Electronic Microscopy Group

Hyderabad, India

Electronic Microscopy Group

Hyderabad, India
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Chandravanshi V.,Titanium Alloy Group | Sarkar R.,Electronic Microscopy Group | Kamat S.V.,Mechanical Behaviour Group | Nandy T.K.,Powder Metallurgy Group
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2013

Tensile properties of boron-modified near alpha titanium alloy were evaluated in α-β- and β-processed conditions after heat treatments at different solution treatment temperatures at both room temperature and 873 K (600 C). Creep behavior was also investigated in these processing and heat-treatment conditions at 873 K (600 C). While the yield strength (YS) and the ultimate tensile strength (UTS) did not show significant dependence on the processing history, a marginal improvement in elongation-to-failure values were observed in α-β-processed condition as compared with β-processed condition at both temperatures. Creep resistance of the alloy at 873 K (600 C) was found to be significantly superior in β-processed condition as compared with α-β-processed condition. © 2012 The Minerals, Metals & Materials Society and ASM International.

Selvakumar N.,National Aerospace Laboratories, Bangalore | Selvakumar N.,Indian Institute of Science | Biswas A.,Bhabha Atomic Research Center | Rao D.V.S.,Electronic Microscopy Group | And 2 more authors.
Solar Energy Materials and Solar Cells | Year: 2016

Ti/Al2O3 coating was designed and developed for the growth of carbon nanotubes (CNTs)-based tandem absorber on stainless steel (SS) substrates. The aluminum and titanium target power densities and oxygen flow rates were optimized to deposit the Ti/Al2O3 coatings. The optimized Ti/Al2O3 coating with a Co catalyst on top was used as an underlying substrate to grow the CNT-based tandem absorber at 800 °C in Ar+H2 atmosphere (i.e., SS/Ti/Al2O3/Co/CNT). The formation of aluminum titanium oxide (AlTiO) was observed during the CNT growth process and this layer enhances the optical properties of the CNT based tandem absorber. At 0.36 µm CNT coating thickness, the tandem absorber exhibits an absorptance of 0.95 and an emittance of 0.20. The optical constants of Ti, Al2O3 and AlTiO coatings were measured using phase modulated spectroscopic ellipsometry in the wavelength range of 300–900 nm. The experimentally measured ellipsometric parameters have been fitted with the simulated spectra using Tauc-Lorentz model for generating the dispersion of the optical constants of the Al2O3 and the AlTiO layers. The Ti and Al2O3 layer thicknesses play a major role in designing CNT based tandem absorber with good optical properties. The transmission electron microscopy studies showed that the as-grown CNTs were multi-walled in nature. The angular and the polarization dependence studies of the CNT based tandem absorber grown at different thicknesses were carried out using UV-VIS-NIR spectrophotometer. © 2016 Elsevier B.V.

Studencka M.,Max Planck Institute for Biophysical Chemistry | Konzer A.,Max Planck Institute for Heart and Lung Research | Moneron G.,Max Planck Institute for Biophysical Chemistry | Wenzel D.,Electronic Microscopy Group | And 10 more authors.
Molecular and Cellular Biology | Year: 2012

Linker histone (H1) and heterochromatin protein 1 (HP1) are essential components of heterochromatin which contribute to the transcriptional repression of genes. It has been shown that the methylation mark of vertebrate histone H1 is specifically recognized by the chromodomain of HP1. However, the exact biological role of linker histone binding to HP1 has not been determined. Here, we investigate the function of the Caenorhabditis elegans H1 variant HIS-24 and the HP1-like proteins HPL-1 and HPL-2 in the cooperative transcriptional regulation of immune-relevant genes. We provide the first evidence that HPL-1 interacts with HIS-24 monomethylated at lysine 14 (HIS-24K14me1) and associates in vivo with promoters of genes involved in antimicrobial response. We also report an increase in overall cellular levels and alterations in the distribution of HIS-24K14me1 after infection with pathogenic bacteria. HIS-24K14me1 localization changes from being mostly nuclear to both nuclear and cytoplasmic in the intestinal cells of infected animals. Our results highlight an antimicrobial role of HIS-24K14me1 and suggest a functional link between epigenetic regulation by an HP1/H1 complex and the innate immune system in C. elegans. © 2012, American Society for Microbiology.

Pramanik P.,University of Calcutta | Sen S.,University of Calcutta | Singha C.,University of Calcutta | Roy A.S.,University of Calcutta | And 3 more authors.
IEEE Journal of Quantum Electronics | Year: 2016

The detection of a specific spectral line in ultraviolet in the presence of broadband ambient lighting is necessary for many applications. We report wavelength-selective photodetection using AlGaN multiple quantum wells grown by molecular beam epitaxy. A near-Gaussian photoresponse peak at 300 nm with a width of 17 nm was achieved in the lateral photocurrent, along with a much faster transient response compared with the devices based on bulk AlGaN. The wavelength selectivity, controlled by the formation and subsequent splitting of excitons, was achieved by the optimization of the alloy properties of the barrier layers, reducing the leakage of photogenerated carriers into the active region. © 1965-2012 IEEE.

PubMed | Electronic Microscopy Group, Howard Hughes Medical Institute, Daresbury Laboratory, University of Colorado at Boulder and 4 more.
Type: Journal Article | Journal: Journal of structural biology | Year: 2015

The MRC binary file format is widely used in the three-dimensional electron microscopy field for storing image and volume data. Files contain a header which describes the kind of data held, together with other important metadata. In response to advances in electron microscopy techniques, a number of variants to the file format have emerged which contain useful additional data, but which limit interoperability between different software packages. Following extensive discussions, the authors, who represent leading software packages in the field, propose a set of extensions to the MRC format standard designed to accommodate these variants, while restoring interoperability. The MRC format is equivalent to the map format used in the CCP4 suite for macromolecular crystallography, and the proposal also maintains interoperability with crystallography software. This Technical Note describes the proposed extensions, and serves as a reference for the standard.

Kataria S.,National Aerospace Laboratories, Bangalore | Srivastava S.K.,Indira Gandhi Center for Atomic Research | Kumar P.,National Aerospace Laboratories, Bangalore | Srinivas G.,National Aerospace Laboratories, Bangalore | And 4 more authors.
Surface and Coatings Technology | Year: 2012

Nanocrystalline titanium nitride (TiN) coatings were deposited on Si (100) substrates using reactive pulsed direct current magnetron sputtering where nitrogen flow rate was pulsed during the deposition. The pulse on time for nitrogen flow rate was 5, 20, 40, 50 and 60s. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), micro-Raman spectroscopy and proton elastic backscattering spectroscopy (PEBS) techniques were employed to study the structure and microstructure of the as-deposited coatings. Complete nano-mechanical characterization of the coatings was carried out using nanoindentation, nanoscratch and wear testing techniques. TEM studies revealed the nanocrystalline nature of the coatings with column size between 25 and 30nm. PEBS analysis revealed an increase in N/Ti ratio from 0.79 to 0.90 in the coatings with increasing pulse on time of nitrogen flow rate. Nanoindentation hardness was found to vary from 17 to 27GPa and fracture toughness values varied from 2.75MPam 1/2 to 1.19MPam 1/2 with increase in pulse on time. The coating deposited at a pulse on time of 20s was found to exhibit optimal nanoindentation hardness and fracture toughness values of around 18GPa and 2.12MPam 1/2, respectively. It is concluded that the pulsing of nitrogen flow rate during reactive deposition of TiN coatings allows one to obtain encouraging combinations of moderate hardness and high toughness. © 2012 Elsevier B.V.

Edgcombe C.J.,TFM Group | Ionescu A.,TFM Group | Loudon J.C.,Electronic Microscopy Group | Blackburn A.M.,Hitachi Cambridge Laboratory | And 2 more authors.
Ultramicroscopy | Year: 2012

Holographic measurements on magnetised thin-film cobalt rings have demonstrated both onion and vortex states of magnetisation. For a ring in the vortex state, the difference between phases of electron paths that pass through the ring and those that travel outside it was found to agree very well with Aharonov-Bohm theory within measurement error. Thus the magnetic flux in thin-film rings of ferromagnetic material can provide the phase shift required for phase plates in transmission electron microscopy. When a ring of this type is used as a phase plate, scattered electrons will be intercepted over a radial range similar to the ring width. A cobalt ring of thickness 20. nm can produce a phase difference of π/2 from a width of just under 30. nm, suggesting that the range of radial interception for this type of phase plate can be correspondingly small. © 2012 Elsevier B.V.

Selvakumar N.,National Aerospace Laboratories, Bangalore | Selvakumar N.,Indian Institute of Science | Vadivel B.,Indian Institute of Science | Rao D.V.S.,Electronic Microscopy Group | And 2 more authors.
Applied Physics A: Materials Science and Processing | Year: 2016

High-quality graphene was grown on polycrystalline copper (Cu) foils (1 cm × 1 cm) using hot-filament chemical vapor deposition method. The role of process parameters such as gas flow rates (methane and hydrogen), growth temperatures (filament and substrate) and durations on the growth of graphene was studied. The process parameters were also optimized to grow monolayer, bilayer and multilayer graphene in a controlled manner, and a growth mechanism was deduced from the experimental results. The presence of graphene on Cu foils was confirmed using X-ray photoelectron spectroscopy, micro-Raman spectroscopy, field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. FESEM micrographs clearly showed that the graphene starts nucleating as hexagonal islands and later evolves as dendritic lobe-shaped islands with an increase in supersaturation. The TEM images substantiate the growth of monolayer, bilayer and multilayer graphene. The I2D/IG ratio = 2 confirmed the presence of the monolayer graphene and the absence of ‘D’ peak in the Raman spectrum indicated the high purity of graphene grown on Cu foils. These results also show that the polycrystalline copper foil morphology has negligible effect on the growth of monolayer graphene. © 2016, Springer-Verlag Berlin Heidelberg.

Deepthi B.,National Aerospace Laboratories, Bangalore | Srinivas G.,National Aerospace Laboratories, Bangalore | Kumar P.,National Aerospace Laboratories, Bangalore | Sridhara Rao D.V.,Electronic Microscopy Group | Barshilia H.C.,National Aerospace Laboratories, Bangalore
Nanoscience and Nanotechnology Letters | Year: 2012

Au-WS 2 nanocomposite coatings with approximately 60 at.% Au were prepared using magnetron sputtering from high purity Au and WS 2 targets. Structural characterization of the coatings using X-ray diffraction indicated the presence of (111), (200) and (220) peaks of cubic Au and broad bands corresponding to (002) and (004) planes of hexagonal WS 2. Surface morphology of Au-WS 2 coatings was studied using field emission scanning electron microscopy (FESEM) and atomic force microscopy which showed formation of uniformly distributed interconnected ligament-like features. High resolution transmission electron microscopy studies showed the presence of a two phase nanocomposite structure wherein nanocrystalline Au was dispersed in a matrix of nanocrystalline and amorphous WS 2. The electrical resistivity of Au-WS 2 coating measured using four-point-probe method was approximately 0.2 μω m compared to Au and WS 2 coatings which exhibited electrical resistivity values of approximately 0.04.m and 0.057 μωm, respectively. Ball-on-disc reciprocating tests at a load of 7 N showed that Au-WS 2 nanocomposite coating exhibited a friction coefficient of 0.22 after 57,600 cycles and outperformed Au and WS 2 coatings. Analyses of the ball and wear track of Au-WS 2 coating using FESEM at the end of the wear test indicated formation of smooth transfer films, less accumulation of wear debris and reduced oxidation. Copyright © 2012 American Scientific Publishers. All rights reserved.

Liu L.Z.-Y.,University of Cambridge | Mcaleese C.,University of Cambridge | Sridhara Rao D.V.,Electronic Microscopy Group | Kappers M.J.,University of Cambridge | Humphreys C.J.,University of Cambridge
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2012

Electron holography was used to measure the electrostatic potential distribution in an LED chip at high spatial resolution, from which the internal polarization field can be derived. A cross-sectional TEM lamella on a workable LED die containing five InGaN/GaN quantum wells (QWs) connected to electrodes that fit into an in-situ biasing TEM holder was prepared using a focused ion beam (FIB). Off-axis electron holography under Lorentz mode was carried out to study the p -MQW-n region and phase profiles were derived at different reverse biasing conditions. p -n contrast has been shown in the calibrated electrostatic potential mapping. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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