M. Tejos

NICKEL TROPOLONATE COMPLEXES AS PRECURSORS FOR THE DIRECT PHOTODEPOSITION OF NiO THIN FILMS

In this paper we report the obtention of amorphous and nanostructured thin films of NiO, through the direct photolysis of the Ni(II)diaquabis(t-amyltropolonate) complex. Surface morphology observed by scanning electron microscopy showed uniform films of excellent quality, without islands or other imperfections. Purity and composition of the films was determined by X-ray difraction and Auger spectroscopy showing that the main product of photolysis is NiO. Sputtering with Ar ions reduces the oxide to Ni(0) and decreases significantly the carbon contamination of the films

USE OF A SINGLE-SOURCE MIXED-METAL PRECURSOR FOR THE PHOTODEPOSITION OF Pd/Ni OXIDES THIN FILMS

La irradiacion de peliculas delgadas de un complejo heteronuclear policetonato de Pd/Ni, PdNi(DBA)2 [DBA = dibenzoilacetona)], produjo peliculas uniformes conteniendo Pd y Ni como lo demostraron los analisis EDAX. El espectro de difraccion de rayos-X mostro peaks asociados con Pd elemental y NiO. La morfologia de los films fue examinada por SEM, mostrando una superficie granular con tamano de particulas igual o menores a 100 nm. Los resultados de analisis por XPS demuestran que la relacion Pd/Ni (1:17) refleja la estequiometria del complejo precursor. El alto porcentaje de carbono (52%) detectado en la superficie de las peliculas puede deberse a la presencia de grupos fenilos en el complejo precursor.

PHOTOCHEMICAL DEPOSITION OF Pd-LOADED AND Pt-LOADED TIN OXIDE THIN FILMS

Pd and Pt loaded tin oxide thin films have been successfully prepared by direct UV irradiation of amorphous films of β-diketonate complexes on Si(100) substrates. Tin oxide films loaded with 10, 30 and 50% Pd and Pt, were characterized by Auger electron spectroscopy (AES). The Auger peak intensity ratios of O KL 23 L 23 to Sn M 4 N 45 N 45 showed that as-deposited films consist of mixed tin oxide phases whereas annealed films consist mainly of single phase SnO 2 . The results showed that the stoichiometry of the resulting films is in relative agreement with the composition of the precursor films. The surface characterization of these thin films was performed using Atomic Force Microscopy (AFM). This analysis revealed that loaded tin oxide films have a much rougher surface than unloaded films, with rms roughness values ranging from 28-54 nm for as-deposited Pd-SnO X films to 3.6-20 nm for as-deposited Pt-SnO X films. It was also found that Pt-loaded tin oxide films present a better particle size distribution and uniformity when compared to Pd-loaded tin oxide films. These results demonstrate the potential use of these deposited films in the manufacture of gas-sensing devices.

New insights on the doping of ZnO films with elements from group IIIA through electrochemical deposition

This study was focused in the electrodeposition of both compact and nanostructured extrinsic n-type doped ZnO films, which was achieved with aluminum, gallium, and indium. These elements were directly added into a Zn(II) rich electrolyte with molecular oxygen acting as an oxide precursor in aqueous perchlorate media. This way, the use of nitrate ions, whose by-products are accumulated in the aqueous electrolyte, and chloride ions, an electrically active element in ZnO, was therefore avoided. Speciation diagrams, conditional solubility diagrams and a potentiodynamic study were used to explain the way in which extrinsic n-type ZnO can be prepared by electrochemical deposition. Relatively compact films with a highly preferred orientation along the c-axis were suitable for impedance measurements, thus allowing the measurement of their doping levels. Al- and Ga-doped lamellar nanostructures were successfully prepared when the nature of the anion was changed from perchlorate to sulfate. Under specific conditions, the structure of these films changed from opened and isolated nanosheets to interconnected ones. Morphological, optical, and crystallographic properties of these films were also analyzed. Results and discussion presented here should provide a better understanding toward the study of alternative materials in fields such as photovoltaics and photocatalysis.

EVALUATION OF b-DIKETONATE TIN AND INDIUM COMPLEXES AS PRECURSORS FOR THE PHOTODEPOSITION OF SnO2 AND In2O3 THIN FILMS

SnO2 and In2O3 thin films have been succesfully prepared by direct UV irradiation of amorphous films of b-diketonate complexes on Si(100) substrates. The as-deposited films were analyzed by Auger electron spectroscopy (AES), whereas annealing was required in order to get X-ray diffraction spectra, indicating the amorphous nature of the films. The surface morphology of the films examined by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) revealed that In2O3 films are much smoother than SnO2 films, with average surface roughness (Ra) of 3 nm and 11 nm respectively. The low resistivity values determined for these metal oxide films (3-4 x 10-4 W cm) demonstrate the potential use of these deposited films in gas-sensing devices for detection of environmentally significant concentrations of oxidizing species such as NO2 and O3

Thin amorphous platinum films photochemically obtained, and their potential use as modified electrodes

Abstract Thin amorphous nanostructured Pt films have been photochemically obtained by means of direct UV radiation (254 nm) of an amorphous Pt[CH 3 (CH 2 ) 8 COCHCOC 4 H 9 ] 3 K film deposited on Si(100) and on ITO glass through the spin-coating technique. The product of this photolysis was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microanalysis. After that, the film was subject to cycles for 1 h, between −0.30 and 1.20 V, in a 0.50 M H 2 SO 4 electrolytic solution. It may be observed that the peak potential shifts in approximately 0.04 V towards less positive values for the modified system, if compared with the platinum bulk. It only showed one peak in the hydrogen discharge if compared with the two peaks in the Pt bulk. Based on these data, the ITO/Pt modified system was tested as an electrodic substrate for aniline polymerization in 0.50 M H 2 SO 4 . The polymeric deposit was obtained at lower potentials than those required when the Pt bulk is used as an electrode.

DIRECT PHOTODEPOSITION OF NANOSTRUCTURED TIO2 THIN FILMS FROM B-DIKETONATE COMPLEXES, AND THEIR PHOTOCATALYTIC BEHAVIOUR

Amorphous Titania thin films have been photochemically obtained by direct UV irradiation (254 nm) of an amorphous TiO(C6H5COCHCOCH3) 2 film spin-coated on Si(100) and borosilicate glass. These materials were characterized by scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD) and Auger electron spectroscopy (AES). SEM analysis showed a porous film with irregular morphology (diameter < 300 nm), whereas the XRD spectrum showed that the as-deposited film was completely amorphous and was transformed by annealing under nitrogen into polycrystalline TiO2. Subsequently, amorphous Titania deposited on borosilicate glass was used in the photocatalytic decomposition of aniline in water. The photoreaction of aniline was monitored by UV in the presence of air and nitrogen, and the product was characterized by infrared spectroscopy (IR). The results showed that aniline can be photooxidized efficiently by the TiO2/ borosilicate system in the presence of oxygen

PREPARATION OF PALLADIUM THIN FILMS AND THEIR USEFULNESS AS MODIFIED ELECTRODES

Se han obtenido, fotoquimicamente, peliculas delgadas nanoestructuradas de paladio, por irradiacion UV directa (254nm) de una pelicula amorfa de Pd[C8H17COCHCOC4H 9]2 depositada sobre Si(100) y sobre vidrio ITO, mediante la tecnica de spin-coating. La fotolisis de la pelicula de complejo b-dicetonato de paladio, por luz UV, conduce a la perdida de los ligandos de la esfera de coordinacion. Los derivados de las acetilacetonas fueron escogidos por su fotoquimica en estado solido, ya que la presencia de sustituyentes ramificados hidrocarbonados disminuye las interacciones moleculares y, mediante spin-coating, conduce a la formacion de peliculas de alta calidad. El producto de la fotolisis fue analizado por difraccion de rayos-X (XRD), microscoscopia electronica de barrido (SEM) y microanalisis. Posteriormente, la pelicula depositada sobre vidrio ITO se estudio eletroquimicamente, aplicando ciclos triangulares sucesivos a potenciales entre 0,00 y 1,30 V vs ECS por 15 minutos, en una disolucion electrolitica de H2SO4 0,50 M. El electrodo modificado presenta un perfil similar al de una lamina de paladio, sin embargo, es posible observar en el sistema modificado un desplazamiento de los potenciales de pico, de aproximadamente 0,04 V hacia valores menos positivos, lo cual es indicativo de un posible efecto catalitico. En base a ello, el sistema modificado ITO/Pd fue usado como sustrato electrodico para la polimerizacion de anilina en H2SO4 0,10 M, obteniendose un deposito polimerico, a potenciales menores que los requeridos sobre la lamina de paladio, indicando que el metodo descrito puede consituir una interesante herramienta para la preparacion de electrodos modificados, que podrian ser ventajosamente usados en la preparacion de materiales polimericos