Towards the Reduction of Optical Losses in Transition Metal-Based Nanomaterials
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Towards the Reduction of Optical Losses in Transition Metal-Based Nanomaterials A. V. Gavrilenko, C. A. Gonder, D. J. Baker, and V. I. Gavrilenko Center for Materials Research, Norfolk State University, 700 Park Ave, Norfolk, VA 23504 ABSTRACT Equilibrium geometries and cohesion energies of Ag0.94Cd0.06, Ag0.94In0.06, Au0.94Cd0.06, and Au0.94In0.06 solid alloys have been studied from the first principles within the Density Functional Theory using ab initio pseudopotentials. Equilibrium geometries are obtained by total energy minimization method using the Local Density Approximation and Generalized Gradient Approximation methods. Optical functions are calculated within the independent particles picture. We report essentially different behavior of Cd and In impurity atoms in Au- and Agbased alloys: the aggregated (or quasi aggregated) phases in In-containing alloys are expected in contrast to the alloys with Cd atom where homogeneous impurity distribution over the bulk should dominate. Study of optical spectra in Ag0.94Cd0.06 and Au0.94Cd0.06 alloys indicate that optical losses in visible and near ultraviolet spectral range remarkably increase at bigger Cd concentrations. In ultraviolet spectral region redistribution of optical oscillator strengths results in both increase and decrease of optical losses in selected spectral regions. INTRODUCTION The artificially prepared materials (the metamaterials) based on transition metals nanoinclusions play an increasingly important role in modern photonics and nano-optics [1]. The applications of metamaterials include surface enhanced Raman scattering (SERS), negative index of refraction, scanning microscopy and spectroscopy with nanometer resolution, superlens and hyperlens with subdiffraction resolution, transformation optics, and optical cloaking [2, 3]. The common drawback of all metal-based metamaterials is high optical loss in metal at optical frequencies. It has been shown theoretically and experimentally that the optical loss in metallic nanostructures can be compensated enhancing emission associated with the surface plasmons (SPs) (see [4, 5] and references therein). Reduction of optical losses in nanostructured materials is one of the most important issues affecting successful engineering of different optoelectronic photonic devices. Optical losses of materials are determined through the imaginary part of the dielectric function (Im(ε)) [6]. Losses could be compensated through external gain. Another possibility is related to engineering of electronic materials: modifications of electronic structure of metallic nanoparticles by high-level doping resulting in creation of metallic alloys. This approach requires detailed understanding of electronic processes accompanied by alloying effects on a microscopic scale. Recently [4], using first principles modeling, we demonstrated that alloying a noble metal (gold) with another metal (cadmium) could significantly modify optical functions improving the optical losses in certain wavelength ranges and make them worse in the other
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