Highly Conductive Tungsten Suboxide Nanotubes.

We demonstrate a high electron conductivity (>100 S/cm and up to 1000 S/cm) of tungsten suboxide W(18)O(52.4-52.9) (or equivalently WO(2.91-2.94)) nanotubes (2-3 nm in diameter, ∼ µm 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 self-assemble in bundles of hundreds of nanotubes forming nanowires (∼ µm long, few tens nm wide). We observe a large anisotropy of the conductivity with a ratio (longitudinal conductivity/perpendicular conductivity) of ∼ 1E5. A large fraction of them (∼ 65-95%) shows a metallic-like, thermal activation less, electron transport behavior. Few of them, with a lower conductivity from 10 to 100 S/cm, display a variable range hopping behavior. In this latter case, a hopping barrier energy of ∼ 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 ∼ 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.

DOI : 10.1063/5.0170761

Authors : Cécile Huez, Maxime Berthe, Florence Volatron, Jean-Michel Guigner, Dalil Brouri, Lise-Marie Chamoreau, Benoît Baptiste, Anna Proust, Dominique Vuillaume.