Substrate-interface interactions between carbon nanotubes and the supporting substrate

By utilizing the current transients in scanning tunneling spectroscopy, the local interfacial electronics between multiwalled carbon nanotubes and several supporting substrates has been investigated. Voltage offsets in the tunneling spectra are directly correlated with the formation of a dipole layer at the nanotube-substrate interface, strongly suggesting the formation of interface states. Further, a systematic variation in this local potential, as a function of tube diameter, is observed for both metallic substrates (Au) and semimetallic substrates (graphite). In both cases, for tubes with diameters between similar to5 nm and 30 nm, the interfacial potential is nearly constant as a function of tube diameter. However, for tube diameters <5 nm, a dramatic change in the local potential is observed. Using ab initio techniques, this diameter-dependent electronic interaction is shown to derive from changes in the tube-substrate hybridization that results from the curvature of the nanotubes.