Modulation of the Electronic Structure of Semiconducting Nanotubes Resulting from Different Metal Contacts

Abstract

Examined in this paper is the role of the metal electrode influencing the structure and electronic properties of semiconducting carbon nanotubes near the interface at low bias. Specifically, we present quantum-chemical calculations of finite sections of a (8,0) semiconducting single wall nanotube contacted with gold and palladium clusters. The calculations at the density functional level of theory, which included full geometry optimizations, indicate the formation of bonds between the metal atoms of the electrode and the carbon atoms of the nanotube. The local work function of the metal electrode can be expected to exhibit significant variations as a result of this bond formation. Compared to the gold-contacted nanotubes, the palladium-contacted nanotubes have a small but interesting increase in both length and diameter. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the gold-contacted nanotube are shown localized at the edges. In contrast, the HOMO and LUMO of the palladium-contacted nanotube are extended over the entire nanotube and the metal cluster contacted to it, providing thereby a better conduction path in the contact region of the electrode and the nanotube. The involvement of the highly directional d orbitals in the interactions involving the palladium cluster leads to an enhanced pi electron density in the nanotube. This enhanced pi electron density is synonymous with an improved electron transmission.

Anchoring Pd nanoclusters onto pristine and functionalized single-wall carbon nanotubes: A combined DFT and experimental study

“…A similar extent of partial charge transfer, about 0.57-0.60 eV, was observed in both cases, which can be ascribed to the electronic reorganization caused by the interaction of the SWCNT and a high work function metal such as Pd [48,49]. That is, the presence of the 4d electrons of Pd in the antibonding orbitals of the nanotube leads to an enhancement of the electron density in the nanotube, and, consequently, a smaller energy gap [50].…”

Metal contacts in carbon nanotube field-effect transistors: Beyond the Schottky barrier paradigm

“…The improved charge exchange at the Pd-C interface also leads to an enhanced redistribution of the electron density of the contacting layer of the CNT. 16 An additional effect of sd hybridization in Pd is that its Fermi surface is almost entirely composed of d-like states, 26 while that of Au is composed of s-like states, with d DOS lying below E F by about 2 eV. 30 The surface bonding is thus expected to give rise to substantial changes in the electronic contact properties of a CNT due to the extended nature of hybridized states as confirmed evidently in Fig.…”

“…In an earlier work, it was shown that relaxation of the atomic positions of both the CNT and metal electrodes leads to distinct differences in the electronic structure of the contacting region of the CNT. 16 We have chosen for investigation Pd and Au electrodes since these metals are often utilized for device fabrication and have the same work function, but induce drastically different device performances. The experimental data are elucidated using the calculated transmission curves, density of states ͑DOS͒, and E F location within the gap.…”

Metal-to-Multilayer-Graphene Contact—Part I: Contact Resistance Modeling

“…To simplify the terminology, the terms "top contact" and "edge contact" will be used here to refer to the side and end contacts, respectively. It has been shown that the edge contact for metal-carbon-nanotube structures substantially reduces the contact resistance compared to side contacts [72]- [75]. Similarly, the first-principle calculations show that the edge-contacted metal-SLG structure exhibits a contact resistance substantially smaller than that of the topcontacted metal-SLG structures [59], [60].…”