A power law behaviour in transport measurements of CNTs is often taken as the signature of the presence of a Luttinger liquid (LL). When electrical measurements are made on a substrate the electron–electron interactions are effectively cut off over a screening length that is roughly twice the distance from the nanotube to the ground plane in the substrate. By making measurements off substrate the electron–electron interactions are effectively cut off by the intrinsic length of the LL itself.

As such, off-substrate measurements are able to probe the electron–electron interactions that are masked by the presence of a ground plane. However, the much larger exponents seen in this study are not consistent with a LL description and an alternative explanation based in Environmental Quantum Fluctuation (EQF) theory has to be used. In the EQF description the exponent is associated with the tunnelling contact not the bulk and the high values of the exponent reported here are associated with impedance reflections at the contact.

Making measurements off substrate is therefore able to distinguish between the TLL and EQF theories. Using nanomanipulation is an ideal way to probe the electrical properties of without-substrate effects.

The researchers presented their work in Nanotechnology.