Browsing by Author "Villarroel, R."

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    Laser ablation fingerprint in low crystalline carbon nanotubes: A structural and photothermal analysis
    (2024) Garcia-Merino, J. A.; Villarroel, R.; Chavez-Angel, E.; Hevia, S. A.
    Carbon nanotubes (CNT) hold promise as photothermal materials due to their cost-effectiveness, stability, and broad optical absorbance. Here, we investigate the structural and morphological modifications in low-crystalline vertically aligned CNT synthetized via chemical vapor deposition on n-type Si substrates at 750 degrees C, followed by annealing treatment with near-infrared laser radiation. Raman spectroscopy revealed laser-induced amorphous regions, facilitating identification of ablation thresholds. Time-dependent nonlinear photothermal emission, associated with CNT ablation, showed a stable thermodynamic equilibrium with broad-band radiation from an electron-hole plasma. We propose a model based on Raman spectra and positional scans of the ablation fingerprint, enabling correlation with the beam temperature profile. This study offers insights into laser beam characterization, with potential applications in plasma and optics disciplines.
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    Mechanical and microstructural properties of broadband anti-reflective TiO2/SiO2 coatings for photovoltaic applications fabricated by magnetron sputtering
    (2021) Zambrano, D. F.; Villarroel, R.; Espinoza-Gonzalez, R.; Carvajal, N.; Rosenkranz, A.; Montano-Figueroa, A. G.; Arellano-Jimenez, M. J.; Quevedo-Lopez, M.; Valenzuela, P.; Gacitua, W.
    Anti-reflective coatings are used in photovoltaic systems to minimize reflectance thus optimizing efficiency. Besides excellent optical properties, these coatings need to provide good mechanical properties due to hostile environmental conditions. Therefore, this study aims at designing anti-reflective coatings based upon multi layers of TiO2 and SiO2 by magnetron sputtering on glass and silicon substrates at room temperature. Afterwards, these coatings were thermally annealed at 400, 500 and 600 degrees C to study the influence of such treatment on their optical and mechanical properties. Samples prepared at room temperature and annealed at 400 degrees C showed an optimized reflectance of about 2%. Advanced materials characterization techniques were used to elucidate the microstructural evolution of the multi-layers. The multi-layers annealed at 400 degrees C demonstrated a dense and smoothly packed microstructure with homogenous grains (50 nm in size), with a phase transformation from amorphous to anatase. In addition, exposure and damage of the glass substrate were detected for elevated temperatures (500 and 600 degrees C), thus increasing the reflectance. Nanoindentation revealed an improved hardness, elasticity, and resistance against plastic deformation for the sample annealed at 400 degrees C. Consequently, anti reflective coatings with post-annealing treatment at 400 degrees C, unify two complementary aspects such as improved mechanical properties (extended durability) and enhanced collection abilities over a broader wavelength range (increased efficiency).
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    Surface plasmon effect in electrodeposited diamond-like carbon films for photovoltaic application
    (2018) Ghosh, B.; Ray, S.; Espinoza Gonzalez, R.; Villarroel, R.; Hevia, Samuel; Alvarez Vega, P.