C. Mejía-García

Influence of the hydrothermal method growth parameters on the zinc oxide nanowires deposited on several substrates

We report the synthesis of ZnO nanowires grown on several substrates (PET, glass, and Si) using a two-step process: (a) preparation of the seed layer on the substrate by spin coating, from solutions of zinc acetate dihydrate and 1-propanol, and (b) growth of the ZnO nanostructures by dipping the substrate in an equimolar solution of zinc nitrate hexahydrate and hexamethylenetetramine. Subsequently, films were thermally treated with a commercial microwave oven (350 and 700 W) for 5, 20, and 35 min. The ZnO nanowires obtained were characterized structurally, morphologically, and optically using XRD, SEM, and UV-VIS transmission, respectively. XRD patterns spectra revealed the presence of Zn(OH)2 on the films grown on glass and Si substrates. A preferential orientation along c-axis directions for films grown on PET substrate was observed. An analysis by SEM revealed that the growth of the ZnO nanowires on PET and glass is better than the growth on Si when the same growth parameters are used. On glass substrates, ZnO nanowires less than 50 nm in diameter and between 200 nm and 1200 nm in length were obtained. The ZnO nanowires band gap energy for the films grown on PET and glass was obtained from optical transmission spectra.

Raman study on Bi–Pb–Sr–Ca–Cu–O superconductor thin films grown by spray pyrolysis on several types of substrate

Abstract We present a Raman study on Bi–Pb–Sr–Ca–Cu–O thin films grown by spray pyrolysis on three different types of substrate, MgO, LaAlO 3 and SrTiO 3 . We applied the technique of Raman difference spectroscopy to obtain a signal representing the spectrum from the Bi–Pb–Sr–Ca–Cu–O thin films, since the contribution of the Raman signal from the underlying substrate may overwhelm the scattering arising from the films. The films investigated were prepared by a two-step procedure, i.e. by the deposition of films on substrates from an aerosol of aqueous nitrate solution, followed by solid-state reaction at high temperature. The Raman spectra between 380 and 800 cm −1 show a series of vibrational optical modes, all of them apparently superimposed on an electronic background. A Fano-type analysis was performed of the lineshape as a function of temperature for the most important modes, which can be associated with stabilization of the phase and related to the Cu–O plane, where superconductivity apparently originates.

Influence of Ammonium in Zinc Oxide Nanostructures Hydrothermally Grown on Glass Substrate

We present the synthesis of ZnO nanostructures grown by the hydrothermal method using the rapid microwave heating process. First, 10 mM solutions of zinc acetate dihydrate and 1-propanol were three cycles spin coated on glass substrates at 2000 rpm by 70 s, 90 s and 90 s, respectively. Second, nanostructures were then grown by dipping the substrates in a solution of zinc nitrate hexahydrate, polyethyleneimine (PEI), hexamethylenetetramine and ammonia. The hydrothermal process were carried out with a commercial microwave at 300, and 600 W power settings during 20 min. The structural and morphological properties were investigated using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The influence of the ammonium concentration in the morphology of the nanostructures was analyzed.Keywords: ZnO, nanostructures, XRD, SEM, spin coating, ammonium, hydrothermal process.

Synthesis and Characterization of Zinc Oxide Nanowires Grown Hydrothermally on Glass Substrate

We report the synthesis of ZnO nanowires grown on glass using a two-step process: (a) preparation of the seed layer, and (b) growth of the nanostructures. First step:solutions of zinc acetate dehydrate and 1-propanol of 10 mM concentrationwere spin coated on glass at 2000 rpm for 58 s. A seed layer was obtained after three layers of spin coating. Second step: vertical ZnO nanowires were grown by dipping the substrate in a 25 mMequimolarsolution of zinc nitrate hexahydrate and hexamethylenetetramine. Subsequently, films were thermally treated with a commercial microwave oven at different power settings (350 and 700 W) for 5, 20 and 35 min. The ZnO nanowires obtained were characterized optical and morphologically. Scanning electron microscopy analysis showed that the size of ZnO nanowires was less than 50 nm in diameter and around 500 nm in length. XRD patterns revealed that when low power in the microwave oven was utilized, the presence of Zn (OH)2 on the films is observed. The ZnO nanowires bandgap energy was obtained from optical transmission spectra.

Synthesis and Structural Characterization of Hg(Re)-Pb-Ca-Ba-Cu-O Superconducting Thin Films Grown by Spray Pyrolysis

We present a statistical study of the crystalline phase distribution in Pb-Ca-Ba-Cu-O precursor films grown by spray pyrolysis technique, with thickness and composition suitable to incorporate Hg by the sealed quartz tube technique in a subsequent treatment. A series of 9 precursor thin films were deposited on MgO substrates. Interdependence among deposition temperature, solution concentration, annealing temperature and annealed time and the effect in the relative percentage of each precursor phases was studied, applying a fractional factorial design 3IV-II. Chemical composition was obtained from atomic absorption measurements. Crystalline phase identification was performed by X-ray diffraction technique (XRD) and the quantification of each one was carried out by Rietveld method. The BaPbO3, Ba4Pb3O10 ternary phases were obtained at 810°C, and the BaCuO2 phase was got between 835°C and 860°C. Deposition temperature and molarity of the solution have clear influence on the thickness of the film. The effect of deposition temperature on the film composition was observed. Introduction

Growth of Bi-Pb-Sr-Ca-Cu-O Films by Organic Chemical Spray Pyrolysis Deposition

Bi-Pb-Sr-Ca-Cu-O films were deposited at 270-420°C by organic chemical spray pyrolysis deposition with triphenyl bismuth (TPB), Pb(tmhd)2, Sr(tmhd)2, Ca(tmhd)2 and Cu(tmhd)2 (tmhd: 2,2,6,6-tetramethyl-3,5-heptanedione). A factorial experimental design was applied in order to study the interaction between composition, deposition temperature, annealing time and annealing temperature and the effect in the formation of crystalline phases. Results of their structural and chemical characterization are presented.