功能薄膜形貌表征技术

Morphology Characterization Techniques of Functional Thin Films

功能薄膜在光电器件、燃料电池、储能电池、气体分离、微电子及生物医学等领域表现出极大的应用潜力,成为学术界和工业界的研究重点.理解薄膜内部形貌形成机理,调控结晶行为和相分离结构,是提高薄膜器件性能的重要途径.散射技术,包括同步辐射X射线广角/小角散射(GIWAXS/GISAXS)、小角中子散射(SANS)、共振软X射线散射(RSoXS),作为表征薄膜内部微纳结构的有效手段,不仅可以研究薄膜材料的结晶行为,包括结晶强度、分子堆积方式和取向性质,还可以研究薄膜内的相分离行为和界面取向与粗糙度等结构细节.同时,原位散射技术可以实时检测薄膜形貌的形成过程,对理解非平衡态形貌形成机制具有重要意义.本文不仅总结了GIWAXS、GISAXS、SANS、RSoXS和原位散射技术的基本工作原理,还通过经典案例详尽地介绍了各形貌表征技术的功能和数据解析过程,为科研工作者快速选择合适的形貌表征技术提供指导作用.

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.