Sergio Alfonso Pérez-García

Optical, Electrical and Photocatalytic Properties of the Ternary Semiconductors , and

The effects of vacuum annealing at different temperatures on the optical, electrical and photocatalytic properties of polycrystalline and amorphous thin films of the ternary semiconductor alloys , and were investigated in stacks of binary semiconductors obtained by chemical bath deposition. The electrical properties were measured at room temperature using a four-contact probe in the Van der Pauw configuration. The energy band gap of the films varied from 2.30 to 2.85 eV. The photocatalytic activity of the semiconductor thin films was evaluated by the degradation of an aqueous methylene blue solution. The thin film of annealed under vacuum at 300°C exhibited the highest photocatalytic activity.

Functionalization Effect on Polymer Nanocomposite Coatings Based on TiO2–SiO2 Nanoparticles with Superhydrophilic Properties

In this study, a novel binary nanocomposite system based on TiO2-SiO2 was functionalized with trimethylolpropane triacrylate (TMPTA) and characterized by XPS and XRD. Results revealed that TiO2-SiO2 nanoparticles were covalently functionalized. Functionalized nanoparticles at low concentrations (0.1 wt % and 0.5 wt %) were dispersed in acrylic acid acting as a polymer matrix. Nanocomposite coatings analysis demonstrate to achieve superhydrophilic properties as well as very good optical characteristics. Water contact angle characterization showed the functionalization effect by achieving a superhydrophilic behavior with a contact angle less than 5°. UV-Vis measurements demonstrated high optical transmittance above 95% for the coatings. Based on the obtained results a mechanism describing the chemical interactions of the constituents responsible for the synergy in the nanocomposite as well as the morphological play role in the behavior are presented.

Thermal decomposition of N-expanded austenite in 304L and 904L steels

In this study, expanded austenite was prepared by an industrial low-temperature plasma nitriding process in 304L and 904L austenitic stainless steels. The current investigation focuses on the assessment of the thermal stability and related phase evolution of the expanded austenite layer during isothermal annealing in protective argon atmosphere at temperatures ranging from 450 to 600°C for 24 and 168 h. Characterisation of the original expanded austenite and the decomposed surface layers was performed. Denitriding, inward N-diffusion and Cr-compounds precipitation occurred at different extent, depending on annealing conditions and alloy composition. Expanded austenite in 304L exhibited a near complete eutectoid decomposition after a short annealing time, while 904L showed significantly better thermal stability. A fine dispersion of small CrN precipitates resulting from expanded austenite decomposition at relatively low annealing temperature or short duration could further positively affect the surface hardness of both materials. Precipitate growth reduces hardness at higher annealing temperatures/times.

Luminescent Devices Based on Silicon-Rich Dielectric Materials

Luminescent silicon‐rich dielectric materials have been under intensive research due to their potential applications in optoelectronic devices. Silicon‐rich nitride (SRN) and sili‐ con‐rich oxide (SRO) films have been mostly studied because of their high luminescence and compatibility with the silicon‐based technology. In this chapter, the luminescent characteristics of SRN and SRO films deposited by low‐pressure chemical vapor deposi‐ tion are reviewed and discussed. SRN and SRO films, which exhibit the strongest pho‐ toluminescence (PL), were chosen to analyze their electrical and electroluminescent (EL) properties, including SRN/SRO bilayers. Light emitting capacitors (LECs) were fabricated with the SRN, SRO, and SRN/SRO films as the dielectric layer. SRN‐LECs emit broad EL spectra where the maximum emission peak blueshifts when the polarity is changed. On the other hand, SRO‐LECs with low silicon content (~39 at.%) exhibit a resistive switch‐ ing (RS) behavior from a high conduction state to a low conduction state, which produce a long spectrum blueshift (~227 nm) between the EL and PL emission. When the silicon content increases, red emission is observed at both EL and PL spectra. The RS behavior is also observed in all SRN/SRO‐LECs enhancing an intense ultraviolet EL. The carrier transport in all LECs is analyzed to understand their EL mechanism.