Deposición, caracterización y actividad electro-catalítica de capas delgadas de ITO fabricadas a ángulo oblicuo por RF Magnetron Sputtering
Date
2020-05-12
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Abstract
Las capas finas de óxido mixto de indio y estaño (Indium Tin Oxide - ITO) han recibido mucha atención tanto científica como tecnológica debido a su alta transparencia en el espectro visible, alta
reflectancia en el rango infrarrojo y baja resistividad eléctrica. Gracias a estas propiedades, las películas
ITO se han utilizado ampliamente en dispositivos optoelectrónicos tales como celdas solares, LED's o
LCD's. Estas capas también tienen aplicaciones en electrocatálisis, donde la actividad electroquímica
se ve modificada por la morfología de la superficie, lográndose mayores reacciones para superficies
porosas. La deposición de capas finas a ángulo oblicuo (Oblique Angle Deposition - OAD) permite
obtener capas nanoestructuradas de alta porosidad de forma directa, lo que resulta atractivo para las
aplicaciones antes nombradas.En el presente trabajo se utilizó un sistema de pulverización catódica de magnetrón activado por plasma de radiofrecuencias (Radio Frequency Magnetron Sputtering - RF-MS) para la deposición de capas finas de ITO. La deposición se realizó con distintas composiciones de plasma, utilizando una mezcla de gases argón y oxígeno, y se depositó a diferentes ángulos con el fin de obtener varias microestructuras. Se analizó cristalinidad, morfología, transmitancia óptica, reflectancia y propiedades eléctricas de las capas para caracterizar su rendimiento.Como resultado se lograron capas delgadas cristalinas de espesores 400 nm, 750 nm y 1000 nm para tres grupos de muestras utilizadas en el estudio: “gamma o”, “delta o” y “beta i”,respectivamente. Las capas presentaron transmitancias superiores al 80% en el visible para las muestras más porosas, y reflectancias de hasta el 40% en la zona de NIR. Las propiedades eléctricas se vieron afectadas por la porosidad, lográndose valores de 18 a 50 Ω/sq para las menos porosas. Para los test electrocatalíticos se seleccionaron las condiciones de deposición que cumplían con la mejor relación porosidad/conductividad eléctrica. Para estos experimentos, se fabricó una estructura en forma de “V” denominada “chevron” para cada ángulo. La estructura chevron se integró a un sustrato compuesto de una capa compacta de ITO sobre vidrio y se generó un sistema que actúa como electrodo. Las pruebas que se realizaron sobre los electrodos incluyeron voltametría cíclica y reacciones de evolución de hidrógeno y oxígeno. Por último, los experimentos electrocatalíticos mostraron que las capas porosas de ITO fabricadas por OAD poseen mayor actividad electrocatalítica que sus homólogas compactas gracias a su porosidad, y, además, se determinó qué condiciones de deposición proporcionan capas con mayor actividad catalítica y con mejor resistencia estructural.
Thin films of mixed indium tin oxide (ITO) have received much scientific and technological attention due to their high transparency in the visible spectrum, high reflectance in the infrared range and low electrical resistivity. Due to these properties, ITO films have been widely used in optoelectronic devices such as solar cells, LED's or LCD's. These films have also applications in electrocatalysis, where the electrochemical activity is modified by the surface morphology, achieving higher reactions for porous surfaces. The deposition of thin layers at oblique angle (Oblique Angle Deposition - OAD) allows to obtain directly nanostructured layers with high porosity, which is attractive for the applications mentioned above.In this work, a magnetron sputtering system activated by radio frequency plasma (RF-MS) was used for the deposition of thin ITO films. The deposition was performed with different plasma compositions, using a mixture of argon and oxygen gases, and the films were deposited at different angles in order to obtain different microstructures. Crystallinity, morphology, optical transmittance, reflectance and electrical properties of the layers were analyzed in order to characterize the film performance.As a result, thin crystalline films were obtained, with thicknesses of 400 nm, 750 nm and 1000 nm for the three groups of samples used in this study: "gamma o", "delta o" and "beta i", respectively. The most porous layers presented transmittances higher than 80 % in the visible region and reflectance up to 40 % in the NIR zone. The electrical properties were affected by the porosity, achieving values from 18 to 50 Ω/sq for the less porous ones. For the electrocatalytic tests, the deposition conditions which met the best porosity/electrical conductivity ratio were selected. For these experiments, a V-shaped structure called "chevron" was developed for each angle. The chevron structure was integrated into a substrate composed of a compact ITO layer over a glass, building a system that acts as an electrode. The tests performed on the electrodes included cyclic voltammetry, and hydrogen and oxygen evolution reactions. Finally, the electrocatalytic experiments showed that the porous ITO films manufactured by OAD have higher electrocatalytic activity than their compact counterparts, due to their porosity. Furthermore, the deposition conditions that provided films with a larger catalytic activity in combination with a better structural resistance were determined.
Thin films of mixed indium tin oxide (ITO) have received much scientific and technological attention due to their high transparency in the visible spectrum, high reflectance in the infrared range and low electrical resistivity. Due to these properties, ITO films have been widely used in optoelectronic devices such as solar cells, LED's or LCD's. These films have also applications in electrocatalysis, where the electrochemical activity is modified by the surface morphology, achieving higher reactions for porous surfaces. The deposition of thin layers at oblique angle (Oblique Angle Deposition - OAD) allows to obtain directly nanostructured layers with high porosity, which is attractive for the applications mentioned above.In this work, a magnetron sputtering system activated by radio frequency plasma (RF-MS) was used for the deposition of thin ITO films. The deposition was performed with different plasma compositions, using a mixture of argon and oxygen gases, and the films were deposited at different angles in order to obtain different microstructures. Crystallinity, morphology, optical transmittance, reflectance and electrical properties of the layers were analyzed in order to characterize the film performance.As a result, thin crystalline films were obtained, with thicknesses of 400 nm, 750 nm and 1000 nm for the three groups of samples used in this study: "gamma o", "delta o" and "beta i", respectively. The most porous layers presented transmittances higher than 80 % in the visible region and reflectance up to 40 % in the NIR zone. The electrical properties were affected by the porosity, achieving values from 18 to 50 Ω/sq for the less porous ones. For the electrocatalytic tests, the deposition conditions which met the best porosity/electrical conductivity ratio were selected. For these experiments, a V-shaped structure called "chevron" was developed for each angle. The chevron structure was integrated into a substrate composed of a compact ITO layer over a glass, building a system that acts as an electrode. The tests performed on the electrodes included cyclic voltammetry, and hydrogen and oxygen evolution reactions. Finally, the electrocatalytic experiments showed that the porous ITO films manufactured by OAD have higher electrocatalytic activity than their compact counterparts, due to their porosity. Furthermore, the deposition conditions that provided films with a larger catalytic activity in combination with a better structural resistance were determined.
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Keywords
Óxido de indio y estaño, Magnetron sputtering, Radio frecuencia, Deposición a ángulo oblicuo, Propiedades eléctricas, Propiedades ópticas, Conductores eléctricos transparentes, Electrocatálisis, Indium tin oxide, Radio frequency, Oblique angle deposition, Electrical properties, Optical properties, Transparent electrical conductors, Electrocatalysis
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PFC 1906A Ingeniería Electromecánica FRCU
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