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Contributed Speaker

Felix Pertl

Soft Matter Physics, Institute of Science and Technology Austria

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felix.pertl@ist.ac.at

Quantifying nanoscale charge density features of contact-charged surfaces with an FEM/KPFM-hybrid approach

Contact electrification (CE), the transfer of electric charge between objects during contact, is a ubiquitous and widely studied phenomenon, yet poorly understood. Static charges can build up on an insulating surface and can lead to electrostatic discharge (ESD) on sensitive semiconductor devices. CE is not only important in industry, but also appears in many different settings, eg, the formation of planets, pollen transport or lightning during thunderstorms.
A powerful tool for studying CE is Kelvin Probe Force Microscopy (KPFM), where electrical signals from an AFM tip allow one to spatially map a voltage above a surface that is caused by the presence of charge. However, a fundamental challenge from KPFM is to convert the voltage map to a surface charge density map. Without a method to convert voltage to charge, the signal from KPFM remains qualitative.
We have developed a method to convert KPFM voltage maps to surface charge density maps [1]. Due to superposition, the measured KPFM voltage at any location is the summed contribution from the point-charge KPFM voltage of each carrier on the surface. We take advantage of this and do finite element simulations (FEM) to determine the Green's function for the tip-sample-ground system. Using this as a kernel, we deconvolve the KPFM map and extract the charge distribution. We are using this approach to precisely extract surface charge densities from experimental data of charge transfer, thus bringing KPFM from qualitative to quantitative.

References:
[1] Pertl, F., Sobarzo, J.C., Shafeek, L., Cramer, T., & Waitukaitis, S. (2022). Quantifying nanoscale charge density features of contact-charged surfaces with an FEM/KPFM-hybrid approach. Physical Review Materials, 6(12), 125605.

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