In a recent study at South-east University in Nanjing, China, free-standing hafnium zirconium oxide (HZO) membranes transferred onto flexible substrates were investigated. The correlative atomic force and scanning electron microscope FusionScope made a decisive contribution to understanding the mechanical behavior of these ultra-thin, ferroelectric membranes.

The unique combination of AFM and SEM in the FusionScope allowed the interaction of the AFM tip with individual folds in the free-standing hafnium membranes to be observed in situ and in real time in the SEM. 
The approach of the cantilever to the folds, the penetration into the structure as well as the retraction and subsequent restoration of the fold profile were visualized using SEM. This direct view of the process, combined with the simultaneously recorded force-distance curves, made it possible to precisely analyze the elastic restoring forces and mechanical resilience of the ultra-thin membranes.
The correlative measurement revealed a delayed reset of the folds after removal of the AFM tip, which can be attributed to the mechanical structure of the folds and the dynamic reorientation of electrical dipoles under mechanical tension. In addition, force-indentation curves were recorded, from which spring constants were extracted. These quantified the elastic behavior of HZO films in the original state and in the folded state: The folded membranes showed an average stiffness of 0.332nN nm.

Overall, the publication impressively demonstrates how the FusionScope's capability for nanoscale, correlative, real-time observation of mechanical processes provides new insights into the behavior of free-standing, functional thin films - particularly with regard to their potential application in flexible nanoelectronics.
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