Kelvin Probe Force Microscopy (KPFM) is the most popular of a wide variety of scanned probe microscopy experiments that use electrical forces to infer sample properties. Applied to organic and perovskite semiconductor materials, time and frequency-resolved electrical scanned probe microscopy experiments can measure local sample properties correlated with overall device performance and degradation. What sample properties are probed by electric force microscope measurements, however, remains an open question. To make matters worse, the equation typically used to interpret these experiments incorrectly assumes that tip and sample charge responds instantaneously to changes in the applied tip-sample voltage. Dwyer, Marohn and coworkers developed an impedance model of KPFM that correctly accounts for tip-sample charge motion in the case of frequency-resolved experiments. Through the introduction of a time-dependent transfer function, this impedance model was extended to apply to time-resolved experiments as well, creating a unified description of electrical scanned probe microscopy experiments. As an application of the model, time and frequency-resolved electric force microscopy experiments were performed on a film of butylammonium lead iodide, a 2D Ruddlesden−Popper perovskite semiconductor. These experiments revealed the sample's transient photoconductivity, which had a rise time and decay time of ~100 µs. To enable the broader community of KPFM users to use this powerful theory, we developed an open-source Python package and website that can simulate or fit experimental data using the model and information about the tip geometry and sample parameters.

Unified impedance description of electrical scanned probe microscopy reveals transient photoconductivity in a Ruddlesden-Popper 2D lead-halide perovskite

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.