Two step synthesis of TlBa2Ca2Cu3Ox films on Ag substrates by spray pyrolysis of metal-acetylacetonates

A two-step synthesis process was performed to obtain TlBa2Ca2Cu3Ox (Tl-1223) superconductor films. The synthesized films were obtainedunder different thallium diffusion conditions in a two-zone furnace precursor films were deposited at 550±C on silver substrates using the spray pyrolysis technique from acetylacetonates (2, 4-pentanedionates) as reagents. Second, a thallium diffusion process is carried out to incorporate Tl in the films. For this task Tl2O3 pellets, as a Tl source, were used at 750±C. Different oxygen flow rates at atmospheric pressure were used in order to get the thallous oxide p(Tl2O) partial pressure in the range of 6:9£10¡4 to 6:1£10¡2 atm. The Tl-1223 phase was obtained in all cases, though for a low p(Tl2O), the films presented the BaCuO2 phase mixed with the Tl-1223 one. Critical temperature (TC) values for these films were in the range of 90 to 102 K

Propiedades eléctricas, ópticas y estructurales de películas delgadas de SnO2 nanoestructuradas, depositadas a partir de acetilacetonatos

Películas delgadas de óxido de estano fueron depositadas mediante la técnica de rocío pirolítico ultrasónico. Las películas se depositaron sobre sustratos de vidrio empleando dicloruro de acetilacetonato de estaño [(C5H8O2)2SnCl2], como material fuente y N,N-DMF como solvente a temperaturas de 400°C a 500 °C. Se presentan propiedades ópticas y estructurales de las películas obtenidas utilizando un precursor organometálico

Irradiación de películas de HfO2 con radiación UV

Se prepararon películas de Óxido de Hafnio mediante la técnica de rocío pirolítico ultrasónico. Las películas se depositaron sobre substratos de vidrio a temperaturas de 300, 400, 500 y 600oC, utilizando cloruros como reactivos precursores. Se prepararon soluciones 0.05 M de HfCl2O.8H2O empleando agua desionizada como disolvente. Para el análisis termoluminiscente, las películas se sometieron a un proceso de borrado inicial precalentándolas a 50oC y llevando a cabo un barrido continuo de temperatura hasta 350oC. Posteriormente las películas se irradiaron de forma individual durante 5 minutos con luz ultravioleta, utilizando una lámpara Long Wave UVL-21. Las características termoluminiscentes se obtuvieron con un equipo lector TLD 4000, bajo las mismas condiciones a las del borrado, obteniéndose las curvas de brillo de cada película, siendo la depositada a 500oC la que mostró mejor resultado

Monitoring of Spectral Map Changes from Normal State to Superconducting State in High-TC Superconductor Films Using Raman Imaging

We have explored the chemical structure of TlBa2Ca2Cu3O9 high-TC superconductor films with Tl-1223 phase to monitor spectral map changes from normal state to superconducting state using the technique of Raman imaging. Raman images were performed for 12 different temperatures in the 77–293 K range. At room temperature, the Raman images were characterized by a single color but as the temperature dropped a new color appeared and when the temperature of 77 K is reached and the superconducting state is assured, the Raman images were characterized by the red, green, and blue colors. Our study could suggest that the superconducting state emerged around 133 K, in full agreement with those reported in the literature. A cross-checking was done applying principal component analysis (PCA) to other sets of Raman spectra of our films measured at different temperatures. PCA result showed that the spectra can be grouped into two temperature ranges, one in the 293–153 K range and the other in the 133–77 K range suggesting that transition to the superconducting state occurred at some temperature around 133 K. This is the first report of preliminary results evaluating the usefulness of Raman imaging in determination of transition temperature of superconductor films

Electrical, optical and structural characteristics of Al2O3 thin films prepared by pulsed ultrasonic sprayed pyrolysis

The optical, structural, and electrical characteristics of aluminum oxide thin films deposited by pulsed ultrasonic sprayed pyrolysis are reported. The films are deposited on crystalline silicon at temperatures from 400 to 550°C using a chemical solution of aluminum acetylacetonate, as source of aluminum, and N, N-dimethylformamide, as solvent. A H2O–NH4OH mist is supplied simultaneously during deposition to improve the films’ properties. The results showed that the properties of the as deposited films depended strongly on the number of pulses used and on the substrate temperature. The thickness of the films is under 300 Å and the best films’ properties showed an index of refraction close to 1.6 and a root mean square surface roughness of about 7.5 Å in average. Infrared spectroscopy shows that SiO2 is observed at the interface with silicon of the Al2O3 films and seemed to play, as expected, a dramatic role in the electrical characteristics of the interface. Films with a dielectric constant higher than 8 and an interface trap density at midgap in the 1010 eV−1 cm−2 range are obtained. Films deposited with three pulses and at 550 °C are able to stand an electric field up to 4 MV/cm

Structural and optical characterization of GaNAs layers grown by molecular beam epitaxy

We have grown GaNxAs1−x layers by molecular beam epitaxy on GaAs 100 substrates using a radio frequency plasma nitrogen source and solid sources for Ga and As. Employing reflection high-energy electron diffraction RHEED , the GaNAs growth mode was in situ monitored. A three dimensional 3D growth mode was obtained at the low growth temperature of 420 °C. At higher temperatures streaky RHEED patterns were observed during all the GaNAs deposition, indicating a two dimensional 2D growth mode. The structural and optical properties of the GaNAs layers were studied by employing high-resolution x-ray diffraction, atomic force microscopy, Raman scattering, and spectroscopic ellipsometry. The films grown in a 3D mode presented high density of crystal defects, degraded structural properties, and broad optical transitions. In contrast, GaNAs layers grown in a 2D mode are pseudomorphic with high crystal quality. The properties of samples with a high N concentration were improved by first growing a GaNAs layer with a low N content

Photoluminescent ZrO2:Tb3+ thin films synthesized by USP technique using a metal-organic precursor

Photoluminescent ZrO _2 and ZrO _2 :Tb ^3+ thin films were synthesized from metal-organic precursor, zirconium acetylacetonate [Zr(C _5 H _7 O _2 ) _4 ], using Ultrasonic Spray Pyrolysis method. These thin films were deposited on Corning glass substrates at several deposition temperatures. ZrO _2 and ZrO _2 :Tb ^3+ (X a/o) films were characterized by x-ray diffraction to identify the crystalline structure; results showed tetragonal phase of zirconia; with a crystalline size of approximately 4 nm according to Scherrer’s formula. Also, SEM micrographs revealed that surface morphology of these films is very flat. Chemical composition microanalysis showed presence of oxygen and zirconium as major species. Analysis by Infrared spectroscopy demonstrates that 900 and 760 nm bands correspond to presence of ZrO _2 . In addition, these films showed optical transmittances from 75 to 98 % in the visible range. Photoluminescent features varied as a function of excitation wavelength; when excited at λ _ex  = 286 nm strong green emission is observed, which is associated to electronic transitions ^5 D _4  →  ^7 F _n (n = 6, 5, 4, 3) corresponding to Tb ^3+ ions. Excitation with λ _ex  = 336 nm exhibits spectra with simultaneous emissions from host lattice and Tb ^3+ ions; here, observed color was blue-green