Showing papers by "Mahesh Kumar published in 2021"

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

Abstract: 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.

Recent advances in ultrathin 2D hexagonal boron nitride based gas sensors

Abstract: The recent advances in the field of 2D hexagonal boron nitride (hBN) for realizing electronic and optoelectronic devices, including wearable and portable devices, have aroused scientific interest in this ultrathin material for a wide range of applications. Its exceptionally high thermal conductivity and temperature stability make it one of the most promising materials for next-generation high-performance gas sensors. Although a number of review articles on hBN have already been published focusing on its synthesis, properties, and functionalities, however, none of them has made a significant contribution to the field of gas sensing. Hence, in this review, we have analytically summarized the state-of-art advances in hBN based devices with a particular emphasis on gas sensors. Moreover, we have also explained the comprehensive physics of hBN based gas sensors. The recent technological advancements to overcome the inherent properties such as poor surface reactivity and low conductivity have also been thoroughly compiled. Finally, we have discussed some of the prominent challenges faced by hBN technology for developing practical gas sensors.

Ion implantation in β-Ga2O3: Physics and technology

Abstract: Gallium oxide, and in particular its thermodynamically stable β-Ga2O3 phase, is within the most exciting materials in research and technology nowadays due to its unique properties The very high breakdown electric field and the figure of merit rivaled only by diamond have tremendous potential for the next generation “green” electronics enabling efficient distribution, use, and conversion of electrical energy Ion implantation is a traditional technological method used in these fields, and its well-known advantages can contribute greatly to the rapid development of physics and technology of Ga2O3-based materials and devices Here, the status of ion implantation in β-Ga2O3 nowadays is reviewed Attention is mainly paid to the results of experimental study of damage under ion irradiation and the properties of Ga2O3 layers doped by ion implantation The results of ab initio theoretical calculations of the impurities and defect parameters are briefly presented, and the physical principles of a number of analytical methods used to study implanted gallium oxide layers are highlighted The use of ion implantation in the development of Ga2O3-based devices, such as metal oxide field-effect transistors, Schottky barrier diodes, and solar-blind UV detectors, is described together with systematical analysis of the achieved values of their characteristics Finally, the most important challenges to be overcome in this field of science and technology are discussed

Gas sensing materials roadmap.

Abstract: Gas sensor technology is widely utilized in various areas ranging from home security, environment and air pollution, to industrial production. It also hold great promise in non-invasive exhaled breath detection and an essential device in future internet of things. The past decade has witnessed giant advance in both fundamental research and industrial development of gas sensors, yet current efforts are being explored to achieve better selectivity, higher sensitivity and lower power consumption. The sensing layer in gas sensors have attracted dominant attention in the past research. In addition to the conventional metal oxide semiconductors, emerging nanocomposites and graphene-like two-dimensional materials also have drawn considerable research interest. This inspires us to organize this comprehensive 2020 gas sensing materials roadmap to discuss the current status, state-of-the-art progress, and present and future challenges in various materials that is potentially useful for gas sensors.

Development of semiconductor based heavy metal ion sensors for water analysis: A review

Abstract: Heavy metal ions are highly toxic, carcinogens, and non-biodegradable in nature and pollute most water resources that lead to severe health-related issues. It is essential to develop highly sensitive, selective, rapid, and accurate approaches for their detection in water. Semiconducting devices and materials with micro and nanostructures have been featured with fast response time, low power, high sensitivity, low detection limit. This review concisely introduces the recent trends in heavy metal ion sensing with semiconductor devices, including ion-sensitive field-effect transistors (ISFETs) and AlGaN/GaN high electron mobility transistors (HEMTs) and semiconductor materials like graphene, two-dimensional metal dichalcogenides, decorated with different nanoparticles with appropriate functionalization.

Recent advances and prospects in reduced graphene oxide-based photodetectors

Abstract: 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.

Growth and NO2 gas sensing mechanisms of vertically aligned 2D SnS2 flakes by CVD: Experimental and DFT studies

Abstract: Two dimensional chalcogenides and metal sulfide materials with their sensitive surfaces are promising and potential postulant for the purpose of chemical gas sensing as a consequence of extraordinary vast surface area to volume ratio and significant band gap. We demonstrate a highly selective and sensitive NO2 gas sensor using vertically aligned 2D SnS2 flakes, grown by a chemical vapor deposition method in controlled gas flow. The vertically aligned SnS2 flakes were confirmed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. The sensing behaviour of the vertical aligned structures was analyzed for various concentrations of NO2 at different temperatures. The sensor exhibits high gas sensing response (ΔR/R%) of ~164 at 120 °C with 50 ppm of NO2 gas, which is the highest response among the SnS2 based reports. The device shows excellent sensing response at room temperature but poor recovery. The selectivity of the sensor was performed under different gas environments and found highly selective towards NO2 gas, and the results are supported by electronic structure calculations. Based on experimental results and electronic structure calculations, a gas sensing mechanism is proposed. The result indicates that fabricated sensor can be used in air purification industries and in air monitoring.

MoS 2 -PVP Nanocomposites Decorated ZnO Microsheets for Efficient Hydrogen Detection

Abstract: Over the past several decades, metal oxide based gas sensors are widely used for hydrogen gas sensing applications. However, their poor sensitivity and very high value of operating temperature (> 300 °C) pose a severe threat over hydrogen detection due to its highly flammable nature. In recent years, a few strategies have been explored by the researchers to address these formidable challenges faced by the sensing technology. Here, we present MoS2/ZnO hybrid exhibiting higher molecular detection at low operating temperature. The ZnO film was grown using the magnetron sputtering technique, while MoS2-PVP nanocomposites (MoS2-PVP NCs) were synthesized through organic polymer assisted liquid exfoliation process. We examined the sensing performance of various MoS2/ZnO hybrids prepared by the decoration of different concentration MoS2-PVP NCs over the ZnO surface. The decoration of ZnO film through MoS2-PVP NCs increases the effective surface area and the number of active sites for the hydrogen molecules to get adsorbed, hence improved the surface reactivity to gas molecules. Interestingly, a 5 mg/mL MoS2-PVP NCs decorated ZnO sensor showed an improvement of $\sim 8$ times in sensing response as compared to the pristine ZnO based sensor upon 50 ppm hydrogen exposure. The improvement in sensing ability is primarily ascribed to electronic sensitization and spillover effects. Our results establish that the MoS2/ZnO hybrid exhibit superior hydrogen sensing behavior indicating the prominent role of MoS2-PVP NCs in hydrogen detection.

Plasmonic Au Nanoparticles Sensitized MoS₂ for Bifunctional NO₂ and Light Sensing

Abstract: The possibility to synergise two-dimensional (2D) materials with 0D nanoparticles has sparked a surge in high performance futuristic electronic devices. Here, we decorated plasmonic Au nanoparticles on surface of chemical vapor deposition (CVD) grown 2D MoS2 nanosheet and demonstrated bifunctional sensing behaviour within a single device. The plasmonic Au nanoparticles functionalized MoS2 device showed about ~5 times higher sensitivity to NO2 than that of pristine MoS2 at room temperature. The enhanced gas sensing performance was attributed to a combination of Schottky barriers modulation at Au/MoS2 nanointerfaces and catalytic effects upon exposing the gas analyte. In addition, the device also exhibited enhanced photoresponse with a high photo-responsivity of ~17.6 A/W and a moderate detectivity of ~ ${6.6} \times {10}^{11}$ Jones due to enhanced local plasmonic effects. Finally, photons and gas molecules are detected in sequence, which proved that only a single Au-MoS2 device exhibited remarkable bifunctional sensing characteristics. Such excellent bifunctional sensing ability of a single Au-MoS2 device paves the way to integrate the 2D material with plasmonic nanostructures for developing an advanced multifunctional sensor.

Two-dimensional transition metal dichalcogenides and their composites for lab-based sensing applications: Recent progress and future outlook

Abstract: Two-dimensional transition metal dichalcogenides (2D TMDCs) including MoS2, WS2, MoSe2, WSe2, etc., have received significant attention from the worldwide scientists for a variety of novel applications owing to their unique electronic, chemical, optical, and physical properties. This review focuses on the advances in the field of sensing based on 2D TMDCs and their composites. In this context, the recent progress of 2D TMDCs and their composites for lab-based detection of different analytes including heavy metals, biomolecules, hydrogen peroxide, toxic gases, and volatile compounds are discussed. Interaction of analytes with TMDCs and their composite is elucidated in accordance with various sensing mechanisms. Finally, the challenges and future opportunities related to the emerging 2D TMDCs and their composites based sensing devices are also presented.

Mercury (II) Ion Detection using AgNWs-MoS2 Nanocomposite on GaN HEMT for IoT Enabled Smart Water Quality Analysis

Abstract: We have demonstrated a highly sensitive novel platform for real-time detection of Mercury (Hg2+) ions after successfully making silver nanowires (AgNWs)-MoS2 nanocomposite and functionalizing it over ungated AlGaN/GaN high electron mobility transistor (HEMT) The AlGaN/GaN HEMT structures were grown over the sapphire substrate using Molecular Beam Epitaxy AgNWs-MoS2 nanocomposites were optimized for the device functionalization and 1:4 ratio was found highly sensitive for Hg2+ ions The sensor exhibits high sensitivity towards Hg2+ ions of 1604 mA/ppb and calculated its Limit of Detection (LoD) up to the range of 20 ppt The observed sensitivity is highest among previously reported AlGaN/GaN fabricated HEMT based sensors for Mercury (Hg2+) ions detection and is well below the standard permissible limits as set by World Health Organization (WHO) and Environmental Protection Agency (EPA) The enhancement in sensitivity is due to the enhanced surface to volume ratio of AgNW-MoS2 nanocomposite and the highly conductive nature of silver nanowires incorporated in MoS2 Moreover, we also performed sensing on real water samples of tap water and lake water Further, we showed the smart sensing capability of our developed sensor by illustrating the Internet of Things (IoT) enabled system for next-generation heavy metal ion sensing

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

Abstract: 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- $8~\mu \text{L}$ ) onto interdigitated electrodes over ZnO nanostructures. The suggested hydrogen sensor based on POQDs ( $6~\mu \text{L}$ )/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( $6~\mu \text{L}$ )/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.

Davydov Splitting, Resonance Effect and Phonon Dynamics in Chemical Vapor Deposition Grown Layered MoS 2

Abstract: We present comprehensive temperature dependent Raman measurements for chemical vapor deposition grown horizontally aligned layered MoS2in a temperature range of 4-330 K under a resonance condition Our analysis of temperature dependent phonon frequency shift and linewidth suggests a finite role of three and four phonon anharmonic effect We observe Davydov splitting of the out-of-plane (A1g) and in-plane (E2g1) modes for both three layer (3L) and few layer (FL) systems The number of Davydov splitting components are found more in FL compared to 3L MoS2, which suggests that it increases with an increasing number of layers Further, Davydov splitting is analyzed as a function of temperature Temperature evaluation of the Raman spectra shows that the Davydov splitting, especially forA1gmode, is very strong and well resolved at low temperature We observe thatA1gmode shows the splitting at low temperature, whileE2g1mode is split even at room temperature, which suggests a prominent role ofA1gmode in the interlayer interaction at low temperature Further, an almost 60-fold increase in the intensity of the phonon modes at low temperature clearly shows the temperature dependent tuning of the resonance effect

Fabrication of Fast and Reliable Pulse Laser-Ablated ZnO Nanoparticles-Based Formaldehyde Sensor

Abstract: In this article, we report the synthesis techniques of ZnO nanoparticles (NPs) in open air atmosphere by pulse laser ablation (PLA) method using solid ZnO polycrystalline palette followed by fabrication of formaldehyde (HCHO) sensor. The crystalline phase and morphology of the obtained ZnO NPs were studied by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The XRD patterns showed that the NPs were polycrystalline structure with good crystallinity. The FESEM images revealed that the NPs were spherical in shape and loosely agglomerated. The average diameter of the NPs was in the range of 30–43 nm. Moreover, the ZnO NPs-based sensor exhibited excellent formaldehyde sensing performance at a temperature of 350 °C. The sensor exhibited a gas response of about 5.2 toward 300 ppm formaldehyde with 25 s response and 12 s recovery time. Furthermore, the ZnO NPs-based sensor exhibited excellent reliability and reproducibility to formaldehyde. On the other hand, the sensor showed high sensitivity of about 0.2% ppm $^{-{1}}$ to formaldehyde with a 50 ppm lower detection limit. In addition, the sensor showed an excellent linear relationship ( ${R} ^{{2}} = {0.7948}$ ) between the response and the concentration of formaldehyde in the range of 50–400 ppm. This work demonstrates that PLA in open air is a rapid and cost-effective method for synthesizing metal oxide NPs for gas-sensing applications without the need for wet chemical routes.

UV Light Detection Using Resonance Frequency of Piezoelectric Quartz Crystal

Abstract: 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.

Visualization of band offsets at few-layer MoS2/Ge heterojunction.

Abstract: The visualization of band alignment for designing heterostructures between transition metal dichalcogenides and germanium plays a vital role in a deeper understanding of carrier dynamics at the heterointerface. Here, to study the band alignment across the MoS2/Ge heterojunction, we have deposited a wafer-scale highly crystalline few atomic layers MoS2film via a highly controllable and scalable sputtering technique coupled with a post sulfurization process in a sulfur-rich environment. The Raman and XRD spectra of as-fabricated MoS2/Ge heterojunction expose the presence of highly crystalline few atomic layer MoS2on top of Ge substrate. Interestingly, we found a type-II band alignment at the MoS2/Ge heterointerface having valence band, and conduction band offset values of 0.88 and 0.21 eV, which can provide very efficient recombination through spatially confining charge carriers. The calculation of band offset parameters offers a promising way for device engineering across the MoS2/Ge heterojunction interface. Moreover, to demonstrate the practicability of the fabricated heterostructure, we explored the suitability of our device for broadband photodetection applications.

Assessment and Mapping of Available Soil Nutrients using GIS for Nutrient Management in Hot Arid regions of North-Western India

Abstract: Soil fertility assessment and mapping for hot arid regions of Thar Desert in the Indian state of Rajasthan was carried out and on the basis of fertility ratings the soils were classified as low, medium and high. In the present assessment a systematic set of 5655 soil samples across the land use systems viz., rainfed croplands, irrigated croplands and rangelands covering 12 districts of hot arid Rajasthan were collected using global positioning system (GPS). The soil samples were analyzed for pH, electrical conductivity (EC), organic carbon (OC), available phosphorus (P), potassium (K), iron (Fe), zinc (Zn), copper (Cu) and manganese (Mn). Results of the soil analysis revealed that OC is low throughout the region, while available P was low to medium, but generally medium to high in available K. Among the micronutrients, Cu and Mn were adequately supplied in most areas, but Zn and Fe were inadequate in large parts. The spatial variability of OC and available plant nutrients viz., P, K, Fe, Zn, Cu and Mn in hot arid regions of Rajasthan across the land uses in region, has been mapped in a geographic information system (GIS), and their adequacy determined as per the criteria followed in the soil testing laboratories. Spatial distribution maps indicated that about 99.4, 48.7, 11.0, 56.1 and 41.0% of the area are under low availability class for OC, P, K, Zn and Fe, respectively. Present study also showed that the hot arid regions of India not only deficient in individual nutrients but they also suffer from multi-nutrients deficiencies which warrants attention for soil test based integrated plant nutrition system. The wide spread deficiencies of P, Fe and Zn were most revealing; their deficiencies varies with topography, soil type and land management practices. Irrigated croplands were better endowed than other land uses in respect of OC, P, Zn and Cu; rangelands in respect of K and Fe, and rainfed croplands in respect of Mn. With use of information technology tools like GIS and GPS helps in generation of spatial data/maps on distribution of available plant nutrients with which we can precisely use the required input at right place (location specific application of inputs). Information on spatial distribution of available micronutrients enables grouping of the soils into homogenous units for better nutrient management.

Spectrum Selective Narrowband Optical Detectors

Abstract: Optical detection is the basic underlying principle of many optoelectronic systems like image sensors, optical communications, biomedical imaging, motion detection, surveillance, machine vision, etc. Applied research in optoelectronics has invested a lot towards the development of photodetectors with a wide spectral response (UV, visual and IR), as well as narrowband spectrum selective photodetectors for special applications. Spectral discrimination is required for colour-selective detection, but current commercial systems use broadband photodetectors combined with optical filters. This approach increases the complexity of the system and degrades the quality of colour detection. In this article, we explain briefly the basics of photodetectors and a method for tuning the spectral response to achieve filter-free, narrowband photodiodes.

Ion implantation in \b{eta}-Ga2O3: physics and technology

Abstract: Gallium oxide and in particular its thermodynamically stable \b{eta}-Ga2O3 phase is within the most exciting materials in research and technology nowadays due to its unique properties, such as an ultra-wide band gap and a very high breakdown electric field, finding a number of applications in electronics and optoelectronics. Ion implantation is a traditional technological method used in these fields, and its well-known advantages can contribute greatly to the rapid development of physics and technology of Ga2O3-based materials and devices. Here, the current status of ion beam implantation in \b{eta}-Ga2O3 is reviewed. The main attention is paid to the results of experimental study of damage under ion irradiation and the properties of Ga2O3 layers doped by ion implantation. The results of ab initio theoretical calculations of the impurities and defects parameters are briefly presented, and the physical principles of a number of analytical methods used to study implanted gallium oxide layers are highlighted. The use of ion implantation in the development of such Ga2O3-based devices as metal oxide field effect transistors, Schottky barrier diodes, and solar-blind UV detectors, is described together with systematical analysis of the achieved values of their characteristics. Finally, the most important challenges to be overcome in this field of science and technology are discussed.