AFM Materials Journal Club

PeakForce AFM Techniques for Interfacial Diagnosis

by D.Y. Li, Liqiu Guo, Lei Li and Hao Lu

Scientific Reports, 2017, 7, 9673

A complex material system has a collection of interfaces among different domains or phases. The local mechanical, electrical, and chemical properties of these interfaces are crucial for the system-level performance. Diagnosis and segmentation of local detrimental interfacial effects are highly desired for guiding practical system designs. Such conventional methods as electron microscopy, simulation, and micro-indentation have known limitations when one requires measurements to be non-invasive, information-rich, and truly local.

In this work, the authors employ PeakForce Tapping AFM techniques for comprehensive interfacial diagnosis on different material systems, e.g., conventional 2507 duplex stainless steel (DSS), Fe-45Cr-5C cast iron, and TiC/Co composite. PeakForce Tapping AFM mode allows fast capture of quantitative nanomechanical data. It has been seamlessly combined with various nanoelectrical modes for simultaneous studies of electrical properties. For interfacial diagnosis in this work, PeakForce-Kelvin Probe Force Microscopy (KPFM) together with Magnetic Force Microscopy (MFM) was used to build the mechanical-electrical correlation. A stable interface generally has a high electron work function (EWF). Interestingly, the authors also demonstrate that the EWF gradient across the interface between two phase domains is an effective indicator of material stability, where a strong interface has lower gradient while a weak one shows steep or even abrupt changes in EWF. The efficacy of this approach was confirmed by analyzing different metal-metal and metal-ceramic interfaces. This work provides a non-invasive, information-rich, and truly-local approach for interfacial diagnosis, which helps guide the practical designs of complex material systems.