A comparative study of the growth, microstructural and electrical properties of multiwall CNTs grown by thermal and microwave plasma enhanced CVD methods

Abstract

Multiwalled carbon nanotubes (CNTs) were grown on silicon substrates by thermal chemical vapour deposition (CVD) and microwave plasma CVD (MPCVD). In this manuscript, an attempt has been made to compare the growth mechanism and electrical and micro-structural properties of CNTs grown by two different methods. CNTs in MPCVD is grown by tip-growth mechanism whereas in TCVD it is grown by base-growth mechanism. To compare these techniques, the CNT samples were examined using scanning and transmission electron microscopy, Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy. Growth rates were 10 and 0.6 μm/min, for thermal CVD and MPCVD, respectively. Diameters ranged from ∼40–60 nm for thermal CVD grown CNTs, and 20–50 nm for MPCVD-grown CNTs. Deposition over 2″ diameter silicon wafers was achieved for the MPCVD growth technique. XRD and Raman studies revealed good crystallinity for both growth methods. However, thermal CVD grown CNTs showed more defects, with a crystallite size of ∼20 nm, compared to ∼37 nm for MPCVD. Static water contact angles of thermal CVD and MPCVD samples were 155° and 136°, respectively, indicating greater hydrophobicity for thermal CVD-grown CNTs. The electrical resistance was 75.40 Ω for MPCVD-grown CNTs, but 782.10 Ω for thermal CVD samples. Field emission studies revealed β values for thermal CVD and MPCVD samples, of 8010 and 13,570, with turn-on fields of 0.96 and 0.60 V/μm, respectively.