Beyond the Meso-/Macroporous boundary: Extending Capillary Condensation-based Pore Size Characterization in Thin Films Through Tailored Adsorptives

The characterization of thin films containing nanopores with diameters exceeding 50 nm poses significant challenges, especially when employing sorption-based techniques. Conventional volumetric physisorption or mercury intrusion methods have limited applicability to thin films, considering factors such as sample preparation time and the need for non-destructive testing. In this context, ellipsometric porosimetry (EP), represents a viable alternative. Its optical principle is highly sensitive to thin layers, offering insights into diverse structural parameters such as surface area, pore size, and porosity. While existing setups rely on capillary condensation of volatile compounds (such as water), their applicability is typically restricted to pore dimensions < 50nm. In this study, we introduce two high-molecular-weight hydrocarbon adsorptives, namely ethylbenzene and n-nonane to EP. These adsorptives show great promise in enhancing the accuracy of physisorption measurements beyond mesoporosity (>50 nm), extending the applicability up to 80 nm pores. The measurement guidelines established herein offer a non-destructive, expeditious (<60 min), low-pressure (<0.03 Bar) approach for investigating nanoporous thin films, with potential for adaptation to diverse structural architectures.