Browsing by Author "Henriquez, Ricardo"

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    Effect of thiol adsorption on the electrical resistance of copper ultrathin films
    (2024) Gray, Gabriel; Marin, Francisca; del Campo, Valeria; Gonzalez-Fuentes, Claudio; Correa-Puerta, Jonathan; Flores, Marcos; Segura, Rodrigo; Haberle, Patricio; Henriquez, Ricardo
    The impact of thiol adsorption on thin copper films, covered with a copper oxide layer, was investigated using electrical resistance measurements at various stages: during film growth, aging, exposure to air, and immersion in thiol solutions. Thin copper films (20 nm) were thermally evaporated, with variations in substrate temperature (RT, 330 and 390 K). Films deposited at 330 K exhibited the smallest percolation thickness and aging rates due to their compact morphology, showcasing lower surface roughness and correlation length. Exposure to air led to the formation of a Cu2O 2 O layer on the film surface. Subsequent immersion in a dodecanethiol solution in ethanol resulted in a resistance increase, ranging from 0.1 % to 0.4 %. This change was dependent on the substrate temperature, with the largest difference observed at 330 K. This observation suggests that samples grown at this temperature exhibited the highest electron-surface scattering. Moreover, by depositing a chromium surfactant layer, the impact of this scattering mechanism was amplified, leading to a resistance increase of up to 1.2 %. Mayadas-Shatzkes theory provided a good description of these resistance changes. The negatively charged S-head of the adsorbed thiols alters the electric field experienced by conduction electrons in the Cu2O/Cu 2 O/Cu interface, modifying the electron-surface scattering.
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    Enhanced photoconversion efficiency of hybrid TiO2/nox-MWCNT/Si photoanode for water splitting in neutral medium
    (2021) Olivares, Fernanda; Segura del Rio, Rodrigo; Reyes, Javier; Peon, Francisco; Henriquez, Ricardo; Hevia, Samuel A.; Duran, Boris; Villalonga, Reynaldo
    Hybrid films composed by TiO2 and functionalized MWCNTs were synthesized and used as photoanodes to perform the water splitting process under neutral and free of sacrificial agents medium. The results show that introducing a sublayer of MWCNTs functionalized with -NO2 and -COOH groups leads to structural modifications on TiO2 that decrease the band gap and reduce the recombination phenomenon. Those groups anchored to nanotubes also play an important role in their dispersibility and provide an additional electron withdrawing effect to the pristine nanotubes. These conditions significantly improve the photoconversion efficiency of the hybrid system until 15-fold regarding pristine TiO2 prepared under the same conditions. (c) 2020 Elsevier B.V. All rights reserved.
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    The effect of oxidative functionalization of carbon nanotubes on the morphological, optical, and photoelectrochemical properties of modified titanium dioxide photoanodes
    (2023) Peon-Diaz, Francisco J.; Segura del Rio, Rodrigo; Hevia, Samuel; Olivares, Fernanda; Carlos Exposito-Galvez, Juan; Escalante, Renan; Valadez-Villalobos, Karen; Riquelme, Antonio J.; Oskam, Gerko; Henriquez, Ricardo
    In this work, we demonstrate the influence of the oxidative treatment of carbon nanotubes (CNTs) on the morphological, optical, and photoelectrochemical properties of CNTs-TiO2 photoanodes. CNTs were synthesized by a chemical vapor deposition method (CVD) and subsequently oxidized in a mixture of HNO3/H2SO4 to introduce nitrogen- and oxygen-containing functional groups. The oxidation time was varied (45, 90, and 180 min) to obtain CNTs with different oxidation levels (CNTs-ox). Pristine and oxidized CNTs were deposited on ITO and used as substrates to fabricate ITO/CNTs/TiO2 photoelectrodes by depositing a TiO2 thin layer using a CVD procedure. The extent of oxidation of the CNTs was found to directly influence the homogeneity and morphology of the TiO2 overlayer, its physical stability, and the optical and photoelectrochemical properties of the photoelectrodes. An optimum oxidative treatment was achieved for 90 min, leading to a CNTs-ox/TiO2 electrode with the best performance. Compared to shorter and longer times, this sample showed the smallest bandgap and the best homogeneity of TiO2 growth on the CNTs' surface. Optimal photoelectrochemical performance was also found for this sample (160 mu A/cm(2) at 0 V vs. Ag/AgCl) in KCl (0.1 M) electrolyte (100 mW/cm(2), Xenon arc lamp).