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

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.

Multimodal characterization of thin polymeric film by digital holography-based methods

“…Herein, DH-based imaging process allows us to quantitatively characterize the full-field thickness information of the membrane, which also creates the possibility for further analysis for membrane features. The thickness distribution ratio is an analytical method used to characterize the film thickness distribution [10]. By dividing the complete FOV of the membrane into numerical pixels and apply the classification of the thickness information according to the specified threshold, the quantitative characterization of the overall thickness distribution of the membrane is finally realized.…”

Automated vitrification of cryo-EM samples with controllable sample thickness using suction and real-time optical inspection

“…With appropriate spectrally resolved detection and analysis methods the quantitative thickness of the liquid film could be determined optically. In principle, interference colour analysis using light of three wavelengths 33 or a combination of holography and interferometry 34 were demonstrated for full-field optical thin film measurement. Though measuring films below 100 nm thickness will likely need shorter wavelengths.…”

Multimodal quantitative phase contrast characterization of thin polymeric film

“…This system is also known as the conventional geometry for thin-film holographic thickness mapping. 22,35 The laser beam emitted from the He-Ne laser is expanded by the beam expander and collimation kit before being reflected by M I . BS I is used to split the original beam into the object and reference beams.…”

“…Figure 3(b) shows the holographic system for recording the imaging plane hologram under 2× magnification. This system is also known as the conventional geometry for thin-film holographic thickness mapping 22 , 35 . The laser beam emitted from the He-Ne laser is expanded by the beam expander and collimation kit before being reflected by M I .…”