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Solution-based synthesis of high yield CZTS (Cu<sub>2</sub>ZnSnS<sub>4</sub>) spherical quantum dots
Rajesh, G.,Muthukumarasamy, N.,Subramanian, E.P.,Venkatraman, M.R.,Agilan, S.,Ragavendran, V.,Thambidurai, M.,Velumani, S.,Yi, J.,Velauthapillai, D. Academic Press 2015 Superlattices and microstructures Vol.77 No.-
High yield CZTS quantum dots have been synthesized using simple precursors by chemical precipitation technique. Formation mechanism of CZTS spherical quantum dots also has been investigated. According to the mechanism, copper sulfide nuclei firstly forms, and serves as the starting point for the nucleation and growth of CZTS. X-ray diffraction pattern, X-ray photoelectron spectra (XPS) and Raman spectra reveals the formation of pure kesterite structure Cu<SUB>2</SUB>ZnSnS<SUB>4</SUB> nanoparticles. HRTEM analysis reveals the formation of CZTS quantum dots with an average particle size of ~8.3nm. The elemental distribution of CZTS quantum dots studied using STEM elemental mapping reveals that Cu, Zn, Sn and S are present in the sample. The photoluminescence spectra of CZTS exhibit a broad red emission band at 657nm. The optical band gap is shifted to the higher energy side and it shows the presence of quantum confinement effect.
Electrosynthesis and studies on Cadmium-Indium-Selenide thin films
Mahalingam, T.,Thanikaikarasan, S.,Chandramohan, R.,Chung, K.,Chu, J.P.,S.Velumani,Rhee, J.K. Elsevier 2010 Materials Science and Engineering B Vol. No.
Thin films of Cadmium Indium Selenide (CdIn<SUB>2</SUB>Se<SUB>4</SUB>) have been deposited on indium doped tin oxide coated conducting glass (ITO) substrates using potentiostatic cathodic electrodeposition technique. Cyclic voltammetry has been carried out in order to fix the deposition potential in the range between -1500 and +600mV versus SCE. X-ray diffraction pattern shows that the deposited films exhibit tetragonal structure with most prominent reflection along (200) plane. The dependency of microstructural parameters such as crystallite size, strain and dislocation density with deposition potential has been studied. Surface morphology and film composition have been analyzed using scanning electron microscopy and energy dispersive analysis by X-rays, respectively. EDX analysis reveals that films with well defined stoichiometry has been obtained at a deposition potential -950mV versus SCE. The optical band gap, refractive index and extinction coefficient are evaluated from optical absorption measurements. The experimental observations are discussed in detail.
One-dimensional ordered growth of magneto-crystalline and biocompatible cobalt ferrite nano-needles
Ravichandran, M.,Oza, G.,Velumani, S.,Ramirez, J.T.,Garcia-Sierra, F.,Andrade, N.B.,Garza-Navarro, M.A.,Garcia-Gutierrez, D.I.,Asomoza, R. North-Holland 2014 Materials letters Vol.135 No.-
<P>In this letter, we have reported a novel synthesis of CoFe2O4 nano-needles by a co-precipitation method using precursors of ferric chloride and cobalt nitrate at 80 degrees C. The structural and magnetic properties of as-grown needle-like CoFe2O4 nanostructures exhibit cubic spinel structure. CoFe2O4 nano-needles have an average diameter of 15 nm with an aspect ratio of 30:50, which was depicted by High-resolution transmission electron microscopy (HRTEM). Superconducting Quantum Interference Device (SQUID) confirmed the property of superparamagnetism. The magnetic measurement illustrated that the coercivity (Hc) of CoFe2O4 nano-needles increased from -145.84 Oe at 5 K to -25.38 Oe at 312 K. The cell viability studies of CoFe2O4 nano-needles were performed in the concentration range of 5-1000 mu g/ml on L6 (Skeletal muscle cell lines) and Hep-2 (Larynx carcinoma) cells using 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. There was more than 50% cell viability for both the cell lines, but Hep-2 cells were more prone to killing as compared to L6 cells. Such biocompatible nanostructures can be used as drug-delivery systems for cancer therapeutics. (C) 2014 Elsevier B.V. All rights reserved.</P>
Mahalingam, T,Kathalingam, A,Velumani, S,Lee, Soonil,Lew, Kyeung Seek,Deak Kim, Yong Institute of Physics 2005 Semiconductor science and technology Vol.20 No.8
<P>In this work the synthesis of zinc mercury selenide thin films (Zn<SUB>1−<I>x</I></SUB>Hg<I><SUB>x</SUB></I>Se) by electrodeposition is carried out. The films were deposited onto conducting glass (SnO<SUB>2</SUB>) substrates from an aqueous solution bath containing ZnSO<SUB>4</SUB>, HgCl<SUB>2</SUB> and SeO<SUB>2</SUB> at bath temperatures between 30 ?C and 70 ?C. The influence of deposition parameters such as electrolyte composition, deposition potential and temperature on the crystallinity and composition of the films is studied. It is found that the amount of mercury content in the solution bath and deposition potential control the composition and structure of the alloy films. The films were characterized by x-ray diffraction (XRD), energy dispersive x-ray analysis (EDAX), optical absorption and scanning electron microscope (SEM) studies. Photoelectrochemical solar cells studies using Zn<SUB>1−</SUB><I><SUB>x</SUB></I>Hg<I><SUB>x</SUB></I>Se thin films showed improved performance for annealed and etched electrodes and the results are discussed.</P>
Latha, M.,Devi, R. Aruna,Velumani, S.,Oza, Goldie,Reyes-Figueroa, P.,Rohini, M.,Becerril-Juarez, I. G.,Yi, Junsin American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.11
<P>Chalcopyrite CuIn1-xGaxSe2 (CIGS) nanoparticles were synthesized by mixing copper (I) chloride (CuCl), Indium (III) chloride (InCl3), gallium (III) chloride (GaCl3) and selenium (Se) in oleylamine (OLA) at 260 degrees C for 4 h under nitrogen atmosphere. The Ga/(In + Ga) ratio was tuned across the entire stoichiometric range from 0 to 1. X-ray diffraction analysis (XRD) revealed chalcopyrite crystal structure for samples prepared with x = 0, 0.3, 0.5, 0.7 and 1. The lattice parameters a and c decreased linearly with increasing Ga concentration which is consistent with Vegard's law. Raman spectra exhibited A(1) optical phonon vibrational mode for synthesized nanoparticles which gradually shifted to higher wavenumber with increasing Ga content. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) images showed irregular as well as hexagonal plate like morphologies in the size range of 100 to 400 nm. High-resolution transmission electron microscopy (HR-TEM) images showed well-defined lattice fringes and d-spacing correspond to (112) plane which gradually decreases with increasing Ga content. The material compositions of synthesized CIGS nanoparticles with x = 0, 0.3, 0.5, 0.7 and 1 were very close to the desired stoichiometry which was confirmed by energy dispersive X-ray analysis (EDAX). Ultra-violet visible near infrared (UV-VIS-NIR) absorption spectra of the synthesized CIGS nanoparticles revealed that the bandgap could be tuned over the range 1 to 1.7 eV by varying the Ga/(In+Ga) ratio.</P>
Morphology control and optical properties of ZnO nanostructures grown by ultrasonic synthesis
Morales-Flores, N.,Galeazzi, R.,Rosendo, E.,Diaz1d, T.,Velumani, S.,Pal, U. Techno-Press 2013 Advances in nano research Vol.1 No.1
ZnO nanostructures of rod-like, faceted bar, cup-end bars, and spindle shaped morphologies could be grown by a low power ultrasonic synthesis process. pH of the reaction mixture seems to plays an important role for defining the final morphology of ZnO nanostructures. While the solution pH as low as 7 produces long, uniform rod-like nanostructures of mixed phase (ZnO and $Zn(OH)_2$), higher pH of the reaction mixture produces ZnO nanostructures of different morphologies in pure hexagonal wurtzite phase. pH of the reaction as high as 10 produces bar shaped uniform nanostructures with lower specific surface area and lower surface and lattice defects, reducing the defect emissions of ZnO in the visible region of their photoluminescence spectra.