Near-field spectroscopy of silicon dioxide thin films

TL;DR

This paper investigates how near-field infrared spectroscopy can analyze silicon dioxide thin films, revealing thickness-dependent surface-phonon resonances and comparing models to improve understanding of the technique's depth profiling capabilities.

Contribution

It introduces a detailed comparison of tip models in near-field spectroscopy, enhancing the interpretation of surface-phonon resonances in thin films.

Findings

Surface-phonon resonance strength varies with film thickness.

Elongated spheroid tip model better matches experimental data.

Near-field technique shows potential for depth profiling layered nanostructures.

Abstract

We analyze the results of scanning near-field infrared spectroscopy performed on thin films of a-SiO2 on Si substrate. The measured near-field signal exhibits surface-phonon resonances whose strength has a strong thickness dependence in the range from 2 to 300 {nm}. These observations are compared with calculations in which the tip of the near-field infrared spectrometer is modeled either as a point dipole or an elongated spheroid. The latter model accounts for the antenna effect of the tip and gives a better agreement with the experiment. Possible applications of the near-field technique for depth profiling of layered nanostructures are discussed.