Modelling of time-dependent electrostatic effects and AFM-based surface conductivity characterization

TL;DR

This paper develops a theoretical model incorporating charge dynamics into AFM electrostatic measurements, validated with experiments on 2D materials, enabling contactless surface conductivity characterization considering time-dependent effects.

Contribution

It introduces a novel theoretical framework that accounts for charge dynamics in AFM electrostatic models, enhancing understanding of surface conductivity measurements in 2D materials.

Findings

Frequency shift depends strongly on surface conductivity.

Temperature affects conductivity consistent with disordered electronic behavior.

Model accurately predicts charge redistribution timescales.

Abstract

Atomic Force Microscopy (AFM) combined with electrical modes provides a powerful contactless approach to characterize material electrical properties at the nanoscale. However, conventional electrostatic models often overlook dynamic charge effects, which are particularly relevant for 2D materials deposited on insulating substrates. In this work, we introduce a theoretical framework that extends traditional electrostatic models by incorporating charge dynamics, analyzing two key cases: quasi-ideal conductors and quasi-ideal insulators. Our model establishes a characteristic timescale, $\tau$, which governs charge redistribution and measurement reliability. Experimental validation using Graphene Oxide, Reduced Graphene Oxide, and lightly reduced GO demonstrates strong dependence of frequency shift on surface conductivity, confirming our predictions. Temperature-dependent measurements further reveal conductivity variations consistent with disordered electronic materials. These findings provide critical insight into the impact of finite surface conductivity on AFM-based techniques and establish a novel method for evaluating charge dynamics in individual flakes of 2D materials and propose an alternative, contactless method for estimating surface conductivity.