Localization and quantization in covalently bonded carbon nanotube junctions

A tight-binding Hamiltonian is used to study the electronic properties of covalently bonded, crossed (5,5) metallic nanotubes with an increasing degree of disorder in the junction region. Ideal junctions with a few topological defects show Ohmic behavior. Upon increasing disorder, Ohmic conduction is suppressed in favor of hopping conductivity. Strongly disordered junctions as could be obtained after electron-beam irradiation of overlayed nanotubes, display weak localization and energy quantization, indicating the formation of a quantum dot contacted to metallic nanowires by tunnel barriers.