Noncatalytic synthesis of carbon nanotubes, graphene and graphite on SiC Z. Goknur Cambaz a , Gleb Yushin b , Sebastian Osswald a , Vadym Mochalin a , Yury Gogotsi a, * a Department of Materials Science and Engineering and A.J. Drexel Nanotechnology Institute, Drexel University, Philadelphia, PA 19104, USA b School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive, N.W., Atlanta, GA 30332-0245, USA ARTICLE INFO Article history: Received 23 October 2007 Accepted 8 February 2008 Available online 21 February 2008 ABSTRACT Graphene and carbon nanotubes (CNT) can be produced by vacuum decomposition of SiC, but discrepancies and conflicting data in the literature limit the use of this method for CNT synthesis. A systematic study of the effects of SiC surface morphology and carbon trans- port through the gas phase leads to reproducible and controlled growth of arrays of small-diameter (1–4 walls) nanotubes, which show pronounced radial breathing modes in Raman spectra, on either carbon ð000 1Þ or silicon (0 0 0 1) face of 6H SiC wafers at 1400–1900 °C. These nanotube arrays have a very high density and are catalyst-free with no internal closures. They show a higher oxidation resistance compared to CNTs produced by catalytic chemical vapor deposition (CVD). Their integration with graphite/graphene or silica layers on SiC wafers is possible in a simple 2-step process and opens new horizons in nanoscale device fabrication. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Remarkable potential of CNTs [1] for applications including electronics, electrical energy storage, composites, gas sen- sors, and field emitters [2] led to development of many meth- ods for their synthesis. However, the yield, purity, controlled synthesis and integration of CNTs on wafers for device appli- cations remain challenging. It is known that both graphene [3] and CNTs can be produced by high temperature decomposi- tion of SiC by the reaction [4]: SiC ! SiðgÞþ C ð1Þ with most attention directed towards graphene during the past year or two [5]. Kusunoki et al. [6–8] observed formation of CNTs growing normally to the carbon terminated ð000 1Þ C- face of hexagonal SiC with primarily zigzag chirality [9] and graphite growth on the Si terminated (0001) Si-face. In con- trary, Derycke et al. [10] reported single-wall carbon nano- tubes (SWCNTs) with 1.2–1.6 nm diameter on the Si-face growing parallel to the crystal surface. Nagano et al. claimed CNT formation on both carbon and silicon faces of hexagonal 6H–SiC [11] and cubic 3C–SiC [12] after HF etching, with tubes growing normal to the surface. However, transmission elec- tron microscope (TEM) images of ‘‘nanotubes’’ show aniso- tropic graphite lamellas instead [13]. While TEM evidence of small-diameter CNTs has been presented [6–8], only a single Raman spectrum containing two weak peaks which were as- signed to RBM modes of nanotubes has been published [14], raising a question about the content of nanotubes in these films. Our recent work on vacuum decomposition of b-SiC whiskers showed well ordered graphene layers but no nanotube formation [15]. The most recent study [16] 0008-6223/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2008.02.013 * Corresponding author: E-mail address: Gogotsi@drexel.edu (Y. Gogotsi). CARBON 46 (2008) 841 – 849 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon