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HL: Halbleiterphysik

HL 46: Quantum dots and wires: Preparation and characterization II

HL 46.5: Vortrag

Donnerstag, 30. März 2006, 16:15–16:30, POT 51

Transition from the multiple quantum dot mode to a quasi-single quantum dot mode formed in individual ropes of single-walled carbon nanotubes — •Klaus Seemann, Jens Ebbecke, and Achim Wixforth — Institut für Physik der Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg

We report on conductance oscillations in a field effect device based on an individual rope of single-walled carbon nanotubes at 1.5 K. A newly developed fabrication method was employed to deposit and align carbon nanotubes onto pre-structured metal contacts of a silicon chip. Crucial for the deposition and alignment process of carbon nanotubes are micro fluidic flow fields combined with electric dipole fields being generated by surface acoustic waves within a gap filled with aqueous carbon nanotube suspension. This gap is formed, when the pre-structured silicon chip is flipped onto the piezoelectric lithium niobate substrate facilitating surface acoustic waves. The electrical characterization of the carbon nanotube junction at low temperatures exhibits very well reproducible current oscillations in the carbon nanotube rope. This indicates the formation of quantum dots between two tunneling contacts being separated by 500 nm. These quantum dots inside the carbon nanotube rope have an energy level spacing of about 10 meV. For source-drain bias beyond the height of the effective tunneling barrier the carbon nanotube junction reveals a transition to coherent tunneling akin a single quantum dot with an energy level spacing of about 1 eV. We interpret this behavior as a voltage induced transition from a multiple quantum dot system to a single larger quantum dot within the carbon nanotube.