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Abstract:
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Material synthesizing and characterization has been one of the major areas of
scientific research for the past few decades. Various techniques have been suggested for
the preparation and characterization of thin films and bulk samples according to the
industrial and scientific applications. Material characterization implies the determination
of the electrical, magnetic, optical or thermal properties of the material under study.
Though it is possible to study all these properties of a material, we concentrate on the
thermal and optical properties of certain polymers. The thermal properties are detennined
using photothermal beam deflection technique and the optical properties are obtained
from various spectroscopic analyses. In addition, thermal properties of a class of
semiconducting compounds, copper delafossites, arc determined by photoacoustic
technique.Photothermal technique is one of the most powerful tools for non-destructive
characterization of materials. This forms a broad class of technique, which includes laser
calorimetry, pyroelectric technique, photoacollstics, photothermal radiometric technique,
photothermal beam deflection technique etc. However, the choice of a suitable technique
depends upon the nature of sample and its environment, purpose of measurement, nature
of light source used etc. The polynler samples under the present investigation are
thermally thin and optically transparent at the excitation (pump beam) wavelength.
Photothermal beam deflection technique is advantageous in that it can be used for the
detennination of thermal diffusivity of samples irrespective of them being thermally thick
or thennally thin and optically opaque or optically transparent. Hence of all the abovementioned
techniques, photothemlal beam deflection technique is employed for the
successful determination of thermal diffusivity of these polymer samples. However, the semi conducting samples studied are themlally thick and optically opaque and therefore, a
much simpler photoacoustic technique is used for the thermal characterization.The production of polymer thin film samples has gained considerable attention
for the past few years. Different techniques like plasma polymerization, electron
bombardment, ultra violet irradiation and thermal evaporation can be used for the
preparation of polymer thin films from their respective monomers. Among these, plasma
polymerization or glow discharge polymerization has been widely lIsed for polymer thin
fi Im preparation. At the earlier stages of the discovery, the plasma polymerization
technique was not treated as a standard method for preparation of polymers. This method
gained importance only when they were used to make special coatings on metals and
began to be recognized as a technique for synthesizing polymers. Thc well-recognized
concept of conventional polymerization is based on molecular processcs by which thc
size of the molecule increases and rearrangemcnt of atoms within a molecule seldom
occurs. However, polymer formation in plasma is recognized as an atomic process in
contrast to the above molecular process. These films are pinhole free, highly branched
and cross linked, heat resistant, exceptionally dielectric etc. The optical properties like
the direct and indirect bandgaps, refractive indices etc of certain plasma polymerized thin
films prepared are determined from the UV -VIS-NIR absorption and transmission
spectra. The possible linkage in the formation of the polymers is suggested by comparing
the FTIR spectra of the monomer and the polymer. The thermal diffusivity has been
measured using the photothermal beam deflection technique as stated earlier. This
technique measures the refractive index gradient established in the sample surface and in
the adjacent coupling medium, by passing another optical beam (probe beam) through
this region and hence the name probe beam deflection. The deflection is detected using a
position sensitive detector and its output is fed to a lock-in-amplifIer from which the amplitude and phase of the deflection can be directly obtained. The amplitude and phase
of the deflection signal is suitably analyzed for determining the thermal diffusivity.Another class of compounds under the present investigation is copper
delafossites. These samples in the form of pellets are thermally thick and optically
opaque. Thermal diffusivity of such semiconductors is investigated using the
photoacoustic technique, which measures the pressure change using an elcctret
microphone. The output of the microphone is fed to a lock-in-amplificr to obtain the
amplitude and phase from which the thermal properties are obtained. The variation in
thermal diffusivity with composition is studied. |