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Annealing Temperature and Substrate Effects on the Raman Spectra of Transferred CVD Graphene

Published online by Cambridge University Press:  29 February 2012

Barbara M. Nichols
Affiliation:
U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, MD 20783, U.S.A.
Yasmine R. Doleyres
Affiliation:
U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, MD 20783, U.S.A.
Gregory P. Meissner
Affiliation:
U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, MD 20783, U.S.A.
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Abstract

This work explores the influence of the post-transfer anneal temperature and the substrate on transferred graphene and its Raman properties. Graphene grown by low pressure chemical vapor deposition on copper foils was transferred to SiO2/Si, fused silica, and silicon substrates via a process that involves coating the graphene with PMMA as a protective handling layer during the wet chemical etching of the copper and then placing the PMMA/graphene onto the substrate. The PMMA layer was then removed by heating in a hydrogen/argon atmosphere at temperatures ranging from 350 to 550 °C or by exposing the PMMA to heated acetone vapor/liquid. Raman spectroscopy measurements, taken before and after PMMA removal, reveal differences in the prominent Raman features, the G and G’ peaks, upon annealing. These changes include (1) a shift in the average G and G’ peak positions when comparing Raman spectra before and after PMMA removal and (2) a decrease in the G’:G peak intensity ratio (IG’/IG), which is typically used as a measure of the number of graphene layers. For both the as-transferred graphene and graphene removed by the heated acetone, the IG’/IG peak ratio was approximately 2, indicating single layer graphene. However, when the graphene was annealed at temperatures above 350 °C, the IG’/IG intensity ratio varied from 0.5 to 1.5. These changes in the Raman spectra are similar to those observed in exfoliated single layer graphene supported on SiO2/Si substrates and are indicative of graphene-substrate interaction effects that lead to hole doping of the graphene [1,2]. These trends were observed for graphene transferred to all three substrates, regardless of the substrate surface roughness and/or composition.

Type
Research Article
Copyright
Copyright © Materials Research Society 2012

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