Department of Electrical and Electronics Engineering
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Item Modulation of 1d ZNO nanostructures for selective formaldehyde sensing: the role of surface energy, polarization, and adatom kinetics toward asymmetric growth(Elsevier, 2025-07) Hazra, Arnab; Gangopadhyay, SubhashisThe precise morphological control of highly dense, crystalline, and asymmetric one-dimensional (1D) metal oxide semiconductor nanostructures is of high practical importance for developing high-performance chemiresistive gas sensors. In this study, various 1D ZnO nanostructures, including nanobelts, nanowires, nanorods, and nanoneedles, were uniformly grown on glass substrates via the controlled thermal oxidation of thin Zn films under ambient air conditions. Comprehensive structural, chemical, optical, and electrical characterizations were conducted to investigate their properties and growth mechanism. Thermal oxidation of thin Zn films initiates only above 400 °C, whereas a transition towards asymmetric growth of 1D ZnO nanostructures starts to occur at 600 °C. Different nanoscale morphologies such as nanobelts (t = 58 nm, w = 460 nm), nanowires (d = 48 nm), nanorods (d = 280 nm), and nanoneedles (d = 85–120 nm) are obtained after thermal oxidation of [600 °C, 5h], [700 °C, 1h], [700 °C, 5h] and [800 °C, 5h], respectively. Chemiresistive gas sensing performance of these 1D nanostructures was evaluated against different volatile organic compounds (VOCs) in a static vapor mode, demonstrating exceptional sensitivity and selectivity for formaldehyde detection. The nanoneedle-based sensor exhibited superior sensitivity (36 %) with rapid response (28 s), while the nanobelt-based sensor demonstrated excellent selectivity. Notably, the nanowire-based sensor with highly porous morphology achieved an ultra-low detection limit, well below 50 ppb. The growth mechanism was explained based on surface free energy, surface polarization, and adatom diffusion kinetics. Additionally, gas sensing performance was analyzed in relation to surface-to-volume ratio, crystal defect states and crystal plane orientation. Mechanism behind controlled electron transport through the nano-junction of 1D nanostructure is also discussed. All these findings establish a growth mechanism of 1D ZnO nanostructures as promising candidates for advanced gas sensing applications.Item Highly selective formaldehyde sensing using ZnO nano-rods(AIP, 2023-03) Choudhary, Sumita; Hazra, Arnab; Gangopadhyay, SubhashisEarly detection of formaldehyde emission from any household materials is technologically very demanding as it can be a serious human health hazard. Even indirect inhaling of formaldehyde may cause significant harm to our eyes, skin, mouth or any other organs. Hence, fabrication of a simple and sensitive formaldehyde sensor would be of high practical importance. Within this work, formation of ZnO nano-rods by controlled thermal oxidation of vacuum deposited thin Zn films in air ambient, followed by fabrication of formaldehyde sensor operating at relatively lower operating temperature are reported. The crystal structure, surface morphology and optical properties of the as grown ZnO nano-rods have been investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Raman spectroscopy, respectively. The XRD patterns of ZnO suggested the formation of highly crystalline oxide films whereas FESEM images have revealed its nano-rods surface morphology with significantly high (length to diameter) aspect ratio. Raman spectroscopy confirms the thermal oxidation of the Zn thin films. As-grown ZnO nano-rods were then subsequently used to fabricate the chemi-resistive formaldehyde sensors. These sensors showed an extremely high formaldehyde sensing performance at a relatively lower operating temperature of 200°C. In a static measurement mode, the sensor exhibited a gas response of about 53% toward 100 ppm of formaldehyde, with a reasonable fast response and recovery time. Moreover, these ZnO nano-rod based sensors have also been tested with similar type of VOCs such as benzene, xylene, alcohols and acetone and appeared with an excellent selectivity towards formaldehyde over the other VOCs.Item Surface energy and stress driven growth of extremely long and high-density ZnO nanowires using a thermal step-oxidation process(RSC, 2024-09) Panda, Sri Aurobindo; Choudhary, Sumita; Hazra, Arnab; Gangopadhyay, SubhashisFormation of highly crystalline zinc oxide (ZnO) nanowires with an extremely high aspect ratio (length = 60 μm, diameter = 50 nm) is routinely achieved by introducing an intermediate step-oxidation method during the thermal oxidation process of thin zinc (Zn) films. High-purity Zn was deposited onto clean glass substrates at room temperature using a vacuum-assisted thermal evaporation technique. Afterwards, the as-deposited Zn layers were thermally oxidized under a closed air ambient condition at different temperatures and durations. Structural, morphological, chemical, optical and electrical properties of these oxide layers were investigated using various surface characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoemission spectroscopy (XPS). It was noticed that the initial thermal oxidation of Zn films usually starts above 400 °C. Homogeneous and lateral growth of the ZnO layer is usually preferred for oxidation at a lower temperature below 500 °C. One-dimensional (1D) asymmetric growth of ZnO started to dominate thermal oxidation above 600 °C. Highly dense 1D ZnO nanowires were specifically observed after prolonged oxidation at 600 °C for 5 hours, followed by short-step oxidation at 700 °C for 30 minutes. However, direct oxidation of Zn films at 700 °C resulted in ZnO nanorod formation. The formation of ZnO nanowires using step-oxidation is explained in terms of surface free energy and compressive stress-driven Zn adatom kinetics through the grain boundaries of laterally grown ZnO seed layers. This simple thermal oxidation process using intermittent step-oxidation was found to be quite unique and very much useful to routinely grow an array of high-density ZnO nanowires. Moreover, these ZnO nanowires showed very high sensitivity and selectivity towards formaldehyde vapour sensing against few other VOCs.Item Harnessing Quantum Wave Nature of Individual Electrons for Single Photon Detection(IEEE, 2018) Kumar, RahulWe propose and examine theoretically a new type of photodetector that senses THz single photons by the wavefunction change of a single electron confined in a quantum dot. A possible readout scheme is also presented.Item Development of Cyber-Physical Systems for Water Quality Monitoring in Smart Water Grid(Springer, 2022-05) Gupta, Raj Kumar; Gupta, Karunesh KumarThere are many challenges while developing a smart city, such as air/water quality monitoring, water resource management, power grid implementation, and transport management. Water quality monitoring is one of them in which many researchers and scientists showed interest. The current water distribution systems always face leakage, failure, and maintenance delays due to the unavailability of real-time monitoring in distribution systems, which results in a high amount of water wastage. This can be solved by implementing a smart water grid. This paper proposes a solution for water quality monitoring for distribution systems in a real-time environment based on low-cost commercial off-the-shelf modules. Various water quality parameters were monitored from the developed setup. The proposed architecture can log, analyze data, make decisions, and remotely represent the data. The data obtained from various sensing nodes were uploaded to the cloud, a service provided by Amazon Web Services (AWSs). Experimental results show that the proposed low-cost sensing network can be an ideal early warning system in smart cities.Item Detection of cadmium ion in aqueous medium by simultaneous measurement of piezoelectric and electrochemical responses(Elsevier, 2018-09) Gupta, Karunesh Kumar; Gupta, Raj Kumar; Manjuladevi, V.Cadmium is one of the important heavy metals which poses health hazards due to its consumption through potable water. Cadmium is known to form complexes with amine group and also it has good affinity towards carbon nanotubes. The octadecylamine functionalized single-walled carbon nanotubes (ODACNTs) can be employed for sensing cadmium ion in aqueous medium. A thin film of ODACNTs offers not only strong adsorption properties towards cadmium ion but also provides an enormous gain in surface to volume ratio, and good mechanical and chemical stability. Therefore, a sensing layer of ODACNTs was formed on the gold deposited quartz wafer and the sensing towards cadmium ion in the aqueous medium was performed. An experimental setup was designed to record the electrochemical and piezo-responses simultaneously. The piezo and electrochemical responses were found to be linear in the given concentration range. Interestingly, the piezoresponse modulates systematically and repeatedly from a maximum to minimum value due to voltage sweep during cyclic voltammetry indicating the interfacial phenomenon of adsorption and desorption.Item Raspberry Pi-based smart sensing platform for drinking-water quality monitoring system: a Python framework approach(DWES, 2019) Gupta, Raj Kumar; Gupta, Karunesh KumarThis paper proposes the development of a Raspberry Pi-based hardware platform for drinking-water quality monitoring. The selection of water quality parameters was made based on guidelines of the Central Pollution and Control Board (CPCB), New Delhi, India. A graphical user interface (GUI) was developed for providing an interactive human machine interface to the end user for ease of operation. The Python programming language was used for GUI development, data acquisition, and data analysis. Fuzzy computing techniques were employed for decision-making to categorize the water quality in different classes like “bad”, “poor”, “satisfactory”, “good”, and “excellent”. The system has been tested for various water samples from eight different locations, and the water quality was observed as being good, satisfactory, and poor for the measured water samples. Finally, the obtained results were compared with the benchmark for authentication.Item Heavy Metal Ion Sensing using Ultrathin Langmuir-Schaefer Film of Tetraphenylporphyrin Molecule(IEEE, 2020) Gupta, Raj Kumar; Gupta, Karunesh Kumar; Manjuladevi, V.; Kumar, DalipThe exciting properties of porphyrin molecules can be employed for several applications like sensing, catalysis, photovoltaics and energy related fields. The assemblies of the molecules at interfaces can give rise to some unique physicochemical properties which can enhance the device performance. In this article, we report our studies on heavy metal ion sensing in aqueous medium using ultrathin film of tetraphenylporphyrin (TPP) molecules. The TPP molecules were synthesized and used for forming Langmuir monolayer at the air-water interface. The monolayer was transferred onto solid substrates by Langmuir-Schaefer (LS) method at different target surface pressure of deposition (πT). The morphological analysis of the films indicated supramolecular assembly of the molecules in the LS film deposited at πT = 30 mN/m. The LS films of TPP molecules were employed for sensing heavy metal cations viz. Pb 2+ , Hg 2+ , Co 2+ and Cd 2+ from the aqueous medium by measuring piezoresponse from a quartz crystal microbalance. The sensing performance was found to be the best with LS film deposited at πT = 30 mN/m. The sensitivity-towards Pb 2+ ion is found to be the highest. The sensing of the heavy metal cations using randomly oriented TPP molecules in spin coated thin film was found to be much inferior as compared to that of LS films of the molecule. The enhanced sensing performance by the LS film of TPP molecules may be attributed to the supramolecular assembly of the molecules. We report that the interference of the sensing measurement for the recognition of Cd 2+ and Pb 2+ ions is least and thus these species can be detected selectively with less errors. The cation species recognition features obtained from scanning electron microscope images and Raman spectroscopy were found to be remarkably different and therefore these cationic heavy metal species can be selectively detected using the LS film of TPPItem Drift compensation of commercial water quality sensors using machine learning to extend the calibration lifetime(Springer, 2020) Gupta, Karunesh Kumar; Gupta, Raj KumarThere are specific issues in the multi-sensor systems used for water quality monitoring, which prevents these systems for routine measurement of water samples. An important issue is drift; related to sensor readings, which may refute the calibration of sensors leads to the necessity of frequent recalibration of the sensors that required effort as well as shut down the system. An alternative approach for drift correction is based on the mathematical correction method. The paper proposed a regression calibration method and implemented by the machine learning approach. In this paper, we have used a feed-forward artificial neural network based regression model to extend the calibration lifetime of sensors. The evaluation of the model was performed based on the root mean square error and the root mean square error for cross-validation. The proposed model is also compared with the traditional statistical method and proved to be superior to the traditional one. The experimental results demonstrate the best performance with a negligible error rate. Based on the results of the current study, ANN appears to be more adaptive for data analysis in environmental monitoring applications.Item Towards the Green Analytics: Design and Development of Sustainable Drinking Water Quality Monitoring System for Shekhawati Region in Rajasthan(Springer, 2021-05) Gupta, Raj Kumar; Gupta, Karunesh KumarIn rural areas, there is limited monitoring of drinking water quality. Reliable water quality monitoring stations are expensive and require high costs for maintenance and calibration process. In this paper, the development of a sustainable water quality monitoring system is proposed. The green analytics principles were considered for developing the proposed system to reduce the measurement’s time consumption and labor cost. Five water quality parameters [pH, oxidation reduction potential (ORP), dissolved oxygen (DO), electrical conductivity (EC), and temperature] have been measured using the developed system. The overall drinking water quality is measured by the proposed partial least squares regression (PLSR) model. The developed system’s performance is determined by mean average percentage error (MAPE), root-mean-square error (RMSE), and R2. The traceability of water quality sensors is defined with required uncertainty in water quality parameters. The measured uncertainty is 0.002, 0.892, 0.015, 0.029, and 0.017 for pH, EC, DO, ORP, and temperature, respectively. The relation between estimated and predicted water quality parameters (R2 > 0.93) shows that the developed system can be a suitable replacement for traditional water quality monitoring techniques.