Carbon
nanotubes are promising building blocks for various nanoelectronic
components. A highly desirable geometry for such applications is a
coil. However, coiled nanotube structures reported so far were inherently
defective or had no free ends accessible for contacting. Here we demonstrate
the spontaneous self-coiling of single-wall carbon nanotubes into
defect-free coils of up to more than 70 turns with identical diameter
and chirality, and free ends. We characterize the structure, formation
mechanism, and electrical properties of these coils by different microscopies,
molecular dynamics simulations, Raman spectroscopy, and electrical
and magnetic measurements. The coils are highly conductive, as expected
for defect-free carbon nanotubes, but adjacent nanotube segments in
the coil are more highly coupled than in regular bundles of single-wall
carbon nanotubes, owing to their perfect crystal momentum matching,
which enables tunneling between the turns. Although this behavior
does not yet enable the performance of these nanotube coils as inductive
devices, it does point a clear path for their realization. Hence,
this study represents a major step toward the production of many different
nanotube coil devices, including inductors, electromagnets, transformers,
and dynamos
