Influence of Ni Catalyst Layer and TiN Diffusion Barrier on Carbon Nanotube Growth Rate
1 Plasmionique Inc., 1650 boul. Lionel Boulet, Varennes, QC, J3X 1S2, Canada
2 Defence Research & Development Canada—Valcartier, 2459 boul. Pie XI Nord, Val-Belair, QC, G3J 1X5, Canada
3 Department of Mechanical and Materials Engineering, University of Western Ontario, London, ON, N6A 5B9, Canada
Nanoscale Research Letters 2010, 5:539-544 doi:10.1007/s11671-010-9544-yPublished: 4 February 2010
Dense, vertically aligned multiwall carbon nanotubes were synthesized on TiN electrode layers for infrared sensing applications. Microwave plasma-enhanced chemical vapor deposition and Ni catalyst were used for the nanotubes synthesis. The resultant nanotubes were characterized by SEM, AFM, and TEM. Since the length of the nanotubes influences sensor characteristics, we study in details the effects of changing Ni and TiN thickness on the physical properties of the nanotubes. In this paper, we report the observation of a threshold Ni thickness of about 4 nm, when the average CNT growth rate switches from an increasing to a decreasing function of increasing Ni thickness, for a process temperature of 700°C. This behavior is likely related to a transition in the growth mode from a predominantly “base growth” to that of a “tip growth.” For Ni layer greater than 9 nm the growth rate, as well as the CNT diameter, variations become insignificant. We have also observed that a TiN barrier layer appears to favor the growth of thinner CNTs compared to a SiO2 layer.