D. Jayaraman

Studies on photoconductivity of C60 and C60-doped poly(vinylchloride)

Abstract Single crystals of buckminsterfullerene (C 60 ) were grown by low-temperature solution growth technique. Using the same technique, poly(vinylchloride) was doped with 1% of C 60 by mass. FTIR spectra were recorded for pure C 60 , pure poly(vinylchloride) and C 60 -doped poly(vinylchloride) by Bruker IFS 66V FTIR spectrometer. From the nature of the FTIR spectrum of the C 60 -doped material, it is found that the material is polycrystalline and the presence of C 60 has been confirmed. The absorption spectra for C 60 and C 60 -doped PVC samples were recorded using SL159 UV–vis spectrophotometer. Photoconductivity studies were also made for these materials. It was interesting to observe that the C 60 -PVC exhibited negative photoconductivity. Stockmann model has been successfully applied to explain this behaviour of the doped sample.

Growth aspects of semi-organic nonlinear optical l-arginine tetrafluoroborate single crystals

Abstract Single crystals of l -arginine tetrafluoroborate ( l -AFB), a semi-organic NLO material, have been grown from aqueous solution. Since l -AFB is known to form highly viscous solution in water, growth by slow cooling has been difficult for optical quality crystals. In this study, highly transparent l -AFB crystals have been successfully grown by slow evaporation by keeping the saturated solution under special condition. The grown crystals were subjected to structural, optical and mechanical property studies. XRD studies reveal that l -AFB crystals possess orthorhombic structure. Fourier transform infrared absorption studies confirm the chemical constituents and presence of functional groups in the grown crystals. l -AFB crystals possess a higher hardness values compared to other semi-organic crystals. The linear and nonlinear optical properties of the grown crystals have also been studied.

Growth and single crystal XRD characterization of undoped and doped 4-hydroxyacetophenone

Abstract Good quality 4-hydroxyacetophenone and nitro-doped 4-hydroxyacetophenone crystals have been successfully grown from saturated methanol solution by slow cooling method. Then, 3-nitro-4-hydroxyacetophenone is incorporated as a dopant into single crystals of 4-hydroxyacetophenone to enhance the NLO property. The crystal structure and the packaging of molecules along the “ a ” and “ c ” directions have been obtained by single crystal X-ray diffraction studies. The mechanical properties of the grown crystals have been analysed using Vickers microhardness tester.

Experimental determination of metastable zonewidth, induction period, interfacial energy and growth of non-linear optical l-HFB single crystals

Abstract Metastable zonewidth, induction period and interfacial energy have been determined for the aqueous solution growth of l -histidine tetrafluoroborate ( l -HFB). Nucleation parameters such as radius of critical nucleus, Gibbs free energy change have also been investigated. The solubility of l -HFB has been estimated at different temperatures. Interfacial energy has been estimated using the experimentally determined induction period values. The evaluated interfacial tension values are found to be comparable with the theoretical values derived from solubility data. Bulk crystals of l -HFB have been grown from optimized growth parameters.

Mechanical and optical studies on pure and nitro doped 4-hydroxyacetophenone

Single crystals of pure and nitro doped 4-hydroxyacetophenone (NLO material) were grown by slow cooling technique. The single crystals were subjected to studies of Vickers microhardness. The Vickers hardness increases with the increase in applied load. The UV cut off wavelength of the grown crystals has been measured as about 280 nm from the optical transmission spectra of the samples. Chemical etching has also been carried out.

Nucleation kinetics of cadmium sulphide thin film — CVD technique

A theoretical study has been made to investigate the nucleation kinetics of cadmium sulphide (CdS) thin film grown by CVD technique. In CVD technique, the temperature gradient between the source zone and the growth zone provides the necessary driving force for the nucleation of CdS thin film over the substrate. The incident flux at the substrate depends mainly upon the temperature gradient between the two zones. In the present work, the equilibrium flux is estimated from the activation energy and heat of reaction due to the reaction and diffusion in the medium and the condensation at the substrate. The nucleation rate and the growth rate of the film have been calculated for different temperature gradients and compared with the available experimental results.

Nucleation Kinetics of C70

Abstract Since the shape of C70 molecule is prolate spheroidal, the same shape is assigned to the clusters of C70 molecules and the nucleation parameters are evaluated using classical nucleation theory. Moreover, C70 molecule is highly rotational and the rotational energy is included in the nucleation kinetics of C70 molecules. the supersaturation required for condensation of C70 molecules is high compared to that of C70. This theoretical prediction is compared with experimental observations.