title: Size-selective growth of double-walled carbon nanotube forests from engineered iron catalysts.
abstract: We have succeeded in synthesizing vertically aligned doubled-walled carbon nanotube (DWNT) forests with heights of up to 2.2 mm by water-assisted chemical vapour deposition (CVD). We achieved 85% selectivity of DWNTs through a semi-empirical analysis of the relationships between the tube type and mean diameter and between the mean diameter and the film thickness of sputtered Fe, which was used here as a catalyst. Accordingly, catalysts were engineered for optimum DWNT selectivity by precisely controlling the Fe film thickness. The high efficiency of water-assisted CVD enabled the synthesis of nearly catalyst-free DWNT forests with a carbon purity of 99.95%, which could be templated into organized structures from lithographically patterned catalyst islands.
authors.affiliation: Research Center for Advanced Carbon Materials, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
authors.forename: Takeo
authors.initials: T
authors.lastname: Yamada
authors.forename: Tatsunori
authors.initials: T
authors.lastname: Namai
authors.forename: Kenji
authors.initials: K
authors.lastname: Hata
authors.forename: Don N
authors.initials: DN
authors.lastname: Futaba
authors.forename: Kohei
authors.initials: K
authors.lastname: Mizuno
authors.forename: Jing
authors.initials: J
authors.lastname: Fan
authors.forename: Masako
authors.initials: M
authors.lastname: Yudasaka
authors.forename: Motoo
authors.initials: M
authors.lastname: Yumura
authors.forename: Sumio
authors.initials: S
authors.lastname: Iijima
mesh_terms: D003460:Crystallization / Q000379:methods*; D007501:Iron / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry*; D008422:Materials Testing; D036103:Nanotechnology / Q000379:methods*; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000648:ultrastructure*
chemical_list: D046911:Macromolecular Substances; D037742:Nanotubes, Carbon; D007501:Iron