J. Díaz-Reyes

Characterization of WO3 Thin Films Grown on Silicon by HFMOD

We studied the effect of annealing temperature on the physical properties of WO3 thin films using different experimental techniques. WO3 has been prepared by hot-filament metal oxide deposition (HFMOD). The films, chemical stoichiometry was determined by X-ray photoelectron spectroscopy (XPS). The monoclinic single-phase nature of the as-deposited films, structure was changed to triclinic structure by annealing them at higher temperatures than 400°C, which has been determined by the X-ray diffraction analysis. By Raman scattering is confirmed the change of crystalline phase, of monoclinic to triclinic, since that lattice vibrational modes of as-deposited WO3 and annealed at 500°C present clearly differences. WO3 band gap energy can be varied from 2.92 to 3.15 eV by annealing WO3 from 0 to 500°C as was obtained by transmittance measurements. The photoluminescence response of the as-deposited film presents three radiative transitions observed at 2.85, 2.41, and 2.04 eV that could be associated with oxygen vacancies; the first one is shifted to higher energies as the annealing temperature is increased due to the change of crystalline phase of the WO3.

Self-normalized photoacoustic technique for thermo-optical characterization of samples mounted between transparent media

A self-normalized photoacoustic technique for thermo-optical characterization of materials, mounted between transparent media, is presented. It involves a complex ratio of photoacoustic signals in transmission and front configurations, taking the modulation frequency as the only variable. The analytical solutions for the corresponding 1D heat diffusion problems are analyzed to provide suitable methodologies for measuring the optical absorption coefficients and thermal diffusivity of such samples. This methodology was tested by measuring the optical absorption coefficient, at 660 nm, of methylene blue solutions at various concentrations and the thermal diffusivity of a black drawing ink sample. In addition, an approximated range of optical absorption coefficients, where this photoacoustic methodology is adequate, was established.

Characterization of Wurtzite Type ZnS Grown by RF Magnetron Sputtering

ZnS was grown on (001) GaAs substrates at different temperatures by RF magnetron sputtering. ZnS chemical stoichiometry was determined by energy-dispersive X-ray spectroscopy (EDS). The XRD analysis and Raman scattering reveal that ZnS deposited thin films showed hexagonal crystalline phase wurtzite type. The average crystallite size range of the film was from 8.15 to 31.95 nm, which was determined using the Scherrer–Debye equation on diffractograms. Besides, an experimental study on first- and second-order Raman scattering of ZnS films is made. The observed emission peaks in the room temperature photoluminescence spectra are associated at oxygen traps and interstitial sulphur.

Optical and structural characterization of antimony doped zinc oxide single crystal

The optical and structural study of the antimony doping in zinc oxide (ZnO) single crystal (001) performed by atomic diffusion is presented. Diffusion was carried out with a temperature of 1000 ° C for periods of 1 and 2 hrs from a solid source prepared by partial oxidation of antimony, characterization of each step process was performed by photoluminescence (PL), x-ray diffraction (XRD) and high resolution x-ray diffraction (HRXRD). The characterization by PL shows the effect of antimony doping on the emission band intensity attributed to reduction of oxygen vacancies by antimony introduction. The results of XRD showed that antimony source has a Sb2O3 crystalline phase. Reciprocal space maps of doped samples revealed the low dimensional structural modification of single crystal produced by the introduction of antimony. Results indicate that antimony is introduced fully into surface of ZnO and produce low dimensional changes on structure.

Spectroscopy Analysis of the Ring Opening Reaction in Functionalized Spiropyran Films

In this work we used the Fourier Transform Infrared spectroscopy and UV/Vis spectroscopy to analyze the behaviour of self-ensemble films of spiropyran when the films were irradiated by UV. In UV/Vis spectroscopy is possible observe the generation of the absorption peak, at 575 nm, associated to the merocyanine state when the ring-opening process is induced by UV light. In ATR the kinetics of the ring-opening was determinate too; following the spectra changes in real time.