Transport, Magnetic and Vibrational Properties of Chemically Exfoliated Few Layer Graphene

TL;DR

This study investigates the vibrational, magnetic, and transport properties of chemically exfoliated few-layer graphene using spectroscopy and conductivity measurements, revealing high sample quality and paramagnetic defect centers.

Contribution

It provides a comprehensive analysis of FLG's properties with different post-processing methods, highlighting the presence of single and few layer graphene and associated defect centers.

Findings

High sample quality indicated by Raman spectroscopy

Presence of paramagnetic defect centers related to sp2 bonds

Temperature-dependent resistance suggests small gap semiconductor behavior

Abstract

We study the vibrational, magnetic and transport properties of Few Layer Graphene (FLG) using Raman and electron spin resonance spectroscopy and microwave conductivity measurements. FLG samples were produced using wet chemical exfoliation with different post-processing, namely ultrasound treatment, shear mixing, and magnetic stirring. Raman spectroscopy shows a low intensity D mode which attests a high sample quality. The G mode is present at $1580$ cm$^{-1}$ as expected for graphene. The 2D mode consists of 2 components with varying intensities among the different samples. This is assigned to the presence of single and few layer graphene in the samples. ESR spectroscopy shows a main line in all types of materials with a width of about $1$ mT and and a $g$-factor in the range of $2.005-2.010$. Paramagnetic defect centers with a uniaxial $g$-factor anisotropy are identified, which shows that these are related to the local sp$^2$ bonds of the material. All kinds of investigated FLGs have a temperature dependent resistance which is compatible with a small gap semiconductor. The difference in resistance is related to the different grain size of the samples.