Esko I. Kauppinen

Department of Applied Physics, Aalto University School of Science

Puumiehenkuja 2, P.O. Box 16100, FI-00076 Aalto, FINLAND

We use ferrocene-CO-CO2 floating catalyst chemical vapour deposition (FC-CVD) reactor to explore the effect of synthesis temperature, ferrocene and as well as CO2 concentration on the (n,m) as well as length distributions of the produced tubes.  Electron diffraction was used to reliably determine tube (n,m) distributions. At 880 oC synthesis temperature tube diameter increases from 1.3 to 1.8 nm when increasing the CO2 concentration from 1 sccm to 1.3 sccm when the CO flow rate was 300 sccm. The corresponding fraction of metallic tubes increased from 24 to 39 %. Similar results were obtained at 850 oC synthesis temperature with the fraction of metallic tubes increasing with the CO2 concentration. At both temperatures the chiral angle distributions peaked at about 25 degree. Remarkably, also the colour of the as produced SWNT thin film can be tuned via CO2 concentration. 

When using ethanol as the carbon source with tiophene as the sulphur source and nitrogen-hydrogen mixture as the carrier gas at 1000 oC synthesis temperature, the fraction of metallic tubes was 23 % and chiral angle distribution peaked 23 degrees, i.e. the results were quite comparable to those obtained with ferrocene-CO-CO2 system at lower synthesis temperature. We also explore the SWNTs made using toluene as the carbon precursor with ferrocene-based catalyst and tiophene as the sulphur source. Interestingly, when using ferrocene with C2H4 as the carbon source in nitrogen-hydrogen carrier gas at 1050 oC synthesis temperature without sulphur, the chiral angle distributions were quite flat with no maxima close to armchair side of the distribution. The fraction of the metallic tubes was 38 %.

These results show that the fraction of metallic tubes as well as the (n,m) distributions can be tuned by the carbon source when using ferrocene-based iron clusters as catalysts in the ambient pressure FC-CVD synthesis.

In addition, we will present the recent results of SWNT gas phase cutting, as well as the use of the transistor array for determining both the tube type i.e. metallic or semiconducting as well as the charge transport characteristics.