Louis, Godfrey; Varughese, George; Santhosh Kumar, A; Philip, J(Indian Academy of Sciences, 2008)
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Abstract:
The double sulfate family (ABSO4), where A and B are alkali metal cations, is the object of great
interest owing to the complexity and richness of its sequence of phase transition induced by temperature
variation. A new sulfate salt characterized by the presence of water molecule in the unit cell with the chemical
formula, Li2Na3(SO4)2⋅6H2O (LSSW), was obtained. The ultrasonic velocity measurement was done with pulse
echo overlap technique [PEO]. All the six second order elastic stiffness constants, C11 = C22, C33, C44 = C55, C12,
C14 and C13 = C23 are reported for the first time. The anisotropy in the elastic properties of the crystal are well
explained by the pictorial representation of the polar plots of phase velocity, slowness, Young’s modulus and
linear compressibility in a–b and a–c planes.
Jayaraj, M K(American Institute of Physics, January 4, 2006)
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Abstract:
The radio frequency plasma generated during the sputtering of Indium Tin Oxide target using Argon
was analyzed by Langmuir probe and optical-emission spectroscopy. The basic plasma parameters
such as electron temperature and ion density were evaluated. These studies were carried out by
varying the RF power from 20 to 50 W. A linear increase in ion density and an exponential decrease
in electron temperature with rf power were observed. The measured plasma parameters were then
correlated with the properties of ITO thin films deposited under similar plasma conditions.
Sudha Kartha,C(Japan society of applied physica, November 8, 2006)
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Abstract:
Copper doped methylene blue sensitized poly(vinyl alcohol) (MBPVA)–acrylamide films were fabricated to improve the
storage life of recorded gratings. The films were fabricated using gravity settling method and the copper chloride
concentration was optimized as 3:18 10 3 mol/l for a dye concentration of 6:2 10 4 mol/l. The gratings recorded on the
optimized film constitution could be stored for months with stable diffraction efficiency (24%) without any chemical or
thermal fixing techniques. The resolution of the material is found to be unaffected with the addition of copper chloride.
Chitra, R N; Kuriakose, V C(American Institute of Physics, 2008)
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Abstract:
A new geometry (semiannular) for Josephson junction has been proposed and theoretical studies have shown that the new geometry is useful for electronic applications [1, 2]. In this work we study the voltage‐current response of the junction with a periodic modulation. The fluxon experiences an oscillating potential in the presence of the ac‐bias which increases the depinning current value. We show that in a system with periodic boundary conditions, average progressive motion of fluxon commences after the amplitude of the ac drive exceeds a certain threshold value. The analytic studies are justified by simulating the equation using finite‐difference method. We observe creation and annihilation of fluxons in semiannular Josephson junction with an ac‐bias in the presence of an external magnetic field.
Chitra, R Nayak; Kuriakose, V C(Elsevier, June 4, 2007)
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Abstract:
We investigate the effect of the phase difference of appliedfields on the dynamics of mutually coupledJosephsonjunctions. A phase difference between the appliedfields desynchronizes the system. It is found that though the amplitudes of the output voltage values are uncorrelated, a phase correlation is found to exist for small values of applied phase difference. The dynamics of the system is found to change from chaotic to periodic for certain values of phase difference. We report that by keeping the value of phase difference as π, the system continues to be in periodic motion for a wide range of values of system parameters. This result may find applications in devices like voltage standards, detectors, SQUIDS, etc., where chaos is least desired.
Shenoy, S D; Joy, P A; Anantharaman, M R(Elsevier, February , 2004)
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Abstract:
Nanosized ZnFe2O4 particles containing traces of a-Fe2O3 by intent were produced by low temperature chemical
coprecipitation methods. These particles were subjected to high-energy ball milling. These were then characterised using
X-ray diffraction, magnetisation and dielectric studies. The effect of milling on zinc ferrite particles have been studied
with a view to ascertaining the anomalous behaviour of these materials in the nanoregime. X-ray diffraction and
magnetisation studies carried out show that these particles are associated with strains and it is the surface effects that
contribute to the magnetisation. Hematite percentage, probably due to decomposition of zinc ferrite, increases with
milling. Dielectric behaviour of these particles is due to interfacial polarisation as proposed by Koops. Also the defects
caused by the milling produce traps in the surface layer contributes to dielectric permittivity via spin polarised electron
tunnelling between grains. The ionic mechanism is enhanced in dielectrics with the rise in temperature which results in
the increase of dielectric permittivity with temperature.
Jayaraj, M K(Electrochemical Society, July 18, 2007)
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Abstract:
ZnGa2O4:Dy3+ phosphor thin films were deposited on quartz substrates by radio frequency rf magnetron sputtering and the effect
of substrate temperature on its structural and luminescent properties was investigated. Polycrystalline film could be deposited even
at room temperature. The crystalline behavior, Zn/Ga ratio, and surface morphology of the films were found to be highly sensitive
to substrate temperature. Under UV illumination, the as-deposited films at and above 300°C gave white luminescence even
without any postdeposition treatments. The photoluminescent PL emission can be attributed to the combined effect of multicolor
emissions from the single luminescence center Dy3+ via host-sensitization. Maximum PL emission intensity was observed for the
film deposited at 600°C, and the CIE chromaticity coordinates of the emission were determined to be x,y = 0.34, 0.31 .
Jayaraj, M K(Institute of Materials Engineering Australasia Ltd, 2005)
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Abstract:
ZnGa2O4 spinel is a promising new UV transparent electronic conductor. Enhancing the electrical conductivity of this
potential oxide phosphor can make it a promising transparent conducting oxide. In this paper, we have investigated the
effects of processing and doping on the conductivity of semiconducting ZnGa2O4, particularly thin films. Crystalline
zinc gallate thin films have been deposited on fused quartz substrates employing the pulsed laser deposition (PLD)
technique at room temperature for an oxygen partial pressure of 0.1 Pa (0.001mbar). The films were found to be UV
transparent, the band gap of which shifted to 4.75eV on hydrogen annealing. The band gap of the oxygen stoichiometric
bulk powder samples (4.55eV) determined from diffuse reflection spectrum (DRS) shifted to 4.81eV on reduction in a
hydrogen atmosphere. The electrical conductivity improved when Sn was incorporated into the ZnGa2O4 spinel. The
conductivity of ZnGa2O4:Sn thin films was further improved on reduction.
Heterojunction diodes of n-type ZnO/p-type silicon (100) were fabricated by
12 pulsed laser deposition of ZnO films on p-Si substrates in oxygen ambient at
13 different pressures. These heterojunctions were found to be rectifying with a
14 maximum forward-to-reverse current ratio of about 1,000 in the applied
15 voltage range of -5 V to +5 V. The turn-on voltage of the heterojunctions was
16 found to depend on the ambient oxygen pressure during the growth of the ZnO
17 film. The current density–voltage characteristics and the variation of the
18 series resistance of the n-ZnO/p-Si heterojunctions were found to be in line
19 with the Anderson model and Burstein-Moss (BM) shift.
Swapna S, Nair; Francis, Wavier; Joy, P A; Kulkarni, S D; Anantharaman, M R(Elsevier, March , 2008)
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Abstract:
Ferrofluids belonging to the series NixFe1 xFe2O4 were synthesised by two different procedures—one by standard co-precipitation
techniques, the other by co-precipitation for synthesis of particles and dispersion aided by high-energy ball milling with a view to
understand the effect of strain and size anisotropy on the magneto-optical properties of ferrofluids. The birefringence measurements were
carried out using a standard ellipsometer. The birefringence signal obtained for chemically synthesised samples was satisfactorily fitted to
the standard second Langevin function. The ball-milled ferrofluids showed a deviation and their birefringence was enhanced by an order.
This large enhancement in the birefringence value cannot be attributed to the increase in grain size of the samples, considering that the
grain sizes of sample synthesised by both modes are comparable; instead, it can be attributed to the lattice strain-induced shape
anisotropy(oblation) arising from the high-energy ball-milling process. Thus magnetic-optical (MO) signals can be tuned by ball-milling
process, which can find potential applications.
The differaction efficiency,sensitivity and storage life of Methylene Blue sencitized poly (vinyl chloride) film was improved by the addition of an electron donor in the matrix. The
addition of pyridine enhanced the diffraction efficiency by two times and storage life of the
gratings was increased to 2-3 days.
Anantaraman, M R; Swapna S, Nair; Mercy, Mathews; Anantharaman, M R(Elsevier, May , 2005)
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Abstract:
Superparamagnetic nanocomposites based on Y-Fe2O3 and sulphonated polystyrene were synthesised by ion-exchange process
and the structural characterisation has been carried out using X-ray diffraction technique. Doping of cobalt in to the Y-Fe2O3 lattice
was effected in situ and the doping was varied in the atomic percentage range 1–10. The optical absorption studies show a band gap
of 2.84 eV, which is blue shifted by 0.64 eV when compared to the reported values for the bulk samples (2.2 eV). This is explained on
the basis of weak quantum confinement. Further size reduction can result in a strong confinement, which can yield transparent magnetic
nanocomposites because of further blue shifting. The band gap gets red shifted further with the addition of cobalt in the lattice
and this red shift increases with the increase in doping. The observed red shift can be attributed to the strain in the lattice caused by
the anisotropy induced by the addition of cobalt. Thus, tuning of bandgap and blue shifting is aided by weak exciton confinement
and further red shifting of the bandgap is assisted by cobalt doping.
Sudha Kartha,C(Optical society of America, June 20, 2004)
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Abstract:
A methylene-blue-sensitized polymer blend of polyvinyl alcohol and polyacrylic acid is fabricated and
tested for holographic recording. It was found to have good characteristics such as high sensitivity,
storage stability, ease of fabrication, and environmental stability. Optimization of the ratio of polyvinyl
alcohol polyacrylic acid, the sensitizer concentration, pH, energy, diffraction efficiency measurements,
etc., have been done. pH is found to have a great influence on the recovery of the dye in this matrix.
The results of experimental investigations into the properties of this new material are reported.
Swapna S, Nair; Rajesh, S; Abraham, V S; Anantharaman, M R(Springer, April , 2011)
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Abstract:
Ferrofluids belonging to the series, Ni x Fe1-x Fe2O4 and Zn x Fe1-x Fe2O4, were synthesized using cold co-precipitation. Liquid films of these ferrofluids were prepared by encapsulating the ferrofluids in between two optically smooth and ultrasonically cleaned glass plates. Magnetic field induced laser transmission through these ferrofluid films has been investigated. Magnetic field values can be calibrated in terms of output laser power in the low field region in which the variation is linear. This set up can be used as a cheap optical gaussmeter in the low field regime. Using the same set-up, the saturation magnetization of the sample used can also be calculated with a sample that is pre-characterized. Hence both magnetization of the sample, as well as applied magnetic field can be sensed and calculated with a precalibrated sample.
Zinc oxide (ZnO) thin films were deposited on quartz, silicon, and polymer substrates by pulsed laser deposition (PLD)
technique at different oxygen partial pressures (0.007 mbar to 0.003 mbar). Polycrystalline ZnO films were obtained at
room temperature when the oxygen pressure was between 0.003 mbar and .007 mbar, above and below this pressure the
films were amorphous as indicated by the X-ray diffraction (XRD). ZnO films were deposited on Al2O3 (0001) at
different substrate temperatures varying from 400oC to 600oC and full width half maximum (FWHM) of XRD peak is
observed to decrease as substrate temperature increases. The optical band gaps of these films were nearly 3.3 eV. A
cylindrical Langmuir probe is used for the investigation of plasma plume arising from the ZnO target. The spatial and
temporal variations in electron density and electron temperature are studied. Optical emission spectroscopy is used to
identify the different ionic species in the plume. Strong emission lines of neutral Zn, Zn+ and neutral oxygen are
observed. No electronically excited O+ cations are identified, which is in agreement with previous studies of ZnO plasma
plume.
Veena Gopalan, E; Al-Omari, I A; Malini, K A; Joy, P A; Sakthi Kumar, D; Yasuhiko, Yoshida; Anantaraman, M R(Elsevier, April , 2009)
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Abstract:
Mn1-xZnxFe2O4 nanoparticles (x=0-1) were synthesized by wet chemical co-precipitation techniques. X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy were effectively utilized to investigate the different structural parameters. The elemental analysis was conducted using energy-dispersive spectrum and inductively coupled plasma analysis. The magnetic properties such as magnetization and coercivity were measured using vibrating sample magnetometer. The observed magnetization values of the nanoparticles were found to be lower compared to the bulk counterpart. The magnetization showed a gradual decrease with zinc substitution except for a small increase from x=0.2 to 0.3. The Curie temperature was found to be enhanced in the case of ferrites in the nanoregime. The variation in lattice constant, reduced magnetization values, variation of magnetization with zinc substitution, the presence of a net magnetic moment for the zinc ferrite and the enhancement in Curie temperature in Mn1-xZnxFe2O4 all provide evidence to the existence of a metastable cation distribution together with possible surface effects at the nanoregime.
Joseph, John; Sajeev, Sivaraman; Jayalekshmy, S.; Anantaraman, M R(Elsevier, July , 2010)
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Abstract:
Plasma polymerization is found to be an excellent technique for the preparation of good quality, pinhole-free, polymer thin films from different monomer precursors. The present work describes the preparation and characterization of polypyrrole (PPy) thin films by ac plasma polymerization technique in their pristine and in situ iodine doped forms. The electrical conductivity studies of the aluminiumpolymeraluminium (AlpolymerAl) structures have been carried out and a space charge limited conduction (SCLC) mechanism is identified as the most probable mechanism of carrier transport in these polymer films. The electrical conductivity shows an enhanced value in the iodine doped sample. The reduction of optical band gap by iodine doping is correlated with the observed conductivity results.