M.C. Bhatnagar

Bio: M.C. Bhatnagar is an academic researcher from Indian Institute of Technology Delhi. The author has contributed to research in topics: Thin film & Spin coating. The author has an hindex of 15, co-authored 22 publications receiving 803 citations.

Highly sensitive SnO2 thin film NO2 gas sensor operating at low temperature

Abstract: Thin films of pure nano-crystalline SnO 2 and WO 3 -doped SnO 2 in different concentrations (3 wt.% and 5 wt.%) are deposited using sol–gel spin coating technique on glass substrates. The structural and morphological properties of these films are investigated using XRD, TEM and AFM. The sensitivity and selectivity of these films are tested to different reducing and oxidizing gases such as SO 2 , NH 3 , NO 2 and ethanol. A SnO 2 thin film with 5 wt.% WO 3 shows very high responses to NO 2 (four orders of magnitude in the value of ( R g − R a )/ R a ; R g and R a are the resistance in NO 2 and in air, respectively) and excellent selectivity for NO 2 gas at a low operating temperature of 150 °C. The effect of WO 3 on the sensing characteristics of these films towards NO 2 is discussed.

Effect of indium-doped SnO2 nanoparticles on NO2 gas sensing properties

Abstract: Undoped and indium-doped SnO2 thin films with different doping concentrations have been prepared by sol–gel spin coating process on float glass substrates. XRD, TEM and AFM studies are carried out to investigate the effect of indium in SnO2 thin films. TEM studies reveal the dispersed nanoparticles of around 3 nm size (∼Debye length). In addition we have observed that indium doping improves the sensor response and selectivity towards NO2 gas at a low operating temperature and also resolves the problem of agglomeration of particles that is responsible for the lowering of sensor response and stability in the above mentioned particle size range. A very high sensor response of around 7200% has been observed in 10 wt% indium-doped SnO2 films to 500 ppm of NO2 gas at an operating temperature of 150 °C.

Effect of Fe doping on the gas sensing properties of nano-crystalline SnO2 thin films

Abstract: In this paper, we report the gas sensing properties of sol–gel derived Fe-doped nano-crystalline SnO2 thin films. Films were doped with Fe in two different concentrations (2 and 5 wt.%). The crystallite size was found to decrease with increase in stacking fault density resulting from increasing Fe content in the SnO2 films. Gas sensing characteristics were investigated for different target gases such as carbon monoxide (CO), ammonia (NH3) and ethanol (C2H5OH). The films with 2% Fe content showed high response and excellent selectivity for CO compared to other gases at 200 °C. But, at 5% Fe content, the response factor to CO decreased while it increased for NH3 and ethanol. However, faster response and recovery times were observed for CO at higher Fe content in the films. These results have been correlated with the defect chemistry and crystallite size effect resulting from Fe incorporation in the SnO2 thin films.

Structural, dielectric and ferroelectric study of Ba0.9Sr0.1ZrxTi1−xO3 ceramics prepared by the sol–gel method

Abstract: In this paper, we report the structural, dielectric and ferroelectric properties of zirconium (Zr)-modified barium strontium titanate (Ba 0.9 Sr 0.1 Zr x Ti 1− x O 3 ) ceramics with varying Zr content as x =0, 0.20, 0.25 and 0.30 synthesized by the sol–gel method. Stable polycrystalline perovskite phase is obtained at a processing temperature of 1150 °C, which is lower than the processing temperature of conventional solid-state reaction method. X-ray diffraction (XRD) shows a systematic peak shift with increasing Zr content, indicating incorporation of Zr in BST lattice. Scanning electron microscope (SEM) is done to investigate microstructure of the pellets. The diffusivity parameter ( γ ) and the standard deviation from the Curie–Weiss law have also been investigated as a function of Zr. The polarization vs electric field shows a decrease in remnant polarization with increasing Zr content.

Intrinsic ripples in graphene

Abstract: The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.

Metal Oxide Nanostructures and Their Gas Sensing Properties: A Review

Abstract: Metal oxide gas sensors are predominant solid-state gas detecting devices for domestic, commercial and industrial applications, which have many advantages such as low cost, easy production, and compact size However, the performance of such sensors is significantly influenced by the morphology and structure of sensing materials, resulting in a great obstacle for gas sensors based on bulk materials or dense films to achieve highly-sensitive properties Lots of metal oxide nanostructures have been developed to improve the gas sensing properties such as sensitivity, selectivity, response speed, and so on Here, we provide a brief overview of metal oxide nanostructures and their gas sensing properties from the aspects of particle size, morphology and doping When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called "small size effect", yet small size of metal oxide nanoparticles will be compactly sintered together during the film coating process which is disadvantage for gas diffusion in them In view of those reasons, nanostructures with many kinds of shapes such as porous nanotubes, porous nanospheres and so on have been investigated, that not only possessed large surface area and relatively mass reactive sites, but also formed relatively loose film structures which is an advantage for gas diffusion Besides, doping is also an effective method to decrease particle size and improve gas sensing properties Therefore, the gas sensing properties of metal oxide nanostructures assembled by nanoparticles are reviewed in this article The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given

Recent Progress on the Development of Chemosensors for Gases.

Abstract: Xin Zhou,†,‡ Songyi Lee,† Zhaochao Xu,* and Juyoung Yoon*,† †Department of Chemistry and Nanoscience, Ewha Womans University, Seoul 120-750, Republic of Korea ‡Research Center for Chemical Biology, Department of Chemistry, Yanbian University, Yanjii 133002, People’s Republic of China Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Shahekou, Dalian, Liaoning, People’s Republic of China

Metal oxide nanoparticles and their applications in nanotechnology

Abstract: Considering metal oxide nanoparticles as important technological materials, authors provide a comprehensive review of researches on metal oxide nanoparticles, their synthetic strategies, and techniques, nanoscale physicochemical properties, defining specific industrial applications in the various fields of applied nanotechnology. This work expansively reviews the recent developments of semiconducting metal oxide gas sensors for environmental gases including CO2, O2, O3, and NH3; highly toxic gases including CO, H2S, and NO2; combustible gases such as CH4, H2, and liquefied petroleum gas; and volatile organic compounds gases. The gas sensing properties of different metal oxides nanoparticles towards specific target gases have been individually discussed. Promising metal oxide nanoparticles for sensitive and selective detection of each gas have been identified. This review also categorizes metal oxides sensors by analyte gas and also summarizes the major techniques and synthesis strategies used in nanotechnology. Additionally, strategies, sensing mechanisms and related applications of semiconducting metal oxide materials are also discussed in detail. Related applications are innumerable trace to ultratrace-level gas sensors, batteries, magnetic storage media, various types of solar cells, metal oxide nanoparticles applications in catalysis, energy conversion, and antennas (including microstrip and patch-type optically transparent antennas), rectifiers, optoelectronic, and electronics.

Semiconducting Metal Oxide Based Sensors for Selective Gas Pollutant Detection

Abstract: A review of some papers published in the last fifty years that focus on the semiconducting metal oxide (SMO) based sensors for the selective and sensitive detection of various environmental pollutants is presented.