Celdas fotoelectroquímicas sensibilizadas con semiconductores

Para la preparación de celdas fotoelectroquímicas sensibilizadas con semiconductores actualmente este proyecto aborda los medios por los que se obtiene una capa lo más porosa posible necesaria como componente esencial de uno de los electrodos de la celda. Resultados anteriormente obtenidos nos mostraron la necesidad de realizar dos depósitos con soluciones precursoras diferentes, así como el mejor rango de temperaturas para realizar dichos depósitos. Para ello se ha estudiado la velocidad de crecimiento y homogeneidad de las capas obtenidas bajo diferentes condiciones. Se presentan los resultados hasta ahora obtenidos de depósitos realizados con la técnica de spray pirolisis (SP)

Low interface states and high dielectric constant Y2O3 films on Si substrates

Y2O3 films were deposited on c-Si substrates at temperatures in the 400–550 °C range, with no further thermal treatment given to these samples, using the spray pyrolysis technique. The spraying solution was yttrium acetilacetonate disolved N,N-dimethylformamide. In addition, a solution of H2O–NH4OH was sprayed in parallel during the deposition process to improve the optical, structural, and electrical properties of the deposited films. The growth of a SiO2 layer between the yttrium oxide and the Si substrate during this deposition process resulted in interface state density values as low as 1010 eV−1 cm−2. An effective refractive index value of 1.86, and deposition rates close to 1 Å/ s were obtained. The Y2O3 films were polycrystalline with a crystalline cubic phase highly textured with the 400 direction normal to the Si surface. An effective dielectric constant up to 13, as well as a dielectric strength of the order of 0.2 MV/cm was obtained for 1000 Å thick as-deposited films incorporated in a metal-oxide-semiconductor structure

Synthesis and characterization of nanostructured cerium dioxide thin films deposited by ultrasonic spray pyrolysis

Nanostructured thin films of cerium dioxide have been prepared on single-crystalline silicon substrates by ultrasonic spray pyrolysis using cerium acetylacetonate as a metal–organic precursor dissolved in anhydrous methanol and acetic acid as an additive. The morphology, structure, optical index, and electrical properties were studied by X-ray diffraction, scanning electron microscopy, atomic force microscopy, ellipsometry, and impedance spectroscopy. The use of additives is very important to obtain crack-free films. The substrate temperature and flow rate was optimized for obtaining smooth (Ra <0.4 nm), dense (n>2), and homogeneous nanocrystalline films with grain sizes as small as 10 nm. The influence of thermal annealing on the structural properties of films was studied. The low activation energy calculated for total conductivity (0.133 eV) is attributed to the nanometric size of the grains

Blue and bluish-white colors from the luminescent ZrO2 and ZrO2: Al3+ films prepared by the USP method

ZrO _2 and ZrO _2 : Al ^3+ (× at.%) films were deposited by ultrasonic spray pyrolysis process. Luminescent films were produced from Oxychloride Zirconium Octahydrate and Aluminium Chloride Hexahydrate as precursors. Measurements of photo and cathodoluminescence were carried out doing variations on deposition temperature and doping concentration (× at.% Al ^3+ ions). With the increase in substrate temperature, an overall growth of photo-cathodoluminescence intensities was perceived. Furthermore, these films presented luminescence concentration quenching with hight Al doping concentration. Chromaticity coordinates indicated blue emission from host lattice (ZrO _2 films) and cold-white emissions from ZrO _2 : Al ^3+ (× at.%) films. Closest CIE coordinates to the perfect white emission were x = 0.303, y  = 0.337. XRD patterns, measured with variations of substrate temperature, showed tetragonal phase of nano-zirconium oxide films. In addition, surface morphology characteristics for studied films are presented

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