Dwight R. Acosta

About the structural, optical and electrical properties of SnO2 films produced by spray pyrolysis from solutions with low and high contents of fluorine

The morphological, structural, optical and electrical properties of tin-oxide-based coatings, obtained by spray pyrolysis using an alcoholic solution of SnCl4, were studied. The fluorine concentration and profile in the deposited material were determined. Samples were produced at a substrate temperature of 300°C and a deposition time of 15 min. Undoped films showed a non-transparent milky appearance, an electrical resistivity of 33 x 10−4 ω cm and an optical transmittance of 70%–75% in the visible range. X-Ray and electron diffraction pattern results showed the presence of SnO2 in the cassiterite structure with a preferential growth in the (200) direction. Scanning electron micrographs showed that the surface coatings were covered by crystalline particles (size, 25 nm). Thin films obtained from NH4F solutions at fluorine concentrations in the range 1–40 wt.% showed a systematic decrease in the surface particle density and an increase in the transmittance with increasing fluorine concentration, attaining values around 85%. The resistivity decreased to 6 x 10−4 ω cm for doping in the 1–8 wt.% range, but for doping values above 8 wt.%, the resistivity increased more than fivefold.

A brief dementia screener suitable for use by non-specialists in resource poor settings--the cross-cultural derivation and validation of the brief Community Screening Instrument for Dementia.

Brief screening tools for dementia for use by non‐specialists in primary care have yet to be validated in non‐western settings where cultural factors and limited education may complicate the task. We aimed to derive a brief version of cognitive and informant scales from the Community Screening Instrument for Dementia (CSI‐D) and to carry out initial assessments of their likely validity.

A comparative cross-cultural study of the prevalence of late life depression in low and middle income countries

Background Current estimates of the prevalence of depression in later life mostly arise from studies carried out in Europe, North America and Asia. In this study we aimed to measure the prevalence of depression using a standardised method in a number of low and middle income countries (LMIC). Methods A one-phase cross-sectional survey involving over 17,000 participants aged 65 years and over living in urban and rural catchment areas in 13 sites from 9 countries (Cuba, Dominican Republic, Puerto Rico, Mexico, Venezuela, Peru, China, India and Nigeria). Depression was assessed and compared using ICD-10 and EURO-D criteria. Results Depression prevalence varied across sites according to diagnostic criteria. The lowest prevalence was observed for ICD-10 depressive episode (0.3 to 13.8%). When using the EURO-D depression scale, the prevalence was higher and ranged from 1.0% to 38.6%. The crude prevalence was particularly high in the Dominican Republic and in rural India. ICD-10 depression was also associated with increased age and being female. Limitations Generalisability of findings outside of catchment areas is difficult to assess. Conclusions Late life depression is burdensome, and common in LMIC. However its prevalence varies from culture to culture; its diagnosis poses a significant challenge and requires proper recognition of its expression.

Effect of deposition methods on the properties of photocatalytic TiO2 thin films prepared by spray pyrolysis and magnetron sputtering

Titanium dioxide thin films were deposited by DC reactive magnetron sputtering and spray pyrolysis methods onto glass and glass coated with fluorine doped tin oxide (FTO). The films were characterized by x-ray diffraction, scanning electron microscopy, atomic force microscopy and UV?visible spectroscopy. For films deposited by the sputtering technique we have studied the effect of the total pressure of an Ar?O2 mixture on the substrate properties, on the deposition rate, phase composition, crystallinity, surface morphology and on the photocatalytic properties. Also transparent TiO2 thin films have been prepared by spray pyrolysis using a low concentration of titanium precursor with different substrate temperatures. At higher substrate temperatures the films were polycrystalline in the anatase phase; at lower substrate temperatures the films presented an amorphous configuration. The photocatalytic properties of TiO2 thin films were tested with the degradation methylene blue under UV light irradiation. The higher degradation rates were reached for films prepared by spray pyrolysis with a substrate temperature close to 400??C, and for a high total pressure (16?mTorr) for films deposited by DC magnetron sputtering.

Indium Doped Zinc Oxide Thin Films Deposited by Ultrasonic Chemical Spray Technique, Starting from Zinc Acetylacetonate and Indium Chloride

The physical characteristics of ultrasonically sprayed indium-doped zinc oxide (ZnO:In) thin films, with electrical resistivity as low as 3.42 × 10−3 Ω·cm and high optical transmittance, in the visible range, of 50%–70% is presented. Zinc acetylacetonate and indium chloride were used as the organometallic zinc precursor and the doping source, respectively, achieving ZnO:In thin films with growth rate in the order of 100 nm/min. The effects of both indium concentration and the substrate temperature on the structural, morphological, optical, and electrical characteristics were measured. All the films were polycrystalline, fitting well with hexagonal wurtzite type ZnO. A switching in preferential growth, from (002) to (101) planes for indium doped samples were observed. The surface morphology of the films showed a change from hexagonal slices to triangle shaped grains as the indium concentration increases. Potential applications as transparent conductive electrodes based on the resulting low electrical resistance and high optical transparency of the studied samples are considered.

High temperature treated Pt/Sn ZnAl2O4 catalysts

Abstract SnZnAl2O4 mixed supports were prepared by coprecipitation method with Sn contents of 0.5, 1.6 and 3 wt.%. Later Pt (1 wt.%) was incorporated by impregnation and samples reduced in hydrogen at 823 and 1073 K. Chemisorption data showed a decrease in hydrogen as temperature increases which is attributed to PtSn alloy formation. Catalytic activity in isobutane dehydrogenation and n-heptane dehydrocyclization seems to be dependent on the amount of metallic Pt phase. Pt/SnZnAl2O4 catalysts were thermally more stable than Pt/ZnAl2O4 preparation. Tin alters the ZnAl2O4 properties towards a higher thermal stability, but if added in more than 1 wt.%, it alloys with platinum inhibiting catalytic performance.

Characteristics of ZnO:F thin films obtained by chemical spray. Effect of the molarity and the doping concentration

The effect of the zinc acetate molarity combined with the substrate temperatures of ZnO:F thin films deposited by spray pyrolysis, on their physical properties, was studied. The main interest was to optimize the resistivity and the optical transmittance of films deposited at different substrate temperatures. It is to be remarked the influence of the aging of the starting solution on the improvement of the electrical properties of the films. The lowest value of the resistivity was obtained with solutions of 0.2 M. In this case, the resistivity obtained for a film 325-nm thick was 5.5×10−2 Ωcm, decreasing to a value of 6.7×10−3 Ωcm for films 1400-nm thick. Mobility values were approximately 7 cm2/V-S. The transmittance in the visible is near 90% at 550 nm. All the films showed a preferred (002) crystalline orientation irrespective of the deposition conditions. Finally, the grain size increased as the molarity of the solution decreased.

Chromium and ruthenium-doped zinc oxide thin films for propane sensing applications.

Chromium and ruthenium-doped zinc oxide (ZnO:Cr) and (ZnO:Ru) thin solid films were deposited on soda-lime glass substrates by the sol-gel dip-coating method. A 0.6 M solution of zinc acetate dihydrate dissolved in 2-methoxyethanol and monoethanolamine was used as basic solution. Chromium (III) acetylacetonate and Ruthenium (III) trichloride were used as doping sources. The Ru incorporation and its distribution profile into the films were proved by the SIMS technique. The morphology and structure of the films were studied by SEM microscopy and X-ray diffraction measurements, respectively. The SEM images show porous surfaces covered by small grains with different grain size, depending on the doping element, and the immersions number into the doping solutions. The sensing properties of ZnO:Cr and ZnO:Ru films in a propane (C3H8) atmosphere, as a function of the immersions number in the doping solution, have been studied in the present work. The highest sensitivity values were obtained for films doped from five immersions, 5.8 and 900, for ZnO:Cr and ZnO:Ru films, respectively. In order to evidence the catalytic effect of the chromium (Cr) and ruthenium (Ru), the sensing characteristics of undoped ZnO films are reported as well.

Thin Films for Photovoltaic Applications

The interest in research and development activities focused in photovoltaic (PV) materials in Mexico is justified by the great potential this country has for photovoltaic applications. In fact, Mexico has one of the highest insolation rates in the World, in addition to more than 5 millions people who are potential users of PV systems.

The effect of sulfate ion on the synthesis and stability of mesoporous materials

The formation of hexagonal MCM-41 structures was studied using cetyltrimethyl ammonium bromide as the surfactant template and tetraethyl-orthosilicate as the silica source under hydrothermal conditions in the presence of sulfate ions. For the as-synthesized samples sulfate ions improved the hydrothermal stability of the MCM-41 material. Increasing sulfate concentration in the synthesis gel the amount of water lost by the sample decreases, indicating the formation of a solid with a more hydrophobic character. Since sulfate groups also favors of condensation of silicate units, which increase of wall thickness.