Abstract
Three-dimensionally structured gold membrane films with nanopores of defined, periodic geometries are designed and fabricated to provide the spatially localised enhancement of electric fields by manipulation of the plasmons inside nanopores. Square nanopores of different size and orientation relative to the pyramid are considered for films in aqueous and air environments, which allow for control of the position of electric fields within the structure. Designs suitable for use with 780 nm light were created. Here, periodic pyramidal cavities produced by potassium hydroxide etching to the {111} planes of (100) silicon substrates are used as templates for creating a periodic, pyramidal structured, free-standing thin gold film. Consistent with the findings from the theoretical studies, a nano-sized hole of 50 nm square was milled through the gold film at a specific location in the cavity to provide electric field control which can subsequently used for enhancement of fluorescence or Raman scattering of molecules in the nanopore.
Highlights
Thin films of micro and nanostructured metals are important for the construction of plasmonic devices and microelectromechanical systems (MEMSs)
The inverted pyramidal pits (54.7° from the surface plane) are 1.5 μm square of 2 μm pitch; these are used as a template for the gold membrane
Our rationale for choosing this inverted pyramidal device geometry is the fact that this substrate has previously been shown to be the best geometry for coupling light, showing a strong resonant absorption at ∼800 nm [24]—at a wavelength similar to that used routinely for Raman spectroscopy (785 nm)
Summary
Thin films of micro and nanostructured metals are important for the construction of plasmonic devices and microelectromechanical systems (MEMSs). Potentially be used to create devices for ‘nanofocusing’ of plasmons to improve surface-enhanced Raman scattering, (SERS) detection [1]. The fabrication of individual metallic, pyramidal shells as well as ultra-smooth metal films with grooves, bumps, pyramids and holes has previously been demonstrated [2, 3], as has direct raster milling with 5 nm machining precision in 100 nm thick gold films using a helium ion microscope (HIM) [4]. Routine fabrication of micro and nanostructured thin films is desirable
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