Technical Physics Division

BARC, India

Technical Physics Division

BARC, India
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Rao K.S.,Technical Physics Division | Salunke H.G.,Technical Physics Division
AIP Conference Proceedings | Year: 2017

The magnetic state of ζ-Fe2N, a metastable phase of iron nitride formed during nitriding process, is being probed by means of spin polarized electronic structure calculations using the state of art VASP package. Our electronic structure calculations and subsequent evaluation of stoner criterion point towards a stable ferromagnetic state for ζ-Fe2N. Crystal Orbital Hamilton Population analysis is also included to elucidate the bonding nature. © 2017 Author(s).


Kaushik S.D.,UGC-DAE Consortium for Scientific Research | Rayaprol S.,UGC-DAE Consortium for Scientific Research | Prajapat C.L.,Technical Physics Division | Singh M.R.,Technical Physics Division
AIP Conference Proceedings | Year: 2017

We have prepared Y doped hexagonal Ho1-xYxMnO3 (x = 0, 0.25) by solid state reaction method. The samples crystallize in the desired P63cm space group. Temperature dependent crystal, magnetic structure and magnetic properties of these samples are studied to understand the effect of Y doping in HoMnO3. Magnetization studies shows robust antiferromagnetic property sets in below 70K and upon Y doping magnetization decreases marginally. Rietveld analysis of low temperature neutron diffraction data shows the cell parameter 'a' decrease while 'c' increases across all the temperature range. Upon microscopically analyzing the data we see the Mn bond length alters significantly and so does the correlated O-Mn-O bond angle, which points out that Y doping induces variation in polyhedral tilt in MnO5 bypyramidal in HoMnO3 sample. © 2017 Author(s).


Tiwari B.,Technical Physics Division | Dixit A.,Glass and Advanced Ceramics Division | Pillai C.G.S.,Chemistry Division | Gadkari S.C.,Technical Physics Division | Kothiyal G.P.,Glass and Advanced Ceramics Division
Journal of the American Ceramic Society | Year: 2012

The non-isothermal crystallization kinetics of the strontium zinc silicate (SZS) glasses, having composition 51SrO-9ZnO-40SiO 2 (wt%), was studied using the differential thermal analysis (DTA). Glasses prepared by quenching the melt in air, were subjected to different heat treatments for studying the crystallization behavior. Formation of crystalline phases and microstructure were studied by using powder X-ray diffraction and scanning electron microscopy. The activation energy and mechanism of crystallization were determined according to Kissinger, Ozawa and Matusita-Sakka equations. The DTA exotherm observed at around 920°C consists of two overlapping crystallization peaks corresponding to two different crystalline phases. Strontium silicate (Sr 3Si 3O 9) and SZS (Sr 2ZnSi 2O 7) phases crystallize almost simultaneously as major phases. The activation energies for the these crystallization peaks are 700 kJ/mol and 704 kJ/mol. Higher activation energies indicate that the kinetics are more thermally activated making the control of crystallization more difficult. The values of growth morphology parameters n (Avarami parameter) and m (dimensionality of crystal growth) suggest a diffusion controlled bulk crystallization with three- and two-dimensional growth. This is also confirmed by an interconnected growth of stubby granular/prismatic shaped crystals in the glass-ceramic. The microstructural evolution of the glass upon heating suggests the occurrence of phase separation with an apparently spinodal decomposition mechanism prior to the crystallization. © 2012 The American Ceramic Society.


Gupta S.K.,Technical Physics Division | Jha P.,Technical Physics Division | Singh A.,Technical Physics Division | Chehimi M.M.,Technical Physics Division | And 2 more authors.
Journal of Materials Chemistry C | Year: 2015

Research on organic semiconductor thin films has been accelerated due to their potential for low cost and large area flexible devices. Already there are various products based on organic semiconductor thin films such as displays which have been commercialized. Further studies are needed for the development of flexible devices. In this paper, investigation of various processes for organic semiconductor thin film deposition on flexible substrates and their characterization carried out by us will be reviewed. Two different strategies have been adopted for the fabrication of flexible thin films using conducting polymers as well as molecular semiconductors and they are: (I) synthesis of freestanding films where there is no need for substrates, and (II) preparation of thin films on flexible substrates. Devices such as organic field effect transistors, memory devices and gas sensors have been demonstrated using various flexible films. The effect of bending on characteristics of films and devices has also been investigated. © The Royal Society of Chemistry 2015.


Joshi A.,University of Pune | Gangal S.A.,University of Pune | Gupta S.K.,Technical Physics Division
Sensors and Actuators, B: Chemical | Year: 2011

Polypyrrole thin films were synthesized in situ by chemical polymerization. Fourier transform infrared spectroscopy revealed formation of polypyrrole. The morphological studies by scanning electron microscopy showed formation of uniform granular structure with average grain size of 0.6 μm. The film composition was characterized by X-ray photoelectron spectroscopy for chemical composition in polypyrrole film. These films were investigated for their sensing behaviour towards NH3 and NO at room temperature. It has been observed that these films are selective for NH3 and the sensitivity exhibited a linear response in range of 4-80 ppm. © 2011 Elsevier B.V. All Rights Reserved.


Tiwari B.,Technical Physics Division | Dixit A.,Glass and Advanced Ceramics Division | Kothiyal G.P.,Glass and Advanced Ceramics Division
International Journal of Hydrogen Energy | Year: 2011

Glasses having composition (in wt.%) 51SrO-9ZnO-(40-x)SiO2 (SZS), where x represents the additives like B2O3, Al 2O3, V2O5, and Cr2O 3, were prepared by melt-quench method and transformed into glass-ceramics by controlled crystallization based on differential thermal analysis (DTA) data. Glasses and glass-ceramics were characterized using dilatometry, X-ray diffraction (XRD), microhardness, and Raman spectroscopy. XRD revealed that glass-ceramics are composed of mainly Sr2ZnSi 2O7 and SrSiO3 crystalline phases along with residual glassy phase. Raman spectroscopy showed that main constitutes of the glass network are the Q1 and Q2 silicate structural units. With the addition of B2O3 and other additives silicate glass network depolymerizes and concentration of Q1 structural units increases at the expense of Q2 units. Formation of phases during crystallization depends on the presence of different silicate structural units in the glass matrix. B2O3 goes into the glass network as triangular (BO3) borate structural units and at higher concentration of B2O3, only a part of the B2O3 forms tetragonal (BO4) structural units. Investigated glasses and glass-ceramics have thermal expansion coefficient (TEC) in the range of 105-120 × 10-7/°C which matches with TEC of other cell components. B2O3 containing SZS glasses show good adhesion/bonding with YSZ and Crofer 22 APU. Elemental line scans indicate that interdiffusion of Fe, Cr and Si across interface is responsible for good bonding with Crofer 22 APU and interdiffusion of Sr, Si, Y and Zr is responsible for good bonding with YSZ. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Kaushik N.,Indian Institute of Technology Bombay | Karmakar D.,Technical Physics Division | Nipane A.,Indian Institute of Technology Bombay | Karande S.,Indian Institute of Technology Bombay | Lodha S.,Indian Institute of Technology Bombay
ACS Applied Materials and Interfaces | Year: 2016

We demonstrate a low and constant effective Schottky barrier height (φB ∼ 40 meV) irrespective of the metal work function by introducing an ultrathin TiO2 ALD interfacial layer between various metals (Ti, Ni, Au, and Pd) and MoS2. Transmission line method devices with and without the contact TiO2 interfacial layer on the same MoS2 flake demonstrate reduced (24×) contact resistance (RC) in the presence of TiO2. The insertion of TiO2 at the source-drain contact interface results in significant improvement in the on-current and field effect mobility (up to 10×). The reduction in RC and φB has been explained through interfacial doping of MoS2 and validated by first-principles calculations, which indicate metallic behavior of the TiO2-MoS2 interface. Consistent with DFT results of interfacial doping, X-ray photoelectron spectroscopy (XPS) data also exhibit a 0.5 eV shift toward higher binding energies for Mo 3d and S 2p peaks in the presence of TiO2, indicating Fermi level movement toward the conduction band (n-type doping). Ultraviolet photoelectron spectroscopy (UPS) further corroborates the interfacial doping model, as MoS2 flakes capped with ultrathin TiO2 exhibit a reduction of 0.3 eV in the effective work function. Finally, a systematic comparison of the impact of selective doping with the TiO2 layer under the source-drain metal relative to that on top of the MoS2 channel shows a larger benefit for transistor performance from the reduction in source-drain contact resistance. © 2015 American Chemical Society.


PubMed | Indian Institute of Technology Bombay and Technical Physics Division
Type: Journal Article | Journal: ACS applied materials & interfaces | Year: 2016

We demonstrate a low and constant effective Schottky barrier height (B 40 meV) irrespective of the metal work function by introducing an ultrathin TiO2 ALD interfacial layer between various metals (Ti, Ni, Au, and Pd) and MoS2. Transmission line method devices with and without the contact TiO2 interfacial layer on the same MoS2 flake demonstrate reduced (24) contact resistance (RC) in the presence of TiO2. The insertion of TiO2 at the source-drain contact interface results in significant improvement in the on-current and field effect mobility (up to 10). The reduction in RC and B has been explained through interfacial doping of MoS2 and validated by first-principles calculations, which indicate metallic behavior of the TiO2-MoS2 interface. Consistent with DFT results of interfacial doping, X-ray photoelectron spectroscopy (XPS) data also exhibit a 0.5 eV shift toward higher binding energies for Mo 3d and S 2p peaks in the presence of TiO2, indicating Fermi level movement toward the conduction band (n-type doping). Ultraviolet photoelectron spectroscopy (UPS) further corroborates the interfacial doping model, as MoS2 flakes capped with ultrathin TiO2 exhibit a reduction of 0.3 eV in the effective work function. Finally, a systematic comparison of the impact of selective doping with the TiO2 layer under the source-drain metal relative to that on top of the MoS2 channel shows a larger benefit for transistor performance from the reduction in source-drain contact resistance.


PubMed | Indian Institute of Technology Bombay and Technical Physics Division
Type: Journal Article | Journal: ACS nano | Year: 2016

P-type doping of MoS2 has proved to be a significant bottleneck in the realization of fundamental devices such as p-n junction diodes and p-type transistors due to its intrinsic n-type behavior. We report a CMOS compatible, controllable and area selective phosphorus plasma immersion ion implantation (PIII) process for p-type doping of MoS2. Physical characterization using SIMS, AFM, XRD and Raman techniques was used to identify process conditions with reduced lattice defects as well as low surface damage and etching, 4X lower than previous plasma based doping reports for MoS2. A wide range of nondegenerate to degenerate p-type doping is demonstrated in MoS2 field effect transistors exhibiting dominant hole transport. Nearly ideal and air stable, lateral homogeneous p-n junction diodes with a gate-tunable rectification ratio as high as 2 10(4) are demonstrated using area selective doping. Comparison of XPS data from unimplanted and implanted MoS2 layers shows a shift of 0.67 eV toward lower binding energies for Mo and S peaks indicating p-type doping. First-principles calculations using density functional theory techniques confirm p-type doping due to charge transfer originating from substitutional as well as physisorbed phosphorus in top few layers of MoS2. Pre-existing sulfur vacancies are shown to enhance the doping level significantly.


Nipane A.,Indian Institute of Technology Bombay | Karmakar D.,Technical Physics Division | Kaushik N.,Indian Institute of Technology Bombay | Karande S.,Indian Institute of Technology Bombay | Lodha S.,Indian Institute of Technology Bombay
ACS Nano | Year: 2016

P-type doping of MoS2 has proved to be a significant bottleneck in the realization of fundamental devices such as p-n junction diodes and p-type transistors due to its intrinsic n-type behavior. We report a CMOS compatible, controllable and area selective phosphorus plasma immersion ion implantation (PIII) process for p-type doping of MoS2. Physical characterization using SIMS, AFM, XRD and Raman techniques was used to identify process conditions with reduced lattice defects as well as low surface damage and etching, 4X lower than previous plasma based doping reports for MoS2. A wide range of nondegenerate to degenerate p-type doping is demonstrated in MoS2 field effect transistors exhibiting dominant hole transport. Nearly ideal and air stable, lateral homogeneous p-n junction diodes with a gate-tunable rectification ratio as high as 2 × 104 are demonstrated using area selective doping. Comparison of XPS data from unimplanted and implanted MoS2 layers shows a shift of 0.67 eV toward lower binding energies for Mo and S peaks indicating p-type doping. First-principles calculations using density functional theory techniques confirm p-type doping due to charge transfer originating from substitutional as well as physisorbed phosphorus in top few layers of MoS2. Pre-existing sulfur vacancies are shown to enhance the doping level significantly. © 2016 American Chemical Society.

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