Role of contact bonding on electronic transport in metal–carbon nanotube–metal systems

Abstract

Abstract:We have investigated the effects of the interfacial bond arrangement on the electronic transport features of metal-nanotube-metal systems. The transport properties of finite, defect-free armchair and zigzag single-walled carbon nanotubes attached to Au(111) metallic contacts have been calculated by means of the non-equilibrium Green functional formalism with the Tight-Binding and the Extended Hückel Hamiltonians. Our calculations show that the electrode material is not the only factor which rules contact transparency. Indeed, for the same electrode, but changing nanotube helicities, we have observed an overall complex behaviour of the transmission spectra due to band mixing and interference. The comparison of the two models shows that the Tight Binding approach fails to give a satisfactory representation of the transmission function when a more accurate description of the C-C and Au-C chemical bonds has to be considered. We have furthermore examined the effect of interface geometry variance on conduction and found that contact-nanotube distance has a significant impact, while contact-nanotube symmetry plays a marginal, yet evident role.

Finite-bias electronic transport of molecules in a water solution

“…37 We note that the exact conformation of the Au-CNT bonding is not known and that changes in bond structure lead to quantitative changes in the transmission spectra. 38 Here however we are mainly interested in investigating how the transmission is affected by the water so that the precise bonding geometry is less important.…”

In situmanipulation and electrical characterization of multiwalled carbon nanotubes by using nanomanipulators under scanning electron microscopy

“…In particular, the nonlinear ͑linear͒ dependence of the current in the high voltage ͑low voltage͒ range observed in our experiment is perfectly consistent with the presence of a tunnel barrier in correspondence of the metallic CNT/movable junction. 9,24,25 The progressive linearization of the I-V curve with the exposure time, and the corresponding reduction of the overall system resistance, can be similarly explained in terms of an electron beam modification of the barrier parameters, which results in an enhancement of the tunnel probability across the CNT/metal junction. In this context, it is worthy to note that all the proposed theoretical model are convergent as indicated by ͑i͒ contact area, ͑ii͒ CNT-electrode distance, and ͑iii͒ chemical composition of the electrode ͑the difference between the CNT and metal work function determining the barrier height͒, the crucial factors which rule the electron tunneling across the CNT/metal junction.…”

“…2 The presence of a high energy barrier at the metal/ nanotubes contacts has been clearly brought to light, 2,6 which leads to an overall resistance value significantly higher with respect to the theoretically predicted quantum ballistic limit ͑h /2e 2 =13 k⍀ for metallic MWCNT 2 ͒ and which, in general, masks the intrinsic electrical conduction properties of the individual CNTs. The reported contact resistance ranges from 10 4 to 10 9 ⍀, 7,8 deeply affected by the nanotube structure 9 and the chemical composition of the metallic pads. 10 A prolonged exposure of the CNT/metal contact area to a highly focused electron beam appears as an effective technique for reducing the contact resistance by several orders of magnitude.…”

Lack of universal conductance features in disordered graphene nanoribbons

“…where s g is the surface Green function of the lead and τ is the interaction between the conductor and the contact [13]. For the leads we consider two semi-infinite ribbons of the same width N a or N z as the conductor, represented by the same Hamiltonian without disorder.…”