Browsing by Author "Cerda, Daniel"

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    Compact TiO2 film thickness optimization and its effect on CsPbBr3-based photoanode performance for oxygen evolution reaction
    (2026) Sosa Acosta, José Raul; Villarroel, Roberto; Cerda, Daniel; Ruiz, Cristóbal; Fernandez Izquierdo, Leunam; Peón-Díaz, Francisco J.; Navarrete-Astorga; Dietmar Leinen, Elena; del Río, Rodrigo; Hevia, Samuel A.
    Compact TiO2 is an effective hole-blocking and electron transport layer (ETL) for perovskite photoanodes, but its performance depends critically on synthesis conditions and layer thickness. Here we report the thermal oxidation of electron-beam-evaporated Ti to produce pinhole-free, thickness-tunable c-TiO2 films (12–83 nm) to evaluate them as ETLs in back-illuminated n–i–p CsPbBr3 photoanodes for the oxygen evolution reaction. Cyclic voltammetry and electrochemical impedance spectroscopy confirmed that films thicker than 51 nm provided complete substrate coverage and yielded pinhole-free, compact layers with effective hole-blocking capabilities, which potentially reduce recombination and improve electron collection. Photoanodes were evaluated via linear sweep voltammetry to determine the influence of TiO2 thickness during water oxidation. An optimal 51 nm cTiO2 layer yielded a photocurrent density of 4.2 mA/cm2 at 1.23 V vs. RHE and an ABPE of 0.93 % at 0.8 V vs. RHE, maintaining >1.5 mA/cm2 over 4 h in aqueous, catalyst-free OER conditions. Thicker ETLs (65–83 nm) reduce photocurrent due to increased series resistance. These results highlight the importance of quality and precise control over TiO2 thickness. Thermal oxidation of e-beam Ti offers a reproducible route to compact, transparent ETLs that balance coverage, transmittance, and resistance for stable aqueous photoelectrochemical operation
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    Tunable Low Crystallinity Carbon Nanotubes/Silicon Schottky Junction Arrays and Their Potential Application for Gas Sensing
    (2021) Adrian, Alvaro R.; Cerda, Daniel; Fernandez-Izquierdo, Leunam; Segura, Rodrigo A.; Garcia-Merino, Jose Antonio; Hevia, Samuel A.
    Highly ordered nanostructure arrays have attracted wide attention due to their wide range of applicability, particularly in fabricating devices containing scalable and controllable junctions. In this work, highly ordered carbon nanotube (CNT) arrays grown directly on Si substrates were fabricated, and their electronic transport properties as a function of wall thickness were explored. The CNTs were synthesized by chemical vapor deposition inside porous alumina membranes, previously fabricated on n-type Si substrates. The morphology of the CNTs, controlled by the synthesis parameters, was characterized by electron microscopies and Raman spectroscopy, revealing that CNTs exhibit low crystallinity (LC). A study of conductance as a function of temperature indicated that the dominant electric transport mechanism is the 3D variable range hopping. The electrical transport explored by I-V curves was approached by an equivalent circuit based on a Schottky diode and resistances related to the morphology of the nanotubes. These junction arrays can be applied in several fields, particularly in this work we explored their performance in gas sensing mode and found a fast and reliable resistive response at room temperature in devices containing LC-CNTs with wall thickness between 0.4 nm and 1.1 nm.