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Micro-Raman and micro-transmission imaging of epitaxial graphene grown on the Si and C faces of 6H-SiC.

Tiberj A, Camara N, Godignon P, Camassel J - Nanoscale Res Lett (2011)

Bottom Line: On the C-face it is shown that the SiC sublimation process results in the growth of long and isolated graphene ribbons (up to 600 μm) that are strain-relaxed and lightly p-type doped.A full graphene coverage of the SiC surface is achieved but anisotropic growth still occurs, because of the step-bunched SiC surface reconstruction.While in the middle of reconstructed terraces thin graphene stacks (up to 5 layers) are grown, thicker graphene stripes appear at step edges.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratoire Charles Coulomb, UMR5221 CNRS-Université Montpellier II, Place Eugène Bataillon - cc074, 34095 Montpellier Cedex 5, France. Antoine.Tiberj@univ-montp2.fr.

ABSTRACT
Micro-Raman and micro-transmission imaging experiments have been done on epitaxial graphene grown on the C- and Si-faces of on-axis 6H-SiC substrates. On the C-face it is shown that the SiC sublimation process results in the growth of long and isolated graphene ribbons (up to 600 μm) that are strain-relaxed and lightly p-type doped. In this case, combining the results of micro-Raman spectroscopy with micro-transmission measurements, we were able to ascertain that uniform monolayer ribbons were grown and found also Bernal stacked and misoriented bilayer ribbons. On the Si-face, the situation is completely different. A full graphene coverage of the SiC surface is achieved but anisotropic growth still occurs, because of the step-bunched SiC surface reconstruction. While in the middle of reconstructed terraces thin graphene stacks (up to 5 layers) are grown, thicker graphene stripes appear at step edges. In both the cases, the strong interaction between the graphene layers and the underlying SiC substrate induces a high compressive thermal strain and n-type doping.

No MeSH data available.


Related in: MedlinePlus

20 × 100 μm2 maps of two graphene ribbons grown on the C-face of 6H-SiC. The step sizes are 0.5 and 2 μm for the X- and Y-axes, respectively. The relative extinction, the normalized intensities, and Raman shifts of the G and 2D band are shown. The right (left) ribbon corresponds to a monolayer (bilayer) graphene. The absolute value of the Fermi level is evaluated from the ratio between the intensities of the 2D and G bands only for the monolayer. It corresponds to a doping level between 3 × 1012 and 9 × 1012 cm-2 with an average of 6 × 1012 cm-2.
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Figure 1: 20 × 100 μm2 maps of two graphene ribbons grown on the C-face of 6H-SiC. The step sizes are 0.5 and 2 μm for the X- and Y-axes, respectively. The relative extinction, the normalized intensities, and Raman shifts of the G and 2D band are shown. The right (left) ribbon corresponds to a monolayer (bilayer) graphene. The absolute value of the Fermi level is evaluated from the ratio between the intensities of the 2D and G bands only for the monolayer. It corresponds to a doping level between 3 × 1012 and 9 × 1012 cm-2 with an average of 6 × 1012 cm-2.

Mentions: In Figure 1, we show the results of a large (20 × 100 μm2) map collected on two neighboring graphene ribbons. The step size was 0.5 μm for the X direction and 2 μm for the Y direction. Six individual maps are shown. The first one corresponds to the extinction values, the second one to the integrated intensity of the G band normalized to the HOPG peak. The third one gives the normalized integrated intensity of the 2D band, while the fourth and fifth ones give the shift of the G and 2D bands, respectively. Finally, the last one corresponds to the absolute value of the Fermi level computed from the previous results. Of course, because of the limited range of the XY piezostage (100 × 100 μm2) the two ribbons could not be completely probed. But a first point to be noticed is that, on both ribbons, no D band map could be given. This is shown in greater details in Figures 2 and 3 and demonstrates the excellent crystalline quality of these graphene samples.


Micro-Raman and micro-transmission imaging of epitaxial graphene grown on the Si and C faces of 6H-SiC.

Tiberj A, Camara N, Godignon P, Camassel J - Nanoscale Res Lett (2011)

20 × 100 μm2 maps of two graphene ribbons grown on the C-face of 6H-SiC. The step sizes are 0.5 and 2 μm for the X- and Y-axes, respectively. The relative extinction, the normalized intensities, and Raman shifts of the G and 2D band are shown. The right (left) ribbon corresponds to a monolayer (bilayer) graphene. The absolute value of the Fermi level is evaluated from the ratio between the intensities of the 2D and G bands only for the monolayer. It corresponds to a doping level between 3 × 1012 and 9 × 1012 cm-2 with an average of 6 × 1012 cm-2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211991&req=5

Figure 1: 20 × 100 μm2 maps of two graphene ribbons grown on the C-face of 6H-SiC. The step sizes are 0.5 and 2 μm for the X- and Y-axes, respectively. The relative extinction, the normalized intensities, and Raman shifts of the G and 2D band are shown. The right (left) ribbon corresponds to a monolayer (bilayer) graphene. The absolute value of the Fermi level is evaluated from the ratio between the intensities of the 2D and G bands only for the monolayer. It corresponds to a doping level between 3 × 1012 and 9 × 1012 cm-2 with an average of 6 × 1012 cm-2.
Mentions: In Figure 1, we show the results of a large (20 × 100 μm2) map collected on two neighboring graphene ribbons. The step size was 0.5 μm for the X direction and 2 μm for the Y direction. Six individual maps are shown. The first one corresponds to the extinction values, the second one to the integrated intensity of the G band normalized to the HOPG peak. The third one gives the normalized integrated intensity of the 2D band, while the fourth and fifth ones give the shift of the G and 2D bands, respectively. Finally, the last one corresponds to the absolute value of the Fermi level computed from the previous results. Of course, because of the limited range of the XY piezostage (100 × 100 μm2) the two ribbons could not be completely probed. But a first point to be noticed is that, on both ribbons, no D band map could be given. This is shown in greater details in Figures 2 and 3 and demonstrates the excellent crystalline quality of these graphene samples.

Bottom Line: On the C-face it is shown that the SiC sublimation process results in the growth of long and isolated graphene ribbons (up to 600 μm) that are strain-relaxed and lightly p-type doped.A full graphene coverage of the SiC surface is achieved but anisotropic growth still occurs, because of the step-bunched SiC surface reconstruction.While in the middle of reconstructed terraces thin graphene stacks (up to 5 layers) are grown, thicker graphene stripes appear at step edges.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratoire Charles Coulomb, UMR5221 CNRS-Université Montpellier II, Place Eugène Bataillon - cc074, 34095 Montpellier Cedex 5, France. Antoine.Tiberj@univ-montp2.fr.

ABSTRACT
Micro-Raman and micro-transmission imaging experiments have been done on epitaxial graphene grown on the C- and Si-faces of on-axis 6H-SiC substrates. On the C-face it is shown that the SiC sublimation process results in the growth of long and isolated graphene ribbons (up to 600 μm) that are strain-relaxed and lightly p-type doped. In this case, combining the results of micro-Raman spectroscopy with micro-transmission measurements, we were able to ascertain that uniform monolayer ribbons were grown and found also Bernal stacked and misoriented bilayer ribbons. On the Si-face, the situation is completely different. A full graphene coverage of the SiC surface is achieved but anisotropic growth still occurs, because of the step-bunched SiC surface reconstruction. While in the middle of reconstructed terraces thin graphene stacks (up to 5 layers) are grown, thicker graphene stripes appear at step edges. In both the cases, the strong interaction between the graphene layers and the underlying SiC substrate induces a high compressive thermal strain and n-type doping.

No MeSH data available.


Related in: MedlinePlus