Probing memristive switching in nanoionic devices

Memristive switching in nanoionic devices involves the interplay between physical, electrochemical and thermochemical processes, which can occur in the bulk or at interfaces. Switching in these devices has been studied using techniques based on imaging and spectroscopy, as well as scanning probe and electrical approaches. The mechanistic insights obtained using these methods have informed the technological development of nanoionic devices over the past few decades, and such knowledge will be key to their further optimization and design. Here we review the different approaches that have been used to examine the underlying processes and dynamics of resistive switching. We evaluate the strengths and weaknesses of these techniques and consider the critical testing conditions and sample requirements needed in these analyses. We show that electron beam and nanotip-based microscopy techniques possess high spatial resolution, which is suited to observing morphological or microstructural properties. However, determining the compositional, valent or local structural attributes demands quantitative, spectroscopic approaches. Based on the respective strengths and weaknesses of the characterization techniques, we propose a general framework for the physical characterization of memristive devices.