Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Using first principles within the framework of density functional theory, the structural and magnetic properties of CrSn are investigated. From total energy calculations, we have observed that the binary alloy, CrSn, could crystallize in hexagonal symmetry with the space group of P63/mmc. The spin polarized calculations suggested that the ground state of CrSn is antiferromagnetic. We have followed the Fixed Spin Moment (FSM) approach to study the metamagnetism. The physical cause of metamagnetism in CrSn is found to be the lattice strain. With negative strain (i.e. when the volume of the unit cell is expanded), the total magnetic moment per unit cell abruptly increased from 3.66 μB to 6.07 μB.

Department of Physics

School of Advanced Sciences

Vellore Campus

J Supercond Nov Magn

Metamagnetism in Hexagonal CrSn : A First Principle Study

We have investigated the structural and magnetic properties of Mn2Ge, using the projector augmented wave (PAW) method within the generalized gradient approximation (GGA). We have observed that the crystal symmetry for Mn2Ge is more likely to be tetragonal like Cu2Sb, rather than the hexagonal symmetry of Ni2In. Different magnetic ordering is assumed for Mn2Ge, based on that the electronic structure calculations are performed for Mn2Ge with antiferromagnetic (AFM), ferrimagnetic (FIM) spin ordering. In the most favorable ground state of Mn2Ge, nearest Mn (I) and Mn (II) are coupled ferromagnetically. The magnetic moments on the Mn(I) and Mn(II) are found to be varying based on their magnetic ordering. When ordering is ferromagnetic between Mn(I) and Mn(II), the magnetic moment on Mn(I) is large and in all other cases Mn(II) has larger magnetic moment. Easy flipping of spins has been observed. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.

World University root node

Journal of Superconductivity and Novel Magnetism

Structural and Magnetic Properties of Mn2Ge: a First Principle Study

Fabrication, physical modeling and dynamic response of p -type Al-doped SnOx active channel thin film transistors (TFTs) are presented for the potential application of ultra-high definition (UHD) displays. After deposition of Al-doped SnOx active layer using reactive co-sputtering, the channel was treated with plasma fluorination which improve the device performance of high ION/IOFF ratio of &gt; 106, low subthreshold swing of 100 mV/dec and high field-effect mobility ( μ FE) of 4.8 cm2V-1s-1. To understand the origin of such high performance, physical modeling and numerical simulations were performed using density of state (DOS) model of defects/traps of oxide semiconductor. This model describes the modifications of donor-like tail states and acceptor-like Gaussian defect states due to Al doping on SnOx and fluorine treatment. To evaluate the device performance for UHD large scale displays, the dynamic responses of p -type TFT pixel circuit for various requirements are simulated with physical models. These results suggest that the Al-doped SnOx TFTs are potential candidates for future high-definition displays and many applications in transparent electronics. © 2013 IEEE.

Centre for Nanotechnology Research

Department of Communication Engineering

School of Electronics Engineering

Fulltext

IEEE Journal of the Electron Devices Society

Physical Modeling of p-Type Fluorinated Al-Doped Tin-Oxide Thin Film Transistors

Acta Physica Polonica A

Electronic Band Structure and Complex Dielectric Function of zb-AlP: A First Principles Study.

We report on the fabrication of sol-gel derived Eu-doped ZnO films and the effects of heat-treatment on their structural and optical properties. X-ray diffraction data analysis confirms the decrease in strain in the thin films with increasing heat-treatment temperatures, and the compressive stress of the samples is found to become tensile for heat-treatments between 650 °C and 800 °C. X-ray-absorption fine-structure spectra performed at the Eu L3-edge confirm the absence of clustering of Eu-ions. The photoluminescence (PL) spectra of undoped and doped films consist of near-band edge emissions along with the defect state emissions of ZnO. Intense red emission (612 nm) is observed under UV excitation attributed to the D05→F27 energy level transition of Eu3+ ions in the doped films. The elemental composition and the existence of Eu2+ as well as Eu3+ has been discussed with the help of X-ray photoelectron spectroscopy. ZnO → Eu3+ energy transfer has also been confirmed with the help of PL excitation spectra in these transparent ZnO thin films for applications in integrated optic devices operating in the UV–visible region. © 2016 Elsevier B.V.

Optical Materials

Heat-treatment controlled structural and optical properties of sol-gel fabricated Eu:ZnO thin films

Streptococcus pneumoniae D39 AdcR (adhesin competence repressor) is the first metal-sensing member of the MarR (multiple antibiotic resistance repressor) family to be characterized. Expression profiling with a {increment}adcR strain grown in liquid culture (brain-heart infusion) under microaerobic conditions revealed upregulation of 13 genes, including adcR and adcCBA, encoding a high-affinity ABC uptake system for zinc, and genes encoding cell-surface zinc-binding pneumococcal histidine triad (Pht) proteins and AdcAII (Lmb, laminin binding). The {increment}adcR, H108Q and H112Q adcR mutant allelic strains grown in 0.2 mM Zn(II) exhibit a slow-growth phenotype and an approximately twofold increase in cell-associated Zn(II). Apo- and Zn(II)-bound AdcR are homodimers in solution and binding to a 28-mer DNA containing an adc operator is strongly stimulated by Zn(II) with KDNA-Zn=2.4×108M-1 (pH 6.0, 0.2M NaCl, 25°C). AdcR binds two Zn(II) per dimer, with stepwise Zn(II) affinities KZn1 and KZn2 of ≥109M-1 at pH 6.0 and ≥1012M-1 at pH 8.0, and one to three lower affinity Zn(II) depending on the pH. X-ray absorption spectroscopy of the high-affinity site reveals a pentacoordinate N/O complex and no cysteine coordination, the latter finding corroborated by wild type-like functional properties of C30A AdcR. Alanine substitution of conserved residues His42 in the DNA-binding domain, and His108 and His112 in the C-terminal regulatory domain, abolish high-affinity Zn(II) binding and greatly reduce Zn(II)-activated binding to DNA. NMR studies reveal that these mutants adopt the same folded conformation as dimeric wild type apo-AdcR, but fail to conformationally switch upon Zn(II) binding. These studies implicate His42, His108 and H112 as metalloregulatory zinc ligands in S. pneumoniae AdcR. © 2010 Elsevier Ltd.

Journal of Molecular Biology

The metalloregulatory zinc site in streptococcus pneumoniae AdcR, a Zinc-activated MarR family repressor

Atm1p is an ABC transporter localized in the mitochondrial inner membrane; it functions to export an unknown species into the cytosol and is involved in cellular iron metabolism. Depletion or deletion of Atm1p causes Fe accumulation in mitochondria and a defect in cytosolic Fe/S cluster assembly but reportedly not a defect in mitochondrial Fe/S cluster assembly. In this study the nature of the accumulated Fe was examined using Mössbauer spectroscopy, EPR, electronic absorption spectroscopy, X-ray absorption spectroscopy, and electron microscopy. The Fe that accumulated in aerobically grown cells was in the form of iron(III) phosphate nanoparticles similar to that which accumulates in yeast frataxin Yfh1p-deleted or yeast ferredoxin Yah1p-depleted cells. Relative to WT mitochondria, Fe/S cluster and heme levels in Atm1p-depleted mitochondria from aerobic cells were significantly diminished. Atm1p depletion also caused a buildup of nonheme Fe(II) ions in the mitochondria and an increase in oxidative damage. Atm1p-depleted mitochondria isolated from anaerobically grown cells exhibited WT levels of Fe/S clusters and hemes, and they did not hyperaccumulate Fe. Atm1p-depleted cells lacked Leu1p activity, regardless of whether they were grown aerobically or anaerobically. These results indicate that Atm1p does not participate in mitochondrial Fe/S cluster assembly and that the species exported by Atm1p is required for cytosolic Fe/Scluster assembly. The Fe/S cluster defect and the Fe-accumulation phenotype, resulting from the depletion of Atm1p in aerobic cells (but not in anaerobic cells), may be secondary effects that are observed only when cells are exposed to oxygen during growth. Reactive oxygen species generated under these conditions might degrade iron-sulfur clusters and lower heme levels in the organelle. ©2009 American Chemical Society.

Biochemistry

Biophysical characterization of the iron in mitochondria from Atm1p-depleted Saccharomyces cerevisiae

Journal of Nanomaterials

Chromium-Induced Nanocrystallization of a-Si Thin Films into the Wurtzite Structure

EXAFS investigation about Metal Induced Crystallization (MIC) of a-Si thin films doped with Ni, has been carried out at the K edge of Ni. Several a-Si films deposited on quartz and annealed at different temperatures and a non-annealed sample have been analyzed in order to study the variation of the nickel surroundings as a function of temperature. Nickel particles were co-sputtered together with silicon to obtain a metal percentage of about at. 0.5%. In all the annealed samples it was found that nickel, in its first shell, is 8-fold coordinated to silicon while a weak signal corresponding to the second shell appears in the Fourier transform of the spectra as in crystalline nickel di-silicide (c- NiSi2) used as reference compound. No presence of Ni clustering has been ascertained. In the non-annealed sample, where the NiSi2 formation has never been observed, EXAFS shows a deformed first shell environment on Ni similar to that of NiSi2. © 2008 Elsevier Ltd. All rights reserved.

Solid State Communications

XAFS study of Ni surroundings in metal induced crystallization of thin film amorphous silicon

Pure amorphous silicon thin films have been deposited by ion beam sputtering onto borosilicate glass substrates at ambient temperature. Optical constants were derived from spectral transmittance measurements in the range of 350-2500 nm. All the samples, regardless of thickness, show a Raman peak centred between 460 and 480 cm-1. The root-mean-square variation in the bond angles, Δθ, obtained from Raman spectra, indicates the presence of relatively good short range order in amorphous silicon thin films. The refractive index at 1.4 eV decreases from 4.35 to 3.52 with an increase in thickness from 30 to 130 nm. The band gap varies with thickness and at a thickness of 130 nm the band gap is 1.3 eV, which increases to 1.8 eV at 30 nm. The narrow band gap values of ion beam sputtered a-Si thin films indicate that they can be explored for photovoltaic applications. © 2008 IOP Publishing Ltd.

Semiconductor Science and Technology

Optical behaviour of ion beam sputtered a-Si thin films

The optical properties of nanocrystalline silicon (nc-Si), formed by nickel (Ni) induced crystallization of amorphous silicon (a-Si) films, are presented. Growth of nc-Si was characterized by Raman spectroscopy and UV-vis-NIR spectrophotometry. Significantly, the onset of crystallization occurred at 600 °C within 15min of annealing, as evidenced from the Raman peak centered at 514cm-1. It is demonstrated that the shape of the optical absorption spectrum is a function of thickness, substrate temperature, topological disorder and metal content in the films. Ni doping of the films results in optical inhomogeneity in the films and therefore anomalous dispersion in the behavior of the refractive index. It is further shown that these parameters also influence the position of the Urbach edges. The present study shows that metal induced crystallization of a-Si does not require extended durations of annealing and that the crystallization process is accompanied by structural, chemical and microstructural inhomogeneity in the films. © IOP Publishing Ltd.

Journal of Physics Condensed Matter

An optical study of Ni induced crystallization of a-Si thin films

This paper reports a detailed structural study on the nucleation of t-HfO2 nanocrystals in thin films of 70 SiO2 - 30 HfO2 prepared by sol-gel route on v-SiO2 substrates. Thermal treatment was performed at different temperatures ranging from 900 to 1200 °C for short (30 min) or long (24 h) time periods. Crystallisation and microstructure evolutions were traced by X-ray diffraction (XRD). The local structure around hafnium ions was determined from Hf L3-edge extended X-ray absorption fine structure (EXAFS) measurements carried out at the BM08-GILDA Beamline of ESRF (France). XRD shows the nucleation of HfO2 nanocrystals in the tetragonal phase after heat treatment at 1000 °C for 30 min, and a partial phase transformation to the monoclinic phase (m-HfO2) starts after heat treatment at 1200 °C for 30 min. The lattice parameters as well as the average crystallites size and their distributions were determined as a function of the heat treatment. EXAFS results are in agreement with the XRD ones, with hafnium ions in the film heat treated at 1100 °C for 24 h are present in mixed phases. © 2006 Elsevier Ltd. All rights reserved.