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Nanoscale structural characterization of epitaxial graphene grown on off-axis 4H-SiC (0001).

Vecchio C, Sonde S, Bongiorno C, Rambach M, Yakimova R, Raineri V, Giannazzo F - Nanoscale Res Lett (2011)

Bottom Line: Tapping mode atomic force microscopy (t-AFM) showed the formation of wrinkles with approx. 1 to 2 nm height and 10 to 20 nm width in the FLG film, as a result of the release of the compressive strain, which builds up in FLG during the sample cooling due to the thermal expansion coefficients mismatch between graphene and SiC.For each Tgr, the number of graphene layers was determined on very small sample areas by HR-XTEM and, with high statistics and on several sample positions, by measuring the depth of selectively etched trenches in FLG by t-AFM.Both the density of wrinkles and the number of graphene layers are found to increase almost linearly as a function of the growth temperature in the considered temperature range.

View Article: PubMed Central - HTML - PubMed

Affiliation: CNR-IMM, Strada VIII, 5, Catania 95121, Italy. filippo.giannazzo@imm.cnr.it.

ABSTRACT
In this work, we present a nanometer resolution structural characterization of epitaxial graphene (EG) layers grown on 4H-SiC (0001) 8° off-axis, by annealing in inert gas ambient (Ar) in a wide temperature range (Tgr from 1600 to 2000°C). For all the considered growth temperatures, few layers of graphene (FLG) conformally covering the 100 to 200-nm wide terraces of the SiC surface have been observed by high-resolution cross-sectional transmission electron microscopy (HR-XTEM). Tapping mode atomic force microscopy (t-AFM) showed the formation of wrinkles with approx. 1 to 2 nm height and 10 to 20 nm width in the FLG film, as a result of the release of the compressive strain, which builds up in FLG during the sample cooling due to the thermal expansion coefficients mismatch between graphene and SiC. While for EG grown on on-axis 4H-SiC an isotropic mesh-like network of wrinkles interconnected into nodes is commonly reported, in the present case of a vicinal SiC surface, wrinkles are preferentially oriented in the direction perpendicular to the step edges of the SiC terraces. For each Tgr, the number of graphene layers was determined on very small sample areas by HR-XTEM and, with high statistics and on several sample positions, by measuring the depth of selectively etched trenches in FLG by t-AFM. Both the density of wrinkles and the number of graphene layers are found to increase almost linearly as a function of the growth temperature in the considered temperature range.

No MeSH data available.


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Increase of the density of wrinkles and of the number of layers as a function of the growth temperature Tgr. Average length of the wrinkles per unit area (a). Average number of grown layers (b).
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Figure 5: Increase of the density of wrinkles and of the number of layers as a function of the growth temperature Tgr. Average length of the wrinkles per unit area (a). Average number of grown layers (b).

Mentions: Comparing the morphology and phase images in Figure 2 for the samples annealed at the different temperatures, it is easy to observe that the density of wrinkles increases with temperature. The average length of the wrinkles per unit area (μm/μm2) as a function of Tgr, as obtained by a statistical analysis of a large number of AFM images collected each sample, is reported in Figure 5a.


Nanoscale structural characterization of epitaxial graphene grown on off-axis 4H-SiC (0001).

Vecchio C, Sonde S, Bongiorno C, Rambach M, Yakimova R, Raineri V, Giannazzo F - Nanoscale Res Lett (2011)

Increase of the density of wrinkles and of the number of layers as a function of the growth temperature Tgr. Average length of the wrinkles per unit area (a). Average number of grown layers (b).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211332&req=5

Figure 5: Increase of the density of wrinkles and of the number of layers as a function of the growth temperature Tgr. Average length of the wrinkles per unit area (a). Average number of grown layers (b).
Mentions: Comparing the morphology and phase images in Figure 2 for the samples annealed at the different temperatures, it is easy to observe that the density of wrinkles increases with temperature. The average length of the wrinkles per unit area (μm/μm2) as a function of Tgr, as obtained by a statistical analysis of a large number of AFM images collected each sample, is reported in Figure 5a.

Bottom Line: Tapping mode atomic force microscopy (t-AFM) showed the formation of wrinkles with approx. 1 to 2 nm height and 10 to 20 nm width in the FLG film, as a result of the release of the compressive strain, which builds up in FLG during the sample cooling due to the thermal expansion coefficients mismatch between graphene and SiC.For each Tgr, the number of graphene layers was determined on very small sample areas by HR-XTEM and, with high statistics and on several sample positions, by measuring the depth of selectively etched trenches in FLG by t-AFM.Both the density of wrinkles and the number of graphene layers are found to increase almost linearly as a function of the growth temperature in the considered temperature range.

View Article: PubMed Central - HTML - PubMed

Affiliation: CNR-IMM, Strada VIII, 5, Catania 95121, Italy. filippo.giannazzo@imm.cnr.it.

ABSTRACT
In this work, we present a nanometer resolution structural characterization of epitaxial graphene (EG) layers grown on 4H-SiC (0001) 8° off-axis, by annealing in inert gas ambient (Ar) in a wide temperature range (Tgr from 1600 to 2000°C). For all the considered growth temperatures, few layers of graphene (FLG) conformally covering the 100 to 200-nm wide terraces of the SiC surface have been observed by high-resolution cross-sectional transmission electron microscopy (HR-XTEM). Tapping mode atomic force microscopy (t-AFM) showed the formation of wrinkles with approx. 1 to 2 nm height and 10 to 20 nm width in the FLG film, as a result of the release of the compressive strain, which builds up in FLG during the sample cooling due to the thermal expansion coefficients mismatch between graphene and SiC. While for EG grown on on-axis 4H-SiC an isotropic mesh-like network of wrinkles interconnected into nodes is commonly reported, in the present case of a vicinal SiC surface, wrinkles are preferentially oriented in the direction perpendicular to the step edges of the SiC terraces. For each Tgr, the number of graphene layers was determined on very small sample areas by HR-XTEM and, with high statistics and on several sample positions, by measuring the depth of selectively etched trenches in FLG by t-AFM. Both the density of wrinkles and the number of graphene layers are found to increase almost linearly as a function of the growth temperature in the considered temperature range.

No MeSH data available.


Related in: MedlinePlus