Wall-Selective Probing of Double-Walled Carbon Nanotubes Using Covalent Functionalization

Abstract

Double-walled carbon nanotubes (DWNTs) present an original coaxial geometry in which the inner wall is naturally protected from the environment by the outer wall. Covalent functionalization is introduced here as an effective approach to investigate DWNT devices. Performed using an aryldiazonium salt, the functionalization is reversible upon thermal annealing and occurs strictly at the surface of the outer wall, leaving the inner wall essentially unaltered by the chemical bonding. Measurements on functionalized DWNT transistors show that the electrical current is carried by the inner wall and provide unambiguous identification of the metallic or semiconducting character of both walls. New insights about current saturation at high bias in DWNTs are also presented as an illustration of new experiments unlocked by the method. The wall-selectivity of the functionalization not only enables selective optical and electrical probing of the DWNTs, but it also paves the way to designing novel electronic devices in which the inner wall is used for electrical transport while the outer wall chemically interacts with the environment.

Electronic and Quantum Transport Properties of Substitutionally Doped Double-Walled Carbon Nanotubes

“…As a matter of fact, doping uniquely the outer tube and increasing the inter-wall separation leads to a practically complete restoration of the hyperconjugated carbon π-network of the inner shell, as the inner tube from being affected by the outer-sidewall modification. This is consistent with experimental results on DWNTs where covalent functionalization occurs strictly at the surface of the outer wall and the inner wall is essentially unaltered by the chemical modification [8].…”

Graft-Induced Midgap States in Functionalized Carbon Nanotubes

“…Conductances of metallic nanotubes and of semiconducting nanotubes in their ON-state exhibit a marked drop by about 1 order of magnitude, which is consistent with previous studies. 28,30,37,44 However, the OFF-state shows a completely different behavior: the conductance increases after addition of the chemical adducts. The increase is strong, with an amplitude reaching at least 2 orders of magnitude above the resolution-limited insulating current of the pristine nanotube.…”

Measurements of the transport gap in semiconducting multiwalled carbon nanotubes with varying diameter and length

“…For DWNTs, a few experimental [23][24][25][26][27] and theoretical [1,[28][29][30][31] papers have focused on their multilayer aspects, but beyond them, in both experiment and theory, numerous practical difficulties for systematic research arise. For the semiconducting MWNTs, the exact nature of the energy gap in the presence of interwall interactions, and especially as a function of the diameter, is not known.…”