A Spectroscopic and ab Initio Study of the Formation of Graphite and Carbon Nanotubes from Thermal Decomposition of Silicon Carbide

Abstract

We report an experimental and first-principles study of the thermal decomposition of 6H-SiC wafers, yielding graphite on the Si-terminated face and carbon nanotubes on the C-terminated face. The asymmetry of the carbon structure formation mechanisms is rationalized in terms of the different termination geometries of the opposite SiC faces. First-principles modeling reveals that horizontal, xr-delocalized carbon structures form on the Si-terminated face. The bonding network geometry of the C-terminated face favors instead the formation of vertically oriented carbon structures, which can be interpreted as nanotube lateral wall precursors.

Freestanding Graphene by Thermal Splitting of Silicon Carbide Granules

“…[14,15] In addition, annealing single-crystal SiC under ultrahigh vacuum can also lead to growth of ultrathin graphite or few-layer graphene on the Si-terminated surface with the layer thickness determined predominantly by temperature. [16][17][18][19] However, these promising epitaxial growth methods have only been employed for the purpose of fundamental studies so far. The resulting graphene sits on a single-crystal surface and the yield of graphene is rather low.…”

In Situ High-Temperature NEXAFS Study on Carbon Nanotube and Graphene Formation by Thermal Decomposition of SiC

“…It should be noted that in the difference spectra, a sharp π* resonance peak with a negligibly weak σ* resonance feature is observed at θ = 30°, while the former disappeared at θ = 90°. To date, many NEXAFS spectra have been reported for graphene ,,− and molecules with conjugated bonds − on metal or semiconductor surfaces. In those systems, one π-orbital overlaps with another across the intervening σ-bond.…”

“…So far, only a few theoretical studies have been reported regarding the initial stage of CNT formation on the SiC C-face. On the basis of ab initio calculations and photoemission results, Levita et al proposed that open-ended CNTs initially grow vertically as a C-sp 2 network structure, followed by closure of the CNT tips after the tube walls have reached sufficient length . Irle and Kusunoki’s group performed density-functional tight-binding molecular dynamics (DFTB/MD) simulations for graphene and CNT formation on the SiC surface by thermal decomposition. − In contrast to the former model, they demonstrated that a large carbon network is formed at the terrace site on the SiC C-face at 1500 K by both removing Si atoms and subsequent carbon rearrangement, resulting in carbon nanocap formation at the initial stage.…”

Plasma Fluorination of Vertically Aligned Carbon Nanotubes

“…The peak at 284.6 eV, observed on all survey spectra, is generated by photoelectrons emitted from the C 1s core level. 29 The XPS of plasma treated samples reveals the presence of carbon and fluorine atoms at the CNT-surface. For increasing functionalization time (Table S1), the amount of fluorine species grafted at the CNT surface increases, while the amount of oxygen and nitrogen slightly decreases.…”