title: Reversibility, dopant desorption, and tunneling in the temperature-dependent conductivity of type-separated, conductive carbon nanotube networks.
abstract: We present a comprehensive study of the effects of doping and temperature on the conductivity of single-walled carbon nanotube (SWNT) networks. We investigated nearly type-pure networks as well as networks comprising precisely tuned mixtures of metallic and semiconducting tubes. Networks were studied in their as-produced state and after treatments with nitric acid, thionyl chloride, and hydrazine to explore the effects of both intentional and adventitious doping. For intentionally and adventitiously doped networks, the sheet resistance (R(s)) exhibits an irreversible increase with temperature above approximately 350 K. Dopant desorption is shown to be the main cause of this increase and the observed hysteresis in the temperature-dependent resistivity. Both thermal and chemical dedoping produced networks free of hysteresis. Temperature-programmed desorption data showed that dopants are most strongly bound to the metallic tubes and that networks consisting of metallic tubes exhibit the best thermal stability. At temperatures below the dopant desorption threshold, conductivity in the networks is primarily controlled by thermally assisted tunneling through barriers at the intertube or interbundle junctions.
authors.affiliation: National Renewable Energy Laboratory, Golden, Colorado 80401, USA. teresa_barnes@nrel.gov
authors.forename: Teresa M
authors.initials: TM
authors.lastname: Barnes
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Blackburn
authors.forename: Jao
authors.initials: J
authors.lastname: van de Lagemaat
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Coutts
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Heben
mesh_terms: D003460:Crystallization / Q000379:methods*; D004553:Electric Conductivity; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D036103:Nanotechnology / Q000379:methods*; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D013499:Surface Properties; D013696:Temperature
chemical_list: D046911:Macromolecular Substances; D037742:Nanotubes, Carbon