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Title: Semiconductor-to-metal transition in rutile TiO 2 induced by tensile strain

Abstract

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 TiO 2 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 TiO 2 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.

Authors:
ORCiD logo [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1347505
Report Number(s):
NREL/JA-5900-68053
Journal ID: ISSN 0897-4756
Grant/Contract Number:
AC36-08GO28308
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 29; Journal Issue: 5; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; semiconductor-to-metal; doping; strain

Citation Formats

Benson, Eric E., Miller, Elisa M., Nanayakkara, Sanjini U., Svedruzic, Drazenka, Ferrere, Suzanne, Neale, Nathan R., van de Lagemaat, Jao, and Gregg, Brian A.. Semiconductor-to-metal transition in rutile TiO2 induced by tensile strain. United States: N. p., 2017. Web. doi:10.1021/acs.chemmater.6b04881.
Benson, Eric E., Miller, Elisa M., Nanayakkara, Sanjini U., Svedruzic, Drazenka, Ferrere, Suzanne, Neale, Nathan R., van de Lagemaat, Jao, & Gregg, Brian A.. Semiconductor-to-metal transition in rutile TiO2 induced by tensile strain. United States. doi:10.1021/acs.chemmater.6b04881.
Benson, Eric E., Miller, Elisa M., Nanayakkara, Sanjini U., Svedruzic, Drazenka, Ferrere, Suzanne, Neale, Nathan R., van de Lagemaat, Jao, and Gregg, Brian A.. Fri . "Semiconductor-to-metal transition in rutile TiO2 induced by tensile strain". United States. doi:10.1021/acs.chemmater.6b04881. https://www.osti.gov/servlets/purl/1347505.
@article{osti_1347505,
title = {Semiconductor-to-metal transition in rutile TiO2 induced by tensile strain},
author = {Benson, Eric E. and Miller, Elisa M. and Nanayakkara, Sanjini U. and Svedruzic, Drazenka and Ferrere, Suzanne and Neale, Nathan R. and van de Lagemaat, Jao and Gregg, Brian A.},
abstractNote = {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.},
doi = {10.1021/acs.chemmater.6b04881},
journal = {Chemistry of Materials},
number = 5,
volume = 29,
place = {United States},
year = {Fri Feb 10 00:00:00 EST 2017},
month = {Fri Feb 10 00:00:00 EST 2017}
}

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