Raman and IR Spectra of UITAR Graphene Paper
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The Raman spectra of the UITAR graphene paper perhaps has created the most confusion among the peer-reviews I have received and responded. The discussion and references included with submitted manuscripts and proposals have discussed why Raman indicates that UITAR is form of graphene.
The G band which usually occurs at about 1580 cm-1 (see below) is assigned to a graphite phonon mode often associated with single-layer graphene. Again in high quality graphite or highly oriented pyrolytic graphite (HOPG) it is common only to observe the G band and 2D (2670 cm-1). See Nano Research 2008, 1, 273-291 and Phys Rev B 2000, 61, 14095-14107 for brief reviews. The D band (about 1350 cm-1) is a breathing mode associated with defects as it is forbidden in perfect single layers of graphene. However, it is quite common to observe D bands with graphene papers.
A Few Examples from Literature showing G and D Raman bands in Graphene Paper.
| Figure number | G-Band Position (cm-1) | |
| Carbon 2009, 47, 2049-2053 | 3 | 1580 |
| ACS Appl. Mater. Interfaces, 2010, 2 (11), 3092–3099 | 3 | 1590 |
| J. Phys. Chem. C, 2009, 113 (19), 7985–798 | 4 | 1585 |
| J. Phys. Chem. C, 2010, 114 (47), 19885–19890 | 4 | 1588 |
| J. Phys. Chem. Lett., 2010, 1 (13), 1987–1993 | 3 | 1600 |
| Nature Communications 2010 DOI: 10.1038/ncomms1067 | 1 | 1581 |
| Carbon 2010, 48, 1146-1152 | 7 | 1591 |
| J. Phys. Chem. C 2010, 114, 12800–12804 | 1 | 1570 |
An important paper on amorphous carbon (a-C) "Raman spectroscopy of amorphous, nanostructured, diamond-like carbon, and nanodiamond" AC Ferrari, and John Robertson, Phil. Trans. R. Soc. Lond. A 2004, 362, 2477-2512 doi: 10.1098/rsta.2004.1452 (full paper here) details the G-band wavenumber position as a function of sp3 content, and excitation wavelength. Figure 11 shows how the G-band position shifts to lower wavenumbers as excitation wavelength increases. At 532 nm, the wavelength of our characterization, the a-C bands are below 1570 cm-1. Our G-band is at 1593cm-1. This places our material between highly oriented pyrolytic graphite (HOPG) and nano-crystalline graphite (nc-G). Also note that the G-band does not shift as a function of excitation wavelength.
UITAR is not Amorphous Carbon (a-C).
Raman of Amorphous Carbon (a-C). AC Ferrari and S Prawer have a contribution to a monograph Properties of Amorphous Carbon, EMIS Data Review Series No.29, 2003 The Institution of Electrical Engineers, SRP Silva editor in which several spectra are presented. The chapter is viewable in the links above. In Figure 6 of that chapter the Raman spectra of a-C the G bands are broader with little D band characteristics.
Raman spectrum for UITAR graphene acquired in ambient air using 532 nm excitation; G mode peak at 1593 cm-1 and D mode peak at 1354 cm-1 at maximum intensity.
IR spectrum of UITAR graphene on a germanium disk. The 861 and 1576 cm-1 bands correspond to the A1u and E1u intralayer graphene stretches.
