White light interferometry analysis for measuring thin film thickness down to few nanometers

TL;DR

This paper introduces a practical white-light interferometry technique with an open-source Python tool for automated nanometer-scale thin film thickness measurement, demonstrated on foam films and applicable to various non-opaque layers.

Contribution

The paper presents a novel, accessible method and software for precise thin film measurement using white-light interferometry, addressing spectral analysis scenarios and limitations.

Findings

Effective measurement of foam film thickness down to a few nanometers.

Demonstrated application in time-resolved foam film thinning studies.

Method adaptable to various non-opaque thin layers.

Abstract

We present a practical white-light interferometric method, supported by an open-source Python library \textit{optifik} for automated spectrum-to-thickness deduction, enabling foam film measurements down to a few nanometers. We describe three typical spectral scenarii encountered in this method: spectra exhibiting numerous interference fringes, spectra with a moderate number of peaks, and spectra with only a few identifiable features, providing illustrative examples for each case. We also discuss the main limitations of the technique, including spectral range constraints, the necessity of knowing the refractive index, and the influence of spectral resolution and signal quality. Finally, we demonstrate the application of the method in a time-resolved study of a TTAB (tetradecyltrimethylammonium bromide) foam film undergoing elongation and thinning. This method can be adapted to measure any thin non-opaque layer.