Study of ultra-thin silver and silver-silica composite films for optical superlensing applications
Abstract
Recent advances in metamaterials have facilitated several new sub-diffraction resolution devices. Examples include the near-field superlens and the far-field hyperlens which have attracted a great deal of both theoretical and experimental research interest. Realization of superlens and hyperlens devices requires extremely smooth, thin and low loss metal films which form their basic structure. Silver is the most often used metal material in recent superlens and hyperlens designs due to the fact that it exhibits the lowest on-resonance loss of any natural noble metal at optical frequencies. However, silver and its dielectric composite films often exhibit high surface roughness in fabrication. It is also difficult to achieve a uniformly continuous silver film at a thickness less than 15nm. These factors limit the ultimate resolution achievable with the superlens and the overall performance of hyperlens-type devices. In this study, a method is demonstrated to fabricate thinner and smoother silver films and silver-silica composite films using a very thin germanium layer as a wetting material. A rapid post-annealing treatment is explored and demonstrated to reduce the ultra-thin Ag-film losses to the ideal values allowed by the quantum size effect in smaller grains. Such ultra-thin, ultra-smooth and low-loss silver films and silver-silica composite films satisfy the demands for fabrication of superlens and hyperlens devices for high resolution sub-wavelength imaging.
Degree
M.S.E.C.E.
Advisors
Shalaev, Purdue University.
Subject Area
Electrical engineering
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