title: Electronic structure and chemical nature of oxygen dopant states in carbon nanotubes.
abstract: We performed low temperature photoluminescence (PL) studies on individual oxygen-doped single-walled carbon nanotubes (SWCNTs) and correlated our observations to electronic structure simulations. Our experiment reveals multiple sharp asymmetric emission peaks at energies 50-300 meV red-shifted from that of the E11 bright exciton peak. Our simulation suggests an association of these peaks with deep trap states tied to different specific chemical adducts. In addition, oxygen doping is also observed to split the E11 exciton into two or more states with an energy splitting <40 meV. We attribute these states to dark states that are brightened through defect-induced symmetry breaking. While the wave functions of these brightened states are delocalized, those of the deep-trap states are strongly localized and pinned to the dopants. These findings are consistent with our experimental observation of asymmetric broadening of the deep trap emission peaks, which can result from interaction between pinned excitons and one-dimensional phonons. Exciton pinning also increases the sensitivity of the deep traps to the local dielectric environment, leading to a large inhomogeneous broadening. Observations of multiple spectral features on single nanotubes indicate the possibility of different chemical adducts coexisting on a given nanotube.
authors.affiliation: Center for Integrated Nanotechnologies, Materials Physics and Applications Division, ‡Theory Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Xuedan
authors.initials: X
authors.lastname: Ma
authors.forename: Lyudmyla
authors.initials: L
authors.lastname: Adamska
authors.forename: Hisato
authors.initials: H
authors.lastname: Yamaguchi
authors.forename: Sibel Ebru
authors.initials: SE
authors.lastname: Yalcin
authors.forename: Sergei
authors.initials: S
authors.lastname: Tretiak
authors.forename: Stephen K
authors.initials: SK
authors.lastname: Doorn
authors.forename: Han
authors.initials: H
authors.lastname: Htoon
keywords: carbon nanotubes; electronic structure; exciton localization; oxygen doping; photoluminescence