  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
semi-metallic substrates (graphite). In both cases, tubes with diameters
between ~ 5 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.
