arXiv subjects

Carmen Lopez-Santos

Publications and source records attributed to Carmen Lopez-Santos.

6 recordsLinked to original sources

arXiv2026

Tunable Conformal Graphene Growth on Oxide Nanotube scaffolds: Towards Superwettable Hierarchical 2D-3D Architectures

Hierarchical hybrid nanoarchitectures that integrate vertically oriented graphene nanowalls, GNWs, with metal oxide, MeOx, nanotube scaffolds offer versatile platform for smart surfaces, nanoelectronics, and electrochemical technologies. Herein we present rapid, dry, plasma-assisted fabrication route that enables direct and conformal growth of GNWs on mechanically robust MeOx nanoforests. The method combines supported single-crystalline organic nanowires as a 1D soft template with sequential plasma-enabled oxide deposition and GNW growth, all performed under mild temperature, power, and vacuum conditions. This approach yields an unprecedented 2D-3D hierarchical architecture consisting of tunable-thickness MeOx nanotubes uniformly decorated with radially oriented graphene nanosheets, forming re-entrant, multiscale surface. Resulting hierarchical roughness imparts fluorine-free, long-term omniphobicity, with contact angles exceeding 170 degree for water, bovine serum, and other complex fluids. GNWs dominate the wetting response across TiO2, Al2O3, and SiO2 nanotube scaffolds, effectively decoupling surface behavior from intrinsic oxide chemistry and maintaining robust repellency under UV irradiation and water condensation. Comprehensive SEM, TEM, XPS, angle-resolved NEXAFS, and Raman analyses elucidate growth mechanism and confirm preservation of the sp2 graphitic framework, together with controlled degree of edge functionalization. Overall, this work establishes universal, substrate-compatible, low-temperature, and scalable route for the fabrication of tunable graphene-metal oxide nano-microstructured multifunctional surfaces.

cond-mat.mtrl-sci↗

arXiv2026

Water-resistant hybrid perovskite solar cell -- drop triboelectric energy harvester

Hybrid energy-harvesting systems combining perovskite solar cells (PSCs) with drop-driven triboelectric nanogenerators (D-TENGs) provide continuous power under various weather conditions. However, halide perovskites' vulnerability to moisture hampers widespread use. We present plasma-deposited fluorinated polymers (CFX) as multifunctional encapsulation layers offering water resistance, triboelectric functionality, and > 90 % optical transparency. These conformal, room-temperature, solvent-free coatings protect PSCs without reducing performance; encapsulated cells maintained a PCE of 17.9 %, and devices kept over 50 % of initial PCE after 10 days in high humidity and temperature. CFx layers also enabled compatibility with UV-curable resins, creating a hybrid PSC/D-TENG capable of harvesting solar and rain energy. This device retained 80 % of its performance after 300 hours of humid operation and stayed stable under continuous dripping and illumination for over 5 hours. Optimizing CFx's chemical composition improved triboelectric performance. Using the same CFx layer for encapsulation and triboelectric function, the device achieved 11.6 mA/cm2 short-circuit current under 0.5 sun and 12 V peak voltage per raindrop, enabling simultaneous solar and rain energy harvesting. A self-charging prototype powered LED arrays via a boost converter, demonstrating practical multisource energy harvesting.

cond-mat.mtrl-sci↗

arXiv2025

Ion mobility and segregation in seed surfaces subjected to cold plasma treatments

Plasma treatment of seeds is an efficient procedure to accelerate germination, to improve initial stages of plant growth and for protection against pathogens infection. Most studies relate these beneficial effects with biochemical modifications affecting the metabolism and genetical growth factors of seeds and young plants. Using barley seeds, in this work we investigate the redistribution of ions in the seed surface upon their treatment with cold air plasmas. In addition, we investigate the effect of plasma in the lixiviation of ions through the seeds hull when they are immersed in water. Ions re-distribution in the outer layers of air plasma treated seeds has been experimentally determined through X-ray Photoelectron Spectroscopy analysis in combination with chemical in-depth profiling with gas cluster ion beams. The results show that in the shallowest layers of the seed hull (at least up to a depth of 100 nm) there is an enrichment of K+ and Ca2+ ions, in addition to changes in the O/C and N/C atomic ratios. These data have been confirmed with the electron microscopy/fluorescence analysis of seed cuts. Observations have been accounted for by a Monte Carlo model simulating the electrostatic interactions that develop between the negative charge accumulated at the seed surface due to the interaction with the plasma sheath and the positive ions existing in the interior of seeds. Furthermore, it is shown that upon water immersion of plasma treated seeds mobilized ions tend to lixiviate more efficiently than in pristine seeds. The detection of a significant concentration of NO3- anions in the water has been attributed to a secondary reaction of nitrogen species incorporated into the seeds during plasma exposure with reactive oxygen species formed on their surface during this treatment. The implications of these findings for the improvement of germination capacity of seeds are discussed.

physics.bio-ph↗

arXiv2024

Triboelectric Pixels as building blocks for microscale and large area integration of drop energy harvesters

The ultimate step towards the exploitation of water as a clean and renewable energy source addresses the energies stored in the low frequencies of liquid flows, which demands flexible solutions to adapt to multiple scenarios, from raindrops to waves, including water moving in pipelines and microdevices. Thus, harvesting low-frequency flows is a young concept compared to solar and wind powers, where triboelectric nanogenerators have been revealed as the most promising relevant actors. However, despite widespread attempts by researchers, the drop energy harvesters' output power is still low, mainly because of the limitations in candidates endowed with ideal triboelectric and wetting properties and also the non-optimal and centimetre-scale device architecture that prevents the conversion of the complete kinetic energy of impinging drops. Herein, we disclose a microscale triboelectric nanogenerator that can harvest a high density of electrical power from drops through a single, submillisecond, long-lasting step. The mechanism relies on an instantaneous electrical capacitance variation owing to the high-speed contact of the drops with the electrodes' active area. We discuss the role of the precharged effect of the triboelectric surface in the time characteristic of the conversion event. The capacitive and microscale structure of the device is endowed with a small form factor that allows for the production of densely packed arrays. The proposed architecture can be adjusted to different liquids and scales and is compatible with a variety of triboelectric surfaces, including flexible, transparent, and thin-film approaches.

physics.app-ph↗

arXiv2023

Conformal TiO$_2$ aerogel-like films by plasma deposition: from omniphobic antireflective coatings to perovskite solar cells photoelectrodes

The ability to control porosity in oxide thin films is one of the key factors that determine their properties. Despite the abundance of dry processes for the synthesis of oxide porous layers, the high porosity range is typically achieved by spin-coating-based wet chemical methods. Besides, special techniques such as supercritical drying are required to replace the pore liquid with air while maintaining the porous network. In this study, we propose a new method for the fabrication of ultra-porous titanium dioxide thin films at room or mild temperatures (T lower or equal to 120 degrees Celsius) by the sequential process involving plasma deposition and etching. These films are conformal to the substrate topography even for high-aspect-ratio substrates and show percolated porosity values above 85 percent that are comparable to advanced aerogels. The films deposited at room temperature are amorphous. However, they become partly crystalline at slightly higher temperatures presenting a distribution of anatase clusters embedded in the sponge-like structure. Surprisingly, the porous structure remains after annealing the films at 450 degrees Celsius in air, which increases the fraction of the embedded anatase nanocrystals. The films are antireflective, omniphobic, and photoactive becoming super-hydrophilic subjected to UV light irradiation The supported percolated nanoporous structure can be used as an electron-conducting electrode in perovskite solar cells. The properties of the cells depend on the aerogel film thickness reaching efficiencies close to those of commercial mesoporous anatase electrodes. This generic solvent-free synthesis is scalable and is applicable to ultra-high porous conformal oxides of different compositions with potential applications in photonics, optoelectronics, energy storage, and controlled wetting.

physics.app-ph↗

arXiv2022

A holistic solution to icing by acoustic waves: de-icing, active anti-icing, sensing with piezoelectric crystals, and synergy with thin film passive anti-icing solutions

Icing has become a hot topic both in academia and in the industry given its implications in strategic sectors such as transport, robotics, wind turbines, photovoltaics, and electricity supply. Recently proposed de-icing solutions involving the propagation of acoustic waves (AWs) at suitable substrates may open the path for a sustainable alternative to standard de-icing or anti-icing protocols. Herein we experimentally unravel some of the basic interactions that contribute to the de-icing and/or hinder the icing (ice accretion) on AW-activated substrates. The response toward icing of a model substrate system consisting of a piezoelectric LiNbO3 plate AW activated by radio-frequency (rf) signaling to planar electrodes has been characterized both at a laboratory scale and in an icing wind tunnel under forced convection conditions. Main features related to de-icing mechanisms, a decrease of ice adhesion, or the avoidance of ice accretion have been disclosed by this holistic investigation. Furthermore, additional experiments have shown that the piezoelectric substrate surfaces modified with a fluorinated ZnO thin film or a ZnO/CFx bilayer present anti-icing functionality and a synergistic response when activated with AWs. A careful analysis of the dependence of resonance frequency of the piezoelectric substrates on experimental variables such as temperature, ice formation, or wind velocity shows that this parameter can be used as an internal control procedure for real-time monitoring of icing processes onto AW-activated devices

cond-mat.mtrl-sci↗