  We demonstrate a high electron conductivity (> 10^2 S/cm and up to 10^3 S/cm)
of tungsten suboxide W18O(52.4-52.9)(or equivalently WO(2.91-2.94)) nanotubes
(2 to 3 nm in diameter, ca. micrometer long). The conductivity is measured in
the temperature range 120 to 300K by a four probe scanning tunneling microscope
in ultra high vacuum. The nanotubes are synthesized by a low temperature and
low cost solvothermal method. They selfassemble in bundles of hundreds of
nanotubes forming nanowires (ca. micrometer long, few tens nm wide). We observe
a large anisotropy of the conductivity with a ratio (longitudinal
conductivity/perpendicular conductivity) of ca. 10^5. A large fraction of them
(ca. 65 to 95%) shows a metallic like, thermal activation less, electron
transport behavior. Few of them, with a lower conductivity from 10 to 10^2
S/cm, display a variable range hopping behavior. In this latter case, a hopping
barrier energy of ca. 0.24 eV is inferred in agreement with the calculated
energy level of the oxygen vacancy below the conduction band. This result is in
agreement with a relative average concentration of oxygen vacancies of ca. 3%,
for which a semiconductor to metal transition was theoretically predicted.
These tungsten suboxide nanostructures are prone to a wide range of
applications in nanoelectronics.
