Ion irradiation effects on conduction in single-wall carbon nanotube networks

Abstract

We have measured how irradiation by Ar + and N + ions modifies electronic conduction in single-wall carbon nanotube (SWNT) networks, finding dramatically different effects for different thicknesses. For very thin transparent networks, ion irradiation increases localization of charge carriers and reduces the variable-range hopping conductivity, especially at low temperatures. However, for thick networks (SWNT paper) showing metallic conductivity, we find a relatively sharp peak in conductivity as a function of irradiation dose. Our investigation of this peak reveals the important role of thermal annealing extending beyond the range of the irradiating ions, and shows the dependence on the morphology of the samples. We propose a simple model that accounts for the temperature-dependent conductivity. Recently, the effect of defects on the conducting properties of individual metallic single-wall carbon nanotubes (SWNTs) was shown [1,2] by the controlled reduction of the electronic localization length by irradiation with Ar + ions. For these SWNTs in the strong Anderson localization regime, the exponential increase of resistance with length of SWNTs between electrodes was greatly enhanced by di-vacancies created by the Ar + ions. In this paper, we report the first measurements (to our knowledge) of the effect of irradiation by ions on conduction in thin transparent SWNT networks, finding that resistance always increases on ion irradiation. In contrast to these results, however, we show that ion irradiation initially decreases the resistance of our thick SWNT networks.Many applications proposed for carbon nanotubes [3][4][5][6] are likely to be sensitive to irradiation effects, which u Fax: +49-711-689-1010, E-mail: v.skakalova@fkf.mpg.de would be particularly significant, for example, for devices used in space or other high-radiation environments. Controlled irradiation also has many applications related to carbon nanotubes. It has been demonstrated by experimental and theoretical studies that irradiation can be used for nano-engineering of carbon nanotubes [7,8]. For example, focused electron beams were shown to result in welding of crossed single-wall carbon nanotubes to form molecular junctions [9], and molecular dynamics simulations showed how such junctions might also be produced by irradiation by Ar + ions [10]. Irradiation by 1.25-MeV electrons at high temperature (800 • C) was able to coalesce neighbouring Ndoped SWNTs as a result of defect formation followed by thermal annealing [11]. Using irradiation by Ar + ions, Stahl et al. [12] introduced defects in the SWNTs in the upper part of a bundle of loosely coupled SWNTs before depositing gold contacts on top of the bundle. They found that to avoid the defects, the current switched to undamaged nanotubes in the lower part of the bundle, tunnelling being the transfer mechanism between nanotubes.In previous work [13], we observed local modifications of the electronic structure in atomically resolved scanning tunnelling microscope (STM) images of multi-wal...

Ion and electron irradiation-induced effects in nanostructured materials

“…58. Several experiments indeed indicate that Young modulus of SWNT bucky paper can be increased due to irradiation, 167,383 as discussed in Sec. V D 2.…”

“…This could be interpreted as evidence for irradiation-induced interconnection of nanotubes or functionalization of SWNTs at irradiation-induced defects by various chemical species due to the contact with air accompanied by chemical doping. Further experiments 383 indicated that thermal annealing of tunneling barriers between individual nanotubes by heat released during collisions of energetic ions with the target atoms may be a possible reason for the improvement in conducting properties. By contrast, high energy irradiation of the samples with 23 MeV C 4+ ions did not give rise to any enhancement in conductivity.…”

Effect of ion irradiation on the properties of carbon nanotube buckypapers

“…Moreover, the present ion beam irradiation technique is useful for defect production in CNTs, which help to alter their structural, optical, magnetic and electrical properties in a highly controlled manner [13,14]. Irradiation-induced changes of buckypaper play a significant role in the case of nanocomposites.…”

Modifying the electronic structure of semiconducting single-walled carbon nanotubes byAr+ion irradiation

“…15 It was shown that ion-irradiation-induced double vacancies ͑DVs͒, in comparison to single vacancies ͑SVs͒, strongly reduce the conductivity of metallic tubes. The effects of irradiation in more complicated systems, such as SWNT bundles 16 and films, 17,18 have also been studied and interesting effects such as an increase in the conductance after moderate irradiation dose have been reported. 17 In the transport experiments discussed above, only indirect information on the type of defects can be deduced.…”

“…The effects of irradiation in more complicated systems, such as SWNT bundles 16 and films, 17,18 have also been studied and interesting effects such as an increase in the conductance after moderate irradiation dose have been reported. 17 In the transport experiments discussed above, only indirect information on the type of defects can be deduced. Other experimental techniques which are frequently used to asses the amount of defects in carbon nanomaterials such as Raman spectroscopy, [19][20][21] x-ray photo electron spectroscopy, [22][23][24] and electron-spin-resonance method 25,26 provide data which is averaged over many defects.…”