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Title: Semiconductor-to-metal transition in rutile TiO2 induced by tensile strain

Journal Article · · Chemistry of Materials

Here, 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.

Research Organization:
National Renewable Energy Laboratory (NREL), Golden, CO (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC36-08GO28308
OSTI ID:
1347505
Report Number(s):
NREL/JA-5900-68053
Journal Information:
Chemistry of Materials, Vol. 29, Issue 5; ISSN 0897-4756
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 17 works
Citation information provided by
Web of Science

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Tuning the Electronic and Photonic Properties of Monolayer MoS 2 via In Situ Rhenium Substitutional Doping journal February 2018
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