Litty, Irimpan; Ambika, D; Kumar, V; Nampoori, V P N; Radhakrishnan, P(American Institute of Physics, 2008)
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Abstract:
The annealing effect on the spectral and nonlinear optical NLO characteristics of ZnO thin films
deposited on quartz substrates by sol-gel process is investigated. As the annealing temperature
increases from 300–1050 °C, there is a decrease in the band gap, which indicates the changes of the
interface of ZnO. ZnO is reported to show two emission bands, an ultraviolet UV emission band
and another in the green region. The intensity of the UV peak remains the same while the intensity
of the visible peak increases with increase in annealing temperature. The role of oxygen in ZnO thin
films during the annealing process is important to the change in optical properties. The mechanism
of the luminescence suggests that UV luminescence of ZnO thin films is related to the transition
from conduction band edge to valence band, and green luminescence is caused by the transition
from deep donor level to valence band due to oxygen vacancies. The NLO response of these
samples is studied using nanosecond laser pulses at off-resonance wavelengths. The nonlinear
absorption coefficient increases from 2.9 ×10−6 to 1.0 ×10−4 m/W when the annealing temperature
is increased from 300 to 1050 °C, mainly due to the enhancement of interfacial state and exciton
oscillator strength. The third order optical susceptibility x(3) increases with increase in annealing
temperature (T) within the range of our investigations. In the weak confinement regime, T2.4
dependence of x(3) is obtained for ZnO thin films. The role of annealing temperature on the optical
limiting response is also studied.
Harilal, S S; Issac, Riju C; Bindhu, C V; Nampoori, V P N; Vallabhan, C P G(American Institute of Physics, April , 1997)
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Abstract:
The emission features of laser ablated graphite plume generated in a helium ambient atmosphere have been investigated with time and space resolved plasma diagnostic technique. Time resolved optical emission spectroscopy is employed to reveal the velocity distribution of different species ejected during ablation. At lower values of laser fluences only a slowly propagating component of C2 is seen. At high fluences emission from C2 shows a twin peak distribution in time. The formation of an emission peak with diminished time delay giving an energetic peak at higher laser fluences is attributed to many body recombination. It is also observed that these double peaks get modified into triple peak time of flight distribution at distances greater than 16 mm from the target. The occurrence of multiple peaks in the C2 emission is mainly due to the delays caused from the different formation mechanism of C2 species. The velocity distribution of the faster peak exhibits an oscillating character with distance from the target surface.
Boban, Thomas; Dr.Krishna Pillai, M G(Cochin University of Science and Technology, December , 1989)
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Abstract:
This thesis deals with preparing stoichiometric crystalline thin films of InSe and In2Se3 by elemental evapouration and their property investigation.In the present study three temperature( or Elemental evapouration) method is utilized for the deposition of crystalline thin films . The deposition mechanism using three temperature method deals’ with condensation of solids on heated surfaces when the critical supersaturation of the vapour phase exceeds a certain limit. The critical values of the incident flux are related to substrate temperature and the interfacial energies of the involved vapours. At a favorable presence of component atoms in the vapour phase these can react and condense onto a substrate even at a elevated temperature. In the studies conducted the most significant factor is the formation of single compositional film namely indium mono selenide in the In –se system of compounds .Further this work shows the feasibility of thin film photovoltaic junctions of the schottky barrier type
Description:
Department of Physics, Cochin University of Science and Technology
Joseph, K S; Dr.George, Joy(Cochin University of Science and Technology, 1983)
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Abstract:
In this thesis the preparation and properties of thin films of certain semiconducting sulphides (sulphides of tin, copper and indium) are reported. As single source evaporation does not yield satisfactory films of these compounds for a variety of reasons, reactive evaporation of the metal in a sulphur atmosphere has been used for film preparation. It was found that for each metal sulphide a stoichimetric interval of fluxes and substrate temperature exists for the formation of the compound in accordance with the analysis of Guenther. The first chapter of the thesis gives a resume of the basic principles of semiconductor physics relevant to the work reported here. In the second chapter is discussed in detail the reactive evaporation techniques like ordinary reactive evaporation, activated reactive evaporation and reactive ion plating. Third chapter deals with the experimental techniques used in this study for film preparation and characterization. In the next seven chapters is discussed the preparation and properties of the compound films studied. The last chapter gives a general theory of the formation of compound films in various deposition techniques in terms of the kinetic energy of the film forming particles. It must be mentioned here that this is of fundamental importance to thin film deposition and is virtually untouched in the literature
Description:
Department of Physics, Cochin University of Science and Technology
Joseph, John; Sajeev, Sivaraman; Jayalekshmy, S; Anantharaman, 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.
Anantharaman, M R; Saravanan, S; Venkatachalam, S; Avasthi, D K(Elsevier, March 26, 2007)
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Abstract:
Polyaniline thin films prepared by RF plasma polymerisation were irradiated with 92MeV Si ions for various fluences of 1 1011,
1 1012 and 1 1013 ions/cm2. FTIR and UV–vis–NIR measurements were carried out on the pristine and Si ion irradiated polyaniline
thin films for structural evaluation and optical band gap determination. The effect of swift heavy ions on the structural and optical
properties of plasma-polymerised aniline thin film is investigated. Their properties are compared with that of the pristine sample. The
FTIR spectrum indicates that the structure of the irradiated sample is altered. The optical studies show that the band gap of irradiated
thin film has been considerably modified. This has been attributed to the rearrangement in the ring structure and the formation of CRC
terminals. This results in extended conjugated structure causing reduction in optical band gap