Ferroelectric topology and electronic structure of BaTiO 3 (001)

Ferroelectric topology andelectronic structure of BaTiO3(001)

1Université Paris-Sud 11 – École Doctorale 107 “Physique de la Région Parisienne”2Laboratoire d’Étude des Nanostructures et Imagerie de Surface

(CEA-Saclay/DSM/IRAMIS/SPCSI)3CEA/DAM – Île-de-France

4Laboratoire Structures, Propriétés et Modélisation des Solides (CNRS-UMR 8580 – École Centrale Paris)

Jelle Dionot1,2

Jointly supervised byGrégory Geneste3,4 and Nick Barrett2

1

Outline• Ferroelectric properties of single crystals

• Physics and chemistry of surfaces– Stoichiometry– Doping– Strain

• Experimental and theoretical approaches– Electron microscopy and spectroscopy– Ab initio simulation

2

Ferroelectric polarization screening on single crystal

- - - - - - - - - - - -

+ + + + + + + +

-+

+ + + +

+ + + + + + + ++ + + +

- - - - - - - - - - - -

-+

-+

-+

-+

- - - - - - - + + + + + + + ++ + + +

+ + + + +

Extrinsic (adsorbates)

- - - - - - - - - - - -

Intrinsic(e-h pairs, defects)

+ + - - + - - -+ - + +

- - - + + + - - - + + +

Domain ordering

Ba2+ Ti4+ O2-

3

Experimental approach:Surface full-field imaging techniques

500 nm 50 nm 5 nm

Polarized Light

DIC

Optical microscopyDomain ordering

PEEMPhotoemission threshold

Work function

4

LEEMSurface PotentialPhase Transition

Spectromicroscopy in real and reciprocal space (chemistry and band structure)

5

Real-space imaging

Work function variationsSurface charge differences inferroelectric domains

3.2 eV

3.5 eV

3.3 eV

3.4 eV

Direct surface chemistryCore level imaging

Reciprocal-space imaging

86

42

0B

indi

ng E

nerg

y (e

V)

k// (Å-1

)

86

42

0B

indi

ng E

nerg

y (e

V)

k// (Å-1

)

• Free standing slabs (~130 atoms)– Surface

• Compensation of internal depolarizing fields

• 2 supercell terminations – BaO

– TiO2

• Density Functional Theory based on minimization of total energy of the system at 0 K

6

Theoretical approach: simulation

-1.2

-0.8

-0.4

0.0

Rel

ativ

e To

tal E

nerg

y (e

V)

4.003.953.903.853.80a (Å)

Theoretical approach: simulation

7

+ + - - + - - -+ - + +

- - - + + + - - - + + +

Out-of-plane polarization with uncompensated depolarizing field

Barium

Titanium

Oxygen

BaO termination

Theoretical approach: simulation

8

Out-of-plane polarization with uncompensated depolarizing field

Barium

Titanium

Oxygen

BaO termination

Theoretical approach: simulation

9

Out-of-plane polarization with uncompensated depolarizing field

Barium

Titanium

Oxygen

TiO2 termination

Experiments & Calculations

10

Experiments Calculations

Oxygen vacancies stabilize inward out-of-plane polarization

Surface band structure of doped BaTiO3

PRL 111, 127602 (2013)

Strain-polarization coupling

Surface relaxation and rumpling

Thank you for your attention!

Jelle Dionot

Pénultième année de thèse

Bât 462, Pe 6

11

So far so good!ISOE 2013