Electrochemical Strain Microscopy (ESM)
ESM is a scanning probe microscopy (SPM) technique used for the characterization of electrochemical processes on the nanoscale. The method aims at detecting local strains in mixed ionic-electronic conductors due to electrochemically induced compositional changes.
By the application of a high frequency AC bias to the SPM tip in contact with a mixed conductor, changes in the local electrochemical potentials are induced. This leads to an ambipolar transport (coupled transport of ions and electrons) and accordingly to a change in the chemical composition inside the probed volume. Due to the coupling between chemical composition and lattice parameters, a periodical sample strain (Vegard strain) is induced. This strain is measured at the resonance frequency of the cantilever, which leads to a signal amplification by a factor of around 100. The method allows an excellent spatial resolution and a high sensitivity (strains in the range of few picometers detectable).
We focus on a combination of both experimental work and theoretical modeling to allow a meaningful interpretation of ESM data. Since proper sample preparation is crucial for successful imaging, we combine several other methods for synthesis, analyzation and preparation (e.g. sol-gel-technique, time-of-flight secundary-ion-mass-spectrometry (TOF-SIMS), conductive atomic force microscopy (c-AFM), …). Furthermore, cantilever dynamics are simulated in the framework of a comprehensive cantilever dynamics model to obtain insights into different signal contributions and to eliminate mechanical crosstalk effects.
Example: Investigation of nanoscale properties of lithium cobalt oxide (LCO) battery cathodes
- Cycling in a standard battery setup to Li0.9CoO2
- Removing resulting interphases by focused ion beam (FIB)
- ESM characterization: Higher amplitudes are associated with faster chemical diffusion
The preparation of a fresh surface led to a significant increase in ESM amplitude.
- S. Bradler, S. R. Kachel, A. Schirmeisen, B.Roling, ‘A theoretical model for the cantilever motion in contact-resonance atomic force microscopy and its application to phase calibration in piezoresponse force and electrochemical strain microscopy‘, Journal of Applied Physics 120 (2016) 165107. doi: 10.1063/1.4964942
- V. Lushta, S. Bradler, B. Roling, A. Schirmeisen, ‘Correlation between drive amplitude and resonance frequency in electrochemical strain microscopy: Influence of electrostatic forces‘, Journal of Applied Physics 121 (2017) 224302. doi: 10.1063/1.4984831
- S. Bradler, A. Schirmeisen, B. Roling, ‘Amplitude quantification in contact- resonance-based voltage-modulated force spectroscopy‘, Journal of Applied Physics 122 (2017) 65106. doi: 10.1063/1.4998435
- S. Bradler, A. Schirmeisen, B. Roling, ‘Piezoresponse force and electrochemical strain microscopy in dual AC resonance tracking mode: Analysis of tracking errors‘, Journal of Applied Physics 123 (2018) 035106. doi: 10.1063/1.5004472