Low-Pressure Chemical Vapor (LPCVD) Graphene Growth Study and Raman Characterization

Report No. ARL-TR-6751
Authors: Barbara M. Nichols
Date/Pages: December 2013; 22 pages
Abstract: Details of the Raman spectroscopy analysis of graphene films deposited for a growth study is discussed. Low pressure chemical vapor deposition was utilized to grow graphene layers onto copper foil substrates. For this study, the hydrogen-tomethane (H2/CH4) gas ratio used for the growths was varied from 20 to 200. Once transferred to patterned SiO2/Si substrates, the graphene layers were characterized by Raman spectroscopy. Using the characteristic Raman peaks for graphene and silicon, maps of the integrated area ratio of the G and Si bands (AG/ASi), peak intensity ratio of the G' and G bands (IG'/IG), and the G' peak full-widthhalf-maximum (FWHM) were used to identify the number of layers and stacking orientation. Distinction between single-layer, Bernal-stacked bilayer, and turbostratic (or disoriented) bilayer graphene was made using this analysis. For the graphene deposited in this study, 100% monolayer graphene coverage was not achieved. All growths exhibited small areas of bilayer graphene. Although no correlation between the H2/CH4 gas ratio and the bilayer composition and/or stacking configuration was found, an increase in the size of the bilayer graphene was observed as the H2/CH4 gas ratio increased. This methodology is useful for relating graphene growth parameters to Raman properties.
Distribution: Approved for public release
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Last Update / Reviewed: December 1, 2013