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We study the optical and electrical properties of silver films with a graded thickness obtained through metallic evaporation in vacuum on a tilted substrate to evaluate their use as semitransparent electrical contacts. We measure their ellipsometric coefficients, optical transmissions and electrical conductivity for different widths, and we employ an efficient recursive method to calculate their macroscopic dielectric function, their optical properties and their microscopic electric fields. The topology of very thin films corresponds to disconnected islands, while very wide films are simply connected. For intermediate widths the film becomes semicontinuous, multiply connected, and its microscopic electric field develops hotspots at optical resonances which appear near the percolation threshold of the conducting phase, yielding large ohmic losses that increase the absorptance above that of a corresponding homogeneous film. Optimizing the thickness of the film to maximize its transmittance above the percolation threshold of the conductive phase we obtained a film with transmittance T = 0.41 and a sheet resistance R max ≈ 2.7Ω. We also analyze the observed emission frequency shift of porous silicon electroluminescent devices when Ag films are used as solid electrical contacts in replacement of electrolytic ones.

En el presente trabajo se propone un método para la fabricación de películas nanoestructuradas de Ag por evaporación al vacío en el cual se mide en tiempo real su resistividad por unidad de espesor durante el crecimiento de la misma. La incorporación de un comparador de resistencias permite un control del corte de evaporación con el cual se ha logrado repetibilidad en la producción de películas con <10 y transmitancia media del 60 % en el espectro visible. Analizamos los efectos de la nanoestructura de las películas delgadas de Ag sobre las propiedades electro-ópticas. Encontramos que la conductividad respecto al bulto puede ser menor a baja frecuencia, mientras que mayor en el rango óptico, debido a disipación de energía por la excitación de plasmones. Palabras clave: películas delgadas, nanoestructuras, conductividad, transmitancia.In this paper we propose a method for making Ag nanostructured films by evaporation under vacuum and is measured in real time the resistivity per unit thickness for the growth of the same. The incorporation of a resistance comparator provides control of evaporation cut and repeatability in the films production with <10 and average transmittance 60 % in the visible spectrum. We analyze the Ag surfaces nanostructure effects for electro-optical properties. We found that the conductivity respect to bulk can be lower at low frequency, while larger in the optical range, due to energy dissipation by plasmonic excitation

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