The effect of Nb substitution on synthesis and photo-response of TiO 2 thin films prepared by direct current magnetron sputtering

Paul A. Desario; Michael E. Graham; Ryan M. Gelfand; Kimberly A. Gray

doi:10.1016/j.tsf.2011.01.264

The effect of Nb substitution on synthesis and photo-response of TiO ₂ thin films prepared by direct current magnetron sputtering

Paul A. Desario, Michael E. Graham, Ryan M. Gelfand, Kimberly A. Gray

Civil and Environmental Engineering

Research output: Contribution to journal › Article › peer-review

10 Scopus citations

Abstract

TiO₂ has a limited photoefficiency for solar energy harvesting and conversion due to its large bandgap. Nb substitution into the TiO ₂ lattice was investigated to red-shift its photoresponse by introducing defect energy levels in the host bandgap. Ti_1-xNb _yO₂ thin films (0 ≥ y ≤ 0.52) were prepared by direct current reactive magnetron sputtering. The effect of Nb concentration on crystal phase formation and subsequent change in optical and electronic properties were determined. Films had an increasing rutile proportion as Nb concentration increased, and all films prepared for y > 0.25 were pure rutile. Nb substituted as Nb(V) or a mixture of Nb(IV)/(V) while Ti remained Ti(IV). Therefore, in these materials cation vacancies formed to electronically compensate for group V doping. Nb-doped rutile films showed no red-shift in optical response while Nb-doped anatase/rutile composites were strongly red-shifted. Photocurrent measurements were made to determine if the enhanced visible light absorption generated mobile electron-hole pairs or was due to localized excitations at color centers. At low Nb concentrations (∼ 2 at.%), visible light absorption generated mobile charge carriers, while at higher concentrations (> 9 at.%), no mobile charge carriers were created. At higher Nb concentrations, the formation of mobile charge carriers was hindered by charge recombination at cation vacancies.

Original language	English (US)
Pages (from-to)	3562-3568
Number of pages	7
Journal	Thin Solid Films
Volume	519
Issue number	11
DOIs	https://doi.org/10.1016/j.tsf.2011.01.264
State	Published - Mar 31 2011

Funding

This work was supported by NSF Grant # CMMI-0700865 . Sample characterizations (XRD, SEM/EDX, and UV-VIS) were performed in the JB Cohen X-ray facility, and the NUANCE and KECK Biophysics centers at Northwestern University. We would like to thank Joy Chen for her assistance with DCMS and Kevin Schulte for his assistance. We would also like to thank Prof. Hooman Mohseni for generous use of his lab equipment.

Keywords

Doped oxides
Niobium
Sputtering
Titanium oxide
Visible light response
X-ray diffraction
X-ray photoelectron spectroscopy

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
Surfaces and Interfaces
Surfaces, Coatings and Films
Metals and Alloys
Materials Chemistry

Access to Document

10.1016/j.tsf.2011.01.264

Cite this

@article{212bc8359be9479fbc49cf47f86ef14b,

title = "The effect of Nb substitution on synthesis and photo-response of TiO 2 thin films prepared by direct current magnetron sputtering",

abstract = "TiO2 has a limited photoefficiency for solar energy harvesting and conversion due to its large bandgap. Nb substitution into the TiO 2 lattice was investigated to red-shift its photoresponse by introducing defect energy levels in the host bandgap. Ti1-xNb yO2 thin films (0 ≥ y ≤ 0.52) were prepared by direct current reactive magnetron sputtering. The effect of Nb concentration on crystal phase formation and subsequent change in optical and electronic properties were determined. Films had an increasing rutile proportion as Nb concentration increased, and all films prepared for y > 0.25 were pure rutile. Nb substituted as Nb(V) or a mixture of Nb(IV)/(V) while Ti remained Ti(IV). Therefore, in these materials cation vacancies formed to electronically compensate for group V doping. Nb-doped rutile films showed no red-shift in optical response while Nb-doped anatase/rutile composites were strongly red-shifted. Photocurrent measurements were made to determine if the enhanced visible light absorption generated mobile electron-hole pairs or was due to localized excitations at color centers. At low Nb concentrations (∼ 2 at.%), visible light absorption generated mobile charge carriers, while at higher concentrations (> 9 at.%), no mobile charge carriers were created. At higher Nb concentrations, the formation of mobile charge carriers was hindered by charge recombination at cation vacancies.",

keywords = "Doped oxides, Niobium, Sputtering, Titanium oxide, Visible light response, X-ray diffraction, X-ray photoelectron spectroscopy",

author = "Desario, {Paul A.} and Graham, {Michael E.} and Gelfand, {Ryan M.} and Gray, {Kimberly A.}",

note = "Funding Information: This work was supported by NSF Grant # CMMI-0700865 . Sample characterizations (XRD, SEM/EDX, and UV-VIS) were performed in the JB Cohen X-ray facility, and the NUANCE and KECK Biophysics centers at Northwestern University. We would like to thank Joy Chen for her assistance with DCMS and Kevin Schulte for his assistance. We would also like to thank Prof. Hooman Mohseni for generous use of his lab equipment. Copyright: Copyright 2011 Elsevier B.V., All rights reserved.",

year = "2011",

month = mar,

day = "31",

doi = "10.1016/j.tsf.2011.01.264",

language = "English (US)",

volume = "519",

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T1 - The effect of Nb substitution on synthesis and photo-response of TiO 2 thin films prepared by direct current magnetron sputtering

AU - Desario, Paul A.

AU - Graham, Michael E.

AU - Gelfand, Ryan M.

AU - Gray, Kimberly A.

N1 - Funding Information: This work was supported by NSF Grant # CMMI-0700865 . Sample characterizations (XRD, SEM/EDX, and UV-VIS) were performed in the JB Cohen X-ray facility, and the NUANCE and KECK Biophysics centers at Northwestern University. We would like to thank Joy Chen for her assistance with DCMS and Kevin Schulte for his assistance. We would also like to thank Prof. Hooman Mohseni for generous use of his lab equipment. Copyright: Copyright 2011 Elsevier B.V., All rights reserved.

PY - 2011/3/31

Y1 - 2011/3/31

N2 - TiO2 has a limited photoefficiency for solar energy harvesting and conversion due to its large bandgap. Nb substitution into the TiO 2 lattice was investigated to red-shift its photoresponse by introducing defect energy levels in the host bandgap. Ti1-xNb yO2 thin films (0 ≥ y ≤ 0.52) were prepared by direct current reactive magnetron sputtering. The effect of Nb concentration on crystal phase formation and subsequent change in optical and electronic properties were determined. Films had an increasing rutile proportion as Nb concentration increased, and all films prepared for y > 0.25 were pure rutile. Nb substituted as Nb(V) or a mixture of Nb(IV)/(V) while Ti remained Ti(IV). Therefore, in these materials cation vacancies formed to electronically compensate for group V doping. Nb-doped rutile films showed no red-shift in optical response while Nb-doped anatase/rutile composites were strongly red-shifted. Photocurrent measurements were made to determine if the enhanced visible light absorption generated mobile electron-hole pairs or was due to localized excitations at color centers. At low Nb concentrations (∼ 2 at.%), visible light absorption generated mobile charge carriers, while at higher concentrations (> 9 at.%), no mobile charge carriers were created. At higher Nb concentrations, the formation of mobile charge carriers was hindered by charge recombination at cation vacancies.

AB - TiO2 has a limited photoefficiency for solar energy harvesting and conversion due to its large bandgap. Nb substitution into the TiO 2 lattice was investigated to red-shift its photoresponse by introducing defect energy levels in the host bandgap. Ti1-xNb yO2 thin films (0 ≥ y ≤ 0.52) were prepared by direct current reactive magnetron sputtering. The effect of Nb concentration on crystal phase formation and subsequent change in optical and electronic properties were determined. Films had an increasing rutile proportion as Nb concentration increased, and all films prepared for y > 0.25 were pure rutile. Nb substituted as Nb(V) or a mixture of Nb(IV)/(V) while Ti remained Ti(IV). Therefore, in these materials cation vacancies formed to electronically compensate for group V doping. Nb-doped rutile films showed no red-shift in optical response while Nb-doped anatase/rutile composites were strongly red-shifted. Photocurrent measurements were made to determine if the enhanced visible light absorption generated mobile electron-hole pairs or was due to localized excitations at color centers. At low Nb concentrations (∼ 2 at.%), visible light absorption generated mobile charge carriers, while at higher concentrations (> 9 at.%), no mobile charge carriers were created. At higher Nb concentrations, the formation of mobile charge carriers was hindered by charge recombination at cation vacancies.

KW - Doped oxides

KW - Niobium

KW - Sputtering

KW - Titanium oxide

KW - Visible light response

KW - X-ray diffraction

KW - X-ray photoelectron spectroscopy

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