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

Abstract

Kelvin probe force microscopy (KPFM) is a powerful tool for studying contact electrification (CE) at the nanoscale, but converting KPFM voltage maps to charge density maps is nontrivial due to long-range forces and complex system geometry. Here we present a strategy using finite-element method (FEM) simulations to determine the Green's function of the KPFM probe/insulator/ground system, which allows us to quantitatively extract surface charge. Testing our approach with synthetic data, we find that accounting for the atomic force microscope (AFM) tip, cone, and cantilever is necessary to recover a known input and that existing methods lead to gross miscalculation or even the incorrect sign of the underlying charge. Applying it to experimental data, we demonstrate its capacity to extract realistic surface charge densities and fine details from contact-charged surfaces. Our method gives a straightforward recipe to convert qualitative KPFM voltage data into quantitative charge data over a range of experimental conditions, enabling quantitative CE at the nanoscale.

Spatially Resolved High Voltage Kelvin Probe Force Microscopy: A Novel Avenue for Examining Electrical Phenomena at Nanoscale

“…First, the surface was neutralized (using positive charges) consequently lowering the surface potential to ≈−9.4 V. The subsequent negative charge injection cycles significantly increased the surface potential value in the negative regime to ≈−119.9 V. Last, positive charges were injected, to raise the surface potential to a value of +68.7 V. These charge states arose from the presence of trapped, uncompensated charges on the surface, and could easily be manipulated, and monitored, as shown here. [ 28 ] The associated charge densities could be harnessed to make more efficient triboelectric nanogenerator devices with still higher voltage outputs.…”

Interface Charge Characteristics in Polymer Dielectric Contacts: Analysis of Acoustic Approach and Probe Microscopy

“…[171] In addition, test conditions can affect the conversion of surface potential into charge density. [172,173] In the typical dual-channel KPFM measurement process, tap mode topography scanning can trigger contact electrification between the probe and the sample, causing significant errors in surface potential measurement. [172] Reasonable decoupling of contact electrification and surface potential measurement can be achieved by decreasing the free amplitude, increasing the set-point amplitude, and using a probe with a lower spring constant.…”

Enhanced Triboelectric Charge Stability by Air‐Stable Radicals

“…If the charged area is similar to the thickness of insulators, or a surface has both positive and negative charge locally, a numerical simulation is required to determine Green's function of probes, insulators, and ground system to accurately quantify charge from surface potential. [ 53 ] The probes were worn down after multiple contacts (Figure S8 , Supporting Information) and were replaced with fresh ones regularly when the charging sign reversed. [ 54 ] After obtaining 8 × 8 µm 2 ‐sized KPFM images, surface potentials of the contact area were quantified by setting the surface potential of a non‐contact area as a baseline.…”