Jayaraj, M K(American Vacuum Society, January 8, 2008)
[+]
[-]
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.
Optical emission spectroscopic studies were carried out on the plasma produced by ablation of zinc
oxide target using the third harmonic 355 nm of Q-switched Nd:YAG laser, in vacuum and at three
different ambient gas oxygen pressures. The spatial variations of electron density Ne and electron
temperature Te were studied up to a distance of 20 mm from the target surface. The kinematics of
the emitted particles and the expansion of the plume edge are discussed. The optimum conditions
favorable for the formation of high quality zinc oxide thin films are thereby suggested.
Jayaraj, M K(Electrochemical Society, July 18, 2007)
[+]
[-]
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 .
Shaju,P D; Kuriakose,V C(Cochin University of Science and Technology, 2002)
[+]
[-]
Abstract:
The thesis deals with detailed theoretical analysis of fluxon dynamics in single and in coupled Josephson junctions of different geometries under various internal and external conditions. The main objective of the present work is to investigate the properties of narrow Long Josephson junctions (LJJs) and to discuss the intriguing physics. In this thesis, Josephson junctions of three types of geometries, viz, rectangular, semiannular and quarter annular geometries in single and coupled format are studied to implement various fluxon based devices. Studies presented in this thesis reveal that mulistacked junctions are extremely useful in the fabrication of various super conducting electronic devices. The stability of the dynamical mode and therefore the operational stability of the proposed devices depend on parameters such as coupling strength, external magnetic fields, damping parameters etc. Stacked junctions offer a promising way to construct high-TC superconducting electronic components. Exploring the complex dynamics of fluxons in coupled junctions is a challenging and important task for the future experimental and theoretical investigations
Geetha,R; Chandramohanakumar,N(Department of Chemical Oceanography,School of marine sciences, 2002)
[+]
[-]
Abstract:
The mangrove ecosystem is one of the earth’s most endangered ecosystems. In this study, geochemical features of three mangrove ecosystems, Mangalavanam, Vypeen and Nettoor were compared. Water, sediment and core samples were collected from these stations for a period of one year. Nutrients, organic compounds orgnic carbon and hydrographical parameters of the samples were estimated. The present study revealed higher concentration of carbon in the surface sediments. The major temporary or ultimate sink for various pollutants in estuaries is the sedimentary reservoir, including intertidal areas. In the present study, higher values for dissolved nutrients, POC and carbohydrates were observed during low tide.
Sindhu,S; Anantharaman,M R(Cochin University of Science and Technology, April , 2001)
[+]
[-]
Abstract:
The objectives of the proposed work are preparation of ceramic nickel zinc ferrite belonging to the series Ni1-XZnXFe2O4 with x varying from 0 to 1in steps of 0.2, structrural, magnetic and electrical characterization of Ni1-XZnXFe2O4, preparation and evaluation of Cure characteristics of Rubber Ferrite Composites (RFCs), magnetic characterization of RFCs using vibrating sample magnetometer (VSM), electrical characterization of RFCs and estimation of magnetostriction constant form HL parameters. The study deals with the structural and magnetic properties of ceramic fillers, variation of coercivity with composition and the variation of magnetization for different filler loadings are compared and correlated. The dielectric properties of ceramic Ni1-XZnXFe2O4 and rubber ferrite composites containing Ni1-XZnXFe2O4 were evaluated and the ac electrical conductivity (ac) of ceramic as well as composite samples can be calculated by using a simple relationship of the form ac = 2f tan 0r, with the data available from dielectric measurements. The results suggest that the ac electrical conductivity is directly proportional to the frequency
Ceramic dielectric resonators in the BaO-RE2O3-TiO2 (RE = rare earth) system have been
prepared by the conventional solid state ceramic route. The dielectric properties have been
tailored by substitution of different rare earth oxides and by bismuth oxide addition. The
dielectric constants increased with Bi addition whereas the 0 decreased. The temperature
coefficient of the resonant frequency improved with bismuth addition