Sunday, August 12, 2007

Peapods are the Same as Nanotubes

Transport Properties of Carbon Nanotube C_{60} Peapods

C.H.L. Quay, et al.

PRB 76, 073404 (2007)

URL: http://link.aps.org/abstract/PRB/v76/e073404

In this article, the authors present data that suggest room temperature transport properties of carbon nanotube peapods are basically the same as unfilled carbon nanotubes. The peapods are either semiconducting or metallic and there is a Coulomb blockade.

The authors are surprised by the similarities with unfilled nanotubes. Since the nanotubes tested were selected from an ensemble containing mostly --- but not all --- peapods, one possible explanation is that the authors happened to select 7 unfilled nanotubes from the ensemble. They present a Bayesian statistical analysis to show that the chance of that happening are small, and that the most likely number of peapods in the experiment is roughly 6 of 7.

The authors' conclusion is that the transport properties of fullerene peapods are not that different from unfilled nanotubes. Although their statistical analysis seems correct, they could bolster their claim with more samples. I share their initial surprise that a lattice of buckyballs inside a nanotube has virtually no effect on its transport properties.

If the authors are correct, there are no signatures of the buckyball lattice in the transport spectra of a nanotube. How else might one go about detecting them?