Resumen El procesamiento de soluciones es un método de bajo costo para preparar una variedad de películas delgadas orgánicas o inorgánicas. Para compuestos de óxidos metálicos, un procesamiento de solución de un compuesto organometálico se usa con frecuencia como solución precursora para ser recubierta por rotación, seguida de un tratamiento térmico para formar el óxido metálico. En este trabajo se obtienen polvos de óxido de vanadio a partir de una simple reacción ácido-base, y luego se dispersan en alcohol isopropílico para formar una solución para spin-coating. También se agregan diferentes cantidades de sal de cobalto junto con VOx en alcohol isopropílico para formar soluciones de VOx:Co2+. Después del tratamiento térmico a 200 °C, se obtienen películas delgadas transparentes. Se analizan las propiedades ópticas, estructurales, morfológicas y químicas. Se encontró que el compuesto VO2:Co2+ es amorfo y se obtiene con una relación atómica V:Co variada de 6.6:1-1.6:1. El material presenta una absorción óptica alrededor de 2.3 eV. Se observa una interesante morfología porosa interconectada cuando la relación atómica de V:Co es ~4.9:1. Se concluye que se pueden obtener películas delgadas amorfas porosas de VO2:Co2+ a partir del spin-coating a una baja temperatura de tratamiento utilizando una solución simple sin agente complejante.

Abstract Solution-processing is a low-cost solution method to prepare a variety of organic or inorganic thin films. For metal oxide compounds, a solution-processing solution of an organometallic compound is frequently used as a precursor to be spin coated, followed by a thermal annealing to form metal oxide. In this work, vanadium oxide powders are obtained from a simple acid-base reaction, and then they are dispersed in isopropyl alcohol to form a solution for spin-coating. Different amount of cobalt salt are also added together with VOx into isopropyl alcohol to form VOx:Co2+ solutions. After thermal annealing at 200 °C, continuous transparent thin films are obtained. Optical, structural, morphological and chemical binding energies of those films are analyzed. It is found that amorphous VO2:Co2+ compound is formed in those films with V:Co atomic ratios between 6.6:1 and 1.6:1. Optical absorption onsets of those films are around 2.3 eV. An interesting interconnected porous morphology is observed when the atomic ratio of V:Co is around 4.9:1. It is concluded that porous amorphous cobalt doped vanadium oxide thin films can be obtained from a spin-coating process at low annealing temperature from a simple solution without any complex agent.

Abstract In a previous paper, we reported that thin films of ZnO:Al [aluminum-zinc oxide (AZO)] deposited after achieving a very low base pressure [from 4.0 × 10 - 7 Torr ( 5.6 × 10 - 5 Pa) to 5.7 × 10 - 7 Torr ( 7.6 × 10 - 5 Pa)] result dark yellow in color and are resistive. These are undesirable characteristics for the application of AZO thin films as front electrodes in solar cells. However, given the increasingly tendency in the acquisition of equipment that allows us to reach excellent vacuum levels, it is necessary to find the deposition conditions that lead to an improving of transmittance without greatly impacting the electrical properties of materials deposited after achieving these levels of vacuum. In this way, the present work is focused on AZO thin films deposited after achieving a very low base pressure value: 4.2 × 10 - 7 Torr ( 5.6 × 10 - 5 Pa). For this, we studied the effect of the variation of the oxygen volume percent in the argon/oxygen mixture (by maintaining the deposition pressure constant) and the effect of deposition pressure with only argon gas on the main properties of AZO thin films. The depositions were done at room temperature on glass substrates by direct-current magnetron sputtering with a power of 120 W (corresponding to a power density of 2.63 W/cm2). As a result, we found that the variation of deposition pressure with only argon gas is a good option for the control of optical and electrical properties, since the addition of oxygen, although improves transmittance, greatly impacts on the electrical properties. Furthermore, an interesting correlation was found between the optical and electrical properties and the chemical composition of the AZO films, the latter depending on the argon pressure (for this, a careful X-ray photoelectron spectroscopy analysis was performed). Also, the inverse relationship between crystallinity and deposition rate was confirmed, in which deposition rate inversely depends on argon pressure.

In this work we have studied the properties of CdS films obtained by the chemical bath deposition technique. We studied the influence of pH control of the reaction solution on the structural and optical properties of chemically deposited CdS films. For this, we deposited two sets of CdS films on glass substrates using two different reaction solutions. The main difference between the solutions was that one included the use of a pH-10 NH4OH/NH4Cl controller solution or buffer, which produces a more uniform pH of the reaction solution during the film-growth process. Using each reaction solution, five CdS films were deposited at 80 °C, varying the deposition time from 15 to 120 minutes. The structural and optical properties of both sets of films were determined by X-ray diffraction and by absorption, transmission and reflection spectroscopy. The differences in the properties of the films were analyzed in terms of pH control.

In this work we report the optical and structural properties of composite materials based on the semiconductor PbS enclosed in type A zeolite. The composite materials were obtained by chemical reaction in several steps of the zeolite in alkaline aqueous solutions containing de Pb2+ and S2- ions successively. Three samples were prepared at temperatures of 40, 50 and 60°C during the chemical reaction with S2- ions. The obtained materials were studied by x-ray diffraction, scanning and transmission electron microscopy, diffuse reflectance spectroscopy and photoluminescence. The experimental results show the formation of spherical-shaped PbS particles with nanometric size and cubic crystalline structure embedded in the zeolite matrix. The absorption spectra of the samples display a well defined absorption band at about 300 nm due to the PbS nanoparticles in the zeolite matrix. In addition, an absorption peak appears in the absorption spectra at about 400 nm assigned to exciton transitions.

En este trabajo se reportan las propiedades ópticas y estructurales de materiales compuestos con base en el semiconductor PbS en matrices de zeolitas tipo A. Estos materiales fueron obtenidos mediante reacción química en varias etapas de la zeolita en medios acuosos alcalinos con iones de Pb2+ y S2- sucesivamente. Se prepararon tres muestras llevando a cabo la reacción química con iones de S2- a las temperaturas de 40, 50 y 60°C, respectivamente. Los materiales obtenidos fueron estudiados por difracción de rayos X, microscopía electrónica de barrido y de transmisión, espectroscopía óptica por reflectancia difusa y fotoluminiscencia. Los resultados muestran la formación de partículas de PbS de tamaño nanométrico, forma esférica y estructura cristalina cúbica distribuidas en la matriz de la zeolita. En el espectro de absorción de las muestras se observa una banda de absorción bien definida centrada en aproximadamente 300 nm debida a las nanopartículas de PbS en la matriz de zeolita. Adicionalmente aparece un pico de absorción alrededor de 400 nm asignado a transiciones excitónicas.