Resonance shift effects in apertureless scanning near-field optical microscopy

TL;DR

This paper presents a comprehensive theory for apertureless SNOM that includes retardation, multipoles, and multiple scattering, highlighting how tip-induced surface plasmon modes shift with tip-surface distance and affect local fields and scattering.

Contribution

It introduces a detailed theoretical model for apertureless SNOM considering complex interactions and plasmon mode shifts, advancing understanding of near-field optical phenomena.

Findings

Local field and scattering cross section are both enhanced near the surface.

No universal correlation between local field enhancement and scattering cross section.

Tip-induced surface plasmon modes shift energy depending on tip-surface distance.

Abstract

We develop a theory to study apertureless scanning near-field optical microscopy which takes into account retardation, higher multipoles of the tip, and the multiple scattering between the tip and the surface. We focus on metallic systems and discuss the implication of the formation of tip-induced surface plasmon modes in the tip-surface system. We discuss the effects associated with the shift in energy of those modes as a function of the tip-surface distance. Both the local field and the scattering cross section are enhanced when the tip approaches the surface, but there is no general correspondence between the two enhancements.