Contributions of oxygen vacancies and titanium interstitials to band-gap states of reduced titania

Li, Jing‐Feng; Lazzari, Rémi; Chénot, Stéphane; Jupille, Jacques

doi:10.1103/physrevb.97.041403

Cited by 16 publications

(77 citation statements)

References 54 publications

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“…To avoid the cumbersome 69 underlying fourth integral over incoming/scattering angles for convergent/divergent beams, analyses have been performed with an equivalent circular detector acceptance θ c and a parallel incident beam. In that case, k depends on θ S (0 < θ S < θ c ), the small angle from the specular direction and on φ S , the azimuth angle looking downwards the origin 22,35 ,…”

Section: Reminder On Dielectric Theory Of Eels and Methodsmentioning

confidence: 99%

“…Fast Fourier transform was used with an energy step down to ∆hω = 10 −4 meV. If not stated afterward, the following simulations parameters corresponding to experiments 22,69 have been used throughout this theoretical study: beam energy E I = 8 eV or E I = 38 eV; incident angle Θ I = 60 • ; circular aperture in detection θ c = 1 • ; gaussian shape for the apparatus resolution function 75…”

Section: Reminder On Dielectric Theory Of Eels and Methodsmentioning

confidence: 99%

“…It shows a gaussian line shape with an asymmetry on the higher energy side and a strong temperature dependence in contrast to the large polaron model. Beside the debate on the location of excess charges in the subsurface region of TiO 2 17,96-99 , little is known about their degree of localization 22,24,33,100 , i.e. the polaron radius.…”

Section: Defect Induced Band Gap States and Optical Absorptionmentioning

confidence: 99%

“…The polaron radius is not settled yet in rutile 24,34,67 , although the small polaron model is currently favored in bulk 25,103 and at (110) surfaces 104 . The apparatus sensitivity function and the actual profile of excess electrons to which several types of defects contribute 22 makes difficult the determination of the polaron radius via the asymmetry of the BGS in EELS. Therefore, it has been chosen herein to represent BGS optical absorptions by a simple oscillator model:…”

Section: Defect Induced Band Gap States and Optical Absorptionmentioning

confidence: 99%

“…On the one hand, excess electrons appear as band gap states (BGS) if the lifetime of the excitation is shorter than the phononic relaxation. In reduced TiO 2 , BGS related to defects [1][2][3][4][5][6][7][8] are evidenced by (i) a photoemission line at 0.8-1 eV below E F 14-17 that reverberates in Auger transitions involving the valence band 18 , (ii) an electron energy loss of ∼ 1 eV [19][20][21][22] , (iii) features in scanning tunneling spectroscopy 23,24 or (iv) near-infrared absorption 25,26 and electron spin-resonance band 27 . On the other hand, transport measurements [28][29][30][31] favor a conduction mechanism through polarons the radius of which remains an open issue 32 .…”

Section: Introductionmentioning

confidence: 99%

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Dielectric study of the interplay between charge carriers and electron energy losses in reduced titanium dioxide

Lazzari

Jupille

2018

Phys. Rev. B

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The transport mechanism in titanium dioxide through polarons is an open issue. High Resolution Electron Energy Loss Spectroscopy (HREELS) is in principle of great relevance in such context, provided the fingerprints on the loss spectrum of the charge carriers involved in the material are disclosed. The present paper aims at evidencing those fingerprints. Through a suitable parametrization of the dielectric function, a theoretical analysis of EELS excitations in defective TiO2 rutile is developed in the framework of the semi-classical dielectric theory. The focus is put on the interplay between phonons, interband transitions and defect related excitations, namely plasmon and band gap states. Transport properties are demonstrated to be more efficiently grasped through the screening they induce on phonons than through the existence of a defined surface plasmon peak. While the corresponding imaginary part of the dielectric function only yields a slight broadening and temperature dependence of the quasi-elastic peak due to the large static dielectric function and electron effective mass, a sizable upward shift in energy and a decrease in intensity of phonons due to the real part are predicted. Band gap states also screen phonons but with downward shift in energy loss. Due to its large oscillator strength, the high energy lying surface phonon at 95 meV is a very sensitive reporter of the combined effects of transport behavior and band gap states. Finally, it is highlighted that extracting quantitative information out of EELS experiments requires an accurate modeling of the depth profile.

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Section: Reminder On Dielectric Theory Of Eels and Methodsmentioning

confidence: 99%

Section: Reminder On Dielectric Theory Of Eels and Methodsmentioning

confidence: 99%

Section: Defect Induced Band Gap States and Optical Absorptionmentioning

confidence: 99%

Section: Defect Induced Band Gap States and Optical Absorptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dielectric study of the interplay between charge carriers and electron energy losses in reduced titanium dioxide

Lazzari

Jupille

2018

Phys. Rev. B

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Coexistence of Both Localized Electronic States and Electron Gas at Rutile TiO₂ Surfaces

et al. 2023

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Localized electron polarons formed through the coupling of excess electrons and ionic vibrations play a key role in the functionalities of materials. However, the mechanism of the coexistence of delocalized electrons and localized polarons remains underexplored. Here, the discovery of high‐mobility 2D electron gas at the rutile TiO2 surfaces through argon ion irradiation induced oxygen vacancies is reported. Strikingly, the electron gas forms localized electronic states at lower temperatures, resulting in an abrupt metal–insulator transition. Moreover, it is found that the low‐temperature conductivity in the insulating state is dominated by excess free electrons with a high mobility of ≈103 cm2 V−1 s−1, whereas the carrier density is dramatically suppressed with decreasing temperature. Remarkably, it reveals that the application of an electric field can lead to a collapse of the localized states, resulting in a metallic state. These results reveal the strongly correlated/coupled nature between the localized electrons and high‐mobility electrons and offer a new pathway to probe and harvest the exotic electron states at the complex oxide surfaces.

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Surfaces of Bulk Oxides

Jupille

2020

Springer Handbook of Surface Science

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Contributions of oxygen vacancies and titanium interstitials to band-gap states of reduced titania

Cited by 16 publications

References 54 publications

Dielectric study of the interplay between charge carriers and electron energy losses in reduced titanium dioxide

Dielectric study of the interplay between charge carriers and electron energy losses in reduced titanium dioxide

Coexistence of Both Localized Electronic States and Electron Gas at Rutile TiO₂ Surfaces

Surfaces of Bulk Oxides

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Contributions of oxygen vacancies and titanium interstitials to band-gap states of reduced titania

Cited by 16 publications

References 54 publications

Dielectric study of the interplay between charge carriers and electron energy losses in reduced titanium dioxide

Dielectric study of the interplay between charge carriers and electron energy losses in reduced titanium dioxide

Coexistence of Both Localized Electronic States and Electron Gas at Rutile TiO2 Surfaces

Surfaces of Bulk Oxides

Contact Info

Product

Resources

About

Coexistence of Both Localized Electronic States and Electron Gas at Rutile TiO₂ Surfaces