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A metal catalyst free direct growth process has been developed for the CVD of carbon nanotubes (CNTs) on carbon implanted SiGe islands or Ge dots on Si substrates. From TEM and Raman measurements, the fabricated CNTs are identified as single-walled CNTs (SWNTs) with diameter ranging from 1.2 to 2.1 nm. Essential parts of the substrate preparation after SiGe or Ge dot growth and carbon ion implantation are a chemical oxidation and preheating at 1000°C prior to CNT growth. We believe that the lower melting point of Ge and oxidation enhanced surface decomposition assist the formation of carbon clusters.