Probing Functional Thin Films with Grazing Incidence X-Ray Scattering: The Power of Indexing

Abstract

Grazing incidence small- and wide-angle X-ray scattering (GISAXS, GIWAXS) has been widely applied for the study of functional thin films, be it for the characterization of nanostructured morphologies in block copolymers, nanocomposites, and nanoparticle assemblies, or for the packing and orientation of aromatic molecules or conjugated polymers. Solution-processed thin films are typically uniaxial powders, with a specific crystallographic plane oriented parallel to the substrate surface while ordered domains assume random orientations laterally. The convenient GISAXS/GIWAXS scattering geometry facilitates obtaining complete information about thin film structure as well as the ability to study samples in well-defined sample environments, as controlled by temperature, exposure to solvent vapor and drying, or coating processes. Moreover, with suitable X-ray sources and detectors, information about the ordering kinetics and phase transitions can be obtained down to the millisecond scale. The scattering geometry and an interactive graphical tool to index such scattering patterns will be discussed here. Furthermore, it will be demonstrated that proper indexing of the X-ray scattering patterns can provide deep insight into thin film structure–property relationships and the kinetics of structure formation. Recent examples of nanostructures and molecular organization in thin films will be discussed, as well as self-assembly processes leading to such structures.

Keywords

• thin films
• functional materials
• self-assembly
• solution processing
• grazing incidence X-ray scattering
• GISAXS