R. Castanedo-Pérez

High transmittance CdO thin films obtained by the sol-gel method

Abstract CdO thin films have been prepared by the sol-gel technique, from a novel precursor solution based on Cd(OOCCH 3 ) 2 ·2H 2 O, ethylene glycol, glycerol, and triethylamine, on slide glass substrates. The films were annealed in open atmosphere at 200°C and were characterized by UV-VIS spectroscopy, X-ray diffraction and atomic force microscopy. The CdO thin films obtained have a high polycrystalline quality and, outstandingly, they show a transmission of 95% at a wavelength of 600 nm, which increases to virtually 100% from 700 to 1100 nm. The indirect and direct band gap energy values were found to be 2.06 and 2.59 eV, respectively. The resistivity of the films was 2×10 −2 Ω cm.

Influence of annealing temperature on the formation and characteristics of sol-gel prepared ZnO films

ZnO thin films have been obtained by the sol-gel method from a Zn(OOCCH3)2 precursor on soda lime glass and silicon wafer substrates. The films, obtained by a single dipping procedure, were characterized by Fourier transform infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopies, atomic force microscopy, x-ray diffraction and ellipsometry measurements. Thermally untreated and annealed (100–450 °C) films were studied in order to analyze the influence of temperature on the formation and properties of the ZnO coatings. Remarkably, these results indicate that ZnO forms at considerably lower temperatures than 450 °C, which is usually considered in the literature as a reference temperature for the formation of ZnO. Thus, a sharp absorption edge of ZnO at ∼380 nm can be easily observed in the UV-vis spectra of films annealed at 200 and 300 °C, accordingly, and the FTIR data indicate the absence of organic groups at these temperatures. The atomic force microscopy results show a uniform, void-free surface...

STRUCTURE AND ELECTRONIC PROPERTIES OF THE NOVEL SEMICONDUCTOR ALLOY CD1 -XCUXTE

In this work an investigation of the structural and electronic properties of the novel semiconductor alloy Cd1−xCuxTe is presented. The samples were prepared as thin films by rf sputtering on substrates made of Corning glass. X-ray diffraction patterns showed that the incorporation of Cu into CdTe did not significantly affect the lattice parameters and that the incorporation of copper favors the growth of films preferentially oriented parallel to the (111) planes of cubic CdTe. Due to its sensitivity to local atomic order, the samples were studied by micro-Raman spectroscopy. The transverse and longitudinal optic modes regularly observed in CdTe were also found in the Cd1−xCuxTe samples with frequencies variations of less than 2 cm−1. The appearance of second and third harmonics of the longitudinal optic mode is indicative of high crystalline quality. The Raman bands become broader as a consequence of the disorder induced by the random incorporation of copper. From the Raman experiments it was also determ...

Band gap tuning and high electrical conductivity in amorphous and polycrystalline films of the Cux(CdTe)yOz system

Thin films of the semiconductor alloy Cux(CdTe)yOz system were grown by reactive rf cosputtering. The effects of incorporating both copper and oxygen into a CdTe matrix were investigated. The films were polycrystalline, however, for the highest oxygen concentrations used in this work the grain size was reduced to nanometric dimensions. It is shown in this work that the optical and charge transport properties of the polycrystalline and amorphous films may be tailored by controlling the relative chemical composition. Remarkably, unusual p-type resistivity and mobility values have been measured for the amorphous films.

Effect of the Sintering Temperature on the Photocatalytic Activity of CdO + CdTiO3 Thin Films

Abstract CdO + CdTiO3 thin films were prepared on glass substrates by means of the sol-gel technique. Two Ti/Cd ratios, 0.54 and 0.67, in the precursor solutions were studied. After the dipping process, the samples were sintered in an open atmosphere during one hour at selected temperatures (Ts) in the range of 350-600 °C. The variation of Ts was in steps of 50 °C. X-ray diffraction, UV-Vis optical absorption, and atomic force spectroscopy techniques were employed for characterization. The photocatalytic activity (PA) was measured by means of the photobleaching of an aqueous solution of methylene blue (MB) after irradiation with an UV lamp. The MB concentration was determined by using optical absorption spectra, measured before and after the photobleaching process, and the Lambert-Beer principle. The best PA was obtained for films sintered at 500 °C for both Ti/Cd ratios studied, as for this Ts value the PA was very similar.

Mechanical and tribological behavior of sol-gel TiO2-CdO films measured at the microscale levels

In this work, we present a mechanical and tribological study at the microscale of sol–gel TiO2–CdO films, which are used in photocatalytic applications. The films were deposited as a good-quality polycrystalline material with majority of CdO or CdTiO3 phases depending on their Ti/Cd concentration ratios. Films with the majority of CdTiO3 phase presented the highest hardness and lowest plastic deformation during the indentation tests. The evolution of wear, friction coefficient, and roughness on the films was quantitatively studied by multiple-passes measurements on a depth-sensing instrumented indentation system. These measurements allowed us to observe the films’ wear mechanisms and correlate them with their microstructure and mechanical properties. To compare the crystal structure, mechanical properties and tribological behavior of these films, we also analyzed sol–gel CdO and TiO2 films deposited under similar conditions.Graphical Abstract

Effect of annealing temperature on structural, morphological and optical properties of CeO2 thin films obtained from a simple precursor solution

CeO2 thin films were obtained starting from a simple precursor solution by the sol–gel technique. The precursor solution was prepared by dissolving cerium nitrate in ethanol with lactic acid as stabilizer at room temperature. The as-deposited films were annealed at different temperatures from 250 to 550 °C, in open atmosphere. The effect of annealing temperature on structural, morphological, and optical properties of the films were studied by X-ray diffraction, UV-vis absorbance spectroscopy, Raman spectroscopy, scanning electron microscopy and atomic force microscopy. The results revealed that the annealing temperature plays an important role for improving film properties. X-ray diffraction shows that all films annealed exhibit fluorite cubic structure and increase in the crystalline size from 4.8 to 18.6 nm as the annealing temperature is increased. Raman spectra show a mode at around 463 cm−1, which is attributed to a symmetrical stretching mode of the Ce-8O vibrational unit. Atomic force microscopy images reveal that CeO2 films with higher surface roughness as the annealing temperature increases. The UV-vis spectra show that all the films have high optical transmittance, ~75% in the visible region. In addition, an increase of the band gap energy from 2.96 to 3.24 eV is obtained when the annealing temperature was raised.Graphical AbstractFig. a XRD patterns of CeO2 thin films annealed at different temperatures. b (111) interplanar spacing as a function of AT.

Photocatalytic Activity in Zn2TiO4 + ZnO Thin Films Obtained by the Sol-gel Process

Abstract The photocatalytic activity of Zn2TiO4 + ZnO thin films by the photobleaching of methylene blue (MB) in aqueous solution, under an UV irradiation, is studied. The films were prepared on glass slide substrates by the sol-gel technique starting from a simple novel precursor solution, which is based on the preparation of both ZnO and TiO2 precursor solutions separately, and subsequent mixing at room temperature. In order to change the films’ composition, several precursor solutions were prepared, each with different Ti/Zn ratio in the solution. The Ti/Zn ratio was in the 0.18 to 2.13 range and for each composition; two sintering temperatures were used, 450 °C and 550 °C. X-ray results show that the films are mainly constituted of the Zn2TiO4 compound (cubic phase). The best photocatalysis was found for a Ti/Zn ratio of 0.5 after an irradiation time of 5 hours.

INFLUENCE OF FIRING TEMPERATURE ON THE PROPERTIES OF CdO THIN FILMS OBTAINED BY THE SOL-GEL METHOD

CdO thin films were prepared by the sol-gel method, by using a precursor solution with cadmium acetate dihydrate as metal source. The films were obtained on slide-glass substrates and fired in open atmosphere at 200-450°C, at 50°C intervals. The X-ray data show that the films are polycrystalline with a NaCl cubic structure. The transmission of the films is 95-100% at wavelengths ≥600 nm, one of the highest obtained so far for CdO thin films. The atomic force microscopy results show that the grains coalesce, which results in morphology changes as the firing temperature increases. The resistivity showed its minimum value around 300°C (~10-3 Ω-cm).

PROPERTIES OF ZnO:AL THIN FILMS, OBTAINED BY THE SOL-GEL METHOD

Al-doped ZnO thin films have been prepared by the sol-gel technique, on slide-glass substrates. Al(NO3)3·9H2O was used as aluminum source and the doping range was 0.001-20 at %. The effect of the Al concentration in solution on the microstructure of the films is presented. The transmittance spectra, as well as the sheet resistance measurements, show the presence of electrically-active aluminum in the films.