Quasi-free Standing Epitaxial Graphene on SiC by Hydrogen Intercalation

Quasi-free Standing Epitaxial Graphene on SiC by Hydrogen Intercalation

Dated: November 10, 2009 | C. Riedl, C. Coletti, T. Iwasaki, A. A. Zakharov, U. Starke
Hydrogen intercalation is used to create quasi-free standing epitaxial graphene on SiC(0001). The hydrogen moves between the (6√3×6√3)R30° reconstructed initial carbon layer and the SiC substrate, saturating the topmost Si atoms that were previously covalently bound to the buffer layer. This process turns the buffer layer into a quasi-free standing graphene monolayer with typical π-bands. Similarly, epitaxial monolayer graphene turns into a decoupled bilayer. The intercalation is stable in air and can be reversed by annealing to around 900°C. Graphene, a mono-atomic layer of graphite, has excellent electronic, optical, mechanical, and thermal properties, making it suitable for various applications. Epitaxial graphene on SiC(0001) can be grown in large areas and is promising for integration into existing device technology. However, the intrinsic electron doping and the influence of the (6√3×6√3)R30° reconstructed interface layer hinder its performance. The interface layer, composed of carbon atoms arranged in a graphene-like structure, is electronically inactive and is often called zero-layer graphene. The second carbon layer grows on top of the interface without covalent interlayer bonds and acts like monolayer graphene. Hydrogen intercalation is used to decouple the epitaxial graphene layers from the SiC substrate by breaking and saturating the respective bonds. This process results in quasi-free standing epitaxial graphene layers with the outstanding properties of graphene. The hydrogen treatment reduces the intrinsic charge carrier density and decouples the graphene layers from the substrate. The process is stable in ambient conditions and can be reversed by annealing. The hydrogen intercalation process was tested on SiC(0001) samples, and the results showed that hydrogen treatment leads to the formation of quasi-free standing graphene layers. The structural and electronic properties of the samples were analyzed using LEED, ARPES, and CLPES. The hydrogen treatment was found to suppress the superstructure spots in the LEED patterns, indicating reduced atomic displacements and weaker interlayer bonding. The ARPES measurements showed the appearance of π-bands in the hydrogen-treated samples, indicating the presence of graphene-like properties. The hydrogen treatment also resulted in a shift in the Fermi level, indicating a change in the electronic properties of the samples. The hydrogen desorption was observed at higher temperatures, leading to the recovery of the original monolayer band structure. The Si 2p and C 1s core level spectra confirmed the presence of Si-H bonds and the decoupling of the graphene layers from the substrate. The LEEM micrographs showed the transformation of multi-layered areas into single-layered areas after hydrogen desorption. In conclusion, hydrogen intercalation is a promising method to produce quasi-free standing epitaxialHydrogen intercalation is used to create quasi-free standing epitaxial graphene on SiC(0001). The hydrogen moves between the (6√3×6√3)R30° reconstructed initial carbon layer and the SiC substrate, saturating the topmost Si atoms that were previously covalently bound to the buffer layer. This process turns the buffer layer into a quasi-free standing graphene monolayer with typical π-bands. Similarly, epitaxial monolayer graphene turns into a decoupled bilayer. The intercalation is stable in air and can be reversed by annealing to around 900°C. Graphene, a mono-atomic layer of graphite, has excellent electronic, optical, mechanical, and thermal properties, making it suitable for various applications. Epitaxial graphene on SiC(0001) can be grown in large areas and is promising for integration into existing device technology. However, the intrinsic electron doping and the influence of the (6√3×6√3)R30° reconstructed interface layer hinder its performance. The interface layer, composed of carbon atoms arranged in a graphene-like structure, is electronically inactive and is often called zero-layer graphene. The second carbon layer grows on top of the interface without covalent interlayer bonds and acts like monolayer graphene. Hydrogen intercalation is used to decouple the epitaxial graphene layers from the SiC substrate by breaking and saturating the respective bonds. This process results in quasi-free standing epitaxial graphene layers with the outstanding properties of graphene. The hydrogen treatment reduces the intrinsic charge carrier density and decouples the graphene layers from the substrate. The process is stable in ambient conditions and can be reversed by annealing. The hydrogen intercalation process was tested on SiC(0001) samples, and the results showed that hydrogen treatment leads to the formation of quasi-free standing graphene layers. The structural and electronic properties of the samples were analyzed using LEED, ARPES, and CLPES. The hydrogen treatment was found to suppress the superstructure spots in the LEED patterns, indicating reduced atomic displacements and weaker interlayer bonding. The ARPES measurements showed the appearance of π-bands in the hydrogen-treated samples, indicating the presence of graphene-like properties. The hydrogen treatment also resulted in a shift in the Fermi level, indicating a change in the electronic properties of the samples. The hydrogen desorption was observed at higher temperatures, leading to the recovery of the original monolayer band structure. The Si 2p and C 1s core level spectra confirmed the presence of Si-H bonds and the decoupling of the graphene layers from the substrate. The LEEM micrographs showed the transformation of multi-layered areas into single-layered areas after hydrogen desorption. In conclusion, hydrogen intercalation is a promising method to produce quasi-free standing epitaxial
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