Modeling of electronic transport in scanning tunneling microscope tip–carbon nanotube systems

A model is proposed for two observed current–voltage (I – V) patterns in a recent experiment with a scanning tunneling microscope tip and a carbon nanotube @Collins et al., Science 278, 100 ~1997!#. We claim that there are two mechanical contact modes for a tip ~metal!–nanotube ~semiconductor! junction ~1! with or ~2! without a tiny vacuum gap ~0.1–0.2 nm!. With the tip grounded, the tunneling case in ~1! would produce large dI/dV with V.0, small dI/dV with V ,0, and I50 near V50 for an either n or p nanotube; the Schottky mechanism in ~2! would result in IÞ0 only with V,0 for an n nanotube, and the bias polarities would be reversed for a p nanotube. The two observed I – V patterns are thus entirely explained by a tip–nanotube contact of the two types, where the nanotube must be n-type. © 2001 American Institute of Physics. @DOI: 10.1063/1.1357206#