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.

Magnetic and electrical resistance behaviour of the oxides, Ca$_{3-x}$Y$_x$LiRuO$_6$ (x= 0.0, 0.5 and 1.0)

Abstract: We have investigated the magnetic and electrical resistance behaviour of Ca$_{3-x}$Y$_x$LiRuO$_6$. The parent compound exhibits magnetic ordering from Ru sublattice at a rather high temperature, 113 K. Though the paramagnetic Curie temperature ($\theta$$_p$) is negative indicative of antiferromagnetic ordering, the large magnitude (-250 K) of $\theta$$_p$ reveals complex nature of the magnetism in this compound. Ru ions appear to be in the pentavalent state. We note that the N\'eel temperature undergoes only a marginal reduction by Y substitution. All these compositions are found to be insulators and thus the electron doping does not result in metallicity. Thus the overall magnetic and transport behaviour are found to be essentially insensitive to Y substitution for Ca, a finding which may favour the idea of quasi-one-dimensional magnetism in these compounds.

Structural Characterization and Ultraviolet Photoresponse of GaN Nanodots Grown by Molecular Beam Epitaxy

Abstract: The present work explores the electrical transport and UV photoresponse properties of GaN nanodots (NDs) grown by molecular beam epitaxy (MBE). Single-crystalline wurtzite structure of GaN NDs is verified by X-ray diffraction and transmission electron microscopy (TEM). The interdigitated electrode pattern was created and current-voltage (I-V) characteristics of GaN NDs were studied in a metal-semiconductor-metal configuration. Dark I-V characteristics of lateral grown GaN NDs obeyed the Frenkel-Poole emission model, and the UV response of the device was stable and reproducible with on/off. The responsivity of the detectors is found to be 330 A/W with an external quantum efficiency of 1100%. (C) 2012 The Japan Society of Applied Physics

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

(7×7) reconstruction as barrier for Schottky-barrier formation at the Ga/Si(111) interface

Abstract: We report the change in electronic properties of the Ga/Si interface by monitoring the Ga(3d) core-level photoelectron spectra and electron diffraction induced by submonolayer Ga adsorption on Si(111)-7×7 surface. The spectra shows a flat band for submonolayer coverages, attributed to the metallic nature of the Si(111)-7×7 reconstruction and a premetallic band structure of two-dimensional Ga islands. At 1 ML, electron diffraction pattern shows metallic (7×7) to semiconducting (1×1) phase-transition and the spin-orbit split branching ratio of Ga(2p) core level attain the metallic bulk value, and the barrier assumes the Schottky–Mott value while full width half maxima and branching ratio attain bulk values.

Modulation of Pb chemical state of epitaxial lead zirconate titanate thin films under high energy 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.

Perspective on the Development of Lead-free Piezoceramics

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.

Room-temperature saturated ferroelectric polarization in BiFeO3 ceramics synthesized by rapid liquid phase sintering

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.

Room-temperature gas sensing of ZnO-based gas sensor: A review

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.