S. Moorthy Babu

Czochralski growth of lead tungstate single crystals and their characterization

Abstract Single crystals of lead tungstate scintillator were grown by the Czochralski method employing resistive heating system. Variations in the nature of crystal cracking were observed and are discussed in relation to seed rotation rate, crystal pulling rate and axial temperature gradient. The problem of melt supercooling occurred very often and was overcome by carefully adjusting the seed rotation rate. Gradual decrease in optical quality from the top part of the growing crystal was also observed and repeated crystallization yielded highly transparent crystals. Excitation-emission spectra evidenced decrease in emission intensity for the bottom part of the crystal due to poor optical quality. The perfection of the grown crystals was analysed by differential thermal analysis and etching studies.

Electrodeposition of CdTe by potentiostatic and periodic pulse techniques

Abstract Cadmium telluride was electrodeposited from an aqueous solution containing the species CdCl 2 and TeO 2 by potentiostatic and periodic pulse techniques. The effect of different parameters such as concentration of the individual species, hydrogen ion concentration, applied potential and temperature are analysed to obtain optimum conditions for codeposition. X-ray diffractograms, X-ray microprobe analysis, scanning electron microscopy and voltammetry were employed to understand the crystalline nature, elemental composition and surface properties of the deposited films. A theoretical model has been developed for the electrodeposition of CdTe to understant the mechanism involved in the process. The results are discussed.

Some aspects on the growth of lead molybdate single crystals and their characterization

Lead molybdate single crystals were grown by the Czochralski technique. The growth conditions using resistive heating furnace are described in terms of internal radiant heat transfer through the crystal. Thorough investigations on the dependence of (i) the shape of the crystal-melt interface on the internal heat transfer through the crystal and (ii) incorporation of voids and inclusions and presence of strains on the seed rotation rate yielded high quality crystals. The tendency of lead molybdate to have a convex crystal-melt interface shape despite a low axial thermal gradient and high seed rotation rate is studied in detail. Annealing, optical transmission and chemical etching studies were also carried out in order to estimate the degree of perfection of the grown crystals.

Investigation of swift heavy ion irradiation effects in CdTe crystals

CdTe crystals grown by the Bridgman technique were irradiated by swift heavy ions (SHIs), 100 MeV Ag7+ ions, with fluences varying from 1011 to 1014 ions cm−2 and the damage is investigated by atomic force microscopy, x-ray diffraction, hall effect measurements and photoluminence. It is found that the behaviour of CdTe crystals under a SHI irradiation induces structural disorder, generation of optically active defects, decrease in the electron mobility but an increase in the carrier concentration compared with as-grown samples. The observed effects are mainly due to the intense electronic excitation created by SHIs.

Synthesis, crystal growth and mechanical properties of lead molybdate

Abstract Single crystals of PbMoO4 were grown by Czochralski method. The growth behaviour has been studied by taking into consideration the different parameters such as seed rotation rate, pulling rate and the axial temperature gradient above the melt level. It was found that the crystal-melt interface shape is always convex despite low axial temperature gradient and high seed rotation rate and is attributable to the fact that the crystal is transparent in the IR region and hence to internal radiant heat transfer through the crystal. To study the chemical entities, the powder sample was examined with the FTIR spectroscopic method. Differential thermal analysis confirmed the melting point and the composition. Optical microscopic observation of single crystals revealed gas bubbles in the crystals grown at faster pulling rate and strain induced surface cracks upon heat treatment in the crystals grown with more convex crystal—melt interface shape. Microhardness studies were also performed on the as grown and heat-treated samples and the values of microhardness and fracture toughness were calculated.

Influence of swift ions and proton implantation on the formation of optical waveguides in lithium niobate

Optically polished titanium doped congruent lithium niobate single crystals were implanted with protons of energy of 120keV (at fluences of 1×1015, 1×1016, and 1×1017ions∕cm2). Some loss of lithium from the surface upon ion implantation was recovered by irradiation with 50MeV lithium ions (at fluences varying from 1×1011to1×1013ions∕cm2). The near surface region defects created in the crystal were analyzed using high resolution x-ray diffraction technique, atomic force microscopy, fourier transform infrared, and optical transmittance (UV-visible) studies. The marked lattice strain induced by the energetic ions was characterized by high resolution x-ray diffraction measurements. Three-dimensional defect clusters were observed from atomic force microscopy with nanoscale resolution. Variations of O–H bond stretching vibrations as a function of fluences were observed. Optical transparency of these samples was found to depend on implantation, irradiation, and combined processes. Correlating the structural info...

Electrocrystallization and characterization of CuInSe2 thin films

Abstract CuInSe 2 thin films were deposited on Mo substrates by electrodeposition from aqueous solution containing the mixture of CuSO 4 , InCl 3 and SeO 2 by potentiostatic technique. The co-deposition conditions were optimized by drawing the voltammogram along with the Pourbaix diagrams. The deposition was carried out by varying the cathode potential from − 0.2 to − 0.8 V to obtain the co-deposition region of CuInSe 2 . As-grown and annealed films were structurally characterized by the X-ray diffraction (XRD) technique. The results reveal that as-deposited films contain CuInSe 2 , Cu 3 Se 2 , In 6 Se 7 and Se. XRD studies show that the effect of annealing at 350 °C in N 2 atmosphere results in the good structural formation of CuInSe 2 chalcopyrite structure. A linear relationship exists between the quantity of charge passed during the deposition and mass of deposition of CuInSe 2 on Mo substrate for a particular co-deposition region. The experimental conditions and the results are briefly analysed.

FT-IR, NIR-FT-Raman and gas phase infrared spectra of 3-aminoacetophenone by density functional theory and ab initio Hartree-Fock calculations.

The gas phase infrared spectrum of 3-aminoacetophenone (3AAP) was measured in the range 5000-500 cm(-1) and with a resolution of 0.5 cm(-1). The Fourier transform Raman (FT-Raman) and Fourier transform infrared (FT-IR) spectra of 3AAP were recorded in the solid phase. Geometry optimizations were done without any constraint and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and density functional theory (DFT) levels invoking 6-311G(2df 2p) basis set and the results are compared with the experimental values. Harmonic-vibrational wavenumber was also calculated for the minimum energy conformer at ab initio and DFT levels using 6-31G(d,p) basis set and the results are compared with related molecules. With the help of specific scaling procedures, the observed vibrational wavenumbers in gas phase, FT-IR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range, the error obtained was in general very low. The appropriate theoretical spectrogram for the FT-IR spectra of the title molecule is also constructed.

Influence of cooling rate on the dislocations and related luminescence in LPE SiGe layers grown on Si (100) substrates

Abstract Thick relaxed SiGe layers have been grown using the liquid phase epitaxy (LPE) technique. The Ge contents in the layers varied from 3.4 to 12.9 at.%. The thickness of the layers was approximately 25–30 μm. The layers grown at low cooling rates and with low Ge contents had low threading dislocation densities. Etch pit density of the layers increased from 2×10 4 to 8×10 5 cm −2 with increasing cooling rates from 20 K/h to 500 K/h during the LPE process. Etch pit density of the SiGe layers increased from 8×10 4 to 7×10 6 cm −2 as the Ge content in the layers increased from 3.4 to 12.9 at.%. The good quality of the layers grown at low cooling rates has been demonstrated by the strong no-phonon and TO phonon near band gap luminescence of the layers. Strong increase in the intensities of D and T bands was observed in the layers having high Ge contents and grown at high cooling rates. The increase in the intensity of the dislocation related D and T band luminescence in the layers has been related to the increase in the dislocation density of the layers.

A study of the optical and mechanical properties of PbWO4 single crystals

Optimised growth conditions were employed to grow good quality lead tungstate single crystals. Data were obtained on the optical absorption and radiation damage. Radiation-induced optical damage was found to be more for yellow-tint crystals than for colourless crystals. Samples cut from different portions of the crystal were analysed with photoluminescence studies which showed quality-dependent intensity variation. Thermoluminescence measurements made on gamma irradiated crystals showed different type of glow curves for different samples. An investigation was also made to determine the mechanical hardness of the material.