  Electronic transport in semiconducting single-wall carbon nanotubes is
studied by combined scanning gate microscopy and scanning impedance microscopy
(SIM). Depending on the probe potential, SIM can be performed in both invasive
and non-invasive mode. High-resolution imaging of the defects is achieved when
the probe acts as a local gate and simultaneously an electrostatic probe of
local potential. A class of weak defects becomes observable even if they are
located in the vicinity of strong defects. The imaging mechanism of tip-gating
scanning impedance microscopy is discussed.
