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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

Uncorrected Raman spectrum extracted from the Raman mapping that corresponds to one of the blue point in the G band intensity map. The first-order Raman scattering of SiC correspond to the bands at 764, 786, and 964 cm-1. Its second overtone falls between 1400 and 2000 cm-1 with the sharp G band around 1590 cm-1. The 2D band is around 2780 cm-1. No D band can be seen on this point. The sharp and intense band around 532 cm-1 correspond to a crystalline Si cluster that is highly compressively stressed by the SiC substrate.
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Figure 7: Uncorrected Raman spectrum extracted from the Raman mapping that corresponds to one of the blue point in the G band intensity map. The first-order Raman scattering of SiC correspond to the bands at 764, 786, and 964 cm-1. Its second overtone falls between 1400 and 2000 cm-1 with the sharp G band around 1590 cm-1. The 2D band is around 2780 cm-1. No D band can be seen on this point. The sharp and intense band around 532 cm-1 correspond to a crystalline Si cluster that is highly compressively stressed by the SiC substrate.

Mentions: Finally, on the G band intensity map we can see several points marked in blue. These blue points correspond to area where crystalline silicon clusters were found. One of the corresponding uncorrected Raman spectrum is shown in Figure 7. The presence of these crystalline silicon (c-Si) clusters is evidenced by the sharp and intense band around 532 cm-1 blue shifted compared to bulk silicon. This high blue shift is again due to a strong compressive stress induced by the SiC substrate (-2 GPa or a strain of -1.3%). First-order Raman scattering of the SiC substrate-1 and the corresponds to the two TO modes of E2 symmetry at 764 and 786 cm-1 and the A1(LO) phonon at 964 cm-1. Its second overtone with its characteristic fingerprint [49] falls between 1400 and 2000 cm-1 under the sharp G band of FLG around 1590 cm-1. The 2D band is around 2780 cm-1. No D band can be seen on these points. Moreover, we can see that no significant variations of the G band intensity and Raman shift can be observed close to these Si clusters. This means that these Si clusters do not alter the graphene growth. These clusters are located close to the step edges, like the graphitic pits. There might be a link between the presence of different defects at the step edges like these clusters, the higher growth rate and the clear electrical anisotropy that has been evidenced by magnetoresistance experiments performed on several Hall bars with different orientations [29].


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)

Uncorrected Raman spectrum extracted from the Raman mapping that corresponds to one of the blue point in the G band intensity map. The first-order Raman scattering of SiC correspond to the bands at 764, 786, and 964 cm-1. Its second overtone falls between 1400 and 2000 cm-1 with the sharp G band around 1590 cm-1. The 2D band is around 2780 cm-1. No D band can be seen on this point. The sharp and intense band around 532 cm-1 correspond to a crystalline Si cluster that is highly compressively stressed by the SiC substrate.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Uncorrected Raman spectrum extracted from the Raman mapping that corresponds to one of the blue point in the G band intensity map. The first-order Raman scattering of SiC correspond to the bands at 764, 786, and 964 cm-1. Its second overtone falls between 1400 and 2000 cm-1 with the sharp G band around 1590 cm-1. The 2D band is around 2780 cm-1. No D band can be seen on this point. The sharp and intense band around 532 cm-1 correspond to a crystalline Si cluster that is highly compressively stressed by the SiC substrate.
Mentions: Finally, on the G band intensity map we can see several points marked in blue. These blue points correspond to area where crystalline silicon clusters were found. One of the corresponding uncorrected Raman spectrum is shown in Figure 7. The presence of these crystalline silicon (c-Si) clusters is evidenced by the sharp and intense band around 532 cm-1 blue shifted compared to bulk silicon. This high blue shift is again due to a strong compressive stress induced by the SiC substrate (-2 GPa or a strain of -1.3%). First-order Raman scattering of the SiC substrate-1 and the corresponds to the two TO modes of E2 symmetry at 764 and 786 cm-1 and the A1(LO) phonon at 964 cm-1. Its second overtone with its characteristic fingerprint [49] falls between 1400 and 2000 cm-1 under the sharp G band of FLG around 1590 cm-1. The 2D band is around 2780 cm-1. No D band can be seen on these points. Moreover, we can see that no significant variations of the G band intensity and Raman shift can be observed close to these Si clusters. This means that these Si clusters do not alter the graphene growth. These clusters are located close to the step edges, like the graphitic pits. There might be a link between the presence of different defects at the step edges like these clusters, the higher growth rate and the clear electrical anisotropy that has been evidenced by magnetoresistance experiments performed on several Hall bars with different orientations [29].

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