Ferroelectric and diluted magnetic
semiconductor based multiferroic
heterostructures for energy applications
Dr. Cristian-Mihail Teodorescu
Nanoscale Condensed Matter Physics
National Institute of Materials Physics
Atomistilor 105b
077125 Magurele-Ilfov Romania
phone +40.21.3690185
fax +40.21.3690177
teodorescu@infim.ro
Dr. Nick Barrett
Service de Physique et Chimie des
Surfaces et Interfaces
Institut Rayonnement Matiere Saclay
Bat 462, CEA Saclay,
F-91191 Gif-sur-Yvette
phone +33169083272
fax +33169088446
e-mail Nick.barrett@cea.fr
The concept
Photolysis: H2O → O2- + 2H+, 2 e- involved
Charge accumulation in a ferroelectric: 10 mC/cm2 ≈ 0.6 x 1014 e- / cm2
→ 3 x 1013 dissociations / (cm2 x charging process)
Cycling at 1000 Hz: → 3 x 1016 dissociations / (cm2 s)
→ 0.05 mmol / (cm2 s) = 0.5 mmol / (m2 s) = 9 mg / (m2 s)
→ (0.5 mmol x 242 KJ/mol) / (m2 s) = 141 W / m2
Multiferroics heterostructures
Ferroelectricity ↔ Feromagnetism
Photolysis
Milestones:
Diluted magnetic
semiconductors
(DMS)
Light-induced
ferromagnetism
(i) epitaxial ferroelectric layers;
(ii) DMS: rapid magnetic switching;
(iii) DMS: light control of ferromagnetism;
(iv) Coupling DMS with ferroelectrics.
Aim of the Project:
● Understanding the interface physics involved in multiferroic archictectures
with a view to their use in novel solutions for energy harvesting.
● Validate a DMS oxide/ferroelectric or multiferroic interface for magnetically
controlled, ferroelectric enhanced hydrogen production by photolysis.
Scientific tasks:
(i) Synthesis of high quality epitaxial layers (combining PLD and molecular beam
epitaxy, MBE) and their master strain tuning via the epitaxy parameters
(choice of the substrate, growth temperature, excess oxygen, etc.)
(ii) Investigation of the chemical reactivity and the alternate photolysis route
driven at a ferroelectric interface.
(iii) Synthesis of reproducible DMS layers or alternatively 2D Stoner
ferromagnets with light-induced ferromagnetism.
(iv) DMS layers need to be investigated from the point of view of their
magnetostrictive properties. To date, no such study was reported.
(v) Fabrication of DMS/ferroelectric multiferroic systems where the electrical
polarization may be triggered by light absorption will be produced.
(vi) Microdevices for collection of hydrogen may then be obtained by
nanolitography.
Tasks of the CEA and NIMP teams → available infrastructure
Synthesis:
Pulsed laser deposition
Molecular beam epitaxy
Characterization:
Photoelectron
spectroscopy
NIMP-NCMP
CEA-SPCSI
X-ray photoelectron
NIMP-NCMP
spectroscopy (XPS)
EXAFS
High-resolution
NIMP-NCMP
CEA-SPCSI
XPS
Synchrotron
X-ray photoelectron
NIMP-NCMP
SOLEIL
CEA-SPCSI
diffraction
Angle-resolved ultraviolet
photoelectron spectroscopy NIMP-NCMP
(ARUPS)
Magneto-optical
Kerr effect (MOKE)
NIMP-NCMP
NIMP-NCMP
Spin-resolved
ARUPS
NIMP-NCMP
Theory CEA-SPCSI
Low-energy and photemission
electron microscopy
(LEEM-PEEM)
NIMP-NCMP
CEA-SPCSI
XPEEM: Elettra Trieste
Scanning probe microscopy
NIMP-NCMP
Obtained results:
PEEM image of a PFM
recorded line on PZT
TEM
LEEM images of
spontaneous polarization
in PZT
LEEM
Vsample = 0
FOV = 196 mm
FOV = 12.6 mm
Vsample = - 0.5 V
FOV = 12.6 mm
Year 1
Ferro
Year 2
DMS
Year 3
Ferro+DMS
Vsample = - 1.0 V
FOV = 12.6 mm
Obtained results:
XPS on PLDsynthesized PZT
Atomic level
line
BE (eV)
At. %
Nature
Assignment (BE from databases)
c1
527.98
0.99
s
surface PbO2 (529.0 eV)
c2
530.04
36.19
b
bulk PZT (529.9 eV)
c3
531.72
14.11
s
Pb(CO3)2 (532 eV)
c4
532.88
14.38
s
contamination (532 eV [8])
Ti 2p3/2
-
459.26
12.03
b
bulk PZT (458.6 eV)
Zr 3d3/2
-
182.07
3.68
b
bulk PZT (181.0 eV [6])
c1
138.78
15.98
b
bulk PZT (137.9 eV [6])
c2
139.76
2.15
s
Pb(CO3)2 (138.3 eV)
c3
137.24
0.48
s
surface PbO2 (137.4 eV)
O 1s
Pb 4f3/2
C. Dragoi et al.,
Phys. Stat. Sol. A,
revised version
(2011).
Results: ARUPS on PZT
New ab initio computations in progress
Comparison with band structure theory
Ferroelectricity in a quasi-amorphous, ultra-thin BaTiO3 film
3.8 nm amorphous BaTiO3 grown by MBE, then post-annealed in oxygen
In- and Out-of-plane XRD and XPD shows no crystalline order
Yet the film is ferroelectric (hysteresis loops)
crystalline
amorphous
Interpretation based on contribution of local polarization, described by dynamic charge,
and initial clamping giving a preferential orientation of the local polarization
XPD done on ANTARES beamline, SOLEIL.
Wang et al. accepted PRB 2011
Electrical measurements, first results:
PZT
BTO
12 V
14V
200
40
100
20
2
Polarization (mC/cm )
2
Polarization (mC/cm )
1 kHz
0
-100
0
-20
-40
-200
-20
-10
0
10
20
-60
-8
Voltage (V)
-6
-4
-2
0
2
4
6
Voltage (V)
160
250
150
200
130


140
150
120
110
100
100
50
90
-3
-2
-1
0
1
Voltage (V)
2
3
-4
-2
0
Voltage (V)
2
4
8
Results: ultralow coercitivity in Fe3Si
MOKE
RT growth: no LEED.
Fe/Si(001)
500 °C growth
AES


 t  (t 0  t )(t  t 0 ) 
 t  (t 0  t )(t  t 0 )   
I (Si)   exp 

x
1

exp
 1

 
1/ 3
1/ 3





1

x

1

x


1
1



  



 (t  t 0 )(t  t 0 ) 
 (t  t 0 )(t  t 0 )  
 exp 
  x 2 1  exp 

1/ 3
1  x2    
1  x2 1 / 3   


Gheorghe et al.,
J. Mater. Sci.,
in press (2011)


 t  (t 0  t )(t  t 0 )   
 (t  t 0 )(t  t 0 ) 
I (Fe)   (1  x1 )1  exp 
exp 



1/ 3
1/ 3






1

x

1

x



1
2

 





 (t  t 0 )(t  t 0 )  
 (1  x 2 )1  exp 

1  x2 1 / 3   


x/T
RT
HT
x1 (%)
7.1
25.5
x2
(%)
0.8
7.9
Fe3Si
Results: Mn-Ge DMS systems with room temperature ferromagnetism: XPS
Sample
/ component
Ge(001)
Mn/Ge(001) @ RT (50 °C)
Mn/Ge(001) @150 °C
Mn/Ge(001) @250 °C
Mn/Ge(001) @350 °C
Mn/Ge(001) @450 °C
Assignment
Mn1
Mn2
638.64
638.66
638.40
638.43
638.44
metal
Mn
639.88
639.58
639.43
639.38
639.29
MnGe
Ge1
29.28*
28.52
28.96
29.10
28.97
surf.*,
MnGe
Ge2
Compound
29.93*
Ge
Mn
29,18
MnGe0,19
29,22
MnGe1,43
29,61
MnGe1,85
29,31
MnGe1,79
bulk*,
Ge
Mn-Ge DMS systems with room temperature ferromagnetism: EXAFS and MOKE
G.A. Lungu et al.,
Appl. Phys. Lett.,
to be submitted
MOKE
N, nature
R (Å)
σ2 (Å2)
13 Mn
2.638
-
Mn/Ge RT
13 ± 3 Mn
2.67 ± 0.01
0.09 ± 0.02
Mn/Ge, 150°C
13 ± 3 Mn
2.59 ± 0.01
0.07 ± 0.02
Mn/Ge, 250°C
6 ± 1 Ge
2.53 ± 0.01
0.09 ± 0.02
Mn/Ge, 350°C
6 ± 1 Ge
2.53 ± 0.01
0.09 ± 0.02
Mn/Ge, 450°C
7 ± 2 Ge
2.54 ± 0.01
0.10 ± 0.02
Sample
Metal Mn film
+ J. Wang et al. accepted PRB 2011
Benefits and collaboration prospects:
New projects submitted to date:
● HArd X-ray energy filtered PhotoElectron Emission Microscopy
(HAXPEEM)
NMP.2011.1.4-3 Tools and Methodologies for imaging structures and
composition at the nanometer scale (11/2010)
- unsuccessful;
● FErroic-ELectrode InTerface electronic structure (FEEL-IT) ,
ANR-ANCS project, submitted (04/2011).
Access to Soleil synchrotron, renewal of the contact with beamline managers
Access to Elettra synchrotron
Usual benefits of collaboration between comparable teams with
complementary infrastructure:
- papers;
- scientific exchanges;
- manpower;
- valorisation issues (European patents, widening of end user panel);
- etc.
Conclusions:
High quality epitaxial PZT films → surface Pb(CO3)2, oxygen vacancies
Promising dielectric / ferroelectric properties of PZT and BTO
→ stable frequency dependence
First band structure measurements in PZT
Ultralow coercitivity Fe3Si
Room temperature ferromagnetism & tunable ferromagnetism in MnGe
3 papers: J. Mater. Sci., Phys. Status Solidi A, Phys. Rev. B
Thank you