Chemistry and catalysis on ferroelectric surfaces
Cristian Mihail Teodorescu
National Institute of Materials Physics
Atomiştilor 105b, 077125 Măgurele - Ilfov, Romania
e-mail [email protected]
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