Scattering near-field optical microscopy at 1-nm resolution using ultralow tip oscillation amplitudes

TL;DR

This paper introduces ultralow tip oscillation amplitude s-SNOM (ULA-SNOM), achieving 1-nm resolution in optical imaging by combining ultra-confined fields with frequency-modulation AFM in cryogenic vacuum, enabling atomic-scale optical studies.

Contribution

The authors developed ULA-SNOM, a novel technique that surpasses traditional s-SNOM resolution limits by using ultralow tip oscillations and cryogenic conditions for atomic-scale optical imaging.

Findings

Achieved 1-nm lateral resolution in optical imaging.

Successfully visualized silicon islands on silver surface.

Demonstrated potential for imaging atomic-scale structures.

Abstract

Scattering-type scanning near-field optical microscopy (s-SNOM) allows for the observation of the optical response of material surfaces with a resolution far below the diffraction limit. Based on amplitude-modulation atomic force microscopy (AFM) with typical tapping amplitudes of tens of nanometers, a spatial resolution of 10-100 nm is routinely achieved in s-SNOM. However, optical imaging and spectroscopy of atomic-scale structures remain a substantial challenge. Here, we developed ultralow tip oscillation amplitude s-SNOM (ULA-SNOM), where the ultra-confined field localized at a 1-nm-scale gap between a plasmonic tip and sample is combined with frequency-modulation (non-contact) AFM in a stable cryogenic ultrahigh vacuum environment. Using a silver tip under visible laser illumination with a constant 1-nm amplitude oscillation, we obtain a material-contrast image of silicon islands on a silver surface with 1-nm lateral resolution, which surpasses the conventional limits of s-SNOM. ULA-SNOM paves the way for the acquisition of optical information from atomic-scale structures, such as single photo-active defects and molecules.