Large-area plasmonic hot-spot arrays: sub-2 nm interparticle separations with plasma-enhanced atomic layer deposition of Ag on periodic arrays of Si nanopillars

Abstract

Initial reports of plasmonic 'hot-spots' enabled the detection of single molecules via surface-enhanced Raman scattering (SERS) from random distributions of plasmonic nanoparticles. Investigations of systems with near-field plasmonically coupled nanoparticles began, however, the ability to fabricate reproducible arrays of such particles has been lacking. We report on the fabrication of large-area, periodic arrays of plasmonic 'hot-spots' using Ag atomic layer deposition to overcoat Si nanopillar templates leading to reproducible interpillar gaps down to <2 nm. These plasmonic 'hot-spots' arrays exhibited over an order of magnitude increase in the SERS response in comparison to similar arrays with larger interpillar separations.

Low-loss, infrared and terahertz nanophotonics using surface phonon polaritons

“…Such large enhancements demonstrate the potential for such systems to enhance local emitters or IR-active vibrational modes for molecular spectroscopy. While higher enhancements have been reported for near-field coupled nanoparticles via plasmonic "hotspot" formation [8,100,101], similar effects are anticipated within SPhP structures. However, this behavior has not yet been explored in any depth, so comparisons of such coupled structures are premature.…”

“…(3.2) does not take into account radiative coupling, important for larger nanoparticles [98], and should be considered as an upper bound for isolated particles. In addition, this also does not take into account near-field coupling [8,[99][100][101], Fanointerference [23,102,103] or other array-induced effects [99,[104][105][106][107] that can lead to increases in Q through coupling of extended modes, all of which are equally applicable to both SPhP and LSP modes. In many cases, it is also of interest to have a FOM that evaluates the maximum electric-field enhancement |E max |/|E inc | possible for a particular geometry.…”

“…The rich physics associated with surface plasmons and their potential for manipulating light at the nanoscale initiated the fields of nanophotonics [5] and metamaterials [6]. Plasmonics research has led to many advancements such as improved chemical detection [7][8][9][10] and enhanced quantum efficiency for detectors in the ultraviolet (UV), visible (vis) and near-infrared (NIR) spectral ranges [11][12][13][14][15][16]. However, while significant effort has been directed toward plasmonics, its promise for many applications has not been realized due to the high optical losses inherent in metals at optical frequencies [17][18][19].…”

“…With the recent advances in ultra high quality and/or purity materials such as SiC, III-V and III-nitride semiconductors, further reductions are anticipated. While significant efforts have been aimed at improving metal surfaces for plasmonics through template removal [65], epitaxial growth [66] and atomic layer deposition [8,67,68], the potential for improvement is even greater in crystalline dielectric and semiconductor materials as point and extended defect densities are reduced further [69][70][71][72]. Therefore high-quality polar dielectric crystals can provide low optical losses, and through modification of their crystal lattice properties offer a wealth of options for supporting localized, propagating and epsilon-near zero (ENZ) [73] SPhP modes over a broad and adaptable spectral range.…”

Periodically Varying Height in Metal Nano-pillars for Enhanced Generation of Localized Surface Plasmon Field

“…The enhancement in LSPR field condition due to coupling of electromagnetic wave depends on how metal nanostructures have been patterned. Most of the works, related to the enhancement of LSPR field condition in metal nanostructures, which have been demonstrated so far were based on metal nano-pillars [9][10][11], nano-domes [12][13][14], sharp metal nanotips [15][16][17][18][19] and nano-clusters [5,6,20,21]. All such metal nanostructures provide tightly bound, highly intense localized plasmonic fields that interact strongly and scatter modulated LSPR signal whenever any external medium or bio-molecular sample comes into its vicinity.…”