Defects at the TiO2(100) surface probed by resonant photoelectron diffraction

Krüger, Péter; Bourgeois, S.; Domenichini, B.; Magnan, H.; Chandesris, D.; Fèvre, P. Le; Floreano, Luca; Cossaro, Albano; Verdini, Alberto; Morgante, A.

doi:10.1016/j.susc.2007.04.033

Cited by 67 publications

(124 citation statements)

References 7 publications

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“…It should be noted that the excess electrons distribution on the reduced rutile titanium dioxide (110) surface has been studied also using resonant photoelectron diffraction and scanning tunneling microscopy experimental techniques. , The experiments indicate that the excess electrons in the TiO 2 (110) surface are mainly distributed on the Ti sites of the subsurface. Meanwhile, recent first-principles calculations ,,, have also suggested that the polarons prefer the subsurface.…”

Section: Resultsmentioning

confidence: 99%

Subspace Occupancy-Constraining Potentials for Modeling Polaron Formation

Chai

Teobaldi

et al. 2021

J. Phys. Chem. C

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Polarons play a vital role for many energy-conversion and storage processes; it is accordingly imperative to understand their system-specific formation and reactivity. In first-principles simulations, the formation of polarons can be modeled by either breaking the symmetry of the initial structure or imposing an implicit or explicit constraining potential on the local orbital occupation. In this work, we propose a subspace occupancy-constraining potential (SOCP) approach to simulate the formation of polarons through constraining the occupancy number of the relevant local orbitals. We illustrate the application of the SOCP method by simulating the formation of polarons in typical bulk metal oxides (anatase and rutile TiO 2 , HfO 2 , and BiVO 4 ), as well as at the rutile TiO 2 (110) surface. The results of the simulation show that the SOCP method is very effective in achieving robust localization of the excess electron or hole and the resulting polarization of the surrounding lattice in the simulations, in agreement with both experimental and previously published computational results.

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Section: Resultsmentioning

confidence: 99%

Subspace Occupancy-Constraining Potentials for Modeling Polaron Formation

Chai

Teobaldi

et al. 2021

J. Phys. Chem. C

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“…However, the spatial extension of t S might depend on the nature of the excitation. To explore the case, fits were done at a fixed thickness t BGS = 6.5–13 Å for BGS (known enrichment of the subsurface ,,,, ) and a thickness t S for transport. Inconsistent decreasing t S values from 40 Å to nearly zero were obtained between 0 and 4 L. But whatever t S is, the product found to be constant (inset of Figure a) indicates a constant density n S ≃ 10 14 cm –2 of surface carriers on the native surface an effective mass , and an anisotropy .…”

Section: Resultsmentioning

confidence: 99%

“…Reduced nonstoichiometric rutile TiO 2 (110) is a n-type semiconductor of which the main point defects, surface oxygen vacancies O b (vac), and titanium interstitials Ti int (Figure ), dominate electronic properties. − The excess electrons they generate have a strong polaronic character; they are located on regular Ti lattice sites on which they populate Ti 3d-derived states lying in the band gap (BGS) at 0.8–1 eV below the Fermi level, − as evidenced by photoemission − and various spectroscopies. − The experimental finding of a high density of excess electrons in subsurface, ,, which relies on the surface electrostatic potential of the oxide, is supported by ab initio methods (DFT+U, hybrid functional, PBE+U − ) that also predict a localization of excess electrons in deep states in agreement with spectroscopic measurements. This configuration is all the more general as injection of electrons or n-doping with hydrogen, , aliovalent cations, or anions lead to charge distributions similar to those produced by stoichiometry defects.…”

Section: Introductionmentioning

confidence: 99%

Point Defects and Related Excess Electrons in the Dielectric Profile of the Reduced TiO₂(110) Surface

Chénot

Jupille

et al. 2021

J. Phys. Chem. C

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The dielectric behavior of the reduced TiO 2 (110) rutile surface has been explored by High-Resolution Electron Energy Loss Spectroscopy as a function of oxygen exposure, temperature and crystal orientation (dielectric anisotropy) to highlight at once the electrical transport of excess electrons and the associated band gap states (BGS), and to establish a dielectric model that encompasses the surface region as a whole. Never explored distribution proles were determined in two steps: charge carriers and then defects themselves. Firstly, surface and bulk carrier excitations were directly evidenced by the temperaturedependent broadening of the quasi-elastic peak and changes in loss features, which legitimates ts via a previous dielectric model accounting for phonons, interband transitions, plasmon excitations and BGS. The density prole of excess electrons, involving a dead zone, a rich subsurface and a lower bulk concentration was quantitatively optimized. Surface and bulk concentrations, donor and Fermi levels match tabulated values. In a second step, three types of defects were distinguished i.e. O b (vac), surface Ti int and bulk Ti int thanks to changes in surface and bulk plasmon and BGS strengths upon oxygen exposure of the reduced surface. Each of them exhibits a specic behavior. While the surface conductivity requires the presence of O b (vac), both O b (vac) and surface Ti int participate in surface reactions and all three species contribute to band bending which evidences that defects, alone or by cross inuences, shape the location and the properties of excess electrons. Making it crucial to take into account the fact, often overlooked, that excess electrons do not behave independently of their source, the nding suggests studying defects taken individually or within controlled combinations.

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“…Moreover, if the crystal structure is known, XPD can be used for assigning an electronic structure to a particular site. Recent papers 13,28 have shown that XPD can be also used in resonant conditions in order to increase the intensity of the measured peak.…”

Section: Resonant Photoelectron Diffraction On Valence Bandmentioning

confidence: 99%

“…We have clearly confirmed that resonance can be used to enhance a particular electronic structure in order to allow XPD measurements as it was already used in previous work concerning TiO 2 defect peak. 13,28 Moreover, when different contributions are mixed in the VB, resonance can be also used to enhance only one particular contribution but only in some cases. The photon energies of resonances must be well separate or one can only use the resonance which has the lower photon energy.…”

Section: Resonant Photoelectron Diffraction On Valence Bandmentioning

confidence: 99%

Resonant photoelectron and photoelectron diffraction across theFe L3edge ofFe3O4
Magnan
¹
,
Fèvre
²
,
Chandesris
³

et al. 2010
Phys. Rev. B
Self Cite
13
0
13
0
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We combined measurements of valence-band photoemission and valence-band photoelectron diffraction on Fe 3 O 4 at the Fe 2p-3d resonance. The different structures in the valence band of magnetite due to the different sites of iron were identified experimentally. Specifically the structure near the Fermi level is unambiguously attributed only to octahedral Fe 2+ sites ͑B-Fe 2+ ͒. We showed that tuning the photon energy to the resonance of B-Fe 2+ , the whole valence band is dominated by signal coming from B sites of iron. Moreover this work shows how resonant photoelectron diffraction is a powerful tool for the study of mixed valence oxides.

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Defects at the TiO2(100) surface probed by resonant photoelectron diffraction

Cited by 67 publications

References 7 publications

Subspace Occupancy-Constraining Potentials for Modeling Polaron Formation

Subspace Occupancy-Constraining Potentials for Modeling Polaron Formation

Point Defects and Related Excess Electrons in the Dielectric Profile of the Reduced TiO₂(110) Surface

Resonant photoelectron and photoelectron diffraction across theFe L3edge ofFe3O4
Magnan
¹
,
Fèvre
²
,
Chandesris
³

et al. 2010
Phys. Rev. B
Self Cite
13
0
13
0
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Defects at the TiO2(100) surface probed by resonant photoelectron diffraction

Cited by 67 publications

References 7 publications

Subspace Occupancy-Constraining Potentials for Modeling Polaron Formation

Subspace Occupancy-Constraining Potentials for Modeling Polaron Formation

Point Defects and Related Excess Electrons in the Dielectric Profile of the Reduced TiO2(110) Surface

Resonant photoelectron and photoelectron diffraction across theFe L3edge ofFe3O4Magnan1, Fèvre2, Chandesris3 et al. 2010Phys. Rev. BSelf Cite130130View full textAdd to dashboardCite

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Point Defects and Related Excess Electrons in the Dielectric Profile of the Reduced TiO₂(110) Surface

Resonant photoelectron and photoelectron diffraction across theFe L3edge ofFe3O4
Magnan
¹
,
Fèvre
²
,
Chandesris
³

et al. 2010
Phys. Rev. B
Self Cite
13
0
13
0
View full text Add to dashboard Cite