Plasmonic near-field probes: a comparison of the campanile geometry with other sharp tips

Abstract

Efficient conversion of photonic to plasmonic energy is important for nano-optical applications, particularly imaging and spectroscopy. Recently a new generation of photonic/plasmonic transducers, the 'campanile' probes, has been developed that overcomes many shortcomings of previous near-field probes by efficiently merging broadband field enhancement with bidirectional coupling of far- to near-field electromagnetic modes. In this work we compare the properties of the campanile structure with those of current NSOM tips using finite element simulations. Field confinement, enhancement, and polarization near the apex of the probe are evaluated relative to local fields created by conical tapered tips in vacuum and in tip-substrate gap mode. We show that the campanile design has similar field enhancement and bandwidth capabilities as those of ultra-sharp metallized tips, but without the substrate and sample restrictions inherent in the tip-surface gap mode operation often required by those tips. In addition, we show for the first time that this campanile probe structure also significantly enhances the radiative rate of any dipole emitter located near the probe apex, quantifying the enhanced decay rate and demonstrating that over 90% of the light radiated by the emitter is "captured" by this probe. This is equivalent to collecting the light from a solid angle of ~3.6 pi. These advantages are crucial for performing techniques such as Raman and IR spectroscopy, white-light nano-ellipsometry and ultrafast pump-probe studies at the nanoscale.

Model for quantitative tip-enhanced spectroscopy and the extraction of nanoscale-resolved optical constants

“…However, the need for a broadband and normalizable probe response is equally crucial for spectroscopy applications 51 . A typical infrared near-field spectroscopy experiment involves normalizing acquired signals to a reference material that exhibits a nominally flat optical response (e.g.…”

Nonlocal plasma spectrum of graphene interacting with a thick conductor

“…The surge in activity to understand and discover novel plasmonic materials is stimulated by possible applications such as light concentration for solar energy 21 , devices for telecommunications 22 , and near-field instrumentation 23 . Investigation of the damped terahertz plasmons in grpahene, interacting with sruface plasmons of a substrate with a large doping due to a large scattering rate, was addressed in 24 .…”

Coupling model for an extended-range plasmonic optical transformer scanning probe

“…[19][20][21] One such tip is based on the concept of an optical transformer (OT) 22,23 -a geometrical device for converting photonic to plasmonic modes-over a large bandwidth in the NIR, achieving strong field enhancement 24 with low background noise. 25 These advantageous properties are inherent to the design of the probe, where excitation of the sample and signal collection are achieved by the same tip. The excitation radiation is injected at the base of the probe and then converted into surface plasmon polariton (SPP) modes that undergo an adiabatic compression 26 at the apex of the structure and couple to the sample.…”