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Kumar, R.Mohan,Babu, D.Rajan,Ravi, G.,Jayavel, R. The Korea Association of Crystal Growth 2003 韓國結晶成長學會誌 Vol.13 No.4
Pure and Ethylenediaminetetraacetic acid (EDTA) doped L-arginine phosphate (LAP) single crystals were grown from the aqueous solution by temperature lowering method. The effect of EDTA additive on the solubility and metastable zone width of LAP solution has been investigated. Addition of EDTA has enhanced the metastable zone width of LAP and hence bulk crystals could be grown. The growth rate along the [100] direction increases with EDTA additive. Powder X-ray diffraction and FTIR studies reveal the absence of EDTA in the lattice of LAP, This reveals that the addition of EDTA to LAP doesn't influence the crystallinity. However, the transmittance and NLO properties significantly increase with EDTA additive and hence bulk LAP crystals are useful for laser fusion experiments.
V. Siva Shankar,R. Siddheswaran,R. Sankar,R. Jayavel,P. Murugakoothan 한국물리학회 2009 Current Applied Physics Vol.9 No.5
Sodium bitartrate monohydrate (SBTMH) a new organometallic nonlinear optical material, with molecular formula, [C4H5NaO6 . H2O] has been synthesized at ambient temperature. Spectral, thermal and optical techniques have been employed to characterize the new material. Bulk single crystals of size 13 × 4 ×4㎣ of SBTMH have been grown by slow cooling method. The unit cell parameters of the grown crystal were determined by single crystal XRD. Functional groups present in the sample were identified by FTIR spectral analysis. Thermal stability of SBTMH was determined using TGA/DTA. The grown crystals exhibit nonlinear properties. The dielectric response of the crystal with varying frequencies was studied. The optical transparency range and the lower cut-off wavelength of the material were identified from the UV–vis–NIR absorption spectrum. Sodium bitartrate monohydrate (SBTMH) a new organometallic nonlinear optical material, with molecular formula, [C4H5NaO6 . H2O] has been synthesized at ambient temperature. Spectral, thermal and optical techniques have been employed to characterize the new material. Bulk single crystals of size 13 × 4 ×4㎣ of SBTMH have been grown by slow cooling method. The unit cell parameters of the grown crystal were determined by single crystal XRD. Functional groups present in the sample were identified by FTIR spectral analysis. Thermal stability of SBTMH was determined using TGA/DTA. The grown crystals exhibit nonlinear properties. The dielectric response of the crystal with varying frequencies was studied. The optical transparency range and the lower cut-off wavelength of the material were identified from the UV–vis–NIR absorption spectrum.
라그하반,A. Bhaskaran,R. Sankar,R. Jayavel 한국물리학회 2010 Current Applied Physics Vol.10 No.2
Single crystals of cadmium mercury thiocyanate glycol monomethyl ether (CMTG) were grown from a mixed solvent of glycol monomethyl ether (GME):water (1:1) by slow evaporation method. The crystal structure and morphology were confirmed by single crystal X-ray diffraction analysis. Presence of functional groups and the coordination of glycol monomethyl ether (GME) and thiocyanate (SCN-) in the CMTG compound were confirmed by FT-IR analysis. Optical transparency of the grown crystal was studied by UV–Vis spectroscopy. Thermal stability and decomposition process were studied by means of TGA and DTA analysis. Dielectric measurement on CMTG single crystal was carried out for various frequency and temperatures. The surface studies by scanning electron microscopy reveals the formation of layer growth pattern indicative of 2D nucleation mechanism. From the second harmonic output power measurement by Kurtz powder method, it is observed that CMTG is a potential material for nonlinear optical applications among the bimetallic thiocyanate adducts series.
A. Bhaskaran,라그하반,R. MohanKumar,R. Jayavel 한국물리학회 2010 Current Applied Physics Vol.10 No.5
Non-linear optical manganese mercury teterathiocyanate glycol monomethyl ether [MnHg(SCN)4(C3H8O2)] compound was synthesized and single crystals were grown from water-glycol monomethyl ether (1:1) mixed solvent by slow cooling method. Structure and crystallinity of the grown crystal were confirmed by both single crystal and powder X-ray diffraction analysis. Presence of functional groups and coordination of glycol monomethyl ether and thiocyanate in MMTG were confirmed by FT-IR analysis. Optical transmittance and second harmonic generation of the grown crystal were studied by UV–Vis spectrum and Kurtz powder technique. A dielectric study was performed on the MMTG single crystal to study the power dissipation of the material in the presence of alternating electric field. Mechanical behaviour was analysed using Vicker’s microhardness test. Optical surface damage measurement was carried out to confirm the suitability of MMTG crystal for NLO applications.
Study on the Effects of H+ and He+ Implantation in Semi-Insulating GaAs by Using Raman Spectroscopy
santhakumar kannappan,Cheul-Ro LEE,Hayakawa Y,Jayavel P,Jin soo Kim,Kesavamoorthy R,Muraleedaran Nair,Tetsuo soga 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Fifty-keV hydrogen-ion (H$^+$) and 70-keV helium-ion (He$^+$) implantation with doses from 10$^{13}$ to 10$^{16}$ cm$^{-2}$ in semi-insulating (100) gallium-arsenide (GaAs) single- crystal substrates have been carried out. Raman spectra of as-grown, implanted, and post-implantation-annealed GaAs samples are analyzed. Two LO phonon modes have been observed for all the samples. The lower wavenumber peak is attributed to the strained surface layer whereas the higher wavenumber peak is due to bulk GaAs crystal. For H$^+$ implantation, the peak positions of both peaks shift towards lower wavenumber up to a dose of 10$^{14}$ cm$^{-2}$ due to passivation of charge carriers. For higher doses, the peak positions shift towards higher wavenumber due to hydrogen-filled vacancy loops. On the other hand, for He$^+$-implanted samples, the peak positions increase for doses up to 10$^{13}$ cm$^{-2}$ and then decrease at higher doses. The immiscible nature of helium at low doses causes the increase in the peak positions. In contrast, implantation-induced damage is dominant at higher doses. Implantation-induced defects are partially annealed by post-implantation annealing, causing a blueshift of the peak positions for the H$^+$-implanted samples. In He$^+$-implanted samples, the peak positions redshift due to annealing of He interstitials at low doses and blueshift due to annealing of implantation-induced defects at high doses.
Electronic Structure of Mn-Doped ZnO Studied by Using X-ray Absorption Spectroscopy
P. Thakur,K. H. Chae,M. Subramanain,R. Jayavel,K. Asokan 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
Mn-doped ZnO thin films that showed ferromagnetism at room temperature were synthesized with nominal compositions Zn1-xMnxO (x = 0.03, 0.05, 0.07, 0.10 and 0.15) by using a spray pyrolysis technique. High-resolution X-ray diffraction studies suggested that the doped Mn ions occupied Zn sites and that all the samples exhibited a wurtzite hexagonal-like crystal structure similar to that of the parent compound, ZnO. The near-edge X-ray absorption fine structure (NEXAFS) measurements at the O K-edge clearly exhibited a pre-edge spectral feature, which evolved with Mn doping, similar to one observed in hole-doped cuprates and manganites. The Mn L3;2-edge NEXAFS spectra exhibited divalent Mn apart from mixed valent Mn3+ / Mn4+ states, which were well supported by Mn K-edge spectra.
X-ray Absorption and Emission Studies of Mn-doped ZnO Thin Films
P. Thakur,S. Gautam,K. H. Chae,M. Subramanain,R. Jayavel,K. Asokan 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.1
The electronic structure of Mn-doped ZnO thin films, a dilute magnetic semiconductor (DMS) having possible room temperature (RT) ferromagnetism, synthesized with nominal compositions of Zn1−xMnxO (x = 0.03, 0.05, 0.07, 0.10, and 0.15) by using the spray pyrolysis method are investigated using soft X-ray absorption and emission spectroscopy. The intensity of the pre-edge spectral feature at the O K-edge increases with Mn concentration, which clearly reveals that there is a strong hybridization of Mn ions with the ZnO matrix. The near-edge X-ray absorption fine structure (NEXAFS) measurements at the Mn K- and L3,2-edges show a mixed valence nature for the Mn ions, with Mn2+ and Mn3+/Mn4+ states, and the Mn3+/Mn4+ states are observed to increase with the Mn-concentration. Mn L2,3 resonant inelastic X-ray scattering (RIXS) measurements show that the excess Mn interstitials appear in the sample and that direct exchange interactions with substitutional Mn atoms may explain the magnetic interaction in Mn-doped ZnO. The electronic structure of Mn-doped ZnO thin films, a dilute magnetic semiconductor (DMS) having possible room temperature (RT) ferromagnetism, synthesized with nominal compositions of Zn1−xMnxO (x = 0.03, 0.05, 0.07, 0.10, and 0.15) by using the spray pyrolysis method are investigated using soft X-ray absorption and emission spectroscopy. The intensity of the pre-edge spectral feature at the O K-edge increases with Mn concentration, which clearly reveals that there is a strong hybridization of Mn ions with the ZnO matrix. The near-edge X-ray absorption fine structure (NEXAFS) measurements at the Mn K- and L3,2-edges show a mixed valence nature for the Mn ions, with Mn2+ and Mn3+/Mn4+ states, and the Mn3+/Mn4+ states are observed to increase with the Mn-concentration. Mn L2,3 resonant inelastic X-ray scattering (RIXS) measurements show that the excess Mn interstitials appear in the sample and that direct exchange interactions with substitutional Mn atoms may explain the magnetic interaction in Mn-doped ZnO.