Abstract
Ferroelectric domain walls are a completely new type of functional interface, which have the potential to revolutionize nanotechnology. In addition to the emergent phenomena at domain walls, they are spatially mobile and can be injected, positioned, and deleted on demand, giving a new degree of flexibility that is not available at conventional interfaces. Progress in the field is closely linked to the development of modern microscopy methods, which are essential for studying their physical properties at the nanoscale. In this article, we discuss scanning electron microscopy (SEM) as a powerful and highly flexible imaging technique for scale-bridging studies on domain walls, continuously covering nano- to mesoscopic length scales. We review seminal SEM experiments on ferroelectric domains and domain walls, provide practical information on how to visualize them in modern SEMs, and provide a comprehensive overview of the models that have been proposed to explain the contrast formation in SEM. Going beyond basic imaging experiments, recent examples for nano-structuring and correlated microscopy work on ferroelectric domain walls are presented. Other techniques, such as 3D atom probe tomography, are particularly promising and may be combined with SEM in the future to investigate individual domain walls, providing new opportunities for tackling the complex nanoscale physics and defect chemistry at ferroelectric domain walls.
Highlights
The research on ferroelectric materials and phenomena has matured significantly since the discovery of ferroelectricity in Rochelle salt in 1920.1 Today, ferroelectrics are used in different fields of technology, for instance, finding application in active damping units, capacitors, and random-access memories.[2]
Due to the small length scales associated with ferroelectric domain walls, which usually have a width in the order of 1–10 nm,[11] progress in this field is closely related to advances in spatially resolved characterization methods.[12]
This combination of scanning electron microscopy (SEM) and atom probe tomography (APT) led to a breakthrough in understanding the origin of grain boundary transport properties, and the same procedure could be applied to study the impact of point defects at domain walls, leading to novel insight regarding the nanoscale physics and defect chemistry at functional domain walls in ferroelectrics
Summary
The research on ferroelectric materials and phenomena has matured significantly since the discovery of ferroelectricity in Rochelle salt in 1920.1 Today, ferroelectrics are used in different fields of technology, for instance, finding application in active damping units, capacitors, and random-access memories.[2]. SEM has an outstanding—yet not fully exploited—potential for domain-wall related investigations, offering contact-free and non-destructive high-speed imaging, nanoscale spatial resolution, and a high flexibility in terms of specimen preparation and geometry that allows, for example, to combine microscopy with nano-structuring or in situ/in operando transport measurements. In this Tutorial, we discuss the practical use of the SEM technique in connection with visualizing ferroelectric domains and domain walls. We discuss how SEM can be integrated/essential/correlated to other techniques such as TEM, SPM, and atom probe tomography (APT), respectively, with a focus on new possibilities for future domain wall research
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