Browsing by Author "Flores, Marcos"

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    Effect of Plasma Argon Pretreatment on the Surface Properties of AZ31 Magnesium Alloy
    (2023) Montero, Cecilia; Ramirez, Cristian Gino; Munoz, Lisa; Sancy, Mamie; Azocar, Manuel; Flores, Marcos; Artigas, Alfredo; Zagal, Jose H.; Zhou, Xiaorong; Monsalve, Alberto; Paez, Maritza
    Climate change has evidenced the need to reduce carbon dioxide emissions into the atmosphere, and so for transport applications, lighter weight alloys have been studied, such as magnesium alloys. However, they are susceptible to corrosion; therefore, surface treatments have been extensively studied. In this work, the influence of argon plasma pretreatment on the surface properties of an AZ31 magnesium alloy focus on the enhancement of the reactivity of the surface, which was examined by surface analysis techniques, electrochemical techniques, and gravimetric measurements. The samples were polished and exposed to argon plasma for two minutes in order to activate the surface. Contact angle measurements revealed higher surface energy after applying the pretreatment, and atomic force microscopy showed a roughness increase, while X-Ray photoelectron spectroscopy showed a chemical change on the surface, where after pretreatment the oxygen species increased. Electrochemical measurements showed that surface pretreatment does not affect the corrosion mechanism of the alloy, while electrochemical impedance spectroscopy reveals an increase in the original thickness of the surface film. This increase is likely associated with the high reactivity that the plasma pretreatment confers to the surface of the AZ31 alloy, affecting the extent of oxide formation and, consequently, the increase in its protection capacity. The weight loss measurements support the effect of the plasma pretreatment on the oxide thickness since the corrosion rate of the pretreated AZ31 specimens was lower than that of those that did not receive the surface pretreatment.
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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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    Pulsed laser deposition of carbon films in low pressure neutral gas background
    (2012) Guzmán Olivos, Fernando Alfredo; Ruiz Araya, Hugo Marcelo; Favre Domínguez, Mario; Hevia, Samuel; Bhuyan, Heman; Chuaqui, Hernán; Wyndham, Edmund; Flores, Marcos
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    The effect of electron-surface scattering and thiol adsorption on the electrical resistivity of gold ultrathin films
    (2017) Henríquez, Ricardo; Del Campo, Valeria; González Fuentes, Claudio; Correa Puerta, Jonathan; Moraga, Luis; Flores, Marcos; Segura Segura, Rodrigo; Donoso, Sebastián; Marín, Francisca; Bravo, Sergio; Häberle, Patricio