Abstract
Direct writing using a focused electron beam allows for fabricating truly three-dimensional structures of sub-wavelength dimensions in the visible spectral regime. The resulting sophisticated geometries are perfectly suited for studying light–matter interaction at the nanoscale. Their overall optical response will strongly depend not only on geometry but also on the optical properties of the deposited material. In the case of the typically used metal–organic precursors, the deposits show a substructure of metallic nanocrystals embedded in a carbonaceous matrix. Since gold-containing precursor media are especially interesting for optical applications, we experimentally determine the effective permittivity of such an effective material. Our experiment is based on spectroscopic measurements of planar deposits. The retrieved permittivity shows a systematic dependence on the gold particle density and cannot be sufficiently described using the common Maxwell–Garnett approach for effective medium.
Highlights
Nowadays, the fast development of nanofabrication methods provides access to functional structures with geometries of sub-wavelength dimensions even in the visible regime
The dielectric function of an electron beam induced deposition (EBID) material consisting of single-crystalline gold particles dispersed in a carbonaceous matrix is studied experimentally
The effective permittivity for the highest metal content represents the best approximation of the material properties of EBID nanostructures
Summary
The fast development of nanofabrication methods provides access to functional structures with geometries of sub-wavelength dimensions even in the visible regime. Nanostructures made of materials having a free electron gas [1], excitable to collective oscillations by light (plasmon-polaritons), provide the possibility of tailored light manipulation and concentration [2,3,4] Such sub-wavelength structures are key for the design of metamaterials [5]. While the electric properties of granular materials such as the EBID material are well understood [12] and proven to be promising for sensing applications [13, 14], a complete optical description of EBID metamaterials based on a combined experimental and theoretical study has not been reported yet This is caused by the relatively small areas which can be conventionally fabricated with the EBID process, not allowing for optical characterization with standard methods such as ellipsometry. This trend was emphasized in a numerical study of similar composite materials [17]
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