Decoupling Structural and Interfacial Effects in Polymer Ultrathin Films through Spin-casting Conditions and Thermal Processes

Polymer ultrathin films exhibit structural and physical properties that can significantly deviate from those of bulk materials due to reduced dimensionality and increased surface interactions. Our previous research has identified a relationship between spin-casting conditions and film thickness, allowing precise control over the formation of films with targeted thicknesses. Building on this foundation, the present study examines the influence of thermal treatments, such as annealing, on films of identical thicknesses produced under varying spin-casting conditions. Changes in refractive index and density profiles were assessed using ellipsometry and X-ray reflectivity to evaluate the effects of annealing. The findings indicate distinct structural responses in the films depending on the initial spin-casting conditions, suggesting unique internal arrangements. While previous studies often explored the internal structural variations affecting thin-film properties by altering film thickness relative to molecular size, fully disentangling the interfacial effects in such comparisons has been challenging. This study seeks to enhance understanding of the role of internal structures in thin-film properties while minimizing confounding influences from thickness variations.