A universal challenge facing the development of electrochemical materials is our lack of knowledge about physical and chemical processes in the 10-100 nm regime. Expanding this knowledge requires a new generation of functional imaging techniques that can resolve local and fast dynamics in electrochemical materials at the time and length scales relevant to strongly coupled reactions and transport phenomena.

In this work, we introduce scanning thermo-ionic microscopy (STIM), an AFM-based technique for probing local ionic concentration at the nanoscale. STIM utilizes dynamic Vegard strain stimulated by simultaneous hydrostatic stress and temperature excitation, which can be accurately measured through the AFM cantilever deflection. We have applied this technique on a variety of electrochemical materials using both photo-thermal heating (blueDrive™ laser) and resistively heated probes. Temporal dynamics of ionic motion can be captured from point-wise spectroscopic studies, whereas spatial variations in ionic concentration or mobility can be revealed by STIM mappings. Since the ionic oscillations are detected at higher order harmonics, their response can be isolated electromechanical, electrostatic, and capacitive effects making in-operando testing possible. In principle, STIM can provide a powerful tool for probing local electrochemical functionalities at the nanoscale.