  We report a combined electronic transport and structural characterization
study of small carbon nanotube bundles in field-effect transistors (FET). The
atomic structures of the bundles are determined by electron diffraction using
an observation window built in the FET. The single-walled nanotube bundles
exhibit electrical transport characteristics sensitively dependent on the
structure of individual tubes, their arrangements in the bundle, deformation
due to intertube interaction, and the orientation with respect to the gate
electric field. Our ab-initio simulation shows that tube deformation in the
bundle induces a bandgap opening in a metallic tube. These results show the
importance of intertube interaction in electrical transport of bundled
nanotubes.
