title: Laser-induced nanoscale thermocapillary flow for purification of aligned arrays of single-walled carbon nanotubes.
abstract: Although aligned arrays of single-walled carbon nanotubes (SWNTs) have outstanding potential for use in broad classes of advanced semiconductor devices, the relatively large population of metallic SWNTs (m-SWNTs) that results from conventional growth techniques leads to significantly degraded performance. Recently reported methods based on thermocapillary effects that enable removal of m-SWNTs from such arrays offer exceptional levels of efficiency, but the procedures are cumbersome and require multiple processing steps. Here we present a simple, robust alternative that yields pristine arrays of purely semiconducting SWNTs (s-SWNTs) by use of irradiation with an infrared laser. Selective absorption by m-SWNTs coated with a thin organic film initiates nanoscale thermocapillary flows that lead to exposure only of the m-SWNTs. Reactive ion etching eliminates the m-SWNTs without damaging the s-SWNTs; removal of the film completes the purification. Systematic experimental studies and computational modeling of the thermal physics illuminates the essential aspects of this process. Demonstrations include use of arrays of s-SWNTs formed in this manner as semiconducting channel materials in statistically relevant numbers of transistors to achieve both high mobilities (>900 cm2 V(-1) s(-1)) and switching ratios (>10(4)). Statistical analysis indicates that the arrays contain at least 99.8% s-SWNTs and likely significantly higher.
authors.affiliation: Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: Frank
authors.initials: F
authors.lastname: Du
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Felts
authors.forename: Xu
authors.initials: X
authors.lastname: Xie
authors.forename: Jizhou
authors.initials: J
authors.lastname: Song
authors.forename: Yuhang
authors.initials: Y
authors.lastname: Li
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Rosenberger
authors.forename: Ahmad E
authors.initials: AE
authors.lastname: Islam
authors.forename: Sun Hun
authors.initials: SH
authors.lastname: Jin
authors.forename: Simon N
authors.initials: SN
authors.lastname: Dunham
authors.forename: Chenxi
authors.initials: C
authors.lastname: Zhang
authors.forename: William L
authors.initials: WL
authors.lastname: Wilson
authors.forename: Yonggang
authors.initials: Y
authors.lastname: Huang
authors.forename: William P
authors.initials: WP
authors.lastname: King
authors.forename: John A
authors.initials: JA
authors.lastname: Rogers
keywords: SWNT; TFT; aligned array; carbon; infrared; laser; nanotube; purification; thin-film transistor