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.
Stable, OH free zinc oxide (ZnO) nanoparticles were synthesized by hydrothermal method by varying the
growth temperature and concentration of the precursors. The formation of ZnO nanoparticles were confirmed by x-ray
diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) studies. The
average particle size have been found to be about 7-24 nm and the compositional analysis is done with inductively
coupled plasma atomic emission spectroscopy (ICP-AES). Diffuse reflectance spectroscopy (DRS) results shows that the
band gap of ZnO nanoparticles is blue shifted with decrease in particle size. Photoluminescence properties of ZnO
nanoparticles at room temperature were studied and the green photoluminescent emission from ZnO nanoparticles can
originate from the oxygen vacancy or ZnO interstitial related defects.
Sudha Kartha,C(American Institute of Physics., January 13, 2007)
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Abstract:
Poly(methyl)methacrylate was made photoconducting by molecular doping and the
photoconductivity was investigated using modulated photocurrent technique . Low-temperature
current-voltage measurements showed that the transport mechanism was thermally activated
hopping. An experimental investigation of the photoconductivity action spectrum along with
theoretical calculation enabled an estimation of the diffusion coefficient of the material. The
presence of states with a distribution of lifetimes could be understood from the frequency response
of the photocurrent . The photocurrent was due to the field-assisted dissociation of these states.
Transparent diode heterojunction on ITO coated glass substrates was fabricated using p-type AgCoO2 and n-type ZnO films by pulsed laser
deposition (PLD). The PLD of AgCoO2 thin films was carried out using the pelletized sintered target of AgCoO2 powder, which was synthesized
in-house by the hydrothermal process. The band gap of these thin films was found to be ~3.89 eV and they had transmission of~55% in the
visible spectral region. Although Hall measurements could only indicate mixed carrier type conduction but thermoelectric power measurements of
Seebeck coefficient confirmed the p-type conductivity of the grown AgCoO2 films. The PLD grown ZnO films showed a band gap of ~3.28 eV,
an average optical transmission of ~85% and n-type carrier density of~4.6×1019 cm− 3. The junction between p-AgCoO2 and n-ZnO was found
to be rectifying. The ratio of forward current to the reverse current was about 7 at 1.5 V. The diode ideality factor was much greater than 2.
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.
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 .
Highly conductive and transparent thin films of amorphous zinc indium tin oxide are prepared at room temperature by co-sputtering of zinc
10 oxide and indium tin oxide. Cationic contents in the films are varied by adjusting the power to the sputtering targets. Optical transmission study of
11 films showed an average transmission greater than 85% across the visible region. Maximum conductivity of 6×102 S cm−1 is obtained for Zn/In/
12 Sn atomic ratio 0.4/0.4/0.2 in the film. Hall mobility strongly depends on carrier concentration and maximum mobility obtained is 18 cm2 V−1 s−1
13 at a carrier concentration of 2.1×1020 cm−3. Optical band gap of films varied from 3.44 eV to 3 eV with the increase of zinc content in the film
14 while the refractive index of the films at 600 nm is about 2.0.
Jayaraj, M K(Electrochemical Society, December 17, 2007)
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Abstract:
Highly transparent, luminescent and biocompatible ZnO quantum dots were prepared in water, methanol, and ethanol using
liquid-phase pulsed laser ablation technique without using any surfactant. Transmission electron microscopy analysis confirmed
the formation of good crystalline ZnO quantum dots with a uniform size distribution of 7 nm. The emission wavelength could be
varied by varying the native defect chemistry of ZnO quantum dots and the laser fluence. Highly luminescent nontoxic ZnO
quantum dots have exciting application potential as florescent probes in biomedical applications.
Chitra, R N; Kuriakose, V C(American Institute of Physics, 2008)
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Abstract:
We consider an array of N Josephson junctions connected in parallel and explore the condition for chaotic synchronization. It is found that the outer junctions can be synchronized while they remain uncorrelated to the inner ones when an external biasing is applied. The stability of the solution is found out for the outer junctions in the synchronization manifold. Symmetry considerations lead to a situation wherein the inner junctions can synchronize for certain values of the parameter. In the presence of a phase difference between the applied fields, all the junctions exhibit phase synchronization. It is also found that chaotic motion changes to periodic in the presence of phase differences.
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 N; Kuriakose, V C(American Institute of Physics, 2008)
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Abstract:
Synchronization in an array of mutually coupled systems with a finite time delay in coupling is studied using the Josephson junction as a model system. The sum of the transverse Lyapunov exponents is evaluated as a function of the parameters by linearizing the equation about the synchronization manifold. The dependence of synchronization on damping parameter, coupling constant, and time delay is studied numerically. The change in the dynamics of the system due to time delay and phase difference between the applied fields is studied. The case where a small frequency detuning between the applied fields is also discussed.
Senoy, Thomas; Sakthikumar, D; Yoshida, Yasuhiko; Anantharaman, M R(Springer, 2008)
[+]
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Abstract:
Sol–gel glasses with Fe3O4 nanoparticles having particle sizes laying in the range 10–20 nm were encapsulated
in the porous network of silica resulting in nanocomposites having both optical and magnetic
properties. Spectroscopic and photoluminescence studies indicated that Fe3O4 nanocrystals are embedded
in the silica matrix with no strong Si–O–Fe bonding. The composites exhibited a blue luminescence. The
optical absorption edge of the composites red shifted with increasing concentration of Fe3O4 in the silica
matrix. There is no obvious shift in the position of the luminescence peak with the concentration of Fe3O4
except that the intensity of the peak is decreased. The unique combinations of magnetic and optical
properties are appealing for magneto–optical applications.
Hysen, Thomas; Senoy, Thomas; Ramanujan, R V; Anantharaman, M R(Springer, 2008)
[+]
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Abstract:
Activation energy for crystallization (Ec) is a
pertinent parameter that decides the application potential of
many metallic glasses and is proportional to the crystallization
temperature. Higher crystallization temperatures are
desirable for soft magnetic applications, while lower values
for data storage purposes. In this investigation, from the
heating rate dependence of peak crystallization temperature
Tp, the Ec values have been evaluated by three different
methods for metglas 2826 MB (Fe40Ni38B18Mo4) accurately.
The Ec values are correlated with the morphological
changes, and the structural evolution associated with
annealing temperatures is discussed.
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.
Louis,Godfrey; Santhosh Kumar, A(Society of Photo-Optical Instrumentation Engineers, 2008)
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Abstract:
The red cells found in the red rain in Kerala, India are now considered as a possible case of extraterrestrial life form.
These cells can undergo rapid replication even at an extreme high temperature of 300 deg C. They can also be cultured in
diverse unconventional chemical substrates. The molecular composition of these cells is yet to be identified. This paper
reports the unusual autofluorescence characteristic of the cultured red rain cells. A spectrofluorimetric study has been
performed to investigate this, which shows a systematic shift of the fluorescence emission peak wavelength as the
excitation wavelength is increased. Conventional biomolecules are not known to have this property. Details of this
investigation and the results are discussed.
Jayaraj, M K(American Vacuum Society, January 8, 2008)
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Abstract:
Structural, electronic, and optical properties of amorphous and transparent zinc tin oxide films
deposited on glass substrates by pulsed laser deposition (PLD) were examined for two chemical
compositions of Zn:Sn=1:1 and 2:1 as a function of oxygen partial pressure PO2 used for the film
deposition and annealing temperature. Different from a previous report on sputter-deposited films
Chiang et al., Appl. Phys. Lett. 86, 013503 2005 , the PLD-deposited films crystallized at a lower
temperature 450 °C to give crystalline ZnO and SnO2 phases. The optical band gaps Tauc gaps
were 2.80−2.85 eV and almost independent of oxygen PO2
, which are smaller than those of the
corresponding crystals 3.35−3.89 eV . Films deposited at low PO2
showed significant subgap
absorptions, which were reduced by postthermal annealing. Hall mobility showed steep increases
when carrier concentration exceeded threshold values and the threshold value depended on the film
chemical composition. The films deposited at low PO2
2 Pa had low carrier concentrations. It is
thought that the low PO2
produced high-density oxygen deficiencies and generated electrons, but
these electrons were trapped in localized states, which would be observed as the subgap absorptions.
Similar effects were observed for 600 °C crystallized films and their resistivities were increased by
formation of subgap states due to the reducing high-temperature condition. High carrier
concentrations and large mobilities were obtained in an intermediate PO2
region for the as-deposited films.
Jayaraj, M K(Electrochemical Society, February 18, 2008)
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Abstract:
The optical and carrier transport properties of amorphous transparent zinc indium tin oxide (ZITO)(a-ZITO) thin films and the
characteristics of the thin-film transistors TFTs were examined as a function of chemical composition. The as-deposited films
were very conductive and showed clear free carrier absorption FCA . The analysis of the FCA gave the effective mass value of
0.53 me and a momentum relaxation time of 3.9 fs for an a-ZITO film with Zn:In:Sn = 0.35:0.35:0.3. TFTs with the as-deposited
channels did not show current modulation due to the high carrier density in the channels. Thermal annealing at 300°C decreased
the carrier density and TFTs fabricated with the annealed channels operated with positive threshold voltages VT when Zn
contents were 25 atom % or larger. VT shifted to larger negative values, and subthreshold voltage swing increased with decreasing
the Zn content, while large on–off current ratios 107–108 were kept for all the Zn contents. The field effect mobilities ranged
from 12.4 to 3.4 cm2 V−1 s−1 for the TFTs with Zn contents varying from 5 to 48 atom %. The role of Zn content is also
discussed in relation to the carrier transport properties and amorphous structures.