Reduction-induced Fermi level pinning at the interfaces between Pb(Zr,Ti)O<sub>3</sub> and Pt, Cu and Ag metal electrodes

Chen, Feng; Schafranek, Robert; Wu, Wenbin; Klein, Andreas

doi:10.1088/0022-3727/44/25/255301

Cited by 45 publications

(42 citation statements)

References 52 publications

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“…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. 22,39 The obtained band alignments support previous studies by Deaḱ et al 15 and Scanlon et al 16 Moreover, the analysis of the electronic structure shows that the higher valence band maximum of rutile is caused by the stronger overlap between the O 2p z orbitals in rutile compared to those in anatase, leading to a substantial splitting of the resulting energy bands. The staggered band alignment explains the enhanced photocatalytic activity of mixed phase TiO 2 particles 4−9 as it provides a driving force for separation of photoexcited charge carriers.…”

supporting

confidence: 87%

“…With the use of oxide contact materials, a Fermi level pinning at the interface caused by deposition-induced interface defects 22 can be avoided. The energy band alignment between anatase and rutile is finally derived independently for both contact materials by making use of the transitivity rule, ΔE VB (A/R) = ΔE VB (A/X) − ΔE VB (R/X), where A, R, and X represent anatase, rutile, and either ITO or RuO 2 .…”

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confidence: 99%

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Energy Band Alignment between Anatase and Rutile TiO₂

Pfeifer

Erhart

et al. 2013

J. Phys. Chem. Lett.

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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: 87%

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confidence: 99%

Energy Band Alignment between Anatase and Rutile TiO₂

Pfeifer

Erhart

et al. 2013

J. Phys. Chem. Lett.

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“…An example for such reactions is given in Fig. , which displays the Pb 4f spectra of three PZT thin films in the course of stepwise deposition of Cu, Ag, and Pt, respectively . The samples were cleaned by heating in 0.5 Pa O 2 before metal deposition.…”

Section: Dielectric/metal Interfacesmentioning

confidence: 99%

“…[96, 107, 109]) or SnO 2 . No metallic species are observed during metal deposition on SrTiO 3 , for example . In the case of SrTiO 3 , reduction in the substrate can be evident either directly from the formation of Ti 3+ species or indirectly from the observation of oxygen on the deposited metal's surfaces .…”

Section: Dielectric/metal Interfacesmentioning

confidence: 99%

Interface Properties of Dielectric Oxides

Klein

2016

J. Am. Ceram. Soc.

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Chemical and electronic properties of dielectric oxide interfaces as obtained using photoelectron spectroscopy are presented and discussed. Interface preparation includes the deposition of metals onto dielectrics and vice versa as well as the effect of postdeposition treatments. Most interfaces are not abrupt as either reduction in the oxide surface occurs during metal deposition or oxidation of the metal substrate is induced by oxide deposition. The Schottky barrier heights at these interfaces are strongly affected by the interface chemistry. Reactive interfaces exhibit a strong Fermi level pinning due to defect formation. Nonreactive interfaces, which are obtained by depositing metallic oxide electrodes, exhibit an unpinned Schottky-Mott-like barrier formation. Barrier heights can therefore be modified by more than 1 eV with suitable electrode material and processing. Postdeposition oxidation and reduction treatments and ferroelectric polarization can lead to comparable changes of barrier height. Interface studies between dielectric oxides reveal the dependence of valence band maximum and conduction band minimum energies. Due to transitivity of band alignment, these can be arranged on an absolute energy scale. The range of Fermi level positions in dielectric oxides, which can also be obtained from photoelectron spectroscopy and which is limited by intrinsic defect formation, is comparable when the oxides aligned on the energy scale determined by the photoemission experiments. The band alignment therefore indicates if a material can be made n-type or p-type by donor or acceptor doping. The range of Fermi levels in the oxides corresponds also with the range of the Fermi levels at oxide/metal interfaces.

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“…Also, the interface of Bi 2 O 3 with RuO 2 as a promising back contact material due to its high work function and metal-like conductivity was measured. In the special case of an all-oxide solar cell RuO 2 could be beneficial, because it is more unlikely, compared to nonoxidic contact materials, to reduce the surface of the material beneath during deposition and create defects [23]. In addition, ITO|Bi 2 O 3 |RuO 2 and ITO|Bi 2 O 3 |Au layer structures were prepared in order to investigate the photovoltaic activity of Bi 2 O 3 .…”

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confidence: 99%

Reactively magnetron sputtered Bi₂O₃ thin films: Analysis of structure, optoelectronic, interface, and photovoltaic properties

Morasch

Brötz

et al. 2013

Physica Status Solidi (a)

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Bi2O3 thin films deposited by RF magnetron sputtering have been studied in situ by using photoelectron spectroscopy. UV/VIS transmission spectroscopy and XRD measurements were carried out to determine the optical and structural properties of the films. Thin film solar cells were built up with ITO|Bi2O3|Au layer structures. These devices were characterized by current–voltage and capacitance–frequency measurements. Open‐circuit voltages up to 680 mV and short‐circuit current densities of about 0.3 mA cm−2 were observed. In addition, relative permittivities of approximately 45 have been measured. In order to determine the energy band alignment of Bi2O3 with different contact materials, interface experiments were carried out. With stepwise depositions of the contact material combined with in situ observation of the Fermi level shift via X‐ray photoelectron spectroscopy, it is possible to measure the energy barrier height between a semiconductor and a metallic contact. The work functions of the different materials were determined by UV photoelectron spectroscopy.

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Reduction-induced Fermi level pinning at the interfaces between Pb(Zr,Ti)O₃ and Pt, Cu and Ag metal electrodes

Cited by 45 publications

References 52 publications

Energy Band Alignment between Anatase and Rutile TiO₂

Energy Band Alignment between Anatase and Rutile TiO₂

Interface Properties of Dielectric Oxides

Reactively magnetron sputtered Bi₂O₃ thin films: Analysis of structure, optoelectronic, interface, and photovoltaic properties

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Reduction-induced Fermi level pinning at the interfaces between Pb(Zr,Ti)O3 and Pt, Cu and Ag metal electrodes

Cited by 45 publications

References 52 publications

Energy Band Alignment between Anatase and Rutile TiO2

Energy Band Alignment between Anatase and Rutile TiO2

Interface Properties of Dielectric Oxides

Reactively magnetron sputtered Bi2O3 thin films: Analysis of structure, optoelectronic, interface, and photovoltaic properties

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Product

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Reduction-induced Fermi level pinning at the interfaces between Pb(Zr,Ti)O₃ and Pt, Cu and Ag metal electrodes

Energy Band Alignment between Anatase and Rutile TiO₂

Energy Band Alignment between Anatase and Rutile TiO₂

Reactively magnetron sputtered Bi₂O₃ thin films: Analysis of structure, optoelectronic, interface, and photovoltaic properties