Electronic Structure and Structural Evolutions of Hydrogenated Graphene Probed by Raman Spectroscopy

TL;DR

This study uses Raman spectroscopy to analyze how hydrogenation affects the electronic structure and defects in graphene, providing a quick method to estimate defect density and understand structural evolution.

Contribution

It introduces an excitation energy dependent saturation method to estimate defect density and reveals structural changes at different hydrogen coverages in graphene.

Findings

Raman intensity ratios correlate with defect density.

High hydrogen coverage leads to sp3 cluster formation.

Electronic structure shifts with hydrogenation levels.

Abstract

The electronic structure and structural evolution of hydrogenated graphene are investigated by Raman spectroscopy with multiple excitations. The excitation energy dependent saturation effect on the ratio of integrated intensities of D and G modes (ID/IG) is revealed and further developed as a quick method for estimation of inter-defect distance and defect density in hydrogenated graphene. At low hydrogen coverage, the chemisorbed H atoms behave like defects in sp2 C=C matrix; while for a high hydrogen coverage, the sp3 C-H bonds become coalescent clusters, resulting in confinement effect on the sp2 C domains. Electronic structure changes caused by varying hydrogen coverage are evidenced by excitation energy dependent red shift of D and 2D bands. Our results provide a useful guide for developing applications of hydrogenated graphene, as well as using Raman spectroscopy as quick metrology of the defect density in further exploring other kinds of graphene derivatives.