Department of Electrical Engineering

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This article reported about the ultraviolet (UV) radiation effect on the resonance frequency response of a AT-cut piezoelectric quartz crystal. A large resonance frequency upshift was observed when the quartz crystal was irradiated by UV light of 355-nm wavelength using a Q-switched pulsed Nd:YVO4 UV laser. The dynamic frequency response behavior was systematically investigated by illuminating the quartz crystal with UV light in which the UV intensity was varied with time in staircase- and linear pulse-shaped patterns. From the experimental analysis, we measured the limit of detection and the sensitivity of the quartz crystal, which are about 0.5 mW/cm2 and 0.706 Hz/(mW/cm2), respectively. For a constant UV irradiation, a moderate response (<10 s) and recovery (<10 s) times were achieved during the on and off cycles of the UV light. The short-term repeatability and maximum operating limit of AT-cut quartz crystal were also further studied upon exposure to UV light with different intensities. In this work, we not only demonstrate the impact of UV irradiation on quartz crystal but also discuss the mechanism of upshift in resonance frequency upon exposure to UV light. This study shows the applicability of quartz crystal for the detection of UV light. © 1963-2012 IEEE.

World University root node

IEEE Transactions on Electron Devices

UV Light Detection Using Resonance Frequency of Piezoelectric Quartz Crystal

Pristine ZnO based hydrogen sensors pose low sensitivity ( 43%) at the operating temperature of 150°. Herein, we explore the decoration of Phosphorene oxide quantum dots (POQDs) on RF sputtered grown ZnO nanostructures for hydrogen gas sensing application. A simplistic approach such as drop cast method is employed to decorate electrosynthesized POQDs (2- 8μ L) onto interdigitated electrodes over ZnO nanostructures. The suggested hydrogen sensor based on POQDs (6μ L)/ZnO nanostructures exhibits an outstanding sensing response (70.6%) as compared to all the sensors for 100 ppm at 150°C. Enhanced sensing response from the POQDs(6μ L)/ZnO nanostructure might be due to the enormous active surface area of POQDs (provides more active sites for hydrogen gas) and modulation of depletion region at the interface of POQDs and ZnO. The proposed sensor can be operated at mild temperature and consume low power which is the need of the hour for the hydrogen sensors for industrial applications. © 2001-2012 IEEE.

IEEE Sensors Journal

Phosphorene Oxide Quantum Dots Decorated ZnO Nanostructure-Based Hydrogen Gas Sensor

Reduced graphene oxide (rGO) has tunable properties and acts as an efficient low-cost alternative for graphene in many applications. It also has its own exciting electronic and optoelectronic characteristics. The properties of rGO can be altered by tuning the amount of reduction, types of defects, doping and functionalization. The reduction of graphene oxide (GO) by various methods and the large-scale production of rGO can be easily achieved. These properties led the research drive for low-cost and high-end applications of rGO-based devices. It has found applications in almost all branches of applied science and engineering. Recent research works show that rGO-based photodetectors achieved high responsivity and detectivity values with fast operation speed. Although there are many reviews on graphene-based photodetectors, there has been much less focus on rGO-based photodetectors. In this review, we focus on rGO-based photodetectors, photodetection mechanism and advancements in the field. Thus, in this review, we provide a much-needed timely update and future prospects to the scientific community. © The Royal Society of Chemistry 2021.

Journal of Materials Chemistry C

Recent advances and prospects in reduced graphene oxide-based photodetectors

In recent years, the utilization of gas sensors has increased tremendously in daily life and industry. Importantly, appropriate material selection should be made for gas sensors in order to achieve outstanding gas sensing performance, such as high sensitivity, good selectivity, a fast response/recovery time, and long-term stability. Numerous studies have shown that neither pure metal oxide semiconductor nor individual 2D nanomaterial (graphene, transition metal dichalcogenides, metal-organic frameworks, metal oxide nanosheets, MXenes, and phosphorene) based gas sensors are capable of showing excellent gas-sensing performance towards gas molecules. However, synergistic combinations of metal oxides and 2D nanomaterials have demonstrated enhanced gas-sensing performance in many studies. This review aims at providing a comprehensive summary of the current advancements in 2D/metal-oxide based heterostructures as gas sensors. Additionally, the underlying sensing mechanisms of various kinds of gas sensors are systematically described, and the device architectures and their corresponding sensing performances are summarized. Finally, the challenges and future prospects of 2D/metal-oxide nanocomposite-based gas sensors for sensing applications have been outlined.

JOURNAL OF MATERIALS CHEMISTRY C

Gas sensing performance of 2D nanomaterials/metal oxide nanocomposites: a review

Drop-casting is a simple deposition technique where a slurry-like solution of nanomaterial is coated on small substrates, which are then allowed to dry under controlled temperature and pressure ambience. The present work focuses on the tyrosine functionalized benzene-tri-carboxyamide (Tyr-BTC) and ZnO composite based sensor deposited using drop-cast method for sensing carbon monoxide (CO) at room temperature. The composition of the composite surface was varied by altering the molar concentration of the constituents. The performance of the mesoporous structures in room temperature gas sensing was studied for the CO concentration range of 5-300 ppm in synthetic air. The highly amplified gas sensing response of approximately 94% at 300 ppm of CO by Tyr-BTC-ZnO in molar concentration 2:3 of Tyr-BTC-ZnO was observed. The improvement in the capacitance change, quicker response time, good linearity and reversibility was attributed to the synergistic effect between ZnO and tyrosine functionalized BTC. © 2020 IEEE.

Mesoporous Tyrosine Functionalized BTC-ZnO Composite for Highly Selective Capacitive CO Sensor

A highly sensitive and robust polysilicon Field Effect transistor (SiFET) has been developed for the detection of an gold standard biomarker of myocardial infarction (AMI) Cardiac Troponin I (cTnI). This paper reports a polysilicon FET device integrated with a thin film of gold layer as a gate terminal which is biofunctionalized with specific cTnI binding single stranded DNA receptor aptamer to detect cTnI. The reported SiFET is fabricated using standard microfabrication unit processes. The detailed characterization of reported device is performed and thoroughly discussed at different stages of device development. The assessment of bio-interface is also studied using various surface characterization techniques such as Raman spectroscopy, Atomic force microscopy (AFM) and Contact angle measurements. The experimental results showed the significant response for cTnI concentration as low as 0.1 ng ml-1 for label free detection. © 2021 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

Journal of the Electrochemical Society

Polysilicon Field Effect Transistor Biosensor for the Detection of Cardiac Troponin-I (cTnI)

Controlled growth of ZnO-based nanostructures, starting from a vertical nanowall surface morphology to laterally grown highly anisotropic nanorods/wires formation has successfully been achieved by controlled thermal oxidation of thin Zn films for a temperature range of 100–700 °C. The as-grown ZnO nanorods were further used for carbon monoxide gas sensing at low temperatures (down to 150 °C) as well as ethanol vapour sensing at room temperatures. Thin films of Zn were deposited on glass and silicon substrate at room temperature, using a vacuum-assisted thermal evaporation technique. Structure, morphology and chemical property of ZnO layers were investigated using various surface characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS) and Raman spectroscopy. The XRD and SEM results are in very good correlation and showed vertical growth morphology of ZnO nanowall/sheet structures at a relatively lower oxidation temperature up to 400 °C. However, at higher oxidation temperature, lateral growths started to dominate over the vertical growth. Oxidation at 700 °C appeared with laterally grown one-dimensional (1D) ZnO nanowires/rods of high density. Raman spectroscopy and XPS results suggested that the vertical growth is mainly initiated by the metallic Zn film morphology, whereas the lateral growth is strongly dominated by the oxide (ZnO) formation. Finally, laterally grown ZnO nanorods could successfully sense CO gas and ethanol vapour. A drastic enhancement in CO gas sensitivity for a concentration of 230 ppm was clearly observed in dynamic gas flow mode even for a wide range of operating temperature. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Springer Proceedings in Mathematics and Statistics

Growth and Characterization of ZnO Nanostructures: Materials for CO and Ethanol Sensing

Tin Oxide (SnO2) has established itself as excellent receptor in chemiresistive detection of ammonia gas in last two decades. There have been several routes developed to obtain a pristine SnO2 film over this time however, physical vapor deposition remains an attractive route for the same due to the control it provides for the growth and its scalability for industry scale production. In this work, we report on the effect of oxygen and argon ratio at different pressure in sputtering unit on the sensitivity of tin oxide. In particular, our investigation revealed that the device based on SnO2 thin film obtained at an sputtering pressure of 10 mTorr and Ar/O2 ratio of 50/50 possess highest response (~27.97% for 30 ppm of ammonia) at optimal temperature of 220 ℃. © 2020 Elsevier B.V.

Materials Letters

Assessing simultaneous effect of Ar/O2 ratio and process pressure on ammonia sensing properties of reactive DC magnetron sputtered SnO2 thin films

Reconfigurable intelligent surface (RIS) is an emerging technology that can achieve reconfigurable radio propagation environments for beyond 5G/6G wireless systems by smartly tuning the signal reflection via a large number of low-cost passive reflecting elements. In this letter, we investigate the effect of co-channel interference (CCI) on RIS-based dual-hop mixed free-space optical (FSO)-radio frequency (RF) communication systems. The source node, equipped with multiple FSO apertures, transmits subcarrier intensity modulated symbols on the FSO link subjected to Gamma-Gamma (GG) distributed atmospheric turbulence with pointing errors (PEs). It is assumed that the relay-RIS and RIS-destination links follow Rayleigh distribution. The destination node is corrupted by multiple CCI (each following Rayleigh distribution). The performance of the considered system is evaluated by deriving novel closed-form expressions for the outage probability (OP) and bit error rate (BER). It is shown through numerical results that RIS-based dual-hop mixed FSO-RF system provide a significant performance enhancement in comparison to a traditional dual-hop mixed FSO-RF system even in presence of CCI. © 1997-2012 IEEE.

IEEE Communications Letters

Reconfigurable Intelligent Surface for Mixed FSO-RF Systems with Co-Channel Interference

Free space optical (FSO) communication is a promising candidate for the next generation (5G and beyond) wireless communication systems, due to its merits (i.e. low latency, high data rate, and license-free band, among others). However, atmospheric turbulence (AT) as well as pointing error (PE) are two of the main challenges with FSO communication that affect its performance. Here, the exact closed-form expression of the average secrecy capacity and secrecy outage probability under the composite effect of AT and non-zero boresight PEs is evaluated. For all the regimes of the AT (weak to strong), a generalised Malaga distribution is used to model the channel fading gain of the FSO link. The expressions are generalised and valid for all turbulence, and are applicable for intensity modulation direct detection as well as heterodyne detection techniques. © 2020 The Authors. IET Communications published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology