Abstract
We have numerically investigated the influence of a nanoscale silicon tip in proximity to an illuminated gold nanoparticle. We describe how the position of the high-permittivity tip and the size of the nanoparticle impact the absorption, peak electric field and surface plasmon resonance wavelength under different illumination conditions. We detail the finite element method (FEM) approach we have used, whereby we specify a volume excitation field analytically and calculate the difference between this source field and the total field (i.e., scattered-field formulation). We show that a nanoscale tip can locally enhance the absorption of the particle as well as the peak electric field at length scales far smaller than the wavelength of the incident light.
Highlights
There have been many studies of the optical behavior of metal nanoparticles under different conditions
We explored how a nanoscale probe made of a high-permittivity material such as silicon (Si) affects the absorption cross-section (Cabs) and electric-field enhancement of spherical gold nanoparticles (AuNP) of different sizes resting on a BK7 glass substrate
Illumination is from below under total internal reflection (TIR) conditions. We considered both transverse electric (TE) and transverse magnetic (TM) excitations, and we varied the position of the Si tip both laterally and vertically with respect to the AuNP
Summary
There have been many studies of the optical behavior of metal nanoparticles under different conditions. The enhanced absorption, scattering, and electric fields associated with the localized surface-plasmon resonances (LSPRs) of metal nanoparticles find application in information processing [1], sensing [2], microscopy [3,4,10] and lithography [5,6], materials processing [3,4,5] and photovoltaics [6] In many of these applications, nanoparticles are immobilized on substrates that strongly influence their optical behavior [7,8]. Most recently Sadiq et al investigated a system in which nanoparticles were probed with a metallic, gratingcoupled near-field optical probe [18] Highly informative, these papers do not address the absorption and field enhancement associated with the geometry of interest here, i.e. a simple high-dielectric-constant tip near a nanoparticle resting on a substrate and illuminated using total internal reflection over a range of wavelengths. Enhanced understanding of these effects will lead to better control of selective absorption and field enhancement, with possible applications in deterministic patterning, sensing and imaging
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