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.

Effect of annealing on carrier transport properties of GaN-incorporated silicon

Abstract: GaN nanocrystals were formed in a silicon matrix by sequential implantation of Ga+ and N2+ ions followed by either Furnace Annealing (FA) or Rapid Thermal Annealing (RTA). The formation of Ga-rich clusters and Ga–N bonds was confirmed by X-ray photoelectron and photoluminescence spectroscopy. A Schottky top contact and ohmic bottom contact were fabricated and current–voltage (I–V) characteristics of the implanted samples were studied. Current values were found to be higher in RTA samples and lower in FA samples. It is observed that the height of the Schottky barrier strongly depends on the kind of annealing and is found to be 0.65 ± 0.02 eV for FA and 0.56 ± 0.02 eV for RTA compared to the value of 0.61 ± 0.02 eV for the pristine Si sample. A carrier transport mechanism is discussed based on experimental results for both kinds of annealing.

Helium exchange gas based variable temperature insert for cryogen-free magnet system

Abstract: A cryocooler based variable temperature inserts (VTI) has been designed and developed for measurement of physical properties at low temperature and high magnetic field. The VTI, designed using the helium exchange gas principle, needs to be integrated in the warm bore of an existing 6 T cryogen free magnet system. The lowest temperature achieved at the sample is 5 K at 34.5 kPa (~5 psi) gaseous helium environment in the sample space. The equilibrium temperature of the sample, at the vacuum condition, is 8.7 K. The cool-down time of the sample at vacuum environment is 9 hrs whereas it takes 7 hrs in presence of helium exchange gas. The temperature of the sample was varied up to 325 K. The stability of the temperature achieved is less than 50 mK. The cooling and heating curves has been studied to estimate time required for a complete cycle of experiment. This paper will briefly present the design and performance of VTI system in temperature range of 5-325 K.

Childhood Somatoform Disorders and Its Associated Stressors

Abstract: Aim: To study the clinical and socio-demographic profile of somatoform disorders and its associated stressors among pediatric population in a rural setting. Settings and Design: This cross-sectional study was done from Jan 2015 to June 2015 at rural tertiary care teaching hospital. Methods and Materials: Fifty children presenting with physically unexplained symptoms during the study period were assessed. Complete physical and psychiatric assessment was done and diagnosis was made using DSM -IV TR criteria. Patient Health questionnaire-15 (PHQ-15) was used for recording presenting symptoms and severity. Data were analyzed with Statistical Package for social sciences (SPSS 17) and association between different variables was determined using Chi-square test. Results: Male: female ratio was 24:26. Forty-two (84%) of our patients were from rural background. Most common presenting symptom was fainting spells (28%) followed by pain in abdomen (20%). Stressors were elicited in 64% patients and most common stressor was strained interpersonal relations (20%) in family. Females presented with significantly more severe illness (p=0.024). Conclusions: Psychosocial stressors especially interpersonal relations are important factor which needs to be evaluated while encountering patients with somatoform disorder.

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.