Morphology Characterization Techniques of Functional Thin Films

The functional thin films have great application potential in the field of optoelectronic device, fuel cells, energy storage cells, gas separation, microelectronics and biomedicine, thus becoming the research focus of academia and industry. Understanding the mechanism of morphology evolution, controlling the crystallization properties and phase separation structure are critical in improving device performance. However, in most cases, traditional morphology characterization techniques, such as transmission electron microscopy (TEM) and atomic force microscopy (AFM), failed to describe the morphology and phase separation structure of blend films due to the limited resolution. The emergence of advanced X-ray and Neutron scattering techniques can solve this problem well, allowing us to deeply understand the structure-performance correlations and providing constructive instructions to optimize device performance. For example, grazing incidence wide-angle X-ray scattering (GIWAXS) can be used to characterize crystallization behavior, and provide more detailed crystallization information, such as crystallinity, crystal size, crystal orientation and molecular packing. Grazing incidence small-angle X-ray scattering (GISAXS), small angle neutron scattering (SANS), and resonant soft X-ray scattering (RSoXS) are complementary methods for characterizing the multiscale phase separation structures, and providing the information of phase separation size, aggregates size, interfacial molecular orientation and roughness. Meanwhile, in situ GIWAXS and GISAXS techniques can be used to characterize the morphology evolution process from the precursor solution to thin film, which is of great significance to understand the formation mechanism of non-equilibrium morphology and realize controllable regulation of morphology. Here, we systematically summarize the most important characterization techniques, such as GIWAXS, GISAXS, SANS, RSoXS, and in situ GIWAXS/GISAXS, from two aspects: basic principle and application. In the application section, we take some classical cases to show how to characterize morphology and how to analyze data in a rational way. This summary is convenient for chemists and material scientists to quickly understand the principles and functions of various morphology characterization techniques, and provide instructions on how to choose proper method to study thin film morphology.