Simultaneous reflectometry and interferometry for measuring thin-film thickness and curvature

Area of Science:

• Materials Science
• Surface Science
• Fluid Dynamics

Background:

• Characterizing thin-film properties at the three-phase contact line is essential for understanding evaporation dynamics.
• Existing methods often lack the precision to measure both nano-scale film thickness and macro-scale meniscus profiles simultaneously.

Purpose of the Study:

• To develop and validate a coupled reflectometer-interferometer apparatus for comprehensive thin-film characterization.
• To investigate the nano-scale absorbed fluid layer and macro-scale liquid meniscus properties in evaporating systems.

Main Methods:

• Utilized a combined reflectometer-interferometer system for simultaneous measurements.
• Performed validation studies on various substrates (Au, Ge, Si) and thin-film coatings (SiO2, hydrogel/Ti/SiO2).
• Conducted liquid/air interference studies using steady-state evaporation of water and isooctane, and solid/air interference studies with optical components.

Main Results:

• Successfully characterized nano-scale absorbed fluid layer thickness and macro-scale meniscus thickness, curvature, and gradient profiles.
• Achieved thickness profile measurement errors between 4.1% and 10.8% for commercial lenses.
• Demonstrated the apparatus's capability for both liquid/air and solid/air interference studies.

Conclusions:

• The coupled reflectometer-interferometer apparatus provides a robust method for thin-film and meniscus characterization.
• This tool enables detailed analysis of fluid behavior at the three-phase contact line during evaporation.
• The validated system offers high accuracy for diverse material and fluid interfaces.