Elektrischer Transport in Bündeln aus einwandigen Kohlenstoff-Nanoröhrchen mit semitransmissiven Kontakten

The temperature dependent electrical transport in ropes of single walled carbon nanotubes was investigated. The aim of the experiments was the study of the interrelation between the nanotubes and the contact electrodes on the transport behaviour. The transport through the heterogeneous ropes consisting of a mixture of semiconducting and single metallic nanotubes are dominated by the metallic ones. Only the tubes in the outer shells of the bundles are contacted. The current-voltage (IV) characteristics can be divided in two voltage ranges which differ in their temperature and voltage dependencies. The temperature independent part is identified by a decreasing differential conductance with rising voltage. The explanation is given by electron scattering on optical phonons. Temperature dependence is found around U=0 in the IV curves. This becomes manifested in a decrease of the linear response conductance and an increased non-linearity at U=0 called zero bias anomaly, respectively. Variations between the samples are found. Intrinsic defect scattering was excluded as the origin of the anomaly. The contact interfaces between the metal electrodes and the nanotube bundles were modelled as energetic barriers. Barrier heights ranging from 5meV to 50meV were determined. The IV characteristics showing the zero bias anomaly scale according predicted power laws based on the theory of Luttinger liquids and Coulomb blockade, respectively. Exponents ranging from 0.1 to 0.9 were extracted. In the frame of known theories a full description was not possible. Correlations between the barrier heights and the exponents are portended to a barrier-induced origin of the anomaly. No hints on predicted magnetic field induced band structure variations were found. The magnetoresistance was interpreted in the frame work of Coulomb blockade. A complete clarification of the observations was not feasible. The transport through the nanotube devices are governed by two major effects: the intrinsic transport properties based on the one dimensionality and the non-ideal coupling to the metal electrodes. The metallic single walled nanotubes are ballistic conductors on the length scale of one micron at ambient temperatures and above. The mean free path for defect scattering is L>>100nm, for scattering on acoustic phonons L>1µm at 300K. The scattering on optical phonons is determined by L