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Kim, Bo Yun,Shim, In-Bo,Araci, Zeynep O.,Saavedra, S. Scott,Monti, Oliver L.A.,Armstrong, Neal R.,Sahoo, Rabindra,Srivastava, Divesh N.,Pyun, Jeffrey American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.10
<P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-10/ja908481z/production/images/medium/ja-2009-08481z_0004.gif'> <P>The preparation of cobalt oxide nanowires with gold nanoparticle (AuNP) inclusions (Au−Co<SUB>3</SUB>O<SUB>4</SUB> nanowires) via colloidal polymerization of dipolar core−shell NPs is reported. Polystyrene-coated ferromagnetic NPs composed of a dipolar metallic cobalt shell and a gold NP core (PS−AuCoNPs) were synthesized by thermolysis of octacarbonyldicobalt [Co<SUB>2</SUB>(CO)<SUB>8</SUB>] in the presence of AuNP seeds and polymeric ligands. The colloidal polymerization process of these dipolar PS−AuCoNPs comprises dipolar nanoparticle assembly and solution oxidation of preorganized NPs to form interconnected cobalt oxide nanowires via the nanoscale Kirkendall effect, with AuNP inclusions in every repeating unit of the one-dimensional mesostructure. Calcination of the polymer-coated nanowires afforded polycrystalline Au−Co<SUB>3</SUB>O<SUB>4</SUB> nanowires that were determined to be electroactive. Nanocomposite materials were characterized by transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction, vibrating sample magnetometry, and cyclic voltammetry. We demonstrate that the optical and electrochemical properties of Au−Co<SUB>3</SUB>O<SUB>4</SUB> nanowires are significantly enhanced in comparison with hollow Co<SUB>3</SUB>O<SUB>4</SUB> nanowires prepared via colloidal polymerization.</P></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja908481z'>ACS Electronic Supporting Info</A></P>
Optimized Synthesis and Improved Transport Properties of Cd-Doped Tl-2223 Films
H.K. Singh,N D Kataria,O.N. Srivastava 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.5I
We present an investigation of the effect of cadmium (Cd) doping on the structural phase evolution, microstructural features, and superconducting properties of Tl bearing high temperature superconducting films. These films were grown by incorporating thallium into precursor films having a nominal composition Ba2Ca2CdxCu3Oy (x = 0.0, 0.1, 0.2, 0.3 and 0.4) and deposited on single-crystal MgO(100) substrates by using ultrasonic spray pyrolysis. For thallium incorporation, the precursor films were annealed for two hours in presence of a Tl source, which was an un-reacted pellet of nominal composition Tl2.05Ba2Ca2Cu3Oz in a evacuated (10.5 Torr) and sealed silica tube at 890 C. The structural characterization reveals that the films are polycrystalline and predominantly c-axis oriented and that around a Cd content of x 0.2 the films are single phase 2223. For these highly textured polycrystalline films, Tc (R = 0) is measured to be 118 K, 120 K, 124 K, 121 K and 116 K for Cd contents of x = 0.0, 0.1, 0.2, 0.3, and 0.4, respectively. The self-field critical current density (Jc) values are found to be (at 77K) 6.85×104 A/cm2, 7.98×104 A/cm2, 1.12×105 A/cm2, 8.2×104 A/cm2 and 3.0×104 A/cm2 for x = 0.0, 0.1, 0.2, 0.3, and 0.4, respectively. The films grown in the present study show a decrease in Tc by 5 K to 11 K on oxygen annealing. This shows that the as-grown films are almost optimally doped. At lower Cd concentrations, the microstructural characteristics, as evaluated by using SEM, reveal the occurrence of spiral growth features in the surface morphology of these films, and these spiral features disappear at higher values of x. The critical current density exhibits a strong dependence on the Cd-induced morphological variations.
RAJESH KUMAR,R. S. TIWARI,O. N. SRIVASTAVA 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2011 NANO Vol.6 No.3
Castor oil (combination of fatty acids) precursor containing hydrocarbon with less amount of oxygen is used first time for synthesis of different carbon nanostructures (i.e., agglomerated carbon nanoparticles, carbon nanobeads and carbon tubular structure). The agglomerated carbon nanoparticles, carbon nanobeads and carbon tubular structure were synthesized by applying CVD method at different temperature using castor oil as new carbon precursor without any catalyst. The synthesis of carbon nanostructure is free from additional catalyst as this hydrocarbon (castor oil) is cheap with abundant sources of carbon. The effect of pyrolysis temperatures on the size, quality and quantity of the synthesized carbon shape were investigated. Interestingly, the morphology of the carbon nanostructures can be controlled in shape from agglomerated carbon nanoparticle to nanobeads to carbon tubular structure just by increasing the temperature from 750°C to 800°C to 850°C, respectively. These nanobeads are chains of uniform size of graphitized carbon spheres. These chains comprised individual carbon particles size of ~ 450 nm. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR).
Effect of growth temperature on gallium nitride nanostructures using HVPE technique
Munawar Basha, S.,Ryu, S.R.,Kang, T.W.,Srivastava, O.N.,Ramakrishnan, V.,Kumar, J. North-Holland 2012 Physica E, Low-dimensional systems & nanostructure Vol.44 No.9
The growth of hexagonal wurzite one dimensional (1D) gallium nitride (GaN) nanostructures on sapphire substrates using hydride vapor phase epitaxy (HVPE) process was carried out at two different temperatures (973K and 1023K). The GaN nanoneedles were formed at 973K and hexagonal nanorods get formed at 1023K. The morphologies of these nanostructures were studied using high resolution scanning electron microscope. X-ray diffraction and micro-Raman spectroscopy measurements confirmed that the as grown GaN nanostructures are of hexagonal wurtzite structure without any oxide phase. The emission properties of these nanostructures have been investigated using photoluminescence.