Fabrication of highly conductive Ti1−xNbxO2 polycrystalline films on glass substrates via crystallization of amorphous phase grown by pulsed laser deposition

Hitosugi, Taro; Ueda, Atsuki; Nakao, Shin-ichi; Yamada, Naoomi; Furubayashi, Yutaka; Hirose, Yasushi; Shimada, Toshihiro; Hasegawa, Tetsuya

doi:10.1063/1.2742310

Cited by 151 publications

(126 citation statements)

References 11 publications

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“…Within this concept, the obtained alignment with a lower conduction band in anatase agrees with the higher electron concentrations, which can be achieved in anatase, for example, by Nb doping compared to rutile. 38 The presented experiments and electronic structure calculations consistently reveal a staggered energy band alignment between anatase and rutile, with the valence band maximum of rutile at 0.7 ± 0.1 eV (experimental) or 0.63 eV (theoretical) above that of anatase. Transitivity of energy band alignment has been demonstrated explicitly using two different conducting oxides as contact materials, which gives confidence that the experimentally determined alignment is not corrupted by defect-induced Fermi level pinning.…”

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confidence: 92%

Energy Band Alignment between Anatase and Rutile TiO₂

Pfeifer

Erhart

et al. 2013

J. Phys. Chem. Lett.

217

155

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Using photoelectron spectroscopy, the interface formation of anatase and rutile TiO 2 with RuO 2 and tin-doped indium oxide (ITO) is studied. It is consistently found that the valence band maximum of rutile is 0.7 ± 0.1 eV above that of anatase. The alignment is confirmed by electronic structure calculations, which further show that the alignment is related to the splitting of the energy bands formed by the O 2p z lone-pair orbitals. The alignment can explain the different electron concentrations in doped anatase and rutile and the enhanced photocatalytic activity of mixed phase particles.SECTION: Surfaces, Interfaces, Porous Materials, and Catalysis A fter Fujishima and Honda 1 had reported on the photocatalytic activity of TiO 2 , the influence of crystal structure on this property was investigated intensively.2,3 Over the past 2 decades, it was commonly observed that mixed anatase/rutile systems show more favorable photocatalytic properties than pristine ones of either modification. 4−9 The synergistic effect of the mixed systems has been attributed to a built-in driving force for separation of photogenerated charge carriers. Such a driving force may result from either a built-in electric field or from energy barriers blocking charge transfer at the interface between anatase and rutile. The latter are described by the energy band alignment, which is well-studied for semiconductor interfaces. Connelly et al.11 recently reviewed several models that are trying to explain the synergistic effect of mixed anatase/rutile systems. Well-known are the rutile sink model of Bickley et al. 4 and the rutile antenna model of Hurum et al., 5 which place the band edges of rutile (energy band gap E g = 3.0 eV 12 ) in between the band edges of anatase (E g = 3.2 eV 13 ). Kavan et al.14 performed electrochemical measurements that located the conduction band edge of anatase 0.2 eV above that of rutile, which corresponds to aligned valence band maxima. These models, however, were not able to convincingly account for the observed synergistic phenomena. Only recently, Deaḱ et al. 15 as well as Scanlon et al. 16 found theoretical and experimental indications for an energy band alignment with valence and conduction band energies in rutile both located higher in energy than in anatase when brought into contact. With such a staggered energy band alignment at the anatase/rutile interface, photogenerated electrons will preferentially move to anatase due to its lower conduction band minimum energy E CB , and holes will move to rutile due to its higher valence band maximum energy E VB . Deaḱ et al. 15 used the alignment of branch point energies 10 for their calculations. For oxides, though, it has been shown that due to a low density of induced interface states, the alignment of branch point energies does not necessarily yield proper results for the energy band alignment. 17In this work, further evidence for a staggered energy band alignment at the anatase/rutile interface is provided by X-ray photoelectron spectroscopy (XPS)...

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confidence: 92%

Energy Band Alignment between Anatase and Rutile TiO₂

Pfeifer

Erhart

et al. 2013

J. Phys. Chem. Lett.

217

155

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“…A recently discovered alternative is doped TiO 2 [3,4], which is different from the other TCOs in that conduction takes place in the d-band rather than in the s-band [5,6]. Earlier work on TCO-type TiO 2 :Nb has employed pulsed laser deposition [3,[7][8][9][10][11][12][13][14], rf magnetron sputtering [15], and dc magnetron sputtering [11,[16][17][18]. The sputtered films were post-treated in H 2 or vacuum at 400 to 600 °C for 1 h, in order to exhibit favorable electrical properties.…”

Section: Introductionmentioning

confidence: 99%

Optical properties of sputter deposited transparent and conducting TiO2:Nb films

2009

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Transparent and conducting thin films of TiO 2 :Nb were prepared on glass by reactive dc magnetron sputtering in Ar + O 2 . Post deposition annealing in vacuum at 450 o C led to good electrical conductivity and optical transparency. The optical properties in the subbandgap region were in good agreement with Drude free electron theory, which accounts for intraband absorption. The band gap of the films was found to be in the range of 3.3 to 3.5 eV and signifies the onset of interband absorption. Electrical conductivities in the 10 -3

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“…Thus, crystallization of amorphous films by annealing in reductive atmosphere [14] or using lower-oxide based such as Ti 2 O 3 -or Ti-metal based targets [15] are effective methods to prepare highly conducting NTO films. Oxygen-deficient NTO showed metallic conductivity [16].…”

Section: Introductionmentioning

confidence: 99%

Electrical Properties of Nb-Doped TiO2 Thin Films Deposited by Co-sputtering Process

Hoang

2017

MaP

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Nb-doped TiO 2 thin films were fabricated by co-sputtering of TiO 2 doped 6%wt by Nb 2 O 5 and Nb targets. The anatase polycrystalline thin films were obtained by post-annealing at 350 o C in vacuum atmosphere. The electrical properties of the film were determined by the Hall method using standard clove-leaf geometry. The results indicated that: when the Nb concentration increases followed by the numbers of electrons increase from 4×10 18 cm -3 to 2.4×10 20 cm -3 . Meanwhile the resistivity fall down from 10 to 3.5×10 -3 Ωcm. It means that this co-sputtering process is good method to improve conducting properties of Nb:TiO 2 thin film. With low resistivity and high optical transmittance (higher than 80% in the visible range), the fabricated thin film can be applicable for transparent conducting electrodes.

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Fabrication of highly conductive Ti1−xNbxO2 polycrystalline films on glass substrates via crystallization of amorphous phase grown by pulsed laser deposition

Cited by 151 publications

References 11 publications

Energy Band Alignment between Anatase and Rutile TiO₂

Energy Band Alignment between Anatase and Rutile TiO₂

Optical properties of sputter deposited transparent and conducting TiO2:Nb films

Electrical Properties of Nb-Doped TiO2 Thin Films Deposited by Co-sputtering Process

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Fabrication of highly conductive Ti1−xNbxO2 polycrystalline films on glass substrates via crystallization of amorphous phase grown by pulsed laser deposition

Cited by 151 publications

References 11 publications

Energy Band Alignment between Anatase and Rutile TiO2

Energy Band Alignment between Anatase and Rutile TiO2

Optical properties of sputter deposited transparent and conducting TiO2:Nb films

Electrical Properties of Nb-Doped TiO2 Thin Films Deposited by Co-sputtering Process

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Energy Band Alignment between Anatase and Rutile TiO₂

Energy Band Alignment between Anatase and Rutile TiO₂