Nitrogen doping of metallic single-walled carbon nanotubes:n-type conduction and dipole scattering

The charge transport properties of individual, metallic nitrogen doped, single-walled carbon nanotubes are investigated. It is demonstrated that n-type conduction can be achieved by nitrogen doping. Evidence was obtained by appealing to electric-field effect measurements at ambient condition. n-type conduction is attributed to the presence of graphite-type nitrogen. The observed temperature dependencies of the zero-bias conductance indicate a disordered electron system with electric-dipole scattering, caused mainly by pyridine-type nitrogen atoms in the honeycomb lattice. Copyright c © EPLA, 2007 In the past, the electronic properties of multiand single-walled carbon nanotubes (MWNTs and SWNTs) have been intensively investigated. The primary reason is that they represent an almost perfect model for fundamental research due to their unique one-dimensional electronic structure. For the same reason nanotubes are promising candidates for applications in molecular devices [1,2], provided their electronic properties, in particular the type of charge carriers, are controllable. Major efforts have been undertaken to this end including chemical modifications, [3] exposure to gaseous atmospheres [4–7] and immersion in electrolytes [8]. Another possibility for tailoring the nanotube’s electronic system is their deliberate doping. In this case, doping refers to the substitution of a carbon atom with other elements such as nitrogen or boron and is expected to have significant impact on the nanotube’s charge transport properties [9]. The successful nitrogen doping of MWNTs has already been achieved [10–13] and confirmed by thermopower measurements [12–14]. Only recently it was shown that it is possible to grow directly nitrogen-doped SWNTs, [15,16] reconfirmed by Raman and absorption spectroscopy [17]. Among these, the metallic SWNTs are of particular interest for the development of all-metal–based molecular nano-electronics. They represent excellent building blocks for devices with low power consumption in combination with large current densities. However, in standard SWNT devices p-type conduction is always observed. This results in severe limits on possible device architectures due to the absence of n-type conducting SWNTs. Here we present the first investigation on individual metallic nitrogen-doped SWNTs, showing that intrinsic n-type conduction is achievable. Furthermore, in the lowenergy limit, the charge carriers of nitrogen-doped SWNTs are found to display a temperature-dependent scattering mechanism, which is attributed to electric-dipole moment interactions. These two experimental observations are correlated to the different nitrogen bonding configurations in the carbon-host lattice. The nitrogen-doped SWNTs used had an average tube diameter of 1.2 nm and an average nitrogen content of 1 atom% [15]. In particular, the nitrogen is mainly bonded in two ways, pyridineand graphite-like, c.f. fig. 1 [13,15,18]. Samples were prepared by standard electron-beam lithography [19]. As electrode material AuPd alloy on top of a SWNT was deposited. The distance between two neighboring electrodes was about