“Any electronic circuit uses electrical resistances of different values, therefore it would be very nice to be able to implement a method to control the electrical resistance of carbon nanotubes for further uses in electronic circuits.”

Because it addressed two different problems: one fundamental that is Anderson Localization and one applied that is the possibility to tune the resistance of carbon nanotubes by ion irradiation.

It describes a new methodology to control the electrical resistance of single-walled carbon nanotubes by introducing defects using Ar⁺ ion irradiation. In addition, our result demonstrates that, in the presence of defects, the electronic transport at low voltage is in the Anderson localization regime.

Carbon nanotubes are expected to be the fundamental components of so-called molecular electronics. Any electronic circuit uses electrical resistances of different values; therefore it would be very nice to be able to implement a method to control the electrical resistance of carbon nanotubes for further uses in electronic circuits. This has been demonstrated to be possible by using Ar⁺ ions to irradiate the nanotubes and create defects along their length.

In addition to this applied idea, there is a fundamental implication in the work published in Nature Materials: the so-called Anderson localization regime. In a macroscopic conductor, let’s say a copper wire, the electrical resistance changes linearly with the length of the wire.

Carbon nanotubes are a good approximation of a one-dimensional conductor, in addition at voltages smaller that 0.3 V the electron-phonon coupling is very weak and then the electrons behave as waves traveling along the nanotube. When these waves scatter with the defects created by ion irradiation the result is a complex interference which gives rise to the so called Anderson Localization.

One of the consequences of this electronic transport regime is that the resistance vs. length dependence along the nanotube is not linear, as in a classical conductor, but exponential. Our experiments show this exponential dependence, as would be expected from theoretical predictions.

I was working in the field of carbon nanotubes for seven years. In particular, I was interested in measuring the electrical resistance of a carbon nanotube as a function of its length, using conductance atomic force microscopy. Then, I got the idea of inducing vacancies with Ar⁺ ions and controlling the electrical resistance of the nanotube by control of the irradiation dose.