Browsing by Author "Hevia, Samuel A."

Now showing 1 - 15 of 15
  • No Thumbnail Available
    Item
    Comparison of Different Synthetic Routes of Hybrid Hematite-TiO2 Nanotubes-Based Electrodes
    (2021) Fornazari, Ana Luiza; Castillo-Rodriguez, Judith; Correa-Encalada, Daniel; Dalchiele, Enrique A.; Hevia, Samuel A.; del Rio, Rodrigo
    Nowadays, green hydrogen is an important niche of interest in which the search for a suitable composite material is indispensable. In this sense, titanium oxide nanotubes (TiO2 nanotube, TNTs) were prepared from double anodic oxidation of Ti foil in ethylene glycol electrolyte. The morphology of the nanotubes was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Once characterized, nanotubes were used as templates for the deposition of hematite. The use of three synthetic procedures was assayed: Chemical Vapor Deposition (CVD), Successive Ionic Layer Adsorption and Reaction (SILAR), and electrochemical synthesis. In the first case, CVD, the deposition of hematite onto TiO2 yielded an uncovered substrate with the oxide and a negative shift of the flat band potential. On the other hand, the SILAR method yielded a considerable amount of hematite on the surface of nanotubes, leading to an obstruction of the tubes in most cases. Finally, with the electrochemical synthesis, the composite material obtained showed great control of the deposition, including the inner surface of the TNT. In addition, the impedance characterization showed a negative shift, indicating the changes of the interface electrode-electrolyte due to the modification with hematite. Finally, the screening of the methods showed the electrochemical synthesis as the best protocol for the desired material.
  • No Thumbnail Available
    Item
    CsPbBr3-based photoanode prepared by single-step Chemical vapor deposition of tunable thickness perovskite films
    (2024) Sosa-Acosta, J. R.; Fernandez-Izquierdo, L.; del Rio, Rodrigo; Navarrete-Astorga, Elena; Leinen, Dietmar; Hevia, Samuel A.
    Cesium Lead Bromide (CsPbBr3) perovskite films have gained significant attention in photoelectrochemistry due to their promising properties. However, their widespread application necessitates scalable processing methods to produce high-quality films. Current techniques often involve post-synthesis steps to achieve desirable crystalline films or surface coverage for optimal performance. This research performed a single-step Chemical Vapor Deposition (CVD) approach to grow high-quality CsPbBr3 films. This methodology offers precise control over film thickness and grain orientation, crucial for optimizing photoelectrochemical response. The procedure simplifies fabrication by bypassing annealing or toxic solvent excess and growing films directly from CsPbBr3 crystals. Film thickness was controlled by adjusting growth time and precursor mass parameters to examine the photoelectrochemical performance across thicknesses ranging from 0.6 mu m to 2.5 mu m. Optimal results were achieved with dense, compact films 1.5 mu m thick, which exhibited oriented grains along the (121) plane. Optical, structural, and morphological analyses confirmed a predominantly pure orthorhombic phase, although slight impurities were noted in thinner films. The 1.5 mu m films showed a four-hour stable photocurrent of 6.2 mA/cm2 at 1.23 V versus reversible hydrogen electrode (RHE) under simulated solar conditions, underscoring their potential in advancing perovskite-based electrodes for efficient photoelectrochemical solar fuel generation.
  • No Thumbnail Available
    Item
    CVD Growth of Hematite Thin Films for Photoelectrochemical Water Splitting: Effect of Precursor-Substrate Distance on Their Final Properties
    (2023) Fernandez-Izquierdo, Leunam; Spera, Enzo Luigi; Duran, Boris; Marotti, Ricardo Enrique; Dalchiele, Enrique Ariel; del Rio, Rodrigo; Hevia, Samuel A.
    The development of photoelectrode materials for efficient water splitting using solar energy is a crucial research topic for green hydrogen production. These materials need to be abundant, fabricated on a large scale, and at low cost. In this context, hematite is a promising material that has been widely studied. However, it is a huge challenge to achieve high-efficiency performance as a photoelectrode in water splitting. This paper reports a study of chemical vapor deposition (CVD) growth of hematite nanocrystalline thin films on fluorine-doped tin oxide as a photoanode for photoelectrochemical water splitting, with a particular focus on the effect of the precursor-substrate distance in the CVD system. A full morphological, structural, and optical characterization of hematite nanocrystalline thin films was performed, revealing that no change occurred in the structure of the films as a function of the previously mentioned distance. However, it was found that the thickness of the hematite film, which is a critical parameter in the photoelectrochemical performance, linearly depends on the precursor-substrate distance; however, the electrochemical response exhibits a nonmonotonic behavior. A maximum photocurrent value close to 2.5 mA/cm(2) was obtained for a film with a thickness of around 220 nm under solar irradiation.
  • No Thumbnail Available
    Item
    Design of highly stable Co3O4/RGO/CoFe2O4 hybrid nanocomposites with multiple nanointerfaces for enhanced supercapacitor performance
    (2024) Kavinkumar, T.; Reddy, N. Ramesh; Pabba, Durga Prasad; Ramadoss, Ananthakumar; Rednam, Udayabhaskar; Dhanabalan, Shanmuga Sundar; Chidhambaram, Natarajan; Asaithambi, Perumal; Hevia, Samuel A.; Thirumurugan, Arun
    In this study, we developed a novel hybrid electrode nanomaterial composed of Co3O4, CoFe2O4, and reduced graphene oxide (RGO) for electrochemical supercapacitor applications. The hybrid nanocomposite of Co3O4/ RGO/CoFe2O4 was prepared using a modified chemical oxidation process and the phase formation of the composites was evidenced by X-ray diffraction (XRD). The grain size for Co3O4 and CoFe2O4 was estimated as 12 nm and 22 nm. For Co3O4/CoFe2O4 the reduced grain size of 19 nm for CoFe2O4 was observed and further it was reduced with RGO up to 15 nm. The bare Co3O4 exhibited a hexagonal plate-like morphology, whereas the bare CoFe2O4 showed mostly a spherical morphology. The reduced saturation magnetization for the hybrid electrode material due to the non-magnetic fraction of Co3O4 and RGO was observed to be 21 emu/g compared to the bare CoFe2O4 (77 emu/g). The Co3O4/RGO/CoFe2O4 electrode exhibited enriched electroactive sites and enhanced diffusion pathways, achieving a high specific capacity of 235C g - 1 at 5 A g - 1 with excellent durability.. This work highlights the significant charge storage potential of the Co3O4/RGO/CoFe2O4 hybrid, making it a promising candidate for advanced energy storage systems.
  • No Thumbnail Available
    Item
    Effects of Pt doping on surface properties and quenching of band edge emission in ZnO
    (2024) Kumar, Promod; Mathpal, Mohan Chandra; Goutaland, F.; Hevia, Samuel A.; Duvenhage, M. M.; Roos, W. D.; Swart, H. C.
    Pt doped ZnO thin films were synthesized on soda-lime glass substrates using a cost-effective sol-gel method, followed by spin coating and thermal annealing at various temperatures. Several characterization techniques such as UV-Vis absorption spectroscopy, photoluminescence (PL), field emission scanning electron microscopy (FESEM), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) are exploited to investigate the Pt doping effects on surface and optical properties of ZnO thin films. UV-Vis analysis demonstrated a slight decrease in the optical band gap from 3.3 eV to 3.2 eV with increased annealing, indicating enhanced suitability for optoelectronic applications. FESEM imaging revealed distinct worm-like structures and small Pt metal nanoparticles in unannealed samples, while thermal treatment supported the formation of spherical Pt nanoparticles and improved conductive pathways in the films. The Wagner diagram, coupled with Auger line transitions from XPS, quantified the oxidation states and chemical environments of Zn and Pt, respectively. Notably, the observed changes in the binding energy of the Zn-2p junction and the kinetic energy of the Zn-LMM Auger junction were significantly influenced by the Pt doping and the electronic properties of the substrate. The Wagner diagram provided a comprehensive visual representation of the parameters, facilitating a deeper understanding of electronic interactions and structural dynamics at the atomic level. XPS results confirmed the presence of ZnO, Zn(OH)(2), Pt-0 and PtO2 phases, indicating stability and constutient's interactions. ToF-SIMS also validated the uniform distribution of Pt nanoparticles within the ZnO thin film, confirming the effectiveness of the sol-gel method. As a result of Pt doping, PL studies revealed a large quenching effect on band edge emission in the UV and visible emission region of ZnO thin film, which is due to Pt acting as a recombination center for photogenerated carriers. Overall, our results highlight the influence of annealing and Pt incorporation on the optical and structural properties of ZnO thin films and highlight their potential applications for photonics and catalysis.
  • No Thumbnail Available
    Item
    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.
  • No Thumbnail Available
    Item
    Enhanced Photoluminescence Quantum Yield, Lifetime, and Photodetector Responsivity of CsPbBr3 Quantum Dots via Antimony Tribromide Post-Treatment
    (2022) Subramaniam, Mohan Raj; Pramod, Ashna K.; Hevia, Samuel A.; Batabyal, Sudip K.
    Herein, we present the synthesis of CsPbBr3 quantum dots (QDs) by a ligand-assisted reprecipitation (LARP) technique under an ambient atmosphere. Besides, the optoelectronic properties of CsPbBr3 QDs were improved through antimony tribromide (SbBr3) post-treatment. Photoluminescence quantum yield (PLQY) was enhanced from 72 to 89% for SbBr3 post-treated QDs compared to as-synthesized QDs. High-resolution transmission electron microscopy (HR-TEM) analysis shows the formation of uniform-size CsPbBr3 QDs (9.4 +/- 1.3 nm) after SbBr3 treatment. The X-ray diffraction (XRD) pattern confirms the presence of the cubic phase of CsPbBr3 QDs before and post-treatment. Moreover, temperature-dependent PL and X-ray photoelectron spectroscopy (XPS) characterizations confirm the effective defect passivation with SbBr3 post-treatment. The time-resolved PL lifetime of CsPbBr3 QDs was enhanced from 24.80 +/- 0.10 to 37.71 +/- 0.09 ns after post-treatment. Finally, the post-treated QD-based self-powered photodetector device showed a high responsivity of 48 mu A/W compared to the as-synthesized QD device's responsivity of 10.2 mu A/W.
  • No Thumbnail Available
    Item
    Fabrication of Translucid Gold-nanocellulose Electrodes and Their Potential Application as Hydrogen Peroxide Sensor
    (2021) Kroff, Macarena; Luiza Fornazari, Ana; Correa-Encalada, Daniel; Jose Rubio, Maria; Hevia, Samuel A.; Rio, Rodrigo
    In this work, we describe the fabrication of a transparent gold electrode based on nanocellulose. The electrode was prepared via electron beam evaporation of gold onto nanocellulose films previously spread over a glass slip. Electrodes with different thickness of Au was fabricated, and the material's optical, morphological and electrical properties were assessed. Finally, as a proof of concept, a possible application of this electrode in hydrogen peroxide sensing was performed. The results show that a thin layer of gold on a nanocellulose translucid film allows obtaining a conductive transparent surface that could be used to design a transparent electrode.
  • No Thumbnail Available
    Item
    High performance of V2O5 thin film electrodes for lithium-ion intercalation
    (2022) Hevia, Samuel A.; Orive, Joseba; Guzman, Fernando; Cisternas, Eduardo; Dietrich, Fabian; Villarroel, Roberto; Lisoni, Judit
    A reduced toxicity production route of vanadium pentoxide thin films together with the study of the fabrication parameters that allow optimizing the performance of this material as a cathode for lithium-ion batteries is presented. V2O5 films were fabricated on silicon and stainless-steel substrates by combining electron beam evaporation of metallic vanadium film followed by an oxidation process. A strong dependence on their performance as cathodes for LiBs to the film thickness and microstructure was found, the later depending mainly on the oxidation temperature. Particularly, V2O5 electrodes with 150 nm of thickness fabricated from 50 nm of metallic vanadium oxidized at 500 degrees C, exhibit excellent performance with a reversible and fast Li storage capability, a high average discharge capacity up to 271 mAh/g at 0.5C, very close to the theoretical capacity (294 mAh/g), with near to 100% of coulombic efficiency. First-principles calculations of Li+ diffusion in three main V2O5 crystallographic directions using density functional theory (DFT) were performed to explain how this remarkable performance is related to the film microstructure.
  • No Thumbnail Available
    Item
    Nickel Nanopillar Arrays Electrodeposited on Silicon Substrates Using Porous Alumina Templates
    (2020) Bejide, Matias; Contreras, Patricio; Homm, Pia; Duran, Boris; Garcia-Merino, Jose Antonio; Rosenkranz, Andreas; Denardin, Juliano C.; del Rio, Rodrigo; Hevia, Samuel A.
    Nickel nanopillar arrays were electrodeposited onto silicon substrates using porous alumina membranes as a template. The characterization of the samples was done by scanning electron microscopy, X-ray diffraction, and alternating force gradient magnetometry. Ni nanostructures were directly grown on Si by galvanostatic and potentiostatic electrodeposition techniques in three remarkable charge transfer configurations. Differences in the growth mechanisms of the nanopillars were observed, depending on the deposition method. A high correlation between the height of the nanopillars and the charge synthesis was observed irrespective of the electrochemical technique. The magnetization measurements demonstrated a main dependence with the height of the nanopillars. The synthesis of Ni nanosystems with a controllable aspect ratio provides an effective way to produce well-ordered networks for wide scientific applications.
  • No Thumbnail Available
    Item
    Structural and photoelectrochemical dynamics of in-situ hydrogenated anatase TiO2 thin films grown by DC reactive magnetron sputtering
    (2023) Villarroel, Roberto; Zambrano-Mera, Dario; Espinoza-Gonzalez, Rodrigo; Paredes-Gil, Katherine; Pantaleone, Stefano; Ballesteros, Luis; Oskam, Gerko; Garcia-Merino, Jose A.; Hevia, Samuel A.; Gonzalez-Moraga, Guillermo
    Hydrogenation has become one of the most used strategies to improve the photoactive properties of titanium dioxide nanomaterials, n-TiO2. In order to obtain more information about the hydrogenated process on anatase TiO2 thin films and the improvement of the photoactivity of this material, we report a study on the structural changes of hydrogenated anatase thin films produced by direct-current reactive magnetron sputtering. In the first stage of the hydrogenation process, the obtained polycrystalline anatase films present an increment of the {0 0 1} facet according to the amount of hydrogen used in the plasma reaction. At higher hydrogen concentrations, amorphous and rutile phases start to appear. The photoactivity of the hydrogenated anatase samples, H:TiO2, presents a redshift of the photoelectrochemical onset and an increase of the reactivity in the UV region. Both results were experimentally and theoretically related to the formation of defects such as oxygen vacancies and TiH/Ti-OH bonds at the surface of the hydrogenated thin films.
  • Thumbnail Image
    Item
    Synergistic effect of electrotrophic perchlorate reducing microorganisms and chemically modified electrodes for enhancing bioelectrochemical perchlorate removal
    (2023) Torres Rojas, Felipe Ernesto; Muñoz Arango, Diana Carolina; Canales, Camila Pía; Hevia, Samuel A.; Leyton Soto, Felipe Arturo; Veloso Cid, Nicolás Eduardo; Isaacs Casanova, Mauricio; Vargas Cucurella, Ignacio Tomás; CEDEUS (Chile)
    Perchlorate has been described as an emerging pollutant that compromises water sources and human health. In this study, a new electrotrophic perchlorate reducing microorganism (EPRM) isolated from the Atacama Desert, Dechloromonas sp. CS-1, was evaluated for perchlorate removal in water in a bioelectrochemical reactor (BER) with a chemically modified electrode. BERs were operated for 17 days under batch mode conditions with an applied potential of −500 mV vs. Ag/AgCl. Surface analysis (i.e., SEM, XPS, FT-IR, RAMAN spectroscopy) on the modified electrode demonstrated heterogeneous transformation of the carbon fibers with the incorporation of nitrogen functional groups and the oxidation of the carbonaceous material. The BERs with the modified electrode and the presence of the EAM reached high cathodic efficiency (90.79 ± 9.157%) and removal rate (0.34 ± 0.007 mol m−3-day) compared with both control conditions. The observed catalytic enhancement of CS-1 was confirmed by a reduction in the charge transfer resistance obtained by electrochemical impedance spectroscopy (EIS). Finally, an electrochemical kinetic study revealed an eight-electron perchlorate bioreduction reaction at −638.33 ± 24.132 mV vs. Ag/AgCl. Therefore, our results show the synergistic effect of EPRM and chemically modified electrodes on perchlorate removal in a BER.
  • No Thumbnail Available
    Item
    Synthesis of lead-free Cs3Sb2Cl3Br6 halide perovskite through solution processing method for self-powered photodetector applications
    (2022) Pramod, Ashna K.; Subramaniam, Mohan Raj; Hevia, Samuel A.; Batabyal, Sudip K.
    Herein, the present study focus on synthesis of lead-free Cs3Sb2Cl3Br6 microcrystals via a simple solution processing method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis confirms the formation hexagonal phase of Cs3Sb2Cl3Br6 perovskite. Scanning electron microscopy (SEM) and TEM morphology reveals the presence of hexagonal shape of Cs3Sb2Cl3Br6 microcrystals. UV-Vis diffuse-reflectance spectroscopy (UV-Vis DRS) endorse the formation of 2.55 eV direct bandgap Cs3Sb2Cl3Br6. A lateral type selfpower photodetector was fabricated via cost-effective method using Cs3Sb2Cl3Br6 and carbon materials and it shows a fast ON and OFF (0.92 s & 0.70 s) with a high responsivity of 1 mu A/W at zero bias.
  • Thumbnail Image
    Item
    The Synthesis of Sponge-like V2O5/CNT Hybrid Nanostructures Using Vertically Aligned CNTs as Templates
    (2024) Picuntureo, Matias; Garcia-Merino, Jose Antonio; Villarroel, Roberto; Hevia, Samuel A.
    The fabrication of sponge-like vanadium pentoxide (V2O5) nanostructures using vertically aligned carbon nanotubes (VACNTs) as a template is presented. The VACNTs were grown on silicon substrates by chemical vapor deposition using the Fe/Al bilayer catalyst approach. The V2O5 nanostructures were obtained from the thermal oxidation of metallic vanadium deposited on the VACNTs. Different oxidation temperatures and vanadium thicknesses were used to study the influence of these parameters on the stability of the carbon template and the formation of the V2O5 nanostructures. The morphology of the samples was analyzed by scanning electron microscopy, and the structural characterization was performed by Raman, energy-dispersive X-ray, and X-ray photoelectron spectroscopies. Due to the catalytic properties of V2O5 in the decomposition of carbonaceous materials, it was possible to obtain supported sponge-like structures based on V2O5/CNT composites, in which the CNTs exhibit an increase in their graphitization. The VACNTs can be removed or preserved by modulating the thermal oxidation process and the vanadium thickness.
  • No Thumbnail Available
    Item
    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.