29 results on '"Kumar, Mahesh"'
Search Results
2. Electrode optimization for improved dielectrophoretic separation of microparticles.
- Author
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Kumar, Mahesh, Gupta, Anmol, Mishra, Abhikrishn, Saxena, Ankur, Kumar, Ashish, and Singh, Kulwant
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DIELECTROPHORESIS , *PARTICLE motion , *CELL separation , *FINITE element method , *ELECTRODES , *DATA extraction - Abstract
Microparticle motion manipulation for effective separation is of great importance and plays major role in understanding micro-entities behavior in fluid. Study on microparticle give great insight on biological cell separation, metal isolation, pathogenic analysis for data extraction. In this work, finite element modeling of microfluidic microparticle cell sorter chip for analysis of the polystyrene particle motion manipulation based on their size. The work focuses on optimization of micro-pointed electrode geometry for separation of three different size polystyrene particle size (3 µm, 6 µm, and 9 µm). Higher separation yield and purity (99.4 and 99.8) is achieved with low micro-point angle of electrodes. [ABSTRACT FROM AUTHOR]
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- 2023
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3. Biomimetic micropump: Leveraging a novel propagative rhythmic membrane function.
- Author
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Kumar, Mahesh, Mansukhani, Jaikishan, Tripathy, Arijeet, and Mondal, Pranab Kumar
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BIOMIMETIC materials , *TRANSPORT equation , *FLOW velocity , *ELECTROMAGNETIC fields , *MICROFLUIDICS , *KINEMATICS - Abstract
We discuss bioinspired pumping mechanism in a microfluidic configuration, consistent with the newly formulated propagative rhythmic contraction–expansion of a membrane attached to the channel wall. We aptly demonstrate the kinematics of the proposed membrane function and describe the wall profile developed due to the propagative expansion–contraction phases of the actuation cycle. The transport equations governing the flow dynamics are solved analytically in the purview of the lubrication theory. An analysis of the proposed model establishes that the fluidic functionality of a channel equipped with a single elastic membrane that operates following the propagation expansion-contraction modes can produce a unidirectional flow, and acts as a micropump in the process. By depicting the flow velocity, velocity contours, and streamlines patterns in the flow pathway, we discuss and demonstrate the eventual consequence of these flow parameters to the net throughput during both the compression and expansion phases of the process. We establish the efficacy of the novel membrane function by demonstrating augmented net throughput obtained from the proposed configuration. The membrane function developed in this endeavor will provide greater flexibility to the researchers to carry out further research in the field and will make the underlying analysis even easier in systems that utilize electromagnetic fields in the flow system. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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4. Bejan's flow visualization of buoyancy-driven flow of a hydromagnetic Casson fluid from an isothermal wavy surface.
- Author
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Kumar, Mahesh and Mondal, Pranab Kumar
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BUOYANCY-driven flow , *NONLINEAR differential equations , *FREE convection , *FLOW visualization , *FLOW velocity , *PARTIAL differential equations , *FLUID flow - Abstract
The proposed work numerically investigates the buoyancy-driven flow of Casson fluid from a vertical wavy surface under the influence of a magnetic field and evaluates the underlying transport of heat in the free convective regime both quantitatively and qualitatively. Pertaining to this analysis, the primitive forms of coupled non-linear partial differential equations are evaluated with the help of an efficient and straightforward Crank–Nicolson implicit finite difference technique. By representing the graphical plots of flow velocity, temperature, and friction-factor coefficients, obtained for different physical parametric values pertinent to this analysis, we discuss the influence of the Hartmann number, surface waviness parameter, and rheological parameter of the fluid on the underlying thermohydrodynamics. In addition to the isotherm and streamline plots, by demonstrating the functional form, we discuss an extensive flow visualization technique that provides unique heat flow visualization for the wavy surface based on Bejan's heat function concept. The results indicate that for increasing the magnitude of the magnetic parameter, the evolution of isotherms, streamlines, and heatlines deviates periodically with a higher amplitude, which signifies the transfer of high heat energy as well as the efficient transport of heat in the convective regime. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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5. Detection of cadmium ions Byg-C3N4 functionalization on AlGaN/GaN high electron mobility transistor.
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Nigam, Adarsh, Kumar, Mahesh, Sharma, Veerendra K., Prajapat, C. L., and Yusuf, S. M.
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MODULATION-doped field-effect transistors , *NITRIDES , *CADMIUM , *IONS - Abstract
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. [ABSTRACT FROM AUTHOR]
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- 2020
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6. Resistance-driven low power H2S sensors based on MWCNT@CuO heterojunction.
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Kumar, Sumit, Mitra, Rahul, Barala, Suraj, Kumar, Ashok, Kwoka, Monika, Biswas, Krishnau, and Kumar, Mahesh
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METAL oxide semiconductors , *MULTIWALLED carbon nanotubes , *GAS detectors , *X-ray photoelectron spectroscopy , *PORE size distribution - Abstract
Low power, high sensitivity, and selectivity chemiresistive gas sensors are in urgent demand for hydrogen sulfide (H2S) detection to protect human health and the world's ecosystem. In this study, multiwalled carbon nanotubes (MWCNTs) and copper oxide (CuO) submicrometer size particles' compositions were utilized to fabricate low-temperature H2S gas sensors, which were prepared using a screen-printing technique on inter-digited patterned SiO2/Si substrates. The heterostructure of MWCNT@CuO was confirmed through high-resolution transmission electron microscopy analysis and x-ray diffraction patterns. The x-ray photoelectron spectroscopy analysis reveals the chemical states, binding energies, and oxygen vacancy (Ov). Brunauer–Emmett–Teller analysis of nitrogen physisorption analysis was conducted on the samples to analyze sensor surface areas and pore size distribution. The as-fabricated MWCNT@CuO sensor shows a relative response (ΔR/R%) of 73% toward 10 ppm H2S at 50 °C temperature in a selective manner, which is 1.6 times higher than that of devices based on bare CuO. The MWCNT@CuO interface modifies the morphology and also constructs a p–p heterojunction. This leads to the reforming of the band structure and results in a low resistance of the matrix, as well as a high chemisorbed oxygen content. The use of metal oxide semiconductors with MWCNTs offers a promising approach for the development of high-performance gas sensors that are energy-efficient. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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7. Investigating bifunctional linker-assisted photocatalytic behavior of Ag–TiO2 nanocomposites.
- Author
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Saroha, Jyoti, Semalti, Pooja, Tanwar, Praveen, Kumar, Mahesh, and Sharma, Shailesh Narain
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CHARGE transfer , *CHARGE exchange , *THIOGLYCOLIC acid , *PHOTODEGRADATION , *PHOTOCATALYSTS - Abstract
Linker-assisted Ag-TiO2 nanocomposite (NC)-based photocatalysts have been successfully synthesized using thioglycolic acid (TGA) and 3-mercaptopropionic acid (MPA) as bifunctional linker molecules (LMs). The Ag–LMs–TiO2 composites showed greatly improved photocatalytic performance for the degradation of an organic dye mixture under direct sunlight over bare Ag–TiO2 NCs. The efficiencies estimated from the degradation curves for Ag–TiO2, Ag–MPA–TiO2, and Ag–TGA–TiO2 are found to be 82.9%, 90.2%, and 96.1%, respectively. Compared to Ag–MPA–TiO2, Ag–TGA–TiO2 NCs exhibit an enhanced photocatalytic activity, which can be attributed to the TGA molecule's shorter chain length and, hence, faster and more charge transfer, which is duly confirmed by photoluminescence (PL) quenching and TRPL decay curves. Furthermore, higher Stern–Volmer quenching constant values (Ksv) have been obtained for Ag–TGA–TiO2 NCs compared to the bare Ag–TiO2 and Ag–MPA–TiO2 NCs from the PL quenching and estimated Ksv values for Ag–TiO2, Ag–MPA–TiO2, and Ag–TGA–TiO2 are 1400, 1950, and 2560 l−1, respectively. Interestingly, the Ag–TGA–TiO2 recycling analysis confirmed high stability and fast photodegradation up to 40 cycles. From the obtained results, it is concluded that the interfacial electron transfer kinetics in Ag–LM–TiO2 assemblies rely on the length of the alkyl-containing molecular linkers; the shorter the length, the more the charge transfer will be, thereby improving the photocatalytic behavior of the NCs. [ABSTRACT FROM AUTHOR]
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- 2024
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8. Response to "Comment on 'Bejan's flow visualization of buoyancy-driven flow of a hydromagnetic Casson fluid from an isothermal wavy surface'" [Phys. Fluids 33, 129101 (2021)].
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Kumar, Mahesh and Mondal, Pranab Kumar
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BUOYANCY-driven flow , *FLOW visualization , *FLUIDS , *NEWTONIAN fluids , *SHEAR (Mechanics) , *DYNAMIC viscosity - Abstract
(4) and (5) of our research article,[1] are written for the Casson fluid model with an assumption of incompressible flow with constant viscosity fluid. Response to "Comment on 'Bejan's flow visualization of buoyancy-driven flow of a hydromagnetic Casson fluid from an isothermal wavy surface'" [Phys. Kumar and P. K. Mondal, " Bejan's flow visualization of buoyancy-driven flow of a hydromagnetic Casson fluid from an isothermal wavy surface", Phys. [Extracted from the article]
- Published
- 2021
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9. Propagative-rhythmic membrane contraction modulated efficient micropumping of non-Newtonian fluids.
- Author
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Mansukhani, Jaikishan, Tripathy, Arijeet, Kumar, Mahesh, and Mondal, Pranab Kumar
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STOKES flow , *FLOW velocity , *TRANSPORT equation , *FLUID flow , *NON-Newtonian fluids , *COMPLEX fluids , *NON-Newtonian flow (Fluid dynamics) - Abstract
We here discuss a novel bioinspired pumping mechanism of non-Newtonian fluids in a microfluidic configuration, consistent with the propagative rhythmic contraction–expansion of a membrane attached to the wall of the fluidic channel. We consider the Rabinowitsch model to represent the rheology of non-Newtonian fluids. By employing lubrication theory and approximating the underlying flow to be in the creeping regime, the transport equations governing the pumping process are framed pertaining to the chosen setup. The transport equations are then evaluated by employing a well-established perturbation technique. By depicting the flow velocity components, streamline patterns, and velocity contours graphically, we aptly discuss the flow structure developed in the flow pathway and demonstrate the eventual consequence of these flow parameters to the net throughput during both compression and expansion phases of the pumping process. Finally, by demonstrating a phase-space diagram, we also discuss the impact of fluid rheology and membrane kinematics on the pumping capacity. The results obtained from the proposed model establish that the net flow owing to propagative rhythmic membrane contraction strongly relies on exponent parameter M and rheological parameter β. These consequences are expected to be of substantial practical relevance in designing micropumps intended to yield unidirectional flow of the complex fluids with improved efficiency, commonly used in biochemical/biomicrofluidic applications. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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10. Design and performance evaluation of video conferencing as a web application.
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Bahl, Isha, Aggarwal, Shubhangi, Agarwal, Sidharth, and Kumar, Mahesh
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VIDEOCONFERENCING , *TELECONFERENCING , *WEB-based user interfaces , *STREAMING video & television , *COMPUTER software installation , *DIGITAL communications , *ARCHITECTURAL acoustics - Abstract
In this technology driven era, effective communication is the backbone for success of any business. In Post- Covid times, effective and engaging digital communications have become integral part of our day to day lives ranging from basic online learning and education delivery to complex remote health care management. This increasing demand has given rise to introduction of many tools to support video conferencing solutions. Many of these tools have limitation that they require dedicated hardware resources and installation of software at client and host end. Increasing use of communication tools inspire us to explore the concept of video conferencing in more depth. The motivation for undertaking this research work is to develop a light-weight chat tool that facilitates peer-peer communication with minimal resources. In simple terms, just a simple web browser at both ends shall be enough to enhance user engagement with customized video calling experiences. Furthermore, many additional attributes like user login authentication, screen recording, screen sharing, text chat, multiuser chat, room management, audio/video controls have been integrated in developed tool. We also performed the performance evaluation of communication quality using various image/video quality measuring metrics like PSNR (Peak signal-to-noise ratio), SSIM (structural similarity index measure) and VMAF (Video Multi-method Assessment Fusion). Our results depict that with the joining of 2nd and 3rd video stream other than the room creator, the PSNR, SSIM and VMAF values are 28.55, 94.84, 61.24 and 26.24, 93.74, 51.62 respectively. The reduction in PSNR and other video quality metrics is observed due the fact that with addition of each user a noise element is inducted in the communicating system. A holistic performance analysis was also performed using different types of browsers and also varying room-sizes. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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11. NoonGil: AI assistance for the visually impaired.
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Raj, K. Ishwari, Gaur, Kaamya, Singh, Prabhdeep, and Kumar, Mahesh
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OPTICAL character recognition , *NATURAL language processing , *PEOPLE with visual disabilities , *ARTIFICIAL intelligence , *CONVOLUTIONAL neural networks , *STANDARD of living - Abstract
Technologies focusing on the visually impaired play an important role in assisting the visually challenged and easing their living standards. Previously there have been several other technologies and papers proposed under this category to help the visually challenged. Applications have been built, and are being developed, to help these people work independently without anybody else's need and complete daily tasks easily, without any difficulty using Artificial Intelligence. The proposed application, Noon Gil, supports voice commands and performs operations accordingly using architectures and algorithms like The technologies used are Optical Character Recognition (OCR), Convolutional Neural Networks (CNNs), Natural Language Processing (NLP), Mobile Vision API, TensorFlow Lite, Google ML Kit, MobileNet SSD, etc. Our project which is an android application with an overall accuracy of 94.74% comprises three main functions: Text Detection with an accuracy of 90.83%, Object Detection with 94.40% accuracy and barcode scanning with 99%. [ABSTRACT FROM AUTHOR]
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- 2024
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12. Determination of band alignment at two-dimensional MoS2/Si van der Waals heterojunction.
- Author
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Goel, Neeraj, Kumar, Rahul, Mishra, Monu, Gupta, Govind, and Kumar, Mahesh
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HETEROJUNCTIONS , *VAN der Waals forces , *RAMAN spectroscopy , *MOLYBDENUM compounds , *ACTIVATION energy , *CHEMOMETRICS , *ENERGY bands , *CRYSTALLOGRAPHY - Abstract
To understand the different mechanism occurring at the MoS2-silicon interface, we have fabricated a MoS2/Si heterojunction by exfoliating MoS2 on top of the silicon substrate. Raman spectroscopy and atomic force microscopy (AFM) measurement expose the signature of few-layers in the deposited MoS2 flake. Herein, the temperature dependence of the energy barrier and carrier density at the MoS2/Si heterojunction has been extensively investigated. Furthermore, to study band alignment at the MoS2/Si interface, we have calculated a valence band offset of 0.66 ± 0.17 eV and a conduction band offset of 0.42 ± 0.17 eV using X-ray and Ultraviolet photoelectron spectroscopy. We determined a type-II band alignment at the interface which is very conducive for the transport of photoexcited carriers. As a proof-of-concept application, we extend our analysis of the photovoltaic behavior of the MoS2/Si heterojunction. This work provides not only a comparative study between MoS2/p-Si and MoS2/n-Si heterojunctions but also paves the way to engineer the properties of the interface for the future integration of MoS2 with silicon. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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13. Modulation of Pb chemical state of epitaxial lead zirconate titanate thin films under high energy irradiation.
- Author
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Singh Barala, Surendra, Roul, Basanta, Banerjee, Nirupam, and Kumar, Mahesh
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ELECTROMETALLURGY , *LEAD , *EPITAXY , *EPITAXIAL layers , *LEAD zirconate titanate films , *IRRADIATION - Abstract
The chemical states of epitaxial PbZrxTi1-xO3 films were investigated by an X-ray photoelectron spectroscopy as a function of the gamma-ray doses. An anomalous behaviour was observed in Pb4f states, and a core level of Pb4f shifts towards a higher binding energy at 50 kGy and towards a lower binding energy at 200 kGy. The behaviour can be explained by a radiation induced reduction of PbO to metallic Pb. The metal-insulator-metal electrodes were fabricated by lithography, and the current-voltage characteristics were measured. A negative differential resistance (NDR) was observed in the leakage currents at room temperature. A higher current and disappearance of NDR characteristics were found in the 200 kGy irradiated samples, which further confirms the presence of metallic Pb. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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14. Charge carrier dynamics and surface plasmon interaction in gold nanorod-blended organic solar cell.
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Rana, Aniket, Gupta, Neeraj, Lochan, Abhiram, Sharma, G. D., Chand, Suresh, Kumar, Mahesh, and Singh, Rajiv K.
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CHARGE carriers , *SURFACE plasmons , *NANORODS , *SOLAR cells , *SURFACE plasmon resonance , *POPULATION density - Abstract
The inclusion of plasmonic nanoparticles into organic solar cell enhances the light harvesting properties that lead to higher power conversion efficiency without altering the device configuration. This work defines the consequences of the nanoparticle overloading amount and energy transfer process between gold nanorod and polymer (active matrix) in organic solar cells. We have studied the hole population decay dynamics coupled with gold nanorods loading amount which provides better understanding about device performance limiting factors. The exciton and plasmon together act as an interacting dipole; however, the energy exchange between these two has been elucidated via plasmon resonance energy transfer (PRET) mechanism. Further, the charge species have been identified specifically with respect to their energy levels appearing in ultrafast time domain. The specific interaction of these charge species with respective surface plasmon resonance mode, i.e., exciton to transverse mode of oscillation and polaron pair to longitudinal mode of oscillations, has been explained. Thus, our analysis reveals that PRET enhances the carrier population density in polymer via non-radiative process beyond the concurrence of a particular plasmon resonance oscillation mode and polymer absorption range. These findings give new insight and reveal specifically the factors that enhance and control the performance of gold nanorods blended organic solar cells. This work would lead in the emergence of future plasmon based efficient organic electronic devices. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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15. Schottky-contacted vertically self-aligned ZnO nanorods for hydrogen gas nanosensor applications.
- Author
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Ranwa, Sapana, Kumar, Mohit, Singh, Jitendra, Fanetti, Mattia, and Kumar, Mahesh
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MAGNETIC properties of nanorods , *NANOSENSORS , *SCANNING electron microscopy , *SCHOTTKY barrier , *ELECTRICAL engineering - Abstract
Vertically well aligned ZnO nanorods (NRs) were grown on Si(100) substrate using RF magnetron sputtering technique. Scanning electron microscopy images confirms uniform distribution of NRs on 2 in. wafer with average diameter, height and density being ~75 nm, ~850 nm, and ~1.5 × 1010 cm-2, respectively. X-ray diffraction reveals that the ZnO NRs are grown along c-axis direction with wurtzite crystal structure. Cathodoluminescence spectroscopy, which shows a single strong peak around 3.24 eV with full width half maxima 130 meV, indicates the high crystalline and optical quality of ZnO and very low defect density. Vertically aligned nanosensors were fabricated by depositing gold circular Schottky contacts on ZnO NRs. Resistance responses of nanosensors were observed in the range from 50 to 150 °C in 1% and 5% hydrogen in argon environment, which is below and above the explosive limit (4%) of hydrogen in air. The nanosensor's sensitivity increases from 11% to 67% with temperature from 50 to 150 °C and also shows fast response time (9-16 s) and moderate recovery time (100-200 s). A sensing mechanism is proposed based on Schottky barrier changes at heterojunctions and change in depletion region of NRs. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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16. Write-once-read-many-times resistive switching behavior of amorphous barium titanate based device with very high on-off ratio and stability.
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Shringi, Amit Kumar, Betal, Atanu, Sahu, Satyajit, and Kumar, Mahesh
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METAL-insulator-metal structures , *GLASS coatings , *COMPUTER storage devices , *RECORDS management , *THIN films , *BARIUM titanate - Abstract
Write once read many times (WORM) memory devices based on the resistive switching mechanism of a sputtered amorphous BaTiO3 (am-BTO) thin film in a metal–insulator–metal structure is fabricated on a FTO coated glass substrate with a silver top contact. Fabricated devices show the switching from a low-conductance state to a high-conductance state with the formation of conductive filament(s) in the am-BTO layer. The memory characteristics are investigated as a function of thickness of am-BTO layer, which is determined by varying the deposition time. Devices with all deposited thicknesses show data retention for more than 4000 s and 300 reading cycle. Devices with 180 nm thickness show a high on-off ratio on the order of 106. The fabricated WORM devices exhibit good reading-endurance and data-retention characteristics. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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17. Ultrafast excited-state dynamics of SnSe2–SnSe composite thin film.
- Author
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Kumar, Manoj, Sharma, Prince, Rani, Sanju, Kumar, Mahesh, and Singh, V. N.
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THIN films , *OPTICAL spectroscopy , *ULTRAVIOLET-visible spectroscopy , *RAMAN spectroscopy , *OPTICAL properties - Abstract
We report the ultrafast carrier dynamics of an SnSe2–SnSe composite thin film (∼150 nm thick) deposited using thermal evaporation of in-house synthesized SnSe2 powder. Raman and UV–visible spectroscopy supports the optical properties (direct and indirect bandgaps of 1.86 eV and 0.96 eV, respectively). Ultrafast transient spectroscopy is used to study the charge excited state dynamics in the SnSe2–SnSe composite thin film in the femtosecond to nanosecond interval. An energy model has been proposed based on the ultrafast transient absorption and the thin film's steady-state absorption studies. This article provides comprehensive knowledge about the excited carriers and their relaxations in 0.9 ps–31.1 ns via different trap states. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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18. NO2 sensing at room temperature using vertically aligned MoS2 flakes network.
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Kumar, Rahul, Goel, Neeraj, Kumar, Mahesh, Singh, Biswas, and Das
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CHEMICAL vapor deposition , *SURFACE morphology , *NITROGEN dioxide , *MOLYBDENUM sulfides , *DETECTORS - Abstract
To exploit the role of alignment of MoS2 flake in chemical sensing, here, we have synthesized the horizontally and vertically aligned MoS2 flake network using conventional chemical vapor deposition technique. The morphology and number of layers were confirmed by SEM and Raman spectroscopy, respectively. The sensing performance of horizontally aligned and vertically aligned flake network was investigated to NO2 at room temperature. Vertically aligned MoS2 based sensor showed higher sensitivity ~51.54 % and ~63.2 % compared to horizontally aligned MoS2 sensor’ sensitivity of ~35.32 % and ~45.2 % to 50 ppm and 100 ppm NO2, respectively. This high sensitivity attributed to the high aspect ratio and high adsorption energy on the edge site of vertically aligned MoS2. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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19. Enhanced sensing response with complete recovery of MoS2 sensor under photoexcitation.
- Author
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Goel, Neeraj, Kumar, Rahul, Kumar, Mahesh, Singh, Biswas, and Das
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MOLYBDENUM disulfide , *SEMICONDUCTORS , *GAS detectors , *NITROGEN dioxide , *ELECTRONIC excitation - Abstract
Molybdenum disulfide (MoS2), a just three atoms thick semiconductor has opened up new avenues in gas sensing because of its high surface–to-volume ratio. However, the low sensitivity, incomplete recovery and poor selectivity at room temperature restricts its uses for practical gas sensors. Here, we report a facile strategy to develop highly sensitive, extremely selective and fully recoverable gas sensor at room temperature through photo excitation. Although, pristine MoS2 gas sensor showed a considerable response and incomplete recovery to NO2 at room temperature. Though after photo excitation, the MoS2 sensor exhibited an improved response along with the complete recovery upon NO2 exposure. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
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20. Highly sensitive H2 gas sensor of Co doped ZnO nanostructures.
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Bhati, Vijendra Singh, Ranwa, Sapana, Kumar, Mahesh, Singh, Biswas, and Das
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ZINC oxide , *NANOSTRUCTURES , *MAGNETRON sputtering , *CHEMICAL reactions , *PHYSICAL vapor deposition - Abstract
In this report, the hydrogen gas sensing properties based on Co doped ZnO nanostructures are explored. The undoped and Co doped nanostructures were grown by RF magnetron sputtering system, and its structural, morphological, and hydrogen sensing behavior are investigated. The maximum relative response was occurred by the 2.5% Co doped ZnO nanostructures among undoped and other doped sensors. The enhancement of relative response might be due to large chemisorbed sites formation on the ZnO surface for the reaction to hydrogen gas. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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- View/download PDF
21. High performance NO2 sensor using MoS2 nanowires network.
- Author
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Kumar, Rahul, Goel, Neeraj, and Kumar, Mahesh
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NANOWIRES , *CRYSTAL structure , *SURFACE morphology , *NITROGEN dioxide , *NANOSTRUCTURED materials - 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 4.6 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 at the intersections of nanowires during adsorption/desorption of gas molecules. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
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22. Revealing charge carrier dynamics in squaraine:[6, 6]-phenyl-C 71-butyric acid methyl ester based organic solar cells.
- Author
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Rana, Aniket, Sharma, Chhavi, Prabhu, Deepak D., Kumar, Mahesh, Karuvath, Yoosaf, Das, Suresh, Chand, Suresh, and Singh, Rajiv K.
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SOLAR cells , *SQUARAINES , *METHYL formate - Abstract
Ultrafast charge carrier dynamics as well as the generation of polaron pair in squaraine (SQ) and squaraine:[6,6]-phenyl-C 71-butyric acid methyl ester (SQ:PCBM71) have been studied using ultrafast transient absorption spectroscopy (UTAS). The current study reveals that the pure SQ exhibits the creation of singlet and triplet states; however, incorporation of PCBM71 in SQ results in the formation of polaron pairs with ∼550ps lifetime, which in turn leads to the creation of free electrons in the device. We show that the considerable increment in monomolecular and bimolecular recombination in SQ:PCBM71 compared to pure SQ which describes the interfacial compatibility of SQ and PCBMC71 molecules. The present work not only provides the information about the carrier generation in SQ and SQ:PCBM71 but also gives the facts relating to the effect of PCBM71 mixing into the SQ which is very significant because the SQ has donor-acceptor-donor (D-A-D) structure and mixing one more acceptor can introduce more complex recombinations in the blend. These findings have been complimented by the charge transport study in the device using impedance spectroscopy. The various important transport parameters are transit time (τt), diffusion constant (Dn), global mobility (μ) and carrier lifetime (τr). The values of these parameters are 26.38 μs, 4.64x10-6 cm2s-1, 6.12x10-6 cm2V-1s-1 and 399 μs, respectively. To the best of our knowledge such study related to SQ is not present in the literature comprehensively. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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- View/download PDF
23. Fast detection and low power hydrogen sensor using edge-oriented vertically aligned 3-D network of MoS2 flakes at room temperature.
- Author
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Agrawal, A. V., Kumar, R., Venkatesan, S., Zakhidov, A., Zhu, Z., Jiming Bao, Kumar, Mahesh, and Kumar, Mukesh
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HYDROGEN detectors , *GAS detectors , *HYDROGEN absorption & adsorption , *CHEMICAL detectors , *DETECTORS - Abstract
The increased usage of hydrogen as a next generation clean fuel strongly demands the parallel development of room temperature and low power hydrogen sensors for their safety operation. In this work, we report strong evidence for preferential hydrogen adsorption at edge-sites in an edge oriented vertically aligned 3-D network of MoS2 flakes at room temperature. The vertically aligned edge-oriented MoS2 flakes were synthesised by a modified CVD process on a SiO2/Si substrate and confirmed by Scanning Electron Microscopy. Raman spectroscopy and PL spectroscopy reveal the signature of few-layer MoS2 flakes in the sample. The sensor's performance was tested from room temperature to 150 °C for 1% hydrogen concentration. The device shows a fast response of 14.3 s even at room temperature. The sensitivity of the device strongly depends on temperature and increases from ~1% to ~11% as temperature increases. A detail hydrogen sensing mechanism was proposed based on the preferential hydrogen adsorption at MoS2 edge sites. The proposed gas sensing mechanism was verified by depositing ~2-3 nm of ZnO on top of the MoS2 flakes that partially passivated the edge sites. We found a decrease in the relative response of MoS2-ZnO hybrid structures. This study provides a strong experimental evidence for the role of MoS2 edge-sites in the fast hydrogen sensing and a step closer towards room temperature, low power (0.3 mW), hydrogen sensor development. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
24. Luminescent GdVO4:Sm3+ quantum dots enhance power conversion efficiency of bulk heterojunction polymer solar cells by Förster resonance energy transfer.
- Author
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Bishnoi, Swati, Gupta, Vinay, Sharma, Chhavi, Haranath, D., Naqvi, Sheerin, Kumar, Mahesh, Sharma, Gauri D., and Chand, Suresh
- Subjects
- *
QUANTUM dots , *HETEROJUNCTIONS , *SOLAR cells , *FLUORESCENCE resonance energy transfer , *SAMARIUM - Abstract
In this work, we report enhanced power conversion efficiency (PCE) of bulk heterojunction polymer solar cells by Förster resonance energy transfer (FRET) from samarium-doped luminescent gadolinium orthovanadate (GdVO4:Sm3+) quantum dots (QDs) to polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) polymer. The photoluminescence emission spectrum of GdVO4:Sm3+ QDs overlaps with the absorption spectrum of PTB7, leading to FRET from GdVO4:Sm3+ to PTB7, and significant enhancements in the charge-carrier density of excited and polaronic states of PTB7 are observed. This was confirmed by means of femtosecond transient absorption spectroscopy. The FRET from GdVO4:Sm3+ QDs to PTB7 led to a remarkable increase in the power conversion efficiency (PCE) of PTB7:GdVO4:Sm3+:PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester) polymer solar cells. The PCE in optimized ternary blend PTB7:GdVO4:Sm3+:PC71BM (1:0.1:1.5) is increased to 8.8% from 7.2% in PTB7:PC71BM. This work demonstrates the potential of rare-earth based luminescent QDs in enhancing the PCE of polymer solar cells. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
25. Electronic states in spherical GaN nanocrystals embedded in various dielectric matrices: The k·p-calculations.
- Author
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Konakov, A. A., Filatov, D. O., Korolev, D. S., Belov, A. I., Mikhaylov, A. N., Tetelbaum, D. I., and Kumar, Mahesh
- Subjects
- *
ELECTRIC properties of gallium nitride , *SILICON oxide , *NANOCRYSTALS - Abstract
Using the envelope-function approximation, the single-particle states of electrons and holes in spherical GaN nanocrystals embedded in different amorphous dielectric matrices (SiO2, Al2O3, HfO2 and Si3N4) have been calculated. Ground state energies of electrons and holes in GaN nanocrystals are determined using the isotropic approximation of the k · p -Hamiltonian. All the ground state energies are found to increase with lowering the nanocrystal size and are proportional to the R-n, where R is the nanocrystal radius, n =1.5-1.9 for electrons and 1.7-2.0 for holes. The optical gap of GaN nanocrystals changes from 3.8 to 5 eV for the nanocrystal radius ranging from 3 to 1 nm. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
26. Investigation of Chemically Synthesized Graphene as Counter Electrode for Dye Sensitized Solar Cells.
- Author
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Prakash, Shejale Kiran, Sharma, Rakesh K., Roy, Mahesh S., and Kumar, Mahesh
- Subjects
- *
GRAPHENE synthesis , *ELECTRODES , *DYE-sensitized solar cells , *SCREEN process printing , *FABRICATION (Manufacturing) , *AGGLOMERATION (Materials) , *TEMPERATURE effect - Abstract
Graphene was synthesized and used as a counter electrode in place of platinum in dye sensitized solar cells. This study reveals that the graphene synthesized by reduction of graphene oxide still contains functional groups even after reduction. The synthesized graphene counter electrodes were prepared by screen printing fabrication techniques. The influence of temperature variation on the films morphology, crystallinity, and its interfacial adhesiveness to the fluorine doped tin oxide coated glass were studied. Screen printing technique has shown uniform surface, decreased agglomeration of nanoparticles and high film adhesiveness. The screen printed film annealed at 400°C reveals best surface morphology [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
27. Carbon Coated Stainless Steel as Counter Electrode for Dye Sensitized Solar Cells.
- Author
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Prakash, Shejale Kiran, Sharma, Rakesh K., Roy, Mahesh S., and Kumar, Mahesh
- Subjects
- *
CARBON , *STAINLESS steel , *SURFACE coatings , *ELECTRODES , *DYE-sensitized solar cells , *FABRICATION (Manufacturing) , *MULTIWALLED carbon nanotubes - Abstract
A new type of counter electrode for dye sensitized solar cells has been fabricated using a stainless steel sheet as substrate and graphite, graphene and multiwall carbon nanotubes as the catalytic material which applied by screen printing technique. The sheet resistances of the substrates and there influence on the dye sensitized solar cells has been studied. The fabricated counter electrodes i.e. SS-graphite, SS-graphene SS-MWCNT and SS-platinum were tested for their photovoltaic response in the form of dye sensitized solar cells. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
28. Growth of residual stress-free ZnO films on SiO2/Si substrate at room temperature for MEMS devices.
- Author
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Singh, Jitendra, Ranwa, Sapana, Akhtar, Jamil, and Kumar, Mahesh
- Subjects
- *
MAGNETRON sputtering , *SEMICONDUCTORS , *PIEZOELECTRIC devices , *THIN films , *SURFACE morphology - Abstract
ZnO thick Stress relaxed films were deposited by reactive magnetron sputtering on 2"-wafer of SiO2/Si at room temperature. The residual stress of ZnO films was measured by measuring the curvature of wafer using laser scanning method and found in the range of 0.18 x 109 × 11.28 x 109 dyne/cm2 with compressive in nature. Sputter pressure changes the deposition rates, which strongly affects the residual stress and surface morphologies of ZnO films. The crystalline wurtzite structure of ZnO films were confirmed by X-ray diffraction and a shift in (0002) diffraction peak of ZnO towards lower 2θ angle was observed with increasing the compressive stress in the films. The band gap of ZnO films shows a red shift from ~3.275 eV to ~3.23 eV as compressive stress is increased, unlike the stress for III-nitride materials. A relationship between stress and band gap of ZnO was derived and proposed. The stress-free growth of piezoelectric films is very important for functional devices applications. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
29. Defect-free ZnO nanorods for low temperature hydrogen sensor applications.
- Author
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Ranwa, Sapana, Kulriya, Pawan K., Sahu, Vikas Kumar, Kukreja, L. M., and Kumar, Mahesh
- Subjects
- *
NANORODS , *ZINC oxide , *HYDROGEN detectors , *LOW temperatures , *X-ray diffraction , *WURTZITE - Abstract
Uniformly distributed and defect-free vertically aligned ZnO nanorods (NRs) with high aspect ratio are deposited on Si by sputtering technique. X-ray diffraction along with transmission electron microscopy studies confirmed the single crystalline wurtzite structure of ZnO. Absence of wide band emission in photoluminescence spectra showed defect-free growth of ZnO NRs which was further conformed by diamagnetic behavior of the NRs. H2 sensing mechanism based on the change in physical dimension of channel is proposed to explain the fast response (~21.6 s) and recovery times (~27 s) of ZnO NRs/Si/ZnO NRs sensors. Proposed H2 sensor operates at low temperature (~70°C) unlike the existing high temperature (>150°C) sensors. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
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