-based H2S gas sensors. The epitaxial growth of the strain-coupled and uncoupled InAs/GaAs QD heterostructures is done using the solid-source molecular beam epitaxy (MBE) tool. For both types of heterostructures, the coverage of the InAs monolayer (ML) for the SQD layer varies from 0.9 to 2 ML. The ML coverage of the buried quantum dots (BQDs) layer for the coupled heterostructures is kept constant (2.7 ML). The atomic force microscopy (AFM) results demonstrated that the coupled heterostructures have higher quantum dot (QD) density in the SQDs layer in comparison to the uncoupled one due to strain propagation from the BQDs toward the SQD layer. The sensor fabricated using the coupled heterostructure with 2 ML SQDs has demonstrated better performance than the uncoupled one for various concentrations (1-1000 ppm) of hydrogen sulfide (H 2S) gas due to inter-dot carrier tunneling between BQDs and SQDs layer. The coupled InAs gas sensor showed the best sensing properties at room temperature (45.9% sensor response at 100 ppm H2S ). We have demonstrated the selectivity of the sensor toward H 2S among various target gases like CO, CO2 , N2O , and NO 2 and the stability over a longer period of time with only 3% deviation (within acceptable limit). These findings have the potential to promote the fabrication of high-performance gas sensors using SQDs-based coupled heterostructures. © 2001-2012 IEEE.Item Understanding the interplay of solution and process parameters on the physico-chemical properties of ZnO nanofibers synthesized by sol-gel electrospinning(Institute of Physics, 2023) Prabhu, N.N.; Rajendra, B.V.; Anandhan, S.; Murthy, K.; Jagadeesh Chandra, R.B.; George, G.; Kumar, B.; Shivamurty, B.Aging populations and the increase in chronic diseases worldwide demand efficient healthcare tools for simple, rapid, and accurate diagnosis and monitoring the human health. In this context, gas sensors are used to analyze the type of gas in the breath to diagnose chronic diseases. Metal oxide and ceramic nanofibers (NFs) produced by the electrospinning (ES) method have been investigated for potential use as gas sensors in the engineering and medical sectors. The material and process parameters are the main influencing factors on the functional performance of electrospun metal oxide NFs. Zinc oxide (ZnO) based NFs are used in various gas sensors due to the wide band gap (3.37eV), large exciton binding energy, and high mobility of charge carriers of ZnO. In this research, we made an attempt to study the effect of poly(vinyl alcohol) (PVA) and zinc acetate dihydrate (ZnAc2) concentrations and feed rate, voltage, spinneret tip-to-collector distance (TCD), and pyrolysis temperature on the physical properties of ZnO NFs. An average fiber diameter of 119 nm was obtained after pyrolysis at 600 °C of electrospun fiber produced from an aqueous PVA solution of concentration 15 w% with 7.5 w% ZnAc2 based on the weight of PVA. The grain size, transmittance, structural defects, and band gap energy of NFs were found to increase as a function of the pyrolysis temperature, which could be beneficial for the functional applications of these NFs. © 2023 The Author(s). Published by IOP Publishing LtdItem Tracing of Ammonia Gas by Solution-Combustion-Derived Pristine and Nb-Doped TiO2 Films: Beneficial Impact of Crystallinity and Adsorbed Oxygen on the Gas Response(Springer, 2023) Vardhan, R.V.; Manjunath, G.; Pothukanuri, P.; Mandal, S.The current work delivers room-temperature ammonia (NH3) gas-detectable pristine, Nb-doped TiO2 air- and vacuum-annealed films obtained through the solution-combustion process. Polycrystalline anatase crystal structured films without any dopant oxide phases were processed at 400°C on glass substrates. The crystallinity was higher in pristine films than in doped films; the morphological features were similar in all the films. The films were > 50% transparent, and the estimated optical energy band gap was greater in doped films than in pristine films. All the films detected NH3 gas (25 ppm to 100 ppm) at room temperature, and the gas response was highly dependent on the crystallinity and relative area fraction of adsorbed oxygen (% of OA). The vacuum-annealed pristine film exhibited a better gas response than the other films at all NH3 gas concentrations due to high crystallinity and % of OA (10.15%). The film demonstrated maximum gas response of ~16 towards 100 ppm of NH3 gas and displayed good selectivity. Even though the doping reduced the crystallite size from ~17 nm to ~9 nm, it also diminished the crystallinity of the films, which significantly impacted the deterioration of their gas response. © 2023, The Minerals, Metals & Materials Society.Item Mechanistic insight and first principle analysis of cation-inverted zinc ferrite nanostructure: A paradigm for ppb-level room temperature NOx sensor(Elsevier B.V., 2024) Nath, V.G.; Ray, S.; Rodney, J.D.; Prakasha Bharath, S.; Roy, S.; Tarafder, K.; Subramanian, A.; Chul Kim, B.Herein, we adopted a new paradigm for developing a high-performance gas sensor by leveraging the mixed spinel ZnFe2O4 structure (mZFO) to enhance the adsorption of NOx molecules. Material characterization reveals the formation of the mZFO due to the cation inversion in lattice sites. The estimated value of the inversion degree is observed to shift from 0.78 to 0.39 with an increase in the calcination temperature. The mZFO nanoparticles calcined at 500 °C show exceptional sensing performance due to their suitable grain size (∼2 times Debye length), neck diameter, and surface area. The sensing studies conducted at various NOx concentrations indicate that the sensor can detect ppb level of NOx with a detection limit of about 9 ppb at room temperature. The detailed sensing mechanism is elucidated based on the density functional theory calculations (DFT) and Bader charge analysis. The outstanding sensor performance is attributed to the formation of a mixed spinel structure, wherein the adsorption energy of NOx (∼-0.6 eV) in the presence of surface adsorbed oxygen is higher than that of the normal spinel structure (∼-0.1 eV). Furthermore, the sensor exhibited a fast response and recovery times (7 and 92 s at 800 ppb NO2), excellent stability, and selectivity. The practical suitability of the mZFO sensor was studied by analyzing the vehicle exhaust emissions. We strongly believe this work would pave a novel approach to developing a high-potential gas sensor by modifying the cation distributions in the spinel ferrites. © 2024 Elsevier B.V.Item Detection of ethanol gas at room temperature by In2O3-based screen-printed films fabricated through particle-free aqueous solution combustible inks(Institute of Physics, 2024) Vardhan, R.V.; Praveen, L.L.; Manjunath, G.; Pothukanuri, P.; Seikh, A.H.; Alnaser, I.A.; Mandal, S.The current work investigates the room temperature ethanol gas detection capabilities of pristine, Sn-doped, Zn-doped, Sn & Zn co-doped In2O3-based screen-printed films, fabricated using particle-free aqueous solution combustible inks on glass substrates. The fabricated films were pure, polycrystalline with cubic bixbyite crystal structure, porous, and transparent (∼75 to 95%) in the visible range. Relatively high surface roughness was detected in pristine film than in doped films. Ethanol gas was detected by all the films at room temperature. Among all, the pristine film showed a relatively greater gas response at all concentrations of ethanol gas ranging from 25 ppm to 100 ppm. This superior gas response was attributed to comparatively greater oxygen vacancy concentration (OV/OL), relative area fraction of surface adsorbed oxygen (% of OA), and high surface roughness with porosity. The maximum ethanol gas response attained was ∼17 at 100 ppm concentration by the pristine film, which also demonstrated high selectivity to ethanol gas. © 2024 The Author(s). Published by IOP Publishing Ltd.Item All-printed WO3 films on an Ag-interdigitated electrode derived from aqueous screen-printable inks for room-temperature ammonia gas detection(Institute of Physics, 2025) Praveen, L.L.; Singh, N.P.; Vardhan, R.V.; Mandal, S.In this work, all-printed tungsten oxide (WO3) sensors were fabricated from nanoparticle-based screen-printable inks, where the WO3 nanopowders were hydrothermally synthesized with various HCl concentrations to give enhanced room-temperature detection of ammonia (NH3) gas. The monoclinic phase of WC powders (calcined WO3) with square nanoplate-like morphology and porosities was identified from x-ray diffraction, field-emission scanning electron microscopy and Brunauer-Emmett-Teller surface area analysis. The silver precursor ink-derived interdigitated electrodes were found to be crystalline with an average finger width and Ag film thickness of 1 ± 0.4 mm and 3.8 ± 0.5 µm, respectively. The formulated WO3 inks with hydroxyethyl cellulose showed a thixotropic fluid-like behavior and exhibited a viscosity of ?9 × 104 mPa s, which is a key requirement for screen printing. Rheological study of the formulated WC inks revealed a thixotropic nature, with all WC inks showing a viscosity of 85 ± 3 Pa s and a recovery rate of 80% in the recovery stage. This work explains the role of pH in hydrothermally synthesis of WO3 by correlating the gas-sensing characteristics of the screen-printed sensors fabricated from formulated inks, where the WC-15 gas sensor showed a maximum gas response of ?340 towards 100 ppm of NH3 gas. This facile and cost-effective method for fabricating chemiresistive gas sensors could pave the way for the development of flexible and printable devices for ppb-level detection of NH3 gas and its monitoring. © 2025 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.Item Ultra-high ammonia gas response of phase-stabilized (Fe0.2Ni0.2Cr0.2Mn0.2Zn0.2)3O4-? high-entropy spinel oxide sensor array and its machine learning predictions(Elsevier Ltd, 2025) Praveen, L.L.; Upadhyay, B.; Potnuri, R.; Mandal, S.In this work, the gas sensing performance of phase-stabilized (FeNiMnZnCr)3O4 high-entropy spinel oxide (HSO) gas-sensors via screen-printing were investigated, where the HSO powders were synthesized via solution combustion synthesis (SCS) using three different fuels: citric acid, urea, and glucose. Although all HSO powders were obtained at 500 °C, the formation of stable spinel phase was evidenced at 600 °C. Among all fabricated sensors, G-800 gas sensor depicted a stable ultra-high response of ?3471 towards 100 ppm of ammonia gas along with a notable response of ?162 even at 10 ppm (where G means glucose and 800 represents calcination temperature in °C) and it demonstrated a strong device-to-device reproducibility with stability of ?35 days. A synergy of crystallinity and increased porosities from XRD and FESEM micrographs resulted in ultra-high gas-response towards ammonia gas compared to volatile organic compounds such as formaldehyde, methanol, and ethanol). The presence of defect band and oxygen vacancies observed from the Raman and XPS analysis, were complemented by the presence of porosities confirmed from BET surface area analysis. Subsequently, the machine learning (ML) algorithms are applied on sensor signals to estimate the concentration of ammonia gas, and among all the ML classifiers, RFC gave reasonably better predictions in three concentrations regimes with a good classification accuracy of 93.3 ± 5.3 %, 90 ± 7.5 %, and 83.3 ± 13.1 % for G-600, G-700, and G-800, respectively. The proposed ML studies enable accurate detection of hazardous ammonia levels using HSO-based sensors, showing strong potential for integration into diagnostic platforms targeting ammonia breath markers. © 2025 Elsevier B.V.Item Deep-eutectic solvent-assisted green synthesis of MAX-phase Cr2AlC and its 2D-MXene derivative Cr2CTxtowards room-temperature detection of ammonia gas(Elsevier Ltd, 2025) Lokeshwar, H.; Lakshmi Praveen, L.; Mandal, S.; Shakti, N.This study explores the novel and eco-friendly chemical etching of bulk Cr2AlC MAX phases using a deep eutectic solvent (DES) mixture of choline chloride (ChCl) and anhydrous ferric chloride (FeCl3) to synthesize chromium carbide (Cr2CTx) MXene nanolayers. ChCl-FeCl3enables a fluoride-free transformation approach to synthesize Cr2CTxMXene via selective etching of aluminium interlayers, resulting in mixed surface terminations (-O, -OH, -Cl) confirmed from bond vibrations observed in FTIR transmittance spectra. Also, the FESEM micrographs confirm the formation of Cr2CTxnanolayers with successful cleavage of Cr2AlC MAX phase nanolaminates identified from a distinct red shift of D-band with the highest ID/IGratio peak intensity ratio, confirming the presence of high defect concentration in Cr2CTxMXene. The hydrothermally synthesized SnO2powders exhibiting a rutile tetragonal phase average particle size of 35.8 ± 0.8 nm were mixed with Cr2CTxto formulate screen-printable inks for the fabrication of Cr2CTx, SnO2, and their composite Cr2CTx-SnO2gas sensors. The addition of Cr2CTxdemonstrated a detrimental effect on the gas-sensing performance of the SnO2sensor, which was further supported from XPS analysis. However, the SnO2sensor recorded the highest gas-response of ?452 towards 100 ppm of ammonia gas among all sensors, highlighting the role of oxygen defects confirmed from photoluminescence spectra. This work paves the way for a novel and eco-friendly etching approach of MAX-phases and helps in their research towards the development of ultra-sensitive gas sensors. © 2025 Elsevier Ltd and Techna Group S.r.l. All rights are reserved, including those for text and data mining, AI training, and similar technologies.