Bharat Sharma

Bio: Bharat Sharma is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: Graphene & Thin film. The author has an hindex of 14, co-authored 50 publications receiving 520 citations. Previous affiliations of Bharat Sharma include Incheon National University & Indian Institute of Technology Roorkee.

Recent advances on H2 sensor technologies based on MOX and FET devices: A review

Abstract: The importance of metal oxide semiconductor (MOX) and field effect transistor (FET) based sensors has been increasing due to their extended practical applications for gas detection. Various investigations have confirmed that gas sensing characteristics depend on the sensitivity of the metal oxide and catalytic materials. In recent years, hydrogen gas sensor technology has been progressively more capable in practical applications. The propagation velocity of hydrogen flames is high enough to cause severe explosion over an extensive range of 4%–75% H2. Therefore, the use of hydrogen carries a great risk, and the requirement for its leakage detection is imperative in hydrogen generation, transportation, stockpiling, and its utilization. Usage of MOX and FETs has increased tremendously in designing precise hydrogen sensors. Therefore, in this review, the authors have focused on the recent development in MOX and FET based hydrogen sensors. MOX sensors are most widely available as commercialized ones.Also, FET-type gas sensors have many advantages, compared with traditional ones owing to their reduced shape, size, and lower production cost. Nevertheless, the processing parameters and reproducibility need to be enhanced for expanding their applications. In this review, the role of the important sensing parameters, e.g., measurement range, sensitivity, selectivity, response and recovery time, on the sensing mechanism and operation, and the most recent innovation and improvement in MOX and FET sensing technologies are discussed. Finally, we report the sensing techniques, mechanism and factors affecting the sensitivity for MOX and MOSFET type sensors.

Molecular Beam Epitaxy of GaN Nanowires on Epitaxial Graphene

Abstract: We demonstrate an all-epitaxial and scalable growth approach to fabricate single-crystalline GaN nanowires on graphene by plasma-assisted molecular beam epitaxy. As substrate, we explore several types of epitaxial graphene layer structures synthesized on SiC. The different structures differ mainly in their total number of graphene layers. Because graphene is found to be etched under active N exposure, the direct growth of GaN nanowires on graphene is only achieved on multilayer graphene structures. The analysis of the nanowire ensembles prepared on multilayer graphene by Raman spectroscopy and transmission electron microscopy reveals the presence of graphene underneath as well as in between nanowires, as desired for the use of this material as contact layer in nanowire-based devices. The nanowires nucleate preferentially at step edges, are vertical, well aligned, epitaxial, and of comparable structural quality as similar structures fabricated on conventional substrates.

Selective ppb-level NO2 gas sensor based on SnO2-boron nitride nanotubes

Abstract: This paper demonstrated a hybrid SnO2–BNNTs (SnO2 decorated boron nitride nanotubes) for trace ppb-level sensing towards NO2. A facile way is utilized for the synthesis of SnO2–BNNTs in which BNNTs are consistently coated with SnO2 nanoparticles (NPs). The existence of SnO2 NPs onto BNNTs was confirmed by XRD, XPS, FESEM, and TEM. Sensing characteristics of SnO2–BNNTs sensor, including the sensor response, repeatability, long-term stability, and response–recovery times were studied by exposure to several NO2 gas concentrations varying from 250 ppb to 5 ppm at different operating temperatures form 25 °C–300 °C. As a result, the SnO2–BNNTs sensor showed an extremely low detection limit (DL) of 250 ppb, as well as a better sensor response as compared to the SnO2 sensor. The maximum sensor response of SnO2–BNNTs sensor was ∼2610 towards 5 ppm NO2 gas at low operating temperature (100 °C). Expanded variation of space charge depleted regions was created at p-n heterojunction which promoted tunneling effect caused by entrapment of NO2 gas molecule and offered conducting channels (CCs) through BNNTs for charge carriers towards an improved sensor response of SnO2–BNNTs sensor.

MEMS based highly sensitive dual FET gas sensor using graphene decorated Pd-Ag alloy nanoparticles for H 2 detection

Abstract: A low power, dual-gate field-effect transistor (FET) hydrogen gas sensor with graphene decorated Pd-Ag for hydrogen sensing applications was developed. The FET hydrogen sensor was integrated with a graphene-Pd-Ag-gate FET (GPA-FET) as hydrogen sensor coupled with Pt-gate FET as a reference sensor on a single sensor platform. The sensing gate electrode was modified with graphene by an e-spray technique followed by Pd-Ag DC/MF sputtering. Morphological and structural properties were studied by FESEM and Raman spectroscopy. FEM simulations were performed to confirm the uniform temperature control at the sensing gate electrode. The GPA-FET showed a high sensing response to hydrogen gas at the temperature of 25~254.5 °C. The as-proposed FET H2 sensor showed the fast response time and recovery time of 16 s, 14 s, respectively at the operating temperature of 245 °C. The variation in drain current was positively related with increased working temperature and hydrogen concentration. The proposed dual-gate FET gas sensor in this study has potential applications in various fields, such as electronic noses and automobiles, owing to its low-power consumption, easy integration, good thermal stability and enhanced hydrogen sensing properties.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Morphology of Ion-Sputtered Surfaces

Abstract: We derive a stochastic nonlinear continuum theory to describe the morphological evolution of amorphous surfaces eroded by ion bombardment. Starting from Sigmund's theory of sputter erosion, we calculate the coefficients appearing in the continuum equation in terms of the physical parameters characterizing the sputtering process. We analyze the morphological features predicted by the continuum theory, comparing them with the experimentally reported morphologies. We show that for short time scales, where the effect of nonlinear terms is negligible, the continuum theory predicts ripple formation. We demonstrate that in addition to relaxation by thermal surface diffusion, the sputtering process can also contribute to the smoothing mechanisms shaping the surface morphology. We explicitly calculate an effective surface diffusion constant characterizing this smoothing effect, and show that it is responsible for the low temperature ripple formation observed in various experiments. At long time scales the nonlinear terms dominate the evolution of the surface morphology. The nonlinear terms lead to the stabilization of the ripple wavelength and we show that, depending on the experimental parameters such as angle of incidence and ion energy, different morphologies can be observed: asymptotically, sputter eroded surfaces could undergo kinetic roughening, or can display novel ordered structures with rotated ripples. Finally, we discuss in detail the existing experimental support for the proposed theory, and uncover novel features of the surface morphology and evolution, that could be directly tested experimentally.

Electronic and Thermal Properties of Graphene and Recent Advances in Graphene Based Electronics Applications

Abstract: Recently, graphene has been extensively researched in fundamental science and engineering fields and has been developed for various electronic applications in emerging technologies owing to its outstanding material properties, including superior electronic, thermal, optical and mechanical properties. Thus, graphene has enabled substantial progress in the development of the current electronic systems. Here, we introduce the most important electronic and thermal properties of graphene, including its high conductivity, quantum Hall effect, Dirac fermions, high Seebeck coefficient and thermoelectric effects. We also present up-to-date graphene-based applications: optical devices, electronic and thermal sensors, and energy management systems. These applications pave the way for advanced biomedical engineering, reliable human therapy, and environmental protection. In this review, we show that the development of graphene suggests substantial improvements in current electronic technologies and applications in healthcare systems.

Tunable band gaps in bilayer graphene-BN heterostructures

Abstract: We investigate band gap tuning of bilayer graphene between hexagonal boron nitride sheets, by external electric fields. Using density functional theory, we show that the gap is continuously tunable from 0 to 0.2 eV and is robust to stacking disorder. Moreover, boron nitride sheets do not alter the fundamental response from that of free-standing bilayer graphene, apart from additional screening. The calculations suggest that graphene−boron nitride heterostructures could provide a viable route to graphene-based electronic devices.