Full-Field and Quantitative Analysis of a Thin Liquid Film at the Nanoscale by Combining Digital Holography and White Light Interferometry

Vincenzo Ferraro,Zhe Wang,Lisa Miccio,Pier Luca Maffettone

doi:10.1021/acs.jpcc.0c09555

Abstract

Visualizing and measuring thin-film thickness at the nanoscale during dynamic evolution has been an open challenge for long term. Here, a joint-imaging method and the thereof innovative procedure are presented for merging digital holography (DH) and white light colorimetric interferometry (WLCI) measurement data in a single intelligent tool. This approach allows a complete quantitative study of the dynamic evolution of freestanding thin films under high spatial resolution and full-field modality over a large area. By merging interferometric and holographic fringes, it is possible to overcome the lack of DH in thickness measurements of ultrathin layers, providing a reliable reference for full-field quantitative mapping of the whole film with interferometric accuracy. Thanks to the proposed approach, the time-related and concentration-related evolution of surfactant film thickness can be studied. The thickness distribution curves reveal the small changes in the film thickness with time and concentration. The reported tool opens a route for comprehending deeply the physics behind the behavior of freestanding thin liquid films as it provides an in situ, continuous monitoring of film formation and dynamic evolution without limits of thickness range and in full-field mode. This can be of fundamental importance to many fields of applications, such as fluids, polymers, biotechnology, bottom-up fabrication, etc.

Highlights

Thin films are indispensable components of modern manufacturing; from electronic chips to household chemicals, they have accompanied mankind for centuries
We present a fusion approach to map the thinfilm thickness; it combines digital holography (DH) and white light colorimetric interferometry (WLCI), both implemented on a thin liquid film simultaneously
We introduced the recording system, the joint reconstruction processing of this method, and a series of thin liquid film measurement experiments based on this approach were performed

Summary

Introduction

Thin films are indispensable components of modern manufacturing; from electronic chips to household chemicals, they have accompanied mankind for centuries. Even children can create a thin film with soap, but we are still looking for effective tools to measure their real-time thickness distribution. Many studies reveal that WLI has the capability to provide accurate local thickness for measurements on smooth films. The reflection appears when the thickness of the film is proportional to a quarter of the recording wavelength so that its axial resolution could reach a quarter of the smallest illumination wavelength. In interferometry, when a transparent region is too thin, the thickness information cannot be probed by the light beam; this area is called black film.[5] it is possible to determine the thickness of the entire film area by interference fringe recognition and calculating the theoretical value where black films appear during recording under visible light.[6] Note-

Methods

Results

Conclusion