Transition from direct tunneling to field emission in carbon nanotube intramolecular junctions

Transport measurements through metal-semiconductor carbon nanotube intramolecular junctions were carried out at high gate voltages in which regime the influence of Schottky barrier to charge transport is weak. The I-V-ds curves exhibit an inflection point in the form of ln(I/V-ds(2))-1/V-ds, showing a transition of transport mechanism from direct tunneling to field emission. The findings are interpreted in terms of quantum tunneling through a rectanglelike barrier at the junction, with a barrier width of similar to 4 nm, in good agreement with that observed on pentagon-heptagon defects at nanotube junctions via scanning tunneling spectroscopy. (c) 2008 American Institute of Physics.