Isolated defects created by gas cluster ion impact and their use for templates of carbon nanotube growth

(1) Unversity of Hyogo
(2) University of Hyogo

Carbon nanotubes (CNTs) are one of an allotrope of carbon with cylindrical structure, and they show excellent mechanical and electrical properties. However, these properties may be altered depending on the chirality and diameter of CNTs. When metal catalysts are used in CVD growth of CNTs, the size of metal catalysts are one of the significant parameters that defines the structure of CNTs. Therefore, it is important to control the size of metal catalysts.

In this study, isolated defects created by gas cluster ion impacts were investigated as a template of CNTs growth. Gas cluster ions are aggregates of atoms or molecules. Upon a gas cluster ion impact, dense energy is deposited on surface layer while energy/atom of gas cluster ion is low. Thus, depending on the energy/atom, gas cluster ion creates crater-like defects on a target surface.
Si and SiO2 were irradiated with Ar gas cluster ion beams (GCIBs) with acceleration voltage of 20 kV, and fluence of 4 × 1011 ions/cm2. Then, cobalt dots on crater defects were formed by subsequent cobalt deposition and annealing. Subsequently, CNTs were grown with a thermal CVD. From SEM and AFM images, it was shown that CNTs were grown on SiO2 or Si surface irradiated with Ar-GCIB. Raman spectroscopy also showed growth of single wall CNTs on Si and SiO2 with Ar-GCIB irradiation. The diameters of CNTs were varied by acceleration voltage of Ar-GCIB. These results showed that isolated defects created by GCIB can be used as templates for cobalt dots formation, which results in the control of diameter of CNTs.