title: Reduction-controlled viologen in bisolvent as an environmentally stable n-type dopant for carbon nanotubes.
abstract: Various viologens have been used to control the doping of single-walled carbon nanotubes (SWCNTs) via direct redox reactions. A new method of extracting neutral viologen (V(0)) was introduced using a biphase of toluene and viologen-dissolved water. A reductant of sodium borohydride transferred positively charged viologen (V(2+)) into V(0), where the reduced V(0) was separated into toluene with high separation yield. This separated V(0) solution was dropped on carbon nanotube transistors to investigate the doping effect of CNTs. With a viologen concentration of 3 mM, all the p-type CNT transistors were converted to n-type with improved on/off ratios. This was achieved by donating electrons spontaneously to CNTs from neutral V(0), leaving energetically stable V(2+) on the nanotube surface again. The doped CNTs were stable in water due to the presence of hydrophobic V(0) at the outermost CNT transistors, which may act as a protecting layer to prevent further oxidation from water.
authors.affiliation: BK21 Physics Division, Center for Nanotubes and Nanostructured Composites, Sungkyunkwan Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 440-746, Republic of Korea.
authors.forename: Soo Min
authors.initials: SM
authors.lastname: Kim
authors.forename: Jin Ho
authors.initials: JH
authors.lastname: Jang
authors.forename: Ki Kang
authors.initials: KK
authors.lastname: Kim
authors.forename: Hyeon Ki
authors.initials: HK
authors.lastname: Park
authors.forename: Jung Jun
authors.initials: JJ
authors.lastname: Bae
authors.forename: Woo Jong
authors.initials: WJ
authors.lastname: Yu
authors.forename: Il Ha
authors.initials: IH
authors.lastname: Lee
authors.forename: Gunn
authors.initials: G
authors.lastname: Kim
authors.forename: Duong Dinh
authors.initials: DD
authors.lastname: Loc
authors.forename: Un Jeong
authors.initials: UJ
authors.lastname: Kim
authors.forename: Eun-Hong
authors.initials: EH
authors.lastname: Lee
authors.forename: Hyeon-Jin
authors.initials: HJ
authors.lastname: Shin
authors.forename: Jae-Young
authors.initials: JY
authors.lastname: Choi
authors.forename: Young Hee
authors.initials: YH
authors.lastname: Lee