Optical Antenna Properties of Scanning Probe Tips:  Plasmonic Light Scattering, Tip−Sample Coupling, and Near-Field Enhancement

Abstract

The optical near-field distribution and enhancement near the apex of model scanning probe tips are calculated within the quasistatic approximation. The optical tip-sample coupling sensitively depends on both the tip and sample material. This, in addition to the tip-sample distance and apex geometry, is found to affect the spatial resolution that can be obtained in scattering near-field microscopy (s-SNOM). A pronounced structural plasmon resonant behavior is found for gold tips, which redshifts upon tip-sample approach on the length scale given by the tip radius. This near-field tip-sample coupling also allows for surface plasmon excitation in the sample. With the critical dimensions of the tip apex in the range of 10 to several 10s of nanometers, the results are found to be in good agreement with experiment and more rigorous theoretical treatments.

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

“…Cumulatively, the calculation remains both realistic and fast, more so than previously reported semi-analytic solutions for realistic probe geometries. 38,39 For example, typical calculations of a demodulated and normalized near-field spectrum across 100 distinct frequencies require less than 10 seconds of computation time.…”

“…A similar hyperboloid probe geometry was applied previously by Behr and Raschke to explore plasmonic field enhancements 39 . However, their fully analytic treatment necessitates a semi-infinite probe geometry treated in the quasi-static approximation, requiring an unconventional field normalization method to obtain finite values for the probe response.…”

Local detection efficiency of a NbN superconducting single photon detector explored by a scattering scanning near-field optical microscope

“…As a rule of thumb, the sharp tip serves as an antenna which localizes the electric field into a limited area within a range of 2r from the end of the tip [29]. Hence, the gap d between the tip and the nanowire is fixed to 5 nm, to place the detector in the area of enhanced electric field.…”

Development of an Ultrafast Low-Energy Electron Diffraction Setup

“…However, the absorption of multiple photons by the same electron requires very high optical field amplitudes. High fields can be reached by intense, short laser pulses in combination with the above mentioned field enhancement effects at regions of small radius of curvature [50,168,169]. This results in a highly selective emission process for a polarization of the driving light field along the tip axis, ultimately leading to an extreme localization of the electron emission site (Fig.…”