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Kumar P.,Indian Institute of Technology Delhi | Malik H.K.,Indian Institute of Technology Delhi | Ghosh A.,Indian School of Mines | Thangavel R.,Indian School of Mines | Asokan K.,Inter University Accelerator Center
Applied Physics Letters | Year: 2013

We propose Mg doping in zinc oxide (ZnO) films for realizing wider optical bandgap in highly c-axis oriented Zn1-xMgxO (0 ≤ x ≤ 0.3) thin films. A remarkable enhancement of 25% in the bandgap by 30% Mg doping was achieved. The bandgap was tuned between 3.25 eV (ZnO) and 4.06 eV (Zn0.7Mg0.3O), which was further confirmed by density functional theory based wien2k simulation employing a combined generalized gradient approximation with scissor corrections. The change of stress and crystallite size in these films were found to be the causes for the observed blueshift in the bandgap. © 2013 AIP Publishing LLC.

Som S.,Indian School of Mines | Sharma S.K.,Indian School of Mines | Lochab S.P.,Inter University Accelerator Center
Materials Research Bulletin | Year: 2013

This paper reports the structural and optical modifications of Y 2O3:Eu3+ nanophosphor induced by 150 MeV Ni7+ swift heavy ions (SHI) in the fluence range 1 × 10 11 to 1 × 1013 ions/cm2. The XRD, TEM and FTIR studies confirm the loss of crystallinity of the nanophosphors after ion irradiation. Diffuse reflectance spectrum shows a blue shift in the absorption band for SHI induced nanophosphors. An increase in the intensity of photoluminescence peaks without any shift in the peak positions was observed. © 2012 Elsevier Ltd.

Mal S.,North Carolina State University | Nori S.,North Carolina State University | Narayan J.,North Carolina State University | Prater J.T.,U.S. Army | Avasthi D.K.,Inter University Accelerator Center
Acta Materialia | Year: 2013

We have introduced defects in ZnO epitaxial thin films by swift heavy 107Ag9+ ion irradiation and investigated systematically their magnetic, electrical and optical properties. Oxygen annealed ZnO films are epitaxial single crystals that exhibit no long-range magnetic order. However, in this paper it is shown that room-temperature ferromagnetism (RTFM) can be introduced in a controlled manner in these films using ion irradiation and that the magnetization increases with ion dose. This qualitatively agrees with earlier studies which showed that RTFM could be induced in ZnO films through either vacuum thermal annealing or pulsed laser annealing below energy densities that lead to melting. Raman studies of the ion irradiated samples revealed dramatic changes in the vibration modes that correlated with increases in the carrier concentration, indicative of lattice disorder and defect creation. We compare these results with those observed in laser irradiated and vacuum annealed samples, and then discuss these findings in the context of defects and defect complexes created during the high-energy heavy ion irradiation process. We propose a unified mechanism to explain RTFM and n-type conductivity enhancements during irradiation, and laser and vacuum annealing. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Banerjee T.,Inter University Accelerator Center | Nath S.,Inter University Accelerator Center | Pal S.,CS 6 1
Physical Review C - Nuclear Physics | Year: 2015

Background: Fusion between two massive nuclei is a very complex process and is characterized by three stages: (a) capture inside the potential barrier, (b) formation of an equilibrated compound nucleus (CN), and (c) statistical decay of the CN leading to a cold evaporation residue (ER) or fission. The second stage is the least understood of the three and is the most crucial in predicting yield of superheavy elements (SHE) formed in complete fusion reactions. Purpose: A systematic study of average fusion probability, ⌠© 2015 American Physical Society.

Dixit G.,Gbpant University Of Ag And Technology Pantnagar | Pal Singh J.,Inter University Accelerator Center | Srivastava R.C.,Gbpant University Of Ag And Technology Pantnagar | Agrawal H.M.,Gbpant University Of Ag And Technology Pantnagar
Journal of Magnetism and Magnetic Materials | Year: 2012

Present work is a study of temperature dependent electron paramagnetic resonance spectra of Ce and Gd doped nickel ferrite nanoparticles. The samples, synthesised by chemical route were characterised by X-ray diffractometer, electron paramagnetic resonance spectroscopy (EPR) and vibrating sample magnetometer (VSM). The average crystallite size of pure nickel ferrite is ∼64 nm and for Gd and Ce doped samples it is ∼20 nm and ∼14 nm, respectively. The EPR spectra were recorded from 120 to 300 K. Doping with Gd and Ce reduces the line width and g-value in comparison to that of pure nickel ferrite. Ce doped samples have the lowest values of both these parameters at room temperature. This indicates that Ce doped samples show lowest loss and is suitable for high frequency devices. EPR spin numbers are reduced while the spin relaxation time is increased after doping with rare earth ions. Gd doped samples have higher values of relaxation time and lower spin numbers in comparison to that of Ce doped samples. VSM results show that the magnetisation and coercivity are reduced after doping with both Ce and Gd rare earth ions. © 2011 Elsevier B.V.

Sultan K.,National Institute of Technology Srinagar | Ikram M.,National Institute of Technology Srinagar | Asokan K.,Inter University Accelerator Center
Vacuum | Year: 2014

Polycrystalline bulk samples of PrFe1-xMnxO 3 (x = 0.0, 0.1, 0.3, 0.5) were synthesized by solid state reaction method to understand their structural, optical and dielectric properties. X-ray diffraction (XRD) and Raman spectroscopy were investigated to confirm chemical phase and the orthorhombic pbnm structure. As the concentration of Mn increases, the lattice parameter b increases while the lattice parameters a and c/√2 decrease but the change of former is less than later. PrFe1-xMn xO3 exhibits O-type (a < c/√2 < b) orthorhombic pbnm structure upto x = 0.5. From XRD it is also evident that the peaks shift towards higher 2θ values with increase in Mn content indicating the development of strain in the crystal structure possibly due to Jahn-Teller distortion after the incorporation of Mn3+ ions in the parent compound PrFeO3. From the Raman study, the modes exhibit a blue shift with broadening of spectral features in the doped samples. The observed shift in wave number with doping clearly indicates change in the bond lengths of Fe-O/Mn-O as well as their impact on FeO6/MnO6 octahedra. The dielectric constant (É′) and dielectric loss (tan δ) are also studied as a function of frequency and temperature. The dielectric constant and ac conductivity increases with Mn doping. The variation of dielectric properties such as ac conductivity, tan δ and É′ suggests that small polarons contribute to the conduction mechanism. Activation energy (Eσ) and optical band gap (E g) decreases with the concentration of Mn. The observed higher values of these quantities reveals that there is hopping between Mn3+ to Mn4+ and Fe3+ to Fe2+ at the octahedral sites of the compound. Possible mechanism contributing to these processes has been discussed. © 2013 Elsevier Ltd. All rights reserved.

Tiwari V.K.,Banaras Hindu University | Avasthi D.K.,Inter University Accelerator Center | Maiti P.,Banaras Hindu University
ACS Applied Materials and Interfaces | Year: 2011

Ion flux dependent swift heavy ions (SHI) induced structural changes have been reported for pristine poly-(vinylidene fluoride) (PVDF). Ordering phenomena has been observed first followed by its transformation from α to β-form (polar metastable piezoelectric phase). The ordering of (020) plane become prominent at higher ion flux SHI irradiation and its further increase induces structural change from R to β phase as revealed by XRD and FTIR analyses. Structural changes are also supported by morphological evidence and thermal studies before and after SHI irradiation. © 2011 American Chemical Society.

Kumar V.V.S.,Inter University Accelerator Center
Applied Surface Science | Year: 2015

Nanocomposite (nc) ZnO-SiOx thin films were grown using rf magnetron sputter deposition technique and post-deposition annealing at 750 °C. These films were irradiated with 750 keV Argon ions at fluences in the range from 1 × 1015 to 1 × 1017 ions/cm2, using Low Energy Ion Beam Facility (LEIBF) at IUAC. X-ray diffraction (XRD) patterns of the as-deposited irradiated films show decrease in intensity of ZnO peaks relative to pristine film. Fourier transform infrared (FT-IR) spectroscopy measurements of the as-deposited irradiated films indicate the breakage of Zn-O, Zn-O-Si and Si-O-Si bonds in them, which is substantiated by FT-IR measurements of 750 °C annealed films that were irradiated at a fluence of 1016 ions/cm2. Photoluminescence (PL) measurements show drastic decrease of visible PL emission from as-deposited irradiated films. Current-Voltage (I-V) measurements show decrease in surface resistance of irradiated films by three orders of magnitude. The results suggest that 750 keV argon ion irradiation of nc ZnO-SiOx films has resulted in the formation of non-radiative defects in ZnO phase and damage in SiOx, and amorphization in Zinc silicate phase. These results are explained on the basis of the dominant energy loss mechanism of low energy ions in materials. © 2015 Elsevier B.V.

Siva Kumar V.V.,Inter University Accelerator Center
Vacuum | Year: 2016

We report studies on growth of nanocrystalline diamond films by electron cyclotron resonance chemical vapour deposition (ECR CVD) and their structural and photoconduction properties. Bias enhanced nucleation (BEN) under higher methane partial pressure has been used to grow diamond nanocrystals with sp2 carbon clusters at grain boundaries in an amorphous carbon matrix. Structural studies indicate the size of diamond nanocrystals decreased and sp2 content increased in the films with increase in methane partial pressure, which is explained using subplantation model. Current- Voltage (I-V) measurements under dark and deep ultraviolet (DUV) light illumination conditions showed higher photocurrent in films with smaller sized diamond nanocrystals (3 nm–8 nm) compared to films having diamond nanocrystals of larger size (∼15 nm). The results indicates that the photocurrent generated in the films has major contributions from photoexcited electrons in diamond nanocrystals and sp2 carbon nanoclusters, with minor contribution from amorphous carbon phase. © 2016 Elsevier Ltd

Muralithar S.,Inter University Accelerator Center
Pramana - Journal of Physics | Year: 2014

A multidetector gamma array (GDA), for studying nuclear structure was built with ancillary devices namely gamma multiplicity filter and charged particle detector array. This facility was designed for in-beam gamma spectroscopy measurements in fusion evaporation reactions at Inter-University Accelerator Centre, New Delhi. Description of the facility and in-beam performance with two experimental studies done are presented. This array was used in a number of nuclear spectroscopic and reaction investigations. © Indian Academy of Sciences.

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