title: Direct wall number control of carbon nanotube forests from engineered iron catalysts.
abstract: We present the direct wall number control of carbon nanotube (CNT) forests grown on engineered iron (Fe) catalysts in a catalytic chemical vapor deposition (CVD). Engineered Fe catalysts were fabricated by annealing thickness-tuned (0.8-3 nm) Fe films with small thickness variations prepared by a low-deposition-rate sputter deposition. Extensive scanning electron microcopy (SEM) characterization confirmed that vertically-aligned CNT forests were grown on Fe catalyst films with thickness larger than 1.5 nm. Detailed high-resolution transmission electron microscopy (HRTEM) and micro Raman spectroscopy analysis indicated that 75% of the CNTs grown on an Fe film with 1.5 nm mean thickness were single-walled CNTs while about 67% and 59% of CNTs grown on Fe films with 2.0 and 3.0 nm mean thickness were double-walled and triple-walled CNTs, respectively. The average wall number and outer diameter of CNT forests were found to linearly depend on the mean thickness of Fe catalyst films.
authors.affiliation: Material and Chemical Research Laboratories, Industrial Technology Research Institute (ITRI), Hsinchu 30013, Taiwan.
authors.forename: Wei-Hung
authors.initials: WH
authors.lastname: Chiang
authors.forename: Don N
authors.initials: DN
authors.lastname: Futaba
authors.forename: Motoo
authors.initials: M
authors.lastname: Yumura
authors.forename: Kenji
authors.initials: K
authors.lastname: Hata