The group lead by Prof. Paul C. McIntyre at Stanford University has recently developed a new methodology to observe in situ these local conductivity changes. The method consists on replacing the top electrode by a conductive liquid electrolyte, which can be polarized to stress the insulator. After the stress, the electrolyte can be rinsed and the surface of the insulator is scanned via conductive atomic force microscopy. The nanoscale studies have been carried by Prof. Mario Lanza's group, and reveal the formation of local spots with diameters below 4 nm that are responsible for the conductivity change. By tuning the conductivity of the liquid electrolyte, this method even allows distinguishing the contribution of electrical field and thermal heat into the currents generated.
This work was recently presented in the first China RRAM International Workshop, which was held at Soochow University on June 12th-14th of 2017. This event, hosted by Prof. Mario Lanza, aggregated most world leaders in the field of memristors, including Prof. Philip Wong, Stanford University; Prof. Wei Lu, Michigan University; and Prof. Tony Kenyon, University College London, among many others. The workshop is expected to hold its second edition in 2019 and become a biannual meeting for the memristors community.