The construction, characterization and control of an electric oven dedicated to the study of thermoresistive polymer nanocomposites is presented. The oven is designed with a heating plate capable of reaching 300 °C with a resolution of 0.3 °C and an area of uniform temperature of 3.8 cm × 2.5 cm. The temperature is regulated by means of a discrete proportional-integral-derivative controller. A heat transfer model comprising three coupled non-linear differential equations is proposed to predict the thermal profiles of the oven during heating and cooling, which are experimentally verified. The oven is used for thermoresistive characterization of polymer nanocomposites manufactured from a polysulfone polymer and multiwall carbon nanotubes.

Cadmium selenide nanoparticles (NPs-CdSe) were synthesized by colloidal route at room temperature and atmospheric pressure using cadmium chloride (CdCl2·2.5 hydrate) and elemental selenium (Se) as precursors. Sodium borohydride (NaBH4) was used as reducing agent to obtain Se2− ions and an aqueous solution with a NaOH and Penta sodium tripolyphosphate (STPP) was used to protect Cd2+ ions. To remove the by-products generated during the chemical reaction and to promote the precipitation of NPs-CdSe, a cleaning process with an aqueous solution of HCl was performed. The HCl volume was varied from 0.2 to 1.2 ml during the cleaning process to study its effects on CdSe synthesis. The crystalline structure was analyzed by inspection of the high-resolution transmission electron microscope (HR-TEM) and X-ray diffraction (XRD). This analysis showed that crystals of CdSe exhibit a face-centered cubic structure (FCC). The calculated crystallite size is 3.5 nm and increases to 4.5 nm as the HCl volume increases. The morphologies of the products were observed by SEM and TEM techniques. HRTEM images showed that NPs-CdSe synthetized to 0.8 ml are composed of a great number of homogeneous and smooth nanospheres which are not appreciable in SEM but are observable in TEM. By contrast, 0.2 and 1.2 ml HCl samples are comprised of a great deal of rods of compounds of Se mixed with CdSe spheres nanostructures. This work, which did not require the use of surfactants complexes or specials environment, is considered to have advantages over other works.

Abstract: In this work, the methodology for obtaining the species distribution diagrams for depositing semiconductor films by chemical bath is discussed. The species distribution diagrams are useful for predicting the physicochemical conditions for achieving major control for materials deposition. By using ZnCl2 or ZnSO4, KOH, NH4NO3 and SC(NH2) 2 as chemical reagents for the bath, as well as the most probably chemical reactions between these chemical reagents, a range of deposition temperature (from 25 to 90 °C) and the different species formed by these reagents concentrations, the species distribution diagrams as a function of the pH were obtained. By using the species diagrams, thin films were deposited under different conditions in order to highlight their importance to obtain ZnS, ZnO and Zn(OH)2 thin films with better optical and structural qualities. The results indicate that the better conditions for obtaining the high quality films can change with the bath temperature and with the concentrations of the chemical reagents.

Resumen: En este trabajo se describe la metodología para obtener el diagrama de distribución de especies para depositar películas delgadas por la técnica de baño químico en forma controlada. El diagrama de especies obtenido resulta de gran utilidad para la predicción de las condiciones fisicoquímicas adecuadas para conseguir mayor control en el depósito de los materiales. Usando como reactivos químicos del baño el ZnCl2 (ZnSO4), KOH, NH4NO3 y SC(NH2)2 , así como las reacciones químicas más probables entre las especies formadas por estos reactivos, un rango de temperatura de depósito (entre 25 y 90 °C) y diferentes concentraciones de los reactivos, se obtuvieron los diagramas de distribución de especies como función del pH. Usando los diagramas de especies, se realizaron depósitos usando diferentes condiciones para corroborar su importancia en la obtención de películas delgadas de ZnS, ZnO y Zn(OH)2 con alta calidad óptica y estructural. Los resultados indican que las mejores condiciones para obtener películas de alta calidad pueden cambiar con la temperatura del baño y con la concentración de los reactivos utilizados.

In this work, the design, construction, calibration and compliance measurement of a universal testing machine for tension tests of materials in film geometry are presented. A commercial load cell of 220 N and sensitivity of 1.2345 mV/V is used to measure the applied load. Material strain is measured by movement of the crosshead displacement of the machine with a digital indicator with 0.001 mm resolution and 25 mm maximum displacement, connected to a PC through an interface. Mechanical strain is achieved by an electric high precision stepper motor capable to obtain displacement velocities as low as 0.001 mm/s. The stress-strain data acquired with a GPIB interface are saved as a file with a home-made program developed in LabView 7.0. Measurements of the elastic modulus and yield point of a commercial polymer film (500 HN Kapton) were used to validate the performance of the testing machine. The obtained mechanical properties are in good agreement with the mean values reported by the supplier and with the values obtained from a commercial machine, taking into account the limitations of thin film testing and experimental conditions.

En este trabajo se discute el diseño, la construcción, la calibración y la medición de la complianza de una máquina universal para pruebas de tensión de materiales en geometría de película. La carga aplicada es medida con una celda de carga comercial de 220 N y sensitividad de 1.2345 mV/V. La elongación de la muestra es medida a través del desplazamiento del cabezal de la máquina con un indicador de carátula digital con resolución de 0.001 mm y desplazamiento máximo de 25 mm, conectada a una PC a través de una interfase de puerto serial. La deformación mecánica es conseguida con un motor a pasos de alta precisión capaz de conseguir velocidades tan bajas como 0.001 mm/s. Los datos adquiridos a través de una interfase GPIB en tiempo real son guardados en un archivo usando un programa de diseño propio desarrollado en LabView 7.0. El módulo de elasticidad y el punto de fluencia medidos en una película polimerica comercial (Kapton 500 HN) fueron utilizados para evaluar el desempeño de la máquina construida. Los valores de las propiedades mecánicas obtenidas muestran buen acuerdo con los valores reportados por el proveedor y con los resultados obtenidos con una máquina comercial, considerando la geometría de capa delgada.

The design and construction of a vacuum quartz cylindrical oven to diffuse two or more metallic thin films for alloying is discussed. The oven has a gas-inert ambient (Ar) anda heater plate whose temperature is controlled by means of a home-made software development in Lab View 7.0. The heater area of 10 × 5 cm² raises the temperature to 600°C over time due to the water-cooled extremes implemented. The oven is heated and controlled with a DC power supply, and a K-type thermocouple is used for monitoring the temperature with a ± 0.1°C resolution. Experiments done with the oven to obtain nanostructured AuCu alloys are detailed.

En este trabajo se discute la fabricación de un horno al vacío basado en un tubo cilíndrico de cuarzo para difundir dos o mas capas delgadas metálicas para formar una aleación. El horno trabaja en un ambiente inerte de argón (Ar) y una temperatura controlada a través de una plancha interior de cerámica y un sistema de control PID basado en un software desarrollado en Lab View 7.0. El área de calentamiento de 10 × 5 cm puede elevar la temperatura hasta 600°C debido a sus tapas circulares que cuentan con un sistema de enfriamiento de agua. El horno es calentado y controlado con una fuente de corriente directa y utiliza un termopar tipo K para monitorear la temperatura con una resolución de ± 0.1°C. Se detallan pruebas realizadas en el horno para obtener la aleaciones nanoestructuradas de AuCu.

Cadmium sulphide (CdS) thin films deposited on indium tin oxide (ITO) substrates were prepared by chemical bath deposition technique by using different conditions to agitate the bath and the substrate. For substrate, an oscillating device working at 37 Hz was adapted to support each ITO substrate in order to agitate the substrate during deposition, meanwhile the chemical solution is heated and/not agitated. The deposited films were characterized on their morphology, on the band gap energy, and on thickness. The implemented novel technique for substrate oscillation has shown to improve the films quality, by the chemical bath without colloidal precipitates and by the clean film surfaces obtained. CdS films with variable deposition time can be achieved depending on the agitating technique. The mean band gap energy obtained around 2.41 eV is similar to the typical value reported in the literature for this material. In addition, by oscillating only the substrate during deposition is possible to obtain clean films and avoid the formation of colloidal precipitates on the chemical bath, normally presented when it is magnetically or ultrasonically agitated.

Cadmium sulphide thin films prepared by chemical bath deposition (CBD) were deposited on indium tin oxide (ITO) substrates with different deposition times (i.e. thickness) and characterised by their morphology and band gap energy. Samples were analysed as deposited and after annealing at 90 and 150°C, in order to study the interface diffusion and its effects on the properties mentioned. Auger depth profiles were used to determine the mass diffusivity coefficient in the CdS/ITO interface. The initial surface rms-roughness measured with AFM, as well as the initial band gap energy, are reduced after the annealing process. We obtained very small diffusion coefficient values, around 10-21 m²/s, for the different elements analysed in the interface.

Capas delgadas de sulfuro de cadmio, preparadas por bano químico, fueron depositadas sobre sustratos de ITO (oxido de estaño impurificado con indio) con diferentes tiempos de deposito (i.e. espesor) y caracterizadas en su morfología y en su brecha de energía. Las muestras fueron analizadas tanto recien depositadas como después de ser recocidas a las temperaturas de 90 y 150°C, con el objetivo de estudiar la difusion en la interfaz CdS/ITO y sus efectos sobre las propiedades mencionadas. Con ayuda de los perfiles Auger, se determinaron los valores de la difusividad masica de dicha interfaz. El valor inicial rms de la rugosidad superficial medida usando imágenes de fuerza atómica, así como la brecha de energía, se ven reducidos despues de los procesos de recocido. Se obtuvieron valores muy pequeños en los coeficientes de difusión, del orden de 10-21 m²/s, para los diferentes elementos analizados en la interfaz.

An elastic circular membrane of uniform density and thickness and subjected to a constant pressure difference is studied theoretically and experimentally. Two solutions of the deformation of an elastic circular membrane and their comparisons with the numerical values of the measured deformations of a surgical rubber glove membrane. The first solution is an analogical calculations using the geometry of soap bubbles, and the second one is the analytical solution of the differential equation of the elastic deformation in the approximation of constant elastic modulus. Both solutions predict a spherical shape which is confirmed by the experimental data. Comparisons with the solution of a deformed plate and with the paraboloidal shape desirable for solar mirrors are also included.

Se estudia teórica y experimentalmente una membrana circular elástica de densidad y espesor uniformes sujeta a una diferencia de presión constante. En este trabajo se analizan dos soluciones de la deformación que presenta una membrana elástica circular, así como su comparación con los valores reales de deformación medidos usando una membrana fabricada con guante de cirujano. La primera solución es un cálculo analógico utilizando la geometría de las pompas de jabón y la segunda es la solución analítica de la ecuación diferencial de la deformación elástica en la aproximación de módulo elástico constante. Ambas soluciones predicen una forma esférica que se confirma con los datos experimentales. También se hacen comparaciones con la solución de una placa deformada y con la forma paraboidal deseada en la fabricación de espejos solares.