The effects of doping, electron coherence, and electron correlation on the transport properties of borondoped multiwalled carbon nanotubes are studied. Substitutional boron lowers the Fermi level of the tubes and increases the number of participating conduction channels without introducing strong carrier scattering. From 300 to about 50 K, the tubes show metallic behavior with weak electron-phonon coupling. At lower temperatures the resistance increases, and a zero-bias anomaly is observed. The magnetoresistance is now negative indicating the importance of coherent back-scattering processes. The coherence lengths are measured and dephasing is found to involve weakly inelastic electron-electron collisions. The temperature dependence of the resistance as well as the other low temperature observations can be accounted for by one-dimensional weaklocalization theory.

An innovative and simple method, based on electron-beam (e-beam) overlapping and overexposure techniques, is developed to fabricate sub-10 nm electrode gaps with very good electrical properties. Gaps with 4 to 10 nm spacing can be fabricated using a proper e-beam dose and pattern-developing time. The fabrication yield is nearly 100% for 8–9 nm gaps, but significantly smaller for 3–4 nm gaps. The gap leakage resistance is around 1012–1013 Ω, implying very good isolation. As an example, we present a transport study on a single 8 nm Co particle junction using a 10 nm gap.

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