| 초록 |
Vertically aligned arrays of mm-long multi-walled carbon nanotubes (MWCNTs) on Si substrates have been synthesized by water-assisted thermal chemical vapor deposition (CVD). The CNTs were grown while a little amount of water vapor was introduced. In particular, the length of as-grown CNTs was in-depthly investigated by varying the deposition parameters such as a growth temperature, a period of growth time, gas flow rates, thickness of the Al underlayer. The 0.5-nm-thick Fe layer served as catalyst, underneath which Al was coated as a catalyst support as well as a diffusion barrier on the Si substrate. H2+Ar and C2H2 were used as carrier gas and feedstock, respectively. We grew CNTs by adding a little amount of water vapor to enhance the activity and the lifetime of the catalyst. Interestingly, the effect of the Al thickness was crucial, implying that Al was very good at producing the nm-size catalyst particles by preventing “Ostwald ripening". The Al underlayer was varied over the range of 15~40 nm in thickness. The optimum conditions for the synthesis parameters were as follows: pressure of 95 torr, growth temperature of 815 °C, growth for 30 min, 60 sccm Ar + 60 sccm H2 + 20 sccm C2H2. The water vapor also had a great effect on the growth of CNTs. CNTs grew 5.03 mm long for 30 min with the water vapor added while CNTs were 1.73 mm long without water vapor at the same condition. As-grown CNTs were characterized by using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. High-resolution transmission electron microscopy showed that the as-grown CNTs were of ~3 graphitic walls and ~ 6.6 nm in diameter. |
