Anomalies in thickness measurements of graphene and few layer graphite crystals by tapping mode atomic force microscopy

TL;DR

This paper investigates how measurement parameters in tapping mode AFM affect the accuracy of thickness measurements of graphene and few-layer graphene, revealing potential deviations and proposing improved measurement strategies.

Contribution

It uncovers the influence of AFM tapping mode parameters on thickness measurement accuracy and suggests optimal measurement practices for graphene and FLG.

Findings

Improper AFM parameters can cause up to 1 nm deviation in thickness measurements.

Optimal measurement parameters reduce deviations and improve accuracy.

Raman spectroscopy confirms the validity of the proposed measurement approach.

Abstract

Atomic Force Microscopy (AFM) in the tapping (intermittent contact) mode is a commonly used tool to measure the thickness of graphene and few layer graphene (FLG) flakes on silicon oxide surfaces. It is a convenient tool to quickly determine the thickness of individual FLG films. However, reports from literature show a large variation of the measured thickness of graphene layers. This paper is focused on the imaging mechanism of tapping mode AFM (TAFM) when measuring graphene and FLG thickness and we show that at certain measurement parameters significant deviations can be introduced in the measured thickness of FLG flakes. An increase of as much as 1 nm can be observed in the measured height of FLG crystallites, when using an improperly chosen range of free amplitude values of the tapping cantilever. We present comparative Raman spectroscopy and TAFM measurements on selected single and multilayer graphene films, based on which we suggest ways to correctly measure graphene and FLG thickness using TAFM.