Standardization of surface potential measurements of graphene domains

TL;DR

This study compares scanning probe techniques for measuring the surface potential of graphene, establishing calibrated work function values for different thicknesses and highlighting FM-KPFM's superior accuracy.

Contribution

It provides a standardized methodology for surface potential measurement of graphene domains using FM-KPFM, improving accuracy over other techniques.

Findings

FM-KPFM yields more accurate surface potential measurements.

Work function values are ~4.55 eV for single-layer and ~4.44 eV for bi-layer graphene.

Identifies non-Ohmic behavior in electrode-graphene contact resistance.

Abstract

We compare the three most commonly used scanning probe techniques to obtain a reliable value of the work function in graphene domains of different thickness. The surface potential (SP) of graphene is directly measured in Hall bar geometry via a combination of electrical functional microscopy and spectroscopy techniques, which enables calibrated work function measurements of graphene domains with values ~4.55+/-0.02 eV and ~4.44+/-0.02eV for single- and bi-layer, respectively. We demonstrate that frequency-modulated Kelvin probe force microscopy (FM-KPFM) provides more accurate measurement of the SP than amplitude-modulated (AM)-KPFM. The discrepancy between experimental results obtained by different techniques is discussed. In addition, we use FM-KPFM for contactless measurements of the specific components of the device resistance. We show a strong non-Ohmic behavior of the electrode-graphene contact resistance and extract the graphene channel resistivity.