Abstract In this work, it is shown the feasibility for obtaining silver nanoparticles by ultrasonic spray pyrolysis and their simultaneous incorporation during deposition of thin layers of aluminum oxide to get a Cermet coating of Al2O3-Ag. The synthesis of these Cermets was achieved on the basis of both the simultaneous pyrolysis of silver nitrate and aluminum acetylacetonate on different substrates: Quartz, glass, crystalline silicon (c-Si), and titanium at temperatures of 500, 550 and 600°C. The structural properties of the Cermets were studied by Scanning Electron Microscopy, Atomic Force Microscopy and X-ray diffraction. For the optical properties, UV-vis spectroscopy was used to obtain the optical Absorbance of the Cermets, while the Reflectance was obtained by UV-vis-IR spectroscopy measurements. UV-Vis spectroscopy showed that the intensity of the absorption peak (plasmon) was limited to the concentration of silver nitrate, and it shifted toward shorter wavelengths with the decrease in the size of the Ag nanoparticles inside the Cermets. The plasmon position of Ag nanoparticles in the different samples was found to be centered at 504 nm, 506 nm, 497 nm and 475 nm for samples deposited with 0.1 mol, 0.05 mol, 0.02 mol, and 0.01 mol of Ag(NO3), respectively. The shape of the Ag nanoparticles was approximately spherical, ranging from 4 nm to 35 nm, and their concentration was proportional to the concentration of Ag(NO3) included in the spray solution. By means of the UV-Vis Spectroscopy-IR and FT-IR, in the best of cases, a solar absorptance of 0.83 and an infrared thermal emittance of 0.14, for a sample of Al2O3-Ag prepared with 0.1 mol of Ag(NO3) in the precursor solution, were obtained.

Abstract Thin solid films of CdS:Cu were synthesized using a wet-chemical. Doping was by thermal diffusion. Films were obtained as a function of: precursor salts, deposition time and annealing temperature. Studies of transmittance, resistivity, photoluminescence at room temperature, X-ray diffraction, high-resolution scanning and transmission electron microscopies, were performed. The CdS and CdS:Cu films obtained had an average thickness of 130 nm and 160 nm, respectively. This study provides evidence of the greater effectiveness of sodium citrate than ammonium chloride as a complexing agent. The crystalline phase of the films was cubic and did not vary with deposition time or the precursor. Studies were consistent in showing a film made up of regularly spaced, asterisk-shaped entities of about 35 nm in size, which in turn were composed of nanocrystals smaller than 10 nm. The resulting films behaved as an n-type semiconductor with an energy gap of about 2.38 eV that varied only slightly with deposition time and the precursors' nature, but increased to 2.93 eV with Cu doping. The resistivity achieved was 5.822 × 10-5 Ω-cm. The PL emission spectra showed variation in optical quality and revealed a de-excitation mechanism due to the presence of cadmium vacancies, sulfur vacancies and interstitial cadmium.

Polystyrene (PS) films doped with blue, yellow and red organic pigments have been deposited on glass and on commercial LED chips by spray pyrolysis using recycled PS as precursor, at deposition rates between 100 and 200 Å/s. Doped films have roughness between 100 and 2500 Å depending on the kind of pigment used; the surface morphology shows that the organic pigments incorporate into the polystyrene host forming globular particles of about 2 μm in diameter. The organic pigments used have luminescent emissions peaked at 440, 509 and 590 nm. The introduction of the proper combination of pigments on the PS film deposited on the LED chips renders a white light emission with (0.29, 0.37) and (0.30, 0.33) CIE (Commission international de l' eclairage) color coordinates. It was determined that the exposure to violet light degrades the luminescent characteristics, however, blue light is not energetic enough to cause a degradation of the luminescent layer over similar period of time.

(ZnO)X-(CdO)1-X thin films were deposited on glass substrates at 300°C and 400°C by ultrasonic spray pyrolysis with compositions ranging from CdO to ZnO. The electrical properties were obtained by impedance spectroscopy and Hall Effect measurements. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction, were used to study the structural characteristics of the films. Ellipsometry, in addition, was used to confirm the structural characteristics. The films as deposited resulted mainly polycrystalline and dense, depending on the substrate temperature and on their relative composition. All the films showed n-type conductivity and the films with intermediate compositions resulted in a mixture of both phases; CdO and ZnO. Hall Effect measurements showed that the highest conductivity of CdO was close to 1x10³ (Ω-cm)-1, the highest value obtained for CdO, without doping. Impedance spectroscopy confirmed the Hall Effect results, showing that the highly conducting character of CdO influenced dramatically the conductivity of the (ZnO)X-(CdO)1-X films. In addition, depending on the substrate temperature and on the relative composition of the films, both, the bulk or grains, as well as the grain boundaries properties limit the conductivity in them.

Películas delgadas de (ZnO)x(CdO)1_x fueron depositadas sobre sustratos de vidrio a 300°C y 400°C por rocío pirolítico ultrasónico con composiciones entre CdO y ZnO. Las propiedades eléctricas fueron determinadas a través de medidas de espectroscopia de impedancia y Efecto Hall. Microscopía electrónica de barrido, espectroscopia por dispersión de energía y difracción de rayos X fueron utilizadas para determinar las características estructurales de las películas. Elipsometría fue empleada para confirmar las características estructurales. Las películas, tal y como son depositadas resultaron policristalinas y densas, dependiendo de la temperatura del sustrato y de la composición relativa de ellas. Todas las películas mostraron una conductividad de tipo n y las películas con concentraciones intermedias resultaron con una mezcla de ambas fases; CdO y ZnO. Las mediciones de Efecto Hall mostraron que la más alta conductividad de las películas de CdO fue cercano a 1 x 10³ (Ω-cm)-1, valor más alto obtenido para CdO sin dopante. Las medidas de espectroscopia de impedancia confirmaron los resultados obtenidos por Efecto Hall, y mostraron además que el alto carácter conductor de las películas de CdO influye de manera importante en la conductividad de las películas de (ZnO)X-(CdO)1-X. Además, dependiendo de la temperatura del sustrato y de la composición relativa de las películas ambos, los granos (o el bulto), así como las fronteras de grano, limitan la conductividad en ellas.

In this work, a comparison between Impedance Spectroscopy (IS) and Plate Counting to probe the growth of Lactobacillus acidophilus (La) was done. It was found that after inoculation, and after 0.8 h, the microbial growth was noticed by IS, inferred by the λ parameter. In contrast, by means of the Plate Counting method, the growth was noticed after 6.8 h. The experimental data obtained by IS were first fitted by an RC series circuit, and then, the curves generated were modeled by the well-known growing models of Gompertz and Boltzmann. When using the IS technique, it was found that the resistance of the medium was a better parameter to describe the growing process of La.

Una comparación entre la técnica de espectroscopia de impedancia eléctrica (EIE) y la técnica tradicional de conteo en placa fue realizada para estudiar el crecimiento del Lactobacillus acidophilus (La). Se encontró que, tras la inoculación, y después de 0.8 h, el crecimiento microbiano fue registrado por medio de la EIE, inferida a través del parámetro λ. En contraste, con la técnica de conteo en placa, el mismo parámetro se estimó en 6.8 h. Los datos experimentales obtenidos mediante la EIE fueron ajustados por un circuito RC en serie, posteriormente, las curvas generadas fueron ajustada a los modelos de crecimiento de Gomperte y Boltzmann. Usando la técnica de espectroscopia de impedancia eléctrica, la resistencia del medio resultó la más eficiente para la estimación de los parámetros del crecimiento de Lactobacillus acidophilus.

A two-step synthesis process was performed to obtain TlBa2Ca2Cu3Ox (Tl-1223) superconductor films. The synthesized films were obtained under different thallium diffusion conditions in a two-zone furnace precursor films were deposited at 550° C on silver substrates using the spray pyrolysis technique from acetylacetonates (2, 4-pentanedionates) as reagents. Second, a thallium diffusion process is carried out to incorporate Tl in the films. For this task Tl2O3 pellets, as a Tl source, were used at 750°C. Different oxygen flow rates at atmospheric pressure were used in order to get the thallous oxide p (Tl2O) partial pressure in the range of 6.9 x 10-4 to 6.1 x 10-2 atm. The Tl-1223 phase was obtained in all cases, though for a low p (Tl2O), the films presented the BaCuO2 phase mixed with the Tl-1223 one. Critical temperature (T C) values for these films were in the range of 90 to 102 K.

El proceso de síntesis de dos pasos fue realizado para obtener películas superconductoras de TlBa2Ca2Cu3Ox (Tl-1223). Las películas sintetizadas fueron obtenidas bajo diferentes condiciones de difusión de talio en un horno de dos zonas. En el primer paso, las películas precursoras se depositaron a 550°C sobre substratos de plata usando la técnica de rocío Pirólitico a partir de acetilacetonatos (2,4-pentanedionatos) como reactivos. En el segundo paso, se llevo a cabo un proceso de difusión de talio para incorporar Tl en las películas. Para esta tarea, se usaron pastillas de Tl2O3 como fuente de talio a 750°C. Se usaron diferentes razones de flujo de oxígeno a presión atmosférica para obtener presiones parciales de óxido taloso p (Tl2O)en el intervalo de 6.9 x 10-4 to 6.1 x 10-2 atm. La fase Tl-1223 se obtuvo en todos los casos, aunque a bajas presiones parciales de p (Tl2O), las películas presentan la fase BaCuO2 mezclada con la fase Tl-1223. Los valores de temperatura crítica para estas películas se encuentran en el intervalo de 90 a 102 K.

Electrical characteristics of thin films of aluminum oxide prepared by spray pyrolysis were studied. The films were prepared from solution onto single crystal GaAs (100) substrates at temperatures from 300°C to 600°C. The electrical characteristics of these films as a function of the substrate temperature were determined from the capacitance and current versus voltage measurements of metal-oxide-semiconductor (MOS) structures incorporating them. The interface states density was of the order of 10(12) 1/eV-cm² and the films can stand electric fields higher than 5MV/cm, without observing destructive dielectric breakdown. The refractive index at 633 nm near to 1.64 was measured by ellipsometry.

Se estudiaron las características eléctricas de películas delgadas de óxido de aluminio preparadas por la técnica de rocío pirolítico ultrasónico. Las películas delgadas se depositaron a partir de una solución de acetilacetonato de aluminio en N,N-dimetilformamida sobre substratos monocristalinos de GaAs (100) tipo-p. La temperatura de depósito fue de 300 a 600 ºC. Las propiedades eléctricas de las películas en función de la temperatura de substrato se determinaron por medidas de capacitancia y corriente contra voltaje mediante la incorporación de las películas en estructuras tipo MOS (metal-óxido-semiconductor). La densidad de estados de interfaz resultó del orden de 10(12) 1/eV-cm² y el dispositivo MOS soportó campos eléctricos mayores a 5MV/cm, sin mostrar rompimiento dieléctrico. El índice de refracción se determinó por elipsometría a 633nm, con un valor máximo del orden de 1.64.

Abstract GaAsN layers were grown on GaAs(100) substrates by MBE employing a radio frequency (RF) plasma nitrogen source, and solid sources for Ga and As. The growth temperature was varied from 420 to 600 °C, and the GaAsN growth mode was in-situ monitored by reflection high-energy electron diffraction (RHEED). The optical properties of the layers were studied by photoreflectance spectroscopy (PR), phase modulated ellipsometry (PME), and photoluminescence. For the growth temperature of 420 °C the films grew in a three-dimensional (3D) mode as indicated by the appearance of transmission spots in the RHEED patterns. In contrast, GaAsN layers grown at higher temperatures presented a two-dimensional (2D) growth mode. These GaAsN layers are pseudomorphic according to high resolution x- ray diffraction (HRXRD). The PR spectra of all samples exhibited Franz-Keldish oscillations (FKO) above of the GaAs band-gap energy. From these oscillations we obtained the built-in internal electric field intensity (F int ) at the GaAsN/GaAs interface. In the low energy region of the PR spectra we observed the transitions associated to the fundamental band-gap of the GaAs1-xNx layers. The variation of the GaAsN fundamental band -gap obtained by PR as a function of the N content was explained according the band anticrossing model (BAC). On the other hand, the E1 and E1+ ∆E1 critical points were obtained from the analysis of spectra of the imaginary part of the dielectric function obtained by PME. We observed a shift of these critical points to higher energies with the increase of N content, which was explained by a combination of strain and alloying effects.

In this work it is shown that the Total Internal Reflection (TIR) phenomenon can be exploited for gas detection. Total internal reflectance measurements for evaporated SnO2 thin films on quartz substrates are measured at ambient conditions. Changes in the reflectance measurements are measured when CO2 or N2 gas flows on the surface of the SnO2 films. The observed shift in the measured reflectance is defined as the signal of the sensor. Preliminary results show that the maximum response takes place at incident angles close to the critical angle of the quartz-air system.

En este trabajo se demuestra como puede ser utilizado el fenómeno de Reflexión Interna Total para la detección de gases. En condiciones ambientales normales se midieron espectros de reflexión interna total de películas de SnO2 evaporadas sobre substratos de cuarzo. Se midieron cambios en los espectros de reflectancia cuando las películas de SnO2 se expusieron a flujos de gas de CO2 o N2. En base a los cambios observados en la reflectancia se define la serial del sensor. Resultados preliminares muestran que la respuesta máxima se obtiene para ángulos de incidencia en la vecindad del ángulo crítico del sistema cuarzo-aire.