Semiconductor-to-Metal Transition in Rutile TiO2 Induced by Tensile Strain

Research output: Contribution to journalArticlepeer-review

20 Scopus Citations


We report the first observation of a reversible, degenerate doping of titanium dioxide with strain, which is referred to as a semiconductor-to-metal transition. Application of tensile strain to a ∼50 nm film of rutile TiO2 thermally grown on a superelastic nitinol (NiTi intermetallic) substrate causes reversible degenerate doping as evidenced by electrochemistry, X-ray photoelectron spectroscopy (XPS), and conducting atomic force microscopy (CAFM). Cyclic voltammetry and impedance measurements show behavior characteristic of a highly doped n-type semiconductor for unstrained TiO2 transitioning to metallic behavior under tensile strain. The transition reverses when strain is removed. Valence band XPS spectra show that samples strained to 5% exhibit metallic-like intensity near the Fermi level. Strain also induces a distinct transition in CAFM current-voltage curves from rectifying (typical of an n-type semiconductor) to ohmic (metal-like) behavior. We propose that strain raises the energy distribution of oxygen vacancies (n-type dopants) near the conduction band and causes an increase in carrier concentration. As the carrier concentration is increased, the width of the depletion region is reduced, which then permits electron tunneling through the space charge barrier resulting in the observed metallic behavior.

Original languageAmerican English
Pages (from-to)2173-2179
Number of pages7
JournalChemistry of Materials
Issue number5
StatePublished - 14 Mar 2017

Bibliographical note

Publisher Copyright:
© 2017 American Chemical Society.

NREL Publication Number

  • NREL/JA-5900-68053


  • doping
  • semiconductor-to-metal
  • solar-photochemistry
  • strain


Dive into the research topics of 'Semiconductor-to-Metal Transition in Rutile TiO2 Induced by Tensile Strain'. Together they form a unique fingerprint.

Cite this