mechanism of graphene on copper to better understand how the orien- tation of the copper substrate affects the quality, thickness, and size of graphene films.4
High spatial resolution Raman imaging was conducted on a mechani- cally exfoliated graphene flake to determine its structure and properties. Figure 4 illustrates an optical image of the flake, along with the cor- responding Raman images. As shown in Figure 4b, this flake contains regions of both a single-layer and bi-layer graphene. Also of interest is the G-band position, which varies significantly across the flake. In particular, it can be seen that the G-band is shifted to higher wave numbers in the single-layer regions. It has been shown elsewhere5
that
the G-band of graphene shifts upwards with increasing electron concen- tration. This is in good agreement with the author’s layer assignment. Variations in the G-position within the layers can in part be explained by the change in electron concentration, but is also influenced by local strain and defects.6
Summary StreamLine fast imaging is a powerful tool for surveying graphene. Using
StreamLine, it was possible to characterize the size and distribution of single-layer, bi-layer, and multilayer regions of graphene over a 1-cm2
area.
High-resolution Raman imaging allowed individual flakes to be character- ized on a submicron-length scale. This enables the number of layers of
graphene present to be determined, and local electron concentration, strain, and defects to be investigated.
References 1.
http://www.graphene-flagship.eu/GF/index.php.
2. Ferrari, A.C.; Meyer, J.C. et al. Raman spectrum of graphene and gra- phene layers. Phys. Review Lett. 2006, 97(18), 187401.
3. Ferrari, A.C.; Basko, D.M. Raman spectroscopy as a versatile tool for studying the properties of graphene. Nature Nanotechnol. 2013, 8(4), 235–46.
4. Murdock, A.T.; Koos, A. et al. Controlling the orientation, edge geom- etry and thickness of chemical vapor deposition graphene. ACS Nano 2013, 7(2), 1351–9.
5. Ferrari, A.C. Raman spectroscopy of graphene and graphite: disorder, electron–phonon coupling, doping and nonadiabatic effects. Solid State Commun. 2007, 143(1), 47–57.
6. Mohiuddin, T.M.G.; Lombardo, A. et al. Uniaxial strain in graphene by Raman spectroscopy: G peak splitting, Grüneisen parameters, and sample orientation. Phys. Rev. B 2009, 79(20), 205433.
Dr. Tim Batten is an Application Scientist, Renishaw plc, Old Town, Wotton- under-Edge, Gloucestershire, GL12 7DW, U.K.; tel.: +44 (0) 1453 524 524; e-mail:
tim.batten@
renishaw.com.
AMERICAN LABORATORY • 17 • SEPTEMBER 2013
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