Electronic Properties of DNA CNT molecular junctions
M. Lee, S. Avdoshenko, R. Gutierrez, and G. Cuniberti
International CECAM-Workshop Quantum Transport on the Molecular Scale
2009.09.14-18; Bremen, Germany
The issue of the electrical conductivity of DNA oligomers is still under debate. One of the main problems from the experimental point of view is the construction of well-defined electrode-molecule junctions where reproducible transport measurements become possible. A very attractive option is given by carbon nanotube (CNT)-DNA junctions , where the low dimensionality as well as their chirality dependent electronic structure opens the possibility to tune the electrical response of the junction. Recently, Guo et al.  have investigated the influence of point mismatches onto the conductance of a 15-base pair DNA chain contacted via amide linkages to CNT electrodes. It was found that a single GT or CA mismatch in a DNA 15-mer increases the resistance of the duplex ~300-fold relative to a well-matched one. Motivated by these experimental work and relying on our past experience on CNT-molecule junctions , we have investigated in detail molecular junctions consisting of semi-infinite (5,5) CNT electrodes which are bridged by a double-strand DNA with variable length. Especially, we have addressed (i) the electronic structure of the CNT-linker-DNA interface which is essential in determining the charge injection efficiency, (ii) the electronic structure and density of states of different DNA oligomers with well-matched sequences as well as with single GT and CA mismatches. We have further carried out first classical molecular dynamics simulations  of the junction to estimate the influence of dynamical disorder onto the junction stability. Using a model Hamiltonian approach  to deal with the charge transport properties we have preliminary results on the I-V characteristics of model junctions, which reveal a quite strong modification of charge transport efficiency upon insertion of mismatches.
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