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.

Very thin transparent, conductive carbon nanotube films on flexible substrates

“…The doping by acid and dedoping by heat treatment hypothesis was confirmed by optical measurements 15 showing the E s 11 transitions disappear after acid treatment and reappear after heat treatment. 13 We note that after acid treatment, the t = 1.3 nm film had R s Ϸ 10 k⍀ / ᮀ for T Ϸ 98%.…”

“…We suggest that this behavior is a manifestation of the changing behavior of the network morphology as the t approaches the bundle size coupled with percolative effects at low t. It is possible to improve the films by acid treatment which is known to remove the surfactant and introduce doping. 7,8,11,13,14 After acid treatment, R s decreases to ϳ30% of its original value. 15 After dedoping by heat treatment, R s typically increased to ϳ80% of its original value, suggesting that acid treatment works predominately by doping, with surfactant removal playing a minor role.…”

Highly conductive and transparent carbon nanotube composite thin films deposited on polyethylene terephthalate solution dipping

“…T h em a i nc h a l l e n g eh e r ei st oa d d r e s st h et r a d e -o f fb e t w e e n transparency and conductivity. Many factors have been studied in order to improve the conductivity of the CNT thin films without sacrificing their transparency [4,[11][12][13][14][15]. For example: processing techniques and parameters [4,11]; length of the CNT [12]; doping [13,14]; and metallic amount of the CNT in the mixture [14].…”

“…The preliminary results are close to those of the commercial available ITO thin films deposited on PET, such as the ones from Sigma-Aldrich (35 Ω/□, N86% transmission at 550 nm). With the optimization of the composition of the SWCNT composite, plus other techniques reported in the literature [11][12][13][14][15], SWCNT/conducting polymer composite thin films might potentially offer better or comparable performances as the conductive oxides.…”

Bundle versus network conductivity of carbon nanotubes separated by type

“…These samples offer a unique opportunity to study the role of intrinsic conductivity vs. intertube contacts in nanotube networks [5,6]. Intertube connections have been studied previously on junctions built from individual nanotubes [7] with similar or dissimilar electronic character (SS, MM or SM, respectively, where M stands for metallic and S for semiconducting tube).…”