M. O. Vazquez-Lepe

Mass transport and thermal stability of TiN/Al2O3/InGaAs nanofilms

The structure of TiN/Al2O3 nanofilms grown on InxGa1-xAs substrates was studied with angle-resolved x-ray photoelectron spectroscopy (ARXPS), high resolution transmission electron microscopy (HRTEM), and density functional theory calculations. From the ARXPS studies, it was possible to characterize in detail the composition and distribution of the various layers constituting the nanofilms; the results were consistent with HRTEM micrographs. The analysis of the ARXPS data showed that annealing causes diffusion of indium atoms from the substrate into the titanium layer. It also allowed for establishing that the thickness and composition of the dielectric layers remain stable under thermal treatments.

Diffusion of In and Ga in TiN/HfO2/InGaAs nanofilms

The structure of TiN/HfO2 nanofilms grown on InxGa1−xAs substrates was assessed through angular-resolved x-ray photoelectron spectroscopy. The quantitative analysis made possible determining the thickness and composition of the various layers constituting the nanofilms treated at different temperatures (un-annealed, 500  °C/120 s and 700  °C/10 s). The TiN layer is crucial to prevent oxygen desorption from the dielectric during annealing. Small amounts of oxidized gallium and metallic arsenic are located at the HfO2/InGaAs interface. The thickness of the HfO2 layer remains stable under the thermal treatments. Annealing affects the In 3d5/2 and Ga 3p signals. From the angular dependence of the peak intensities and the detailed knowledge of the structure of the films, it was possible to determine that annealing causes In and Ga out-diffusion into the metallic layer, and also to quantify the amount of transported matter. This, along with density functional theory calculations, allowed for an estimation of th...

Aperture-time of oxygen-precursor for minimum silicon incorporation into the interface-layer in atomic layer deposition-grown HfO2/Si nanofilms

Hafnium oxide nanofilms were grown with atomic layer deposition on H-terminated Si (001) wafers employing tetrakis dimethyl amino hafnium (TDMA-Hf) and water as precursors. While the number of cycles (30) and the aperture-time for TDMA-Hf (0.08 s) were kept constant, the aperture-time ( τH2O) for the oxidant-agent (H2O) was varied from 0 to 0.10 s. The structure of the films was characterized with robust analysis employing angle-resolved x-ray photoelectron spectroscopy. In addition to a ∼1 nm hafnium oxide layer, a hafnium silicate interface layer, also ∼1 nm thick, is formed for τH2O > 0. The incorporation degree of silicon into the interface layer (i.e., the value of 1 − x in HfxSi1−xOy) shows a minimum of 0.32 for τH2O = 0.04 s. By employing the simultaneous method during peak-fitting analysis, it was possible to clearly resolve the contribution from the silicate and from oxide to the O 1s spectra, allowing for the assessment of the oxygen composition of each layer as a function of oxidant aperture ti...

Eco-friendly Production of Metallic Nanoparticles in Polymeric Solutions and Their Processing into Biocompatible Composites

Silver and gold nanoparticles were produced and embedded in poly(vinyl alcohol) (PVA) and chitosan (CTS) solutions by the photoreduction of metallic salt precursors triggered by direct sunlight irradiation, in which the polymers acted as reducing, dispersing and stabilizing agents. Sunlight photoreduction can be standardized using a constant UV index regardless of the season. This strategy was found to be an improvement over other common energy sources used to trigger the reduction of metal ions, including UV light irradiation and high-temperature reduction with mechanical stirring. The resulting PVA/metal nanoparticle and CTS/metal nanoparticle composite solutions were processed into thin films and nanofiber composites. In vitro testing of the cytotoxicity and biocompatibility demonstrates that the film composites are non-toxic and biocompatible with the HT-29 human colon cancer cell line. Promotion of HT-29 cell growth using our hybrid composites was observed, in contrast to other studies in which colloidal NPs were tested. Therefore, a sustainable approach for the onestep preparation of biocompatible polymer/metallic nanoparticle composites is reported.