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Mahesh Kumar

Bio: Mahesh Kumar is an academic researcher from Indian Institute of Technology, Jodhpur. The author has contributed to research in topics: Molecular beam epitaxy & Heterojunction. The author has an hindex of 29, co-authored 204 publications receiving 4864 citations. Previous affiliations of Mahesh Kumar include Indian Institutes of Technology & Indian Institute of Technology Delhi.


Papers
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TL;DR: This highly hydrogen selective Pd contacted ZnO nanorods based sensor detecting low concentration even at low operating temperature of 50 °C is reported, which exhibits dual characteristics as metal contact and excellent catalyst to hydrogen molecules.
Abstract: We report highly hydrogen selective Pd contacted ZnO nanorods based sensor detecting low concentration even at low operating temperature of 50 °C. The sensor performance was investigated for various gases such as H2, CH4, H2S and CO2 at different operating temperatures from 50 °C to 175 °C for various gas concentrations ranging from 7 ppm to 10,000 ppm (1%). The sensor is highly efficient as it detects hydrogen even at low concentration of ~7 ppm and at operating temperature of 50 °C. The sensor’s minimum limit of detection and relative response at 175 °C were found 7 ppm with ~38.7% for H2, 110 ppm with ~6.08% for CH4, 500 ppm with ~10.06% for H2S and 1% with ~11.87% for CO2. Here, Pd exhibits dual characteristics as metal contact and excellent catalyst to hydrogen molecules. The activation energy was calculated for all the gases and found lowest ~3.658 kJ/mol for H2. Low activation energy accelerates desorption reactions and enhances the sensor’s performance.

112 citations

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TL;DR: In this paper, RF sputtered Ni-doped ZnO nanostructures for detection of extremely low concentration (1ppm) of hydrogen gas at moderate operating temperature of 75°C.
Abstract: We demonstrate RF sputtered Ni-doped ZnO nanostructures for detection of extremely low concentration (1 ppm) of hydrogen gas at moderate operating temperature of 75 °C. Structural, morphological, electrical and hydrogen sensing behavior of the Ni-doped ZnO nanostructures strongly depends on doping concentration. Ni doping exceptionally enhances the sensing response and reduces the operating temperature of the sensor as compared to undoped ZnO. The major role of the Ni-doping is to create more active sites for chemisorbed oxygen on the surface of sensor and, correspondingly, to improve the sensing response. The 4 at% of Ni-doped ZnO exhibits the highest response (∼69%) for 1% H 2 at 150 °C, which are ∼1.5 times higher than for the undoped ZnO. This is ascribed to lowest activation energy ∼6.47 KJ/mol. Diminishing of the relative response was observed in 6% Ni- doped ZnO due to separation of NiO phase.

92 citations

Journal ArticleDOI
TL;DR: Cui et al. as mentioned in this paper proposed a hybrid MoS2-MoO3 microflower sensor with a low response time (≈19 s) and excellent selectivity toward NO2 against various other gases.
Abstract: DOI: 10.1002/admi.201800071 thin devices. From the past few years, transition metal dichalcogenides (TMDCs) materials analogous to graphene have received captivated attention because of their unconventional mechanical, electrical, physical, and structural properties.[1,2] MoS2, being the frontrunner of TMDC family, has opened up new avenues because of its tunable band gap, a great degree of flexibility, high surface to volume ratio, and its chemical and mechanical robustness.[3,4] Consequently, MoS2 has attained importance in the developement of transistor,[5] water splitting,[6] photodiode,[7] and sensing.[8] MoS2 has also been extensively used as a potential gas-sensing material because of its high selectivity, low detection limit, and having various reactive sites such as sulfur defects, edge sites, and vacancies.[9,10] Nonetheless, incomplete recovery and slow detection to gases at room temperature restrict to MoS2 for practical gas sensing. Moreover, a poor charge transport in MoS2 and an adverse effect of ambiental oxygen and humidity represent the MoS2 limitations for use in advanced applications and must be mitigated.[11,12] In recent years, hybrid MoS2 structures with different morphologies have received considerable attention due to their high sensing performance, exceptional optoelectronic relevance, and potential use in several other low-power applications. For instance, Yin et al. synthesized MoS2–MoO3 hybrid nanomaterial using lithium-exfoliation and as a proof-of-concept this hybrid nanomaterial was used as an active layer for light-emitting diodes.[13] Chen et al. synthesized a strain-gated field effect transistor (FET) hybrid structure consisting of 2D MoS2 flake and 1D ZnO nanowire.[14] A MoS2/SnO2 nanohybrids sensor was reported by Cui et al. for high-performance stable gas sensing in air. Here, the hole injection from SnO2 to MoS2 resulted in better stability of MoS2 toward ambiental oxygen.[15] Chen et al. synthesized a core–shell MoO3–MoS2 nanowires structure to drive a stable hydrogen evolution reaction through a highly efficient mechanism.[16] A partially reduced MoO3 has high conductivity and MoS2 has poor conductivity along particular crystallographic direction. So, MoO3 mitigate the the deficiencies of MoS2 after design a particular architecture. All these investigations depicts that the morphology of the hybrid structures crucially influence A nucleation controlled one-step process to synthesize MoS2–MoO3 hybrid microflowers using vapor transport process and its application in efficient NO2 sensing at room temperature are reported. The morphology and crystal structure of the microflowers are characterized by scanning electron microscope (SEM), Raman, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy techniques. A cathodoluminence mapping reveals that the core of the microflower consists of MoO3, and the flower petals as well as nanosheet are composed of a few layers of MoS2. Further, the MoS2–MoO3 hybrid microflower sensor exhibits a high sensitivity of ≈33.6% with a complete recovery to 10 ppm NO2 at room temperature without any extra stimulus like optical or thermal source. Unlike many earlier reports on MoS2 sensor, this advanced approach shows that the sensor is exhibited a low response time (≈19 s) with complete recovery at room tepmerature and excellent selectivity toward NO2 against various other gases. The efficient conventional sensing of the sensor is attributed to a combination of high hole injection from MoO3 to MoS2 and modulation of a potential barrier at MoS2–MoO3 interface during adsorption/ desorption of NO2. It is believed that the modified properties of MoS2 by such composite could be used for various advanced device applications. Room Temperature Sensors

84 citations

Journal ArticleDOI
TL;DR: In this paper, a high-performance NO2 sensor based on a one dimensional MoS2 nanowire (NW) network was synthesized using chemical transport reaction through controlled turbulent vapor flow.
Abstract: We report on a high-performance NO2 sensor based on a one dimensional MoS2 nanowire (NW) network The MoS2 NW network was synthesized using chemical transport reaction through controlled turbulent vapor flow The crystal structure and surface morphology of MoS2 NWs were confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy Further, the sensing behavior of the nanowires was investigated at different temperatures for various concentrations of NO2 and the sensor exhibited about 2-fold enhanced sensitivity with a low detection limit of 46 ppb for NO2 at 60 °C compared to sensitivity at room temperature Moreover, it showed a fast response (16 s) with complete recovery (172 s) at 60 °C, while sensitivity of the device was decreased at 120 °C The efficient sensing with reliable selectivity toward NO2 of the nanowires is attributed to a combination of abundant active edge sites along with a large surface area and tuning of the potential barrier

83 citations


Cited by
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7,335 citations

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TL;DR: In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented, ranging from atom to phase diagram, and the current development stage in lead free piezoceramics is then critically assessed.
Abstract: A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

2,510 citations

Journal ArticleDOI
TL;DR: In this article, a single-phased ferroelectromagnet BiFeO3 ceramics with high resistivity were synthesized by a rapid liquid phase sintering technique.
Abstract: Single-phased ferroelectromagnet BiFeO3 ceramics with high resistivity were synthesized by a rapid liquid phase sintering technique. Saturated ferroelectric hysteresis loops were observed at room temperature in the ceramics sintered at 880 °C for 450 s. The spontaneous polarization, remnant polarization, and the coercive field are 8.9 μC/cm2, 4.0 μC/cm2, and 39 kV/cm, respectively, under an applied field of 100 kV/cm. It is proposed that the formation of Fe2+ and an oxygen deficiency leading to the higher leakage can be greatly suppressed by the very high heating rate, short sintering period, and liquid phase sintering technique. The latter was also found effective in increasing the density of the ceramics. The sintering technique developed in this work is expected to be useful in synthesizing other ceramics from multivalent or volatile starting materials.

970 citations

Journal ArticleDOI
Ling Zhu1, Wen Zeng1
TL;DR: In this paper, the room-temperature gas sensing properties of ZnO-based gas sensors are comprehensively reviewed, and more attention is particularly paid to the effective strategies that create room temperature gas sensing, mainly including surface modification, additive doping and light activation.
Abstract: Novel gas sensors with high sensing properties, simultaneously operating at room temperature are considerably more attractive owing to their low power consumption, high security and long-term stability. Till date, zinc oxide (ZnO) as semiconducting metal oxide is considered as the promising resistive-type gas sensing material, but elevated operating temperature becomes the bottleneck of its extensive applications in the field of real-time gas monitoring, especially in flammable and explosive gas atmosphere. In this respect, worldwide efforts have been devoted to reducing the operating temperature by means of multiple methods In this communication, room-temperature gas sensing properties of ZnO based gas sensors are comprehensively reviewed. Much more attention is particularly paid to the effective strategies that create room-temperature gas sensing of ZnO based gas sensors, mainly including surface modification, additive doping and light activation. Finally, some perspectives for future investigation on room-temperature gas-sensing materials are discussed as well.

756 citations