No Time for Surface Charge: How Bulk Conductivity Hides Charge Patterns from Kelvin Probe Force Microscopy in...

Area of Science:

• Surface science
• Materials science
• Tribology

Background:

• Kelvin probe force microscopy (KPFM) is a key technique for studying contact electrification.
• Existing studies often assume static charge distributions, overlooking dynamic processes.
• The speed at which charge dissipates after contact remains poorly understood.

Purpose of the Study:

• To determine the timescale of charge dynamics after contact electrification.
• To investigate the limitations of stationary KPFM in capturing these dynamics.
• To identify the underlying mechanisms (surface vs. bulk conductivity) driving charge dissipation.

Main Methods:

• Utilized a rapid transfer system to perform KPFM measurements immediately after sample contact.
• Investigated a range of materials, from insulators to conductors.
• Analyzed charge decay curves to quantify dynamic processes.

Main Results:

• Observed that charge dynamics are too rapid for stationary KPFM in all but the best insulating materials.
• Data indicate that bulk conductivity, rather than surface conductivity, is the primary driver of charge dissipation.
• Found evidence suggesting charge-transfer heterogeneity is less significant than previously assumed.

Conclusions:

• Stationary KPFM is insufficient for accurately studying charge dynamics in most materials due to rapid dissipation.
• Bulk conductivity plays a dominant role in the fast charge transfer processes observed.
• The prevalence of charge heterogeneity in contact electrification may be overestimated.