Following the Long-Term Evolution of sp$^3$-type Defects in Tritiated Graphene using Raman Spectroscopy

TL;DR

This study tracks the long-term evolution of tritium-induced sp$^3$ defects in graphene using Raman spectroscopy, revealing a significant defect depletion over two years, exceeding decay expectations and indicating defect healing.

Contribution

First longitudinal Raman analysis of tritium-induced defects in graphene showing defect depletion beyond radioactive decay effects.

Findings

Almost complete depletion of sp$^3$ defects over two years

Defect reduction exceeds decay-based predictions by a factor of three

Recovery of the graphene 2D-band and decreased defect density

Abstract

We report on the evolution of tritium-induced sp$^3$-defects in monolayer graphene on a Si/SiO$_2$ substrate, by comparing large-area Raman maps of the same two samples, acquired just after fabrication and twice thereafter, about 9-12 months apart. Inbetween measurements the samples were kept under standard laboratory conditions. Using a conservative classification of sp$^3$-type spectra, based on the D/D' peak intensity ratio, we observed almost complete depletion of sp$^3$-type defects over the investigation period of about two years. This by far exceeds the ~5.5% annual reduction expected from tritium decay alone (~3x larger). This change in the defect composition is accompanied by a recovery of the 2D-band of graphene and an overall decrease in defect-density, as determined via the D/G intensity ratio. Hydogenated graphene is reported to be reasonably stable over several months, when kept under vacuum, but suffers substantial hydrogen loss under laboratory air conditions. While the results shown here for tritiated graphene exhibit similarities with hydrogenated graphene, however, some distinct differences are observed.