Probing the Intrinsic Properties of Exfoliated Graphene: Raman Spectroscopy of Free-Standing Monolayers

TL;DR

This study uses Raman spectroscopy to analyze the intrinsic properties of free-standing graphene monolayers, revealing their undoped nature, low disorder, and differences from supported regions.

Contribution

It provides detailed Raman spectral characterization of free-standing graphene, highlighting differences from supported graphene and insights into its intrinsic properties.

Findings

Free-standing graphene is essentially undoped.

Free-standing graphene shows minimal local disorder.

The 2D Raman mode is downshifted and narrowed in free-standing graphene.

Abstract

The properties of pristine, free-standing graphene monolayers prepared by mechanical exfoliation of graphite are investigated. The graphene monolayers, suspended over open trenches, are examined by means of spatially resolved Raman spectroscopy of the G-, D-, and 2D-phonon modes. The G-mode phonons exhibit reduced energies (1580 cm-1) and increased widths (14 cm-1) compared to the response of graphene monolayers supported on the SiO2 covered substrate. From analysis of the G-mode Raman spectra, we deduce that the free-standing graphene monolayers are essentially undoped, with an upper bound of 2x10^11 cm-2 for the residual carrier concentration. On the supported regions, significantly higher and spatially inhomogeneous doping is observed. The free-standing graphene monolayers show little local disorder, based on the very weak Raman D-mode response. The two-phonon 2D mode of the free-standing graphene monolayers is downshifted in frequency compared to that of the supported region of the samples and exhibits a narrowed, positively skewed line shape.