John Kurian,P; Radhakrishna,M(Department of Marine Geology and Geophysics, School of Marine Sciences, 2000)
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Abstract:
The primary aim of the present study is to acquire a large amount of gravity data, to prepare gravity maps and interpret the data in terms of crustal structure below the Bavali shear zone and adjacent regions of northern Kerala. The gravity modeling is basically a tool to obtain knowledge of the subsurface extension of the exposed geological units and their structural relationship with the surroundings. The study is expected to throw light on the nature of the shear zone, crustal configuration below the high-grade granulite terrain and the tectonics operating during geological times in the region. The Bavali shear is manifested in the gravity profiles by a steep gravity gradient. The gravity models indicate that the Bavali shear coincides with steep plane that separates two contrasting crustal densities extending beyond a depth of 30 km possibly down to Moho, justifying it to be a Mantle fault. It is difficult to construct a generalized model of crustal evolution in terms of its varied manifestations using only the gravity data. However, the data constrains several aspects of crustal evolution and provides insights into some of the major events.
Vanaja, K A; Dr. Jayalekshami, S(Cochin University of Science and Technology, May , 2011)
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Abstract:
In the present studies, various copper delafossite materials viz; CuAlO2,
CuGaO2, CuFeO2 , CuGa1-xFexO2, CuYO2 and CuCaxY1-xO2 were synthesised by
solid state reaction technique. These copper delafossite materials were grown in
thin film form by rf magnetron sputtering technique. In general copper
delafossites exhibit good optical transparency. The conductivity of the CuYO2
could be improved by Ca doping or by oxygen intercalation by annealing the film in oxygen atmosphere. It has so far been impossible to improve the p-type
conductivity of CuGaO2 significantly by doping Mg or Ca on the Ga site. The ptype
conductivity is presumed to be due to oxygen doping or Cu Vacancies [6].
Reports in literature show, oxygen intercalation or divalent ion doping on Ga
site is not possible for CuGaO2 thin films to improve the p-type conductivity.
Sintered powder and crystals of CuFeO2 have been reported as the materials
having the highest p-type conductivity [14, 15] among the copper and silver
delafossites. However the CuFeO2 films are found to be less transparent in the
visible region compared to CuGaO2. Hence in the present work, the solid
solution between the CuGaO2 and CuFeO2 was effected by solid state reaction,
varying the Fe content. The CuGa1-xFexO2 with Fe content, x=0.5 shows an
increase in conductivity by two orders, compared to CuGaO2 but the
transparency is only about 50% in the visible region which is less than that of
CuGaO2 The synthesis of α−AgGaO2 was carried out by two step process which
involves the synthesis of β-AgGaO2 by ion exchange reaction followed by the
hydrothermal conversion of the β-AgGaO2 into α-AgGaO2. The trace amount of
Ag has been reduced substantially in the two step synthesis compared to the
direct hydrothermal synthesis. Thin films of α-AgGaO2 were prepared on silicon
and Al2O3 substrates by pulsed laser deposition. These studies indicate the
possibility of using this material as p-type material in thin film form for
transparent electronics. The room temperature conductivity of α-AgGaO2 was
measured as 3.17 x 10-4 Scm-1and the optical band gap was estimated as 4.12 eV.
A transparent p-n junction thin film diode on glass substrate was fabricated
using p-type α-AgGaO2 and n-ZnO.AgCoO2 thin films with 50% transparency in the visible region were deposited
on single crystalline Al2O3 and amorphous silica substrates by RF magnetron
sputtering and p type conductivity of AgCoO2 was demonstrated by fabricating
transparent p-n junction diode with AgCoO2 as p-side and ZnO: Al as n-side
using sputtering. The junction thus obtained was found to be rectifying with a
forward to reverse current of about 10 at an applied voltage of 3 V.The present
study shows that silver delafossite thin films with p-type conductivity can be
used for the fabrication of active devices for transparent electronics applications.
Description:
Department of Physics,
Cochin University of Science and Technology
Nisha, M; Jayaraj, M K(Department of Physics, December , 2006)
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Abstract:
The increasing interest in the interaction of light with electricity and
electronically active materials made the materials and techniques for producing
semitransparent electrically conducting films particularly attractive. Transparent
conductors have found major applications in a number of electronic and
optoelectronic devices including resistors, transparent heating elements,
antistatic and electromagnetic shield coatings, transparent electrode for solar
cells, antireflection coatings, heat reflecting mirrors in glass windows and many
other. Tin doped indium oxide (indium tin oxide or ITO) is one of the most
commonly used transparent conducting oxides. At present and likely well into
the future this material offers best available performance in terms of
conductivity and transmittivity combined with excellent environmental stability,
reproducibility and good surface morphology.
Although partial transparency, with a reduction in conductivity, can be obtained
for very thin metallic films, high transparency and simultaneously high
conductivity cannot be attained in intrinsic stoichiometric materials. The only
way this can be achieved is by creating electron degeneracy in a wide bandgap
(Eg > 3eV or more for visible radiation) material by controllably introducing
non-stoichiometry and/or appropriate dopants. These conditions can be
conveniently met for ITO as well as a number of other materials like Zinc oxide,
Cadmium oxide etc.
ITO shows interesting and technologically important combination of properties
viz high luminous transmittance, high IR reflectance, good electrical
conductivity, excellent substrate adherence and chemical inertness. ITO is a key
part of solar cells, window coatings, energy efficient buildings, and flat panel
displays. In solar cells, ITO can be the transparent, conducting top layer that lets
light into the cell to shine the junction and lets electricity flow out. Improving
the ITO layer can help improve the solar cell efficiency. A transparent
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conducting oxide is a material with high transparency in a derived part of the
spectrum and high electrical conductivity. Beyond these key properties of
transparent conducting oxides (TCOs), ITO has a number of other key
characteristics. The structure of ITO can be amorphous, crystalline, or mixed,
depending on the deposition temperature and atmosphere. The electro-optical
properties are a function of the crystallinity of the material. In general, ITO
deposited at room temperature is amorphous, and ITO deposited at higher
temperatures is crystalline. Depositing at high temperatures is more expensive
than at room temperature, and this method may not be compatible with the
underlying devices.
The main objective of this thesis work is to optimise the growth conditions of
Indium tin oxide thin films at low processing temperatures. The films are
prepared by radio frequency magnetron sputtering under various deposition
conditions. The films are also deposited on to flexible substrates by employing
bias sputtering technique. The films thus grown were characterised using
different tools. A powder x-ray diffractometer was used to analyse the
crystalline nature of the films. The energy dispersive x-ray analysis (EDX) and
scanning electron microscopy (SEM) were used for evaluating the composition
and morphology of the films. Optical properties were investigated using the UVVIS-
NIR spectrophotometer by recording the transmission/absorption spectra.
The electrical properties were studied using vander Pauw four probe technique.
The plasma generated during the sputtering of the ITO target was analysed using
Langmuir probe and optical emission spectral studies.
Ajimsha, R S; Jayaraj, M K(Department of Physics, February , 2008)
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Abstract:
Transparent conducting oxides (TCO’s) have been known and used for technologically important applications for more than 50 years. The oxide materials such as In2O3, SnO2 and impurity doped SnO2: Sb, SnO2: F and In2O3: Sn (indium tin oxide) were primarily used as TCO’s. Indium based oxides had been widely used as TCO’s for the past few decades. But the current increase in the cost of indium and scarcity of this material created the difficulty in obtaining low cost TCO’s. Hence the search for alternative TCO material has been a topic of active research for the last few decades. This resulted in the development of various binary and ternary compounds. But the advantages of using binary oxides are the easiness to control the composition and deposition parameters. ZnO has been identified as the one of the promising candidate for transparent electronic applications owing to its exciting optoelectronic properties. Some optoelectronics applications of ZnO overlap with that of GaN, another wide band gap semiconductor which is widely used for the production of green, blue-violet and white light emitting devices. However ZnO has some advantages over GaN among which are the availability of fairly high quality ZnO bulk single crystals and large excitonic binding energy. ZnO also has much simpler crystal-growth technology, resulting in a potentially lower cost for ZnO based devices.
Most of the TCO’s are n-type semiconductors and are utilized as transparent electrodes in variety of commercial applications such as photovoltaics, electrochromic windows, flat panel displays. TCO’s provide a great potential for realizing diverse range of active functions, novel functions can be integrated into the materials according to the requirement. However the application of TCO’s has been restricted to transparent electrodes,
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notwithstanding the fact that TCO’s are n-type semiconductors. The basic reason is the lack of p-type TCO, many of the active functions in semiconductor originate from the nature of pn-junction. In 1997, H. Kawazoe et al reported the CuAlO2 as the first p-type TCO along with the chemical design concept for the exploration of other p-type TCO’s. This has led to the fabrication of all transparent diode and transistors.
Fabrication of nanostructures of TCO has been a focus of an ever-increasing number of researchers world wide, mainly due to their unique optical and electronic properties which makes them ideal for a wide spectrum of applications ranging from flexible displays, quantum well lasers to in vivo biological imaging and therapeutic agents. ZnO is a highly multifunctional material system with highly promising application potential for UV light emitting diodes, diode lasers, sensors, etc. ZnO nanocrystals and nanorods doped with transition metal impurities have also attracted great interest, recently, for their spin-electronic applications
This thesis summarizes the results on the growth and characterization of ZnO based diodes and nanostructures by pulsed laser ablation. Various ZnO based heterojunction diodes have been fabricated using pulsed laser deposition (PLD) and their electrical characteristics were interpreted using existing models. Pulsed laser ablation has been employed to fabricate ZnO quantum dots, ZnO nanorods and ZnMgO/ZnO multiple quantum well structures with the aim of studying the luminescent properties.
Selven, S; Dr. Rosamma, Philip(Cochin University of Science and Technology, May , 2008)
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Abstract:
Aquaculture has developed to become one of the fastest growing food producing sectors in the world.Today India is one among the major shrimp producing countries in the world.There are extensive and intensive shrimp culture practices. In
extensive shrimp culture, shrimps are stocked at low densities (< 25 PLs m'2)in large ponds or tidal enclosures in which little or no management is exercised or possible. Farmers depend almost entirely on natural conditions in extensive cultures. Intensive shrimp culture is carried out in
high densities (>200 PLs m'2). Much of the world shrimp production still comes from extensive culture.There is a growing demand for fish and marine products for human and animal consumption. This demand has led to rapid growth of
aquaculture, which some times has been accompanied by ecological impacts and economic loss due to diseases. The expansion of shrimp culture always accompanies local environmental degradation and
occurrence of diseases.Disease out breaks is recognised as a significant constraint to aquaculture production. Environmental factors, water quality, pollution due to effluent discharge and pathogenic invasion due to vertical
and horizontal transmission are the main causes of shrimp disease out breaks. Nutritional imbalance, toxicant and other pollutants also account for the onset of diseases.
pathogens include viruses, bacteria, fungi and parasites.Viruses are the most economically significant pathogens of the cultured shrimps world wide. Disease control in shrimp aquaculture should focus first on preventive measures for eliminating disease promoting factors.ln order to design prophylactic and proactive measures against shrimp diseases, it is mandatory to understand the immune make up of the cultivable species,
its optimum culture conditions and the physico chemical parameters of the rearing environment. It has been proven beyond doubt that disease is an end result of complex interaction of environment, pathogen and the host animal. The aquatic environment is abounded with infectious microbes.The transmission of disease in this environment is extremely easy,
especially under dense, culture conditions. Therefore, a better understanding of the immune responses of the cultured animal in relation to its environmental alterations and microbial invasions is essential indevising strategic measures against aquaculture loss due to diseases. This study accentuate the importance of
proper and regular health monitoring in shrimps employing the most appropriate haematological biomarkers for application of suitable prophylactic measures in order to avoid serious health hazards in shrimp culture systems.