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

Abstract

Carbon nanotubes (CNTs) and epitaxial graphene on SiC substrates formed by thermal decomposition are of great interest for electronic and optoelectronic applications. The initial decomposition process of a SiC surface is critical to the formation of subsequent nanocarbon materials, such as CNTs or graphene. We present here an in situ near-edge X-ray absorption fine structure (NEXAFS) spectroscopy study of the initial formation processes of CNTs on the SiC C-face and graphene on the Si-face by thermal decomposition at high temperature. On both surfaces, desorption of Si atoms and subsequent graphitization of the remaining carbon atoms were observed above 1000 °C by carbon K-edge NEXAFS measurements in real time, but the incidence angle dependence of NEXAFS spectra showed marked difference between the SiC C-face and Si-face; on the SiC Si-face, the orientations of graphene layers are kept parallel to the surface during the graphene growth. In contrast, on the SiC C-face, graphene layers are initially oriented parallel to the SiC surface, but their orientations change toward the surface normal during the progression of CNT formation above 1300 °C. In addition, at the very initial stage of thermal decomposition, aromatic fragments composed of a few carbon hexagons are present parallel to the surface. Our NEXAFS results are consistent with previous density-functional tight-binding molecular dynamic simulations for CNT growth on the SiC C-face by thermal decomposition.