Chemistry and catalysis on ferroelectric surfaces

Cristian Mihail Teodorescu

National Institute of Materials Physics

Atomiştilor 105b, 077125 Măgurele - Ilfov, Romania

e-mail teodorescu@infim.ro

Outline:

1. Ferroelectric materials and ferroelectric surfaces

2. Chemistry at ferroelectric surfaces

3. Basics of photoelectron spectroscopy (PES, XPS)

4. Domain imaging by spectro-microscopy

5. Selective adsorption of contaminants (fatty acids) on Pb(Zr,Ti)O3(001)

6. CO/Pb(Zr,Ti)O3(001): dependence on polarization, dissociation, oxidation

7. Conclusions

Existence

Shape

conservation

Replication,

carbon reduction

Sensing, motion

World

transformation /

generation

New entities

(fully information)

Growth

???

Sexuate

reproduction,

data analysis

Consciousness,

Modelling the

world around

2nd Law of Thermodynamics: DS 0

In our cosmic neighborhood: Stored and analyzed information DI 0, DA 0

Memory

Organic

Anorganic

Life,

Consciousness,

Intelligence

Life ≡ correlated chemical reactions

Ferromagnetism Ferroelectricity Electrostatics

Ferromagnetism Ferroelectricity

Chemistry

Catalysis

Biological

processes

Multiferroics

Magneto-chemistry

Ferroelectric

chemistry

Mechanical

motion, stress

Life

Physics Chemistry

Surface Reactivity

Catalysis Redox reactions Ferroelectricity

gas / humidity sensing

FERAM modeling / limitations tunable catalysis

three way catalysts (automotive)

Ferroelectric single domain thin layers

Popescu et al., PCCP 2015

Photoelectric effect in metals: KE = hn - F (A. Einstein, 1905; Nobel 1921)

X-ray photoelectron spectroscopy ≡ photoelectric effect on inner shells

(K. Siegbahn, '60s to '70s; Nobel 1981)

Alternate name: Electronic Structure for Chemical Analysis (ESCA)

hn = BE + KE + F

BE = f(Z, q, environment)

Zj, elemental analysis

qj, environmentj chemical

composition

surface sensitivity

excitation energy:

most frequently used

1486.7 eV Al Ka

1253.6 eV Mg Ka

50-2000 eV synchrotron

X-ray photoelectron spectroscopy: basic aspects

“Universal curve” of the inelastic mean free path

substrat

- chemical composition

- charge transfer

- ionization states

- (environment)

Surface sensitivity

d I0

I0 exp(- d / l)

emiţător probă

vid

hn = BE + KE + F

X-ray photoelectron spectroscopy: main information

Origin of chemical shifts

Validation of XPS for band bending determination

PZT(001) Au/PZT(001)

Apostol et al., Thin Solid Films 2013

EV

EC

EF

VO

≡

donors

T

Apostol, Teodorescu, Springer 2015

Band bending at ferroelectric surfaces

Apostol et al.,

Mat. Sci. Eng. B, 2013

band bending

catalytic properties

God made solids, but surfaces were the work

of the Devil.

(Wolfgang Pauli)

Elettra Sincrotrone Trieste

CoSMOS at Elettra: Combined Spectroscopy and

Microscopy Operational at SuperESCA

Gr/Ir(111)

Advances in Nanophysics and Nanophotonics, Măgurele, August 31 - September 2, 2014

Spectromicroscopy beamline

http://www.elettra.trieste.it/lightsources/elettra/

elettra-beamlines/spectro-microscopy/beamline

Spectromicroscopy

Preparation: PLD in NIMP

In situ annealing in O2

(5 x 10-5 mbar / 3 h)

Measurement: UHV

(2 x 10-10 mbar)

hn = 74 eV, fixed

PZT(001), P(-) imprint

D.G. Popescu et al., PCCP 2014

Preferential adsorption of contaminants on P(+) areas

cont.,

P(+)

cont.,

P(0)

PZT,

P(-)

PZT,

P(0)

cont.,

P(+)

PZT,

P(-) PZT,

P(0)

PFM

Apostol et al., Appl. Surf. Sci., 2013

Ştoflea et al., J. Mater. Chem. A 2014.

Free ferroelectric Pb(Zr,Ti)O3(001)

CO/PZT(001)

Follow-up of polarization by binding energies

Selective adsorption / desorption of CO

Photodesorption

Energy diagram (Koopman)

COequil.: p = 0.11 D

from Cd- to Od+

But: a = 1.95 Å3

→ p[D] = 7.34 x P [C/m2]

→ E[eV] ≈ 17.4 x P2 [C/m2]

P(+)

C+

O-

P(-)

C+

O-

E = P/0 E = P/0 O

e-

C

h+

Dissociation

mechanism

polarization strenghtening

Tk

W

h

Tmk

P

Tk

B

2/3

2

BB

0

expπ2

1

)(1

ln2

51ln 1

00 TW

T

C

TC

2/1

2/1

)0(

)0(

3

111

111

TT

TT

TTT

TTTP

b

a

CC

CC

r

W(T) = p∙Pr(T)/0

Oxygen depletion: PbO-term. → (Ti,Zr)O2-term.

Pb(Zr,Ti)O3 → Pb(Zr,Ti)O2.12 Tănase et al., PCCP, submitted

Conclusions:

A. 'self-doping' mechanism in PZT(001):

Pb(Zr,Ti)O3-d, ∂d/∂q > 0

B. contaminants R-COOH/PZT(001):

adsorb on P(+) areas up to a critical coverage;

afterwards split over the whole surface;

reduce surface band bending.

C. CO/PZT(001):

P(-) polarization stable on extremely clean surfaces;

CO/P(-)-PZT adsorbs up to 0.3 ML; CO/P(+), P(0) doesn't adsorb;

CO adsorption correlated to the existence of polarization;

dissociation, induced by substrate polarization;

desorption by oxygen uptake from the film;

not 'real' catalyst (?) Thank you for your attention

Coworkers:

C.M. Teodorescu

M.A. Huşanu N.G. Apostol

D.G. Popescu

L.E. Abramiuc L.C. Tănase C.A. Tache

L.M. Hrib L. Trupină L. Pintilie