Physics of multiwalled carbon nanotubes
1D TDOS in disordered carbon nanotubes
The tunneling conductance of junctions between a highly disordered carbon nanotube and a metallic electrode shows a characteristic zero-bias anomaly due to electron-electron interactions. Due to the high resistivity of the nanotube material, around 50 kΩ/μM, the field diffusion is rather slow. In wide enough contacts, the finite size of the junctions comes into play, and the observed anomaly can be described using theoretical model for 1D tunnel junctions.
The disorder-enhanced anomaly is well known in metallic systems, where the anomaly typically is small, only a few percent. In our disordered nanotubes we observe a much larger anomaly, and this opens a possibility to study the phenomenon in non-perturbative regime. The temperature dependence of the conductivity in our samples is found to be in good agreement with recent theoretical work (Rollbühler and Grabert, PRL 87, 126804 (2001); Mischenko et al. PRL 87, 246801 (2001)). The tunneling conductance is roughly given by G ~ e-(T/T0)/2.
In order to realize future nanotube electronics, it is not only necessary to thoroughly understand their transport properties, but also to be able to fabricate devices possessing the desirable qualities. While the latter goal is still distant, the transport in single-walled nanotubes is already understood quite well.
With multiwalled carbon nanotubes the situation is more complicated. Room temperature ballistic transport has been reported, but in the typical configuration with MWNTs on an insulating substrate, diffusive transport behaviour is mainly observed: interference effects are found to be significant, either in 1D or 2D depending on the electron mean free path.
We have investigated electron transport in extremely disordered MWNTs as a function of magnetic field and temperature. Our AFM studies reveal that the curvature of CVD tubes is intrinsic, and due to a high concentration of structural defects. We find that in our CVD grown tubes the electron mean free path l and phase coherence length Lφ are very short. In fact, l turns out to be so short that our nanotube samples are near the strong localization regime.
The basic charged excitations in carbon nanotubes are plasmons, in a similar fashion as in ordinary transmission lines. Owing to their small density of conduction electrons, however, carbon nanotubes display rather extraordinary line parameters.
Tunneling conductance at high voltages was used to determine the transmission-line parameters of the arc-discharge-grown multiwalled carbon nanotube samples. The fits yield a characteristic impedance of 1.3 - 7.7 kΩ and kinetic inductance of 0.1 - 4.2 nH/μm for the measured samples.
At low voltages, the tunneling conductance obeys non-Ohmic power law, which is predicted both by the Luttinger liquid and the environment-quantum-fluctuation theories. However, at higher voltages we observe a crossover to Ohm's law with a Coulomb-blockade offset, which agrees with the environmental quantum-fluctuation theory, but cannot be explained by the Luttinger-liquid theory.
- Low-frequency current noise and resistance fluctuations in multiwalled carbon nanotubes
R. Tarkiainen, L. Roschier, M. Ahlskog, M.A. Paalanen, and P.J. Hakonen
Physica E 28, 57 (2005)
- Tunneling spectroscopy of disordered multiwalled carbon nanotubes
R. Tarkiainen, M. Ahlskog, M.A. Paalanen, A. Zyuzin, P.J. Hakonen
Phys. Rev. B 71, 125425 (2005)
- Transport in strongly disordered multiwalled carbon nanotubes
R. Tarkiainen, M. Ahlskog, A. Zyuzin, P.J. Hakonen, and M.A. Paalanen
Phys. Rev. B 69, 033402 (2004)
- Transport in disordered carbon nanotubes
R. Tarkiainen, M. Ahlskog, P.J. Hakonen, and M.A. Paalanen
Physica E 18, 206 (2003)
- Multiwalled carbon nanotube: Luttinger versus Fermi liquid
R. Tarkiainen R, M. Ahlskog, J.S. Penttilä, L. Roschier, P.J. Hakonen, M.A. Paalanen, and E.B. Sonin
Phys. Rev. B 64, 195412 (2001)