Department of Electrical Engineering

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Accumulation of industrial solid waste necessitates the development of utilization processes and technologies to reduce their negative environmental impact. Herein, molybdenite concentrate from the mining-metallurgy industry is systematically characterized as a valuable starting material for the fabrication of an efficient and low-cost nanostructured gas sensor. Few-layer MoS2 is obtained from molybdenite concentrate by liquid nitrogen exfoliation and deposited on different substrates by spin coating and drop casting. It is found that spin coating is advantageous over drop casting in fabricating a homogeneous and dense few-layer MoS2 film. The charge-transfer-based sensing performance of the fabricated few-layer MoS2 film is investigated upon exposure to NO2 at different temperatures (50, 100, and 120 °C). At an optimized temperature of 120 °C, a faster recovery is achieved, and the fabricated device exhibits 28, 38, and 44% sensitivity to 10, 50, and 100 ppm NO2, respectively, making it suitable for practical applications. Furthermore, the adsorption affinity of NO2 to the predominant (002) crystallographic plane of MoS2 is estimated from the distribution of field density and the calculated differential adsorption energies. According to the molecular modeling data, NO2 in the Ar/NO2 mixture has better interaction (dEad/dNNO2 = 4.77 kcal mol-1) with the few-layer MoS2 surface than individual NO2 (dEad/dNNO2 = 2.57 kcal mol-1), and van der Waals interaction (≈14 kcal mol-1) is the main adsorption force compared to the relatively weaker electrostatic interaction (<1 kcal mol-1). This work demonstrates a straightforward approach not only for the conversion of molybdenite concentrate into an efficient and low-cost nanostructured gas sensor but also for the reduction of the negative impact of accumulated molybdenum concentrate on the environment and human health. This journal is © The Royal Society of Chemistry.

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Green Chemistry

Efficient NO2sensing performance of a low-cost nanostructured sensor derived from molybdenite concentrate

Synthesis of nanoparticles in insulators attracts tremendous attention due to their unique electrical and optical properties. Here, the gallium (Ga) and gallium nitride (GaN) nanoclusters have been synthesized in the silicon nitride matrix by sequential ion implantation (gallium and nitrogen ions) followed by either furnace annealing (FA) or rapid thermal annealing (RTA). The presence of Ga and GaN nanoclusters has been confirmed by Fourier-transform infrared, Raman and X-ray photoelectron spectroscopy. Thereafter, the effect of RTA and FA on the conduction of charge carriers has been studied for the fabricated devices. It is found from the current–voltage measurements that the carrier transport is controlled by the space charge limited current conduction mechanism, and the observed values of parameter m (trap density and the distribution of localized state) for the FA and RTA devices are ~2 and ~4.1, respectively. This reveals that more defects are formed in the RTA device and that FA provides better performance than RTA from the viewpoint of opto- and nano-electronic applications. © 2020, Indian Academy of Sciences.

Bulletin of Materials Science

Gallium nitride nanocrystal formation in Si3N4 matrix by ion synthesis

In recent years, two-dimensional (2D) layered materials, such as MoS2, MoSe2, WS2, WSe2, SnS2, etc., have gained enormous interest in sensing applications with low-power consumption owing to their unique electrical, chemical, and mechanical properties. Among a broad range of sensors, rapid advances in flexible and wearable sensors have paved the way for smart sensing applications, including electronic skin (e-skin), home security, air- and health-monitoring, etc. This review aims at summarizing recent progress in energy-efficient flexible gas sensors by utilizing 2D transition metal dichalcogenides (TMDCs) materials. Main concepts and different approaches are overviewed for optimizing the gas sensing characteristics on flexible sensing platforms. The different strategies and challenges for incorporating 2D TMDCs materials into e-skin-oriented and e-textiles gas sensors are also highlighted. In addition, this review also includes the challenges and future perspectives for TMDCs materials in emerging flexible and wearable gas sensing field. © 2020 Elsevier B.V.

Sensors and Actuators, A: Physical

Transition metal dichalcogenides-based flexible gas sensors

In this study, a novel, highly sensitive AlGaN/ GaN high electron mobility transistor (HEMT) sensor is demonstrated for the detection of cadmium ions by the functionalization of graphitic carbon nitride (g-C3N4). The preparation of g-C3N4 was done using the pyrolysis process of urea. The prepared g-C3N4 was functionalized on Au gated AlGaN/ GaN HEMT and the sensing performance was observed by the measurement of electrical characteristics of the device. The sensitivity and limit of detection of the modified g-C3N4 based AlGaN/ GaN HEMT sensor was observed as 0.2606 µA/ppb and 0.533 ppb respectively. The observed limit of detection is very low than the standard guideline values of World Health Organization (WHO) for drinking water. Furthermore, using AlGaN/GaN HEMT theory, we show that the sensing response is very fast due to the availability of 2-D electron gas (2DEG) and very sensitive due to the change in gate potential. The mechanism suggests that the decrement in the drain current was due to the reduction of Cd2+ ions on the g-C3N4 surface which generates negative redox potential at the gate terminal while exposing the functionalized HEMT to Cd2+ ions. Hence, a simple, miniaturized, sensitive and real-time sensor has been developed using AlGaN/GaN HEMT functionalized by g-C3N4 to detect Cd2+ ions in an aqueous environment. © 2020 American Institute of Physics Inc.. All rights reserved.

AIP Conference Proceedings

Detection of cadmium ions Byg-C3N4 functionalization on AlGaN/ GaN high electron mobility transistor

This paper presents an efficient method to estimate jitter in a chain of CMOS inverters in the presence of multiple noise sources, including the power supply noise, input data noise, and the ground bounce noise. For this purpose, necessary noise transfer functions are derived and the recently developed EMPSIJ method is advanced to handle cascaded CMOS inverter stages. Results from the proposed method are compared with the results from a conventional EDA simulator, which demonstrate a significant speed-up using the proposed method for a comparable accuracy. © 2018 IEEE.

IEEE Transactions on Electromagnetic Compatibility

Efficient Jitter Analysis for a Chain of CMOS Inverters

Iot has a main role in the raising technology. It's application is almost used in every fields. It has been found that upto 9.4 billion individuals will start to use IoT in their agricultural farms. When the agriculture is done with the help of IoT, farmers will earn more profit than the normal farming methods. This IoT uses sensors like soil moisture, Humidity, temperature, Light sensor, Motion sensors, pH meter in the farming field. This provides automation in irrigation system, Lighting system, Animal alert system and also finds the pH level of the soil. These operations are done by using the solar energy. These data are sent to the microcontroller called PIC. Based on the respective threshold level each system will operate automatically. In this way the farms can be monitored in the user friendly way. This is achieved by accessing MQTT(Message Queuing Telemetry Transport). This is an application that can be viewed in mobile. In this automation system Relay is used to make the system 'ON' and 'OFF'. If the moisture content becomes less the irrigation system gets accessed. The artificial lighting system is automated by using Incandescent or Fluorescent light, when there is minimal light source is available for the plants. In addition to this the motion sensor is used to sense the movement of animals which makes the alarm sound along with glow of light. The camera in the field will capture the animal. These updates and notifications are sent to the farmer's mobile, so that they can monitor it at any time. This is a conventional way of farming method that provides higher yield and efficiency. © 2020 IEEE.

2020 6th International Conference on Advanced Computing and Communication Systems, ICACCS 2020

Smart Monitoring and Management System for Efficient Cultivation

The IEEE 802.11ad standard operates in the mmWave frequency band and supports data transfer speeds of up to 7 Gbps. However, the signal propagation characteristics in the mmWave band are adverse, and the achievable coverage area is less (around 6m). Hence, the coverage area around the access point (AP) is partitioned into virtual sectors and, AP communicates with stations in each sector by employing directional beamforming for improved coverage. Therefore, at any given instance, the AP serves only one sector, and in general, AP chooses the sectors in a round-robin policy. However, this round-robin based sector selection results in inefficient channel utilization when the traffic generated across the sectors is non-uniform. In this paper, a short-term memory based online learning framework is developed for efficient sector selection by the AP for improving throughput while balancing medium access delay and average queue size at the STAs. The performance of the proposed optimal sector selection policy is compared with the traditional round-robin based sector selection and random sector selection policies. From the performance analysis, it is observed that the proposed sector allocation framework improves the throughput by 51% and 112% when compared with round-robin and random sector allocation policies, respectively. © 2020 IEEE.

2020 IEEE Sensors Applications Symposium, SAS 2020 - Proceedings

Short-Term Memory Based Online Learning Framework for Intelligent Sector Selection in IEEE 802.11ad

This article reports the fabrication of a dual-ion beam sputtering (DIBS)-grown MgZnO/CdZnO (MCO)-based gateless heterostructure field-effect transistor (HFET). In addition, this article presents that by introducing a 30-nm yttria spacer layer, the crystallinity of the CdZnO buffer layer can be enhanced and the interface roughness at the heterojunction of the MCO heterostructure can be reduced. Furthermore, the source and drain metal contacts were optimized for the least specific contact resistivity ( \boldsymbol {\rho }_{c} ) yielding metal combination and annealing conditions. The results suggest that the introduction of the yttria spacer layer improves the overall conductance [product of sheet carrier density ( {n}_{s} ) and electron mobility ( \boldsymbol {\mu } )] of MCO up to 3.5\times 10^{15}\,\,\text{V}^{-1}\text{s}^{-1} compared to 9\times 10^{14}\,\,\text{V}^{-1}\text{s}^{-1} in the non-yttria spacer-based MCO. In addition, the drain current ( {I}_{d} )-drain voltage ( {V}_{d} ) characteristic of the as-developed yttria spacer-based MCO HFET shows a high drain current value (400 mA/mm). These results establish the DIBS-grown MCO heterostructure as a viable option for low-cost HFETs necessary for the fabrication of large-scale HFET-based power and sensor devices. © 1963-2012 IEEE.

IEEE Transactions on Electron Devices

Drain Current Optimization in DIBS-Grown MgZnO/CdZnO HFET

This paper reports a novel shadow mask aligner, which is capable of aligning planar with ∼1 μm alignment error as well as provision to compensate the wedge error by using movements of three precision linear actuators, spotted under optical microscope. The use of three points leveling also overcomes the common error of the upper assembly bending, which could occur with time after its continuous use. The reported wafer/mask holding mechanism is able to accommodate substrates of 3′ to 6′ diameter. The unique magnetic clamping mechanism after alignment has been successfully demonstrated. The fabricated system is useful for alignment of mask and wafer, as well as for other applications like nano-imprint and micro-contact printing lithography. In these cases, moulds/stamp is aligned with the patterned/un-patterned target substrate; to create complex 3D structures microassembly of independently fabricated 2D components by proper aligning and clamping. © 2020 IOP Publishing Ltd.

Engineering Research Express

A novel shadow mask aligner based on three points levelling for wedge error compensation

Single-walled carbon nanotubes (SWNTs) are incorporated in different device configurations such as chemiresistors and field-effect transistors (FETs) as a sensing element for the fabrication of highly sensitive and specific biochemical sensors. For this purpose, sorting and aligning of semiconducting SWNTs between the electrodes is advantageous. In this work, a silicon shadow mask fabricated using conventional semiconductor processes and silicon bulk micromachining was used to make metal contacts over SWNTs with a minimum feature of 1 μm gap between the electrodes. The developed silicon shadow mask-based metal contact patterning process is cost-effective and free from photoresist (PR) chemical coatings and thermal processing. After a detailed investigation, sodium dodecyl sulfate (SDS), an anionic surfactant, along with ultrasonication process, was found to be effective for the removal of unclamped and metallic SWNTs, resulting in aligned and clamped semiconducting SWNTs between the electrodes. The presence of aligned semiconducting SWNTs was confirmed using atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), and Raman spectroscopy techniques. The fabricated devices were tested for nitrogen dioxide (NO2) gas sensing as a test case. The sensitivity enhancement of ∼21 to 76% in the 20-80 ppm NO2 concentration range has been observed in the case of aligned semiconducting SWNT devices compared to the random network SWNT-based sensors. © 2020 American Chemical Society.