Highly Conductive Tungsten Suboxide Nanotubes

TL;DR

This paper reports the synthesis and characterization of highly conductive tungsten suboxide nanotubes with anisotropic electrical properties, demonstrating potential for nanoelectronic applications.

Contribution

It introduces a low-cost solvothermal synthesis method for tungsten suboxide nanotubes with record-high conductivity and detailed analysis of their electrical transport behaviors.

Findings

Conductivity exceeds 10^2 S/cm, reaching up to 10^3 S/cm.

Nanotubes exhibit large anisotropy in conductivity with a ratio of ca. 10^5.

Majority show metallic-like transport, some display variable range hopping.

Abstract

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.