Rahana, Yoosuf; Dr.Jayaraj, M K(Cochin University of Science & Technology, October , 2007)
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Abstract:
Two stage processes consisting of precursor preparation by thermal
evaporation followed by chalcogenisation in the required atmosphere is
found to be a feasible technique for the PV materials such as n-Beta In2S3,
p-CulnSe2, p-CulnS2 and p-CuIn(Sel_xSx)2. The growth parameters such as
chalcogenisation temperature and duration of chalcogenisation etc have been
optimised in the present study.Single phase Beta-In2S3 thin films can be obtained by sulfurising the indium
films above 300°C for 45 minutes. Low sulfurisation temperatures required
prolonged annealing after the sulfurisation to obtain single phase Beta-1n2S3,
which resulted in high material loss. The maximum band gap of 2.58 eV was
obtained for the nearly stoichiometric Beta-In2S3 film which was sulfurised at
350°C. This wider band gap, n type Beta-In2S3 can be used as an alternative to
toxic CdS as window layer in photovoltaics .The systematic study on the structural optical and electrical properties of
CuInSe2 films by varying the process parameters such as the duration of
selenization and the selenization temperature led to the conclusion that for
the growth of single-phase CuInSe2, the optimum selenization temperature is
350°C and duration is 3 hours. The presence of some binary phases in films
for shorter selenization period and lower selenization temperature may be
due to the incomplete reaction and indium loss. Optical band gap energy of
1.05 eV obtained for the films under the optimum condition.In order to obtain a closer match to the solar spectrum it is desirable to
increase the band gap of the CulnSe2 by a few meV . Further research
works were carried out to produce graded band gap CuIn(Se,S)2 absorber
films by incorporation of sulfur into CuInSe2. It was observed that when the
CulnSe2 prepared by two stage process were post annealed in sulfur atmosphere, the sulfur may be occupying the interstitial positions or forming
a CuInS2 phase along with CuInSe2 phase. The sulfur treatment during the
selenization process OfCu11 ln9 precursors resulted in Culn (Se,S)2 thin films.
A band gap of 1.38 eV was obtained for the CuIn(Se,S)2.The optimised thin films n-beta 1n2S3, p-CulnSe2 and p-Culn(Sel-xSx)2 can be
used for fabrication of polycrystalline solar cells.
Description:
Department of Physics,
Cochin University of Science and Technology
Ajitha, S; Dr.Sugunan, S(Cochin University of Science and Technology, September , 2008)
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Abstract:
Mesoporous materials are of great interest to the materials community because of their potential applications for catalysis,separation of large molecules,medical implants,semiconductors,magnetoelectric devices.The thesis entitled 'Ordered Mesoporous Silica as supports for immobilization of Biocatalyst' presents how the pore size can be tuned without the loss in ordered structure for the entrapment of an industially important biocatalyst-amylase.Immobilization of enzymes on ordered mesoporous material has triggered new ooportunities for stabilizing enzymes with improved intrinsic and operational stabilities.
Description:
Department of Applied Chemistry,
Cochin University of Science and Technology
Kannan, V; Dr. Sreekumar, K(Cochin University of Science & Technology, August , 2011)
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Abstract:
Catalysis is a technologically important field which determines the quality of life in future. Catalyst research in pharmaceutical industry,fine chemical synthesis and emission control demands supported catalysts in bulk quantities.In the present work it was observed that clay supported catalysts mentioned in various chapters could also be used for the synthesis of similar molecules. The K10Ti catalyst can be used for the synthesis similar substituted imidazole derivatives under solvent free conditions and synthetically important Mannich bases of substrates containing various substitutes.Al-pillared saponite can be used for acetalation of other polyhydroxy compounds like glycerol,mannitol etc.Cu-Pd KSF catalyst has found application in C-C bond forming reactions which can be applied to other reactions and similar methods can be adopted for the synthesis of other catalyst by changing the transition metals. Montmorillonite K10 catalysed synthesis of triarylpyridines can be extended to the synthesis tetrasubstuted pyroles.K10Ti can also be utilized for the synthesis of similar heterocycles.
Description:
Dept.of Applied Chemistry,Cochin University of Science and Technology
Rani, Rajan; Dr.Radhakrishnan, K V(Cochin University Of Science And Technology, April , 2013)
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Abstract:
The reactions involving fulvenes and its derivatives have received a great
deal of attention over the years in synthetic organic chemistry. Functionalizations
of fulvenes provide versatile and powerful approaches to various polycyclic
systems and natural products. They serve as versatile intermediates in the
construction of various ring systems through inter- as well as intramolecular
cycloadditions. Compared to the rich literature on the cycloaddition reactions of
pentafulvenes, much less attention has been paid to the synthetic utilization of
their cycloadducts. Tactical manipulations on the chosen adduct offer the
prospects for designing a variety of useful molecular skeletons.
Addition of heterodienophiles to fulvenes offers an efficient strategy towards
the synthesis of azabicyclic olefins. However, there have been no serious attempts
to study the synthetic utility of these substrates. In this context and with the
intention of utilizing pentafulvenes towards synthetically important molecules, author
decided to explore the reactivity of pentafulvene derived azabicyclic olefins. Our
attention was focused on the synthetic potential associated with the ring opening
of fulvene derived bicyclic hydrazines under palladium catalysis. It was envisioned
that the desymmetrization of these adducts using various soft nucleophiles will
provide a novel access to synthetically and biologically important alkylidene
cyclopentenes. The investigations along this line form the focal theme of this
thesis entitled “PALLADIUM CATALYZED CARBONCARBON/
CARBON-HETEROATOM BOND FORMATION REACTIONS
UTILIZING PENTAFULVENE DERIVED BICYCLIC HYDRAZINES
Description:
Organic
Chemistry Section, National Institute for Interdisciplinary Science and Technology
Satheesh, Kumar M K; Dr.Girijavallabhan,C P(Cochin University of Science and Technology, August 27, 1987)
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Abstract:
The discovery of the Photoacoustic (PA) effect was a remarkable
achievement and was relegated to the scientific footnotes of the nineteenth
century. However, after the advent of lasers and sophisticated
electronics this effect was rediscovered and it has established itself
as an important research and analytical tool in numerous areas, including
physics, chemistry, biology and medicine. Quite recently, this phenomenon
has made its impact in the field of laser technology for applications
such as the developments of highly efficient active media for
lasers, high quality optics and sensitive laser power monitoring devices.
This thesis presents the work carried out by the author in this field
during the past few years at the Department of Physics in Cochin University
of Science and Technology.
The studies discussed here are mostly based on the development
of a sensitive PA laser power meter and its various applications using
different laser systems available in the laboratory. This includes the
development of a current regulated CW C0 laser and its application
in material processing. The thesis contains seven chapters which by and large are self
contained with separate abstracts and references. The first chapter
which is divided into two parts presents an introduction to the PA effect
and its present status. Part A reviews the basic theory of laser and
gives a sum mary of various lasers and their applications. Part B presents
a brief description of PA effect and its suitability as a spectroscopic
tool followed by its applications to various branches of science and
technology.
Description:
Department of Physics, Cochin
University of Science and Technology
Madhusoodanan, K N; Dr. Jacob, Philip(Cochin University of Science And Technology, November , 1988)
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Abstract:
This thesis work has mainly concentrated on the investigation of the ,optical and thermal properties of binary semiconducting chalcogenide glasses belonging to the AivB¥5x and AZBXEX families. The technique used for these studies is a relatively new one namely, the photoacoustic (PA) technique. This technique is based on the detection of acoustic signal produced in an enclosed volume when the sample is irradiated by an intensity modulated radiation. The signal produced depends upon the optical properties of the sample, and the thermal properties of the sample, backing material and the surrounding gas. For the present studies an efficient signal beam gas-microphone PA spectrometer, consisting of a high power
Xenon lamp, monochromator, light beam chopper, PA cell with microphone and lock-in amplifier, has been set up. Two PA cells have been fabricated: one for room temperature measurements and another for measurements at high temperatures. With the high temperature PA cell measurements can be taken upto 250°C. Provisions are incorporated. in both the cells to change the volume and to use different backing materials for the sample. The cells have been
calibrated by measuring the frequency response of the cells using carbon black as the sample
Description:
Department of physics, Cochin University of Science And Technology
Syamala,S B; Dr.Sudha Kartha,C(Cochin University of Science & Technology, January , 2004)
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Abstract:
Photoconductivity (PC) processes may
be the most suitable technique for obtaining information about the states in the
gap. It finds applications in photovoItaics, photo detection and radiation
measurements. The main task in the area of photovoltaics, is to increase the
efficiency of the device and also to develop new materials with good optoelectronic
properties useful for energy conversion, keeping the idea of cost
effectiveness. Photoconduction includes generation and recombination of carriers
and their transport to the electrodes. So thermal relaxation process, charge
carrier statistics, effects of electrodes and several mechanisms of recombination
are involved in photoconductivity.A major effect of trapping is to make the experimentally observed decay
time of photocurrent, longer than carrier lifetime. If no trapping centers are
present, then observed photocurrent will decay in the same way as the density
of free carriers and the observed decay time will be equal to carrier lifetime. If
the density of free carriers is much less than density of trapped carriers, the
entire decay of photocurrent is effectively dominated by the rate of trap emptying
rather than by the rate of recombination.In the present study, the decay time of carriers was measured using
photoconductive decay (PCD) technique. For the measurements, the film was
loaded in a liquid Helium cryostat and the temperature was controlled using
Lakshore Auto tuning temperature controller (Model 321). White light was
used to illuminate the required area of the sample. Heat radiation from the light
source was avoided by passing the light beam through a water filter. The decay current. after switching off the illumination. was measured using a Kiethely
2000 multi meter. Sets of PCD measurements were taken varying sample
temperature, sample preparation temperature, thickness of the film, partial
pressure of Oxygen and concentration of a particular element in a compound.
Decay times were calculated using the rate window technique, which is a decay
sampling technique particularly suited to computerized analysis. For PCD curves
with two well-defined regions, two windows were chosen, one at the fast decay
region and the other at the slow decay region. The curves in a particular window
were exponentially fitted using Microsoft Excel 2000 programme. These decay
times were plotted against sample temperature and sample preparation
temperature to study the effect of various defects in the film. These studies
were done in order to optimize conditions of preparation technique so as to get
good photosensitive samples. useful for photovoltaic applications.Materials selected for the study were CdS, In2Se3, CuIn2Se3 and CuInS2•
Photoconductivity studies done on these samples are organised in six chapters
including introduction and conclusion.
Description:
Department of Physics,
Cochin University of Science and Technology