Joint Workshop GDRi CNRS mecano and GDR CNRS

Transcription

Joint Workshop
GDRi CNRS mecano and GDR
CNRS OXYFUN
Quantifying and engineering
strain in metal oxides coupling with magnetic and
electrical properties
UC Louvain (Belgium), April 16
and 17, 2015
Chairs :
Catherine Dubourdieu, Jean-Pierre Raskin, Olivier Thomas
Website :
www.im2np.fr/GDRI_CNRS_Mecano/
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Program
Thursday April 16, 2015
12 :00
Lunch
13:30 -14:00
Introduction
14:00 - 14:40
Nava Setter, EPFL, Lausanne, Switzerland - Invited
Controlled patterns and properties of ferroelectric domain walls
14:40 - 15:10
Thomas Cornelius, IM2NP, Marseille, France
In situ X-ray diffraction studies on PZT thin films
15:10 -15:40
Thibaud Deneulin, CEMES, Toulouse, France
Structural characterization of piezoelectric materials by transmission electron microscopy
15:40 - 16:10
Sylvie Schamm-Chardon, CEMES, Toulouse, France
Strain at the nanoscale in epitaxial BaTiO3 films on silicon
16:10 - 16:40
Coffee Break
16:40 -17:20
Damien Faurie, LSPM, Villetaneuse, France - Invited
Strains in thin films on flexible substrates and associated effects on magnetic properties
17:20-17:50
Guillaume Agnus, IEF, Orsay, France
Strain analysis in manganites integrated on silicon
17:50-18:20
Joe Sakai, GREMAN, Tours, France
Strain effect on transport properties of pulsed laser deposited V2O3 thin films
18:45 - 20:15
Poster session
20:30
Dinner
Friday April 17, 2015
08:30 - 09:10
Gustau Catalan, ICREA and ICN2, Barcelona, Spain - Invited
Flexoelectricity and Strain Gradient Engineering in Oxides
09:10 - 09:40
Ingrid Cañero Infante, SPMS, Châtenay Malabry, France
Ultrafast photoinduced strain in ferroelectric BiFeO3 and its mechanisms
09:40 - 10:10
Umesh Kumar Bhaskar, IC2N, Barcelona, Spain
Flexoelectric MEMS on silicon
10:10 - 10:40
Coffee Break
10:40 - 11:20
Gustavo Ardila, IMEP-LAHC, Grenoble, France - Invited
Semiconductor piezoelectric nanowires for mechanical energy harvesters & sensors
11:20 -11:50
Jonathan Amodeo, MATEIS, Lyon, France
Small-scale simulations of MgO mechanical properties
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11:50 - 12:20
Conclusion – End of Workshop
12:30
Lunch
Joint Workshop GDRi CNRS MECANO and GDR CNRS OXYFUN – Louvain, April 2015
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Attendees
AGNUS Guillaume IEF / Université Paris-Sud Orsay France [email protected]
AMODEO Jonathan INSA-Lyon/MATEIS laboratory France Lyon France
[email protected]
ARDILA Gustavo IMEP-LaHC Grenoble France [email protected]
BHASKAR Umesh Kumar ICN2 Bellaterra España [email protected]
CATALAN Gustau ICREA and ICN2 Barcelona España [email protected]
CHALUVADI SANDEEP KUMAR GREYC- UMR 6072, CNRS-ENSICAEN CAEN FRANCE
[email protected]
CORNELIUS Thomas IM2NP (UMR 7334) CNRS Marseille France
[email protected]
DENNEULIN Thibaud CEMES CNRS Toulouse France [email protected]
DEVEL Michel FEMTO-ST Besançon FRANCE [email protected]
DEVOS Arnaud IEMN Lille France [email protected]
DUBOURDIEU Catherine Institut des Nanotechnology de Lyon - CNRS - ECL Ecully France
[email protected]
FANIEL Sébastien UCL/Winfab Louvain-la-Neuve Belgium [email protected]
FAURIE Damien LSPM-CNRS Villetaneuse France [email protected]
GARCIA-SANCHEZ Alexis LSPM - UPR 3407 du C.N.R.S. Villetaneuse France
[email protected]
GUEYE Mouhamadou LSPM-CNRS Villetaneuse France [email protected]
HIRSINGER Laurent Institut FEMTO-ST Besançon FRANCE [email protected]
INFANTE Ingrid C UMR8580 CNRS & CentraleSupélec, SPMS lab Chatenay Malabry France
[email protected]
LECOUTRE Gautier Institut FEMTO-ST Besancon France [email protected]
MECHIN Laurence GREYC Caen France [email protected]
MERCONE Silvana LSPM Villetaneuse France [email protected]
NEGULESCU Beatrice Univ. Rabelais / GREMAN Tours France [email protected]
PARDOEN Thomas UCL Louvain-la-Neuve Belgium [email protected]
PROOST Joris UC Louvain, Division of Materials and Process Engineering (IMAP) Louvainla-Neuve Belgium [email protected]
RASKIN Jean-Pierre UCL Louvain-la-Neuve Belgium [email protected]
SA Pedro Institute of Condensed Matter and Nanosciences (IMCN) Louvain la Neuve
Belgium [email protected]
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SAHOO TAPAS RANJAN POLITECNICO DI TORINO TORINO ITALY [email protected]
SAKAI Joe GREMAN, Univ. Tours Tours France [email protected]
SCHAMM-CHARDON Sylvie CEMES-CNRS Toulouse cedex4 France
[email protected]
SETTER Nava Ceramics Laboratory, EPFL Lausanne Switzerland [email protected]
THOMAS Olivier IM2NP Marseille France [email protected]
TUYAERTS Romain Université catholique de Louvain / Division of Materials and Process
Engineering Louvain-la-Neuve Belgium [email protected]
UREÑA Ferran ICTEAM Louvain-la-Neuve Belgium [email protected]
VAN OVERMEERE Quentin Université catholique de Louvain / iMMC Louvain-la-Neuve
Belgique [email protected]
VAYRETTE renaud UCL / IMMC / IMAP Louvain-la--Neuve Belgium
[email protected]
ZIGHEM Fatih Université Paris 13/ CNRS-LSPM Villetaneuse France [email protected]
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Setter Nava Ceramics Laboratory, EPFL Lausanne Switzerland [email protected] (invited lecture)
Controlled patterns and properties of ferroelectric domain walls
Ludwig Feigl a, Mahamudu Mtebwa a, Tomas Sluka a, Petr Yudin a, Petr Bednyakov a, Leo McGilly
a, Arnaud Crassous a, Xian-Kui Wei a,b, Alexander Kvasov a, Cosmin Sandu a, Igor Stolichnov a,
Alexander K Tagantsev a, Nava Setter a
a Ceramics Laboratory, EPFL Swiss Federal Institute of Technology, Lausanne 1015, Switzerland
b Ernst Ruska Center for Microscopy, Research, Jülich, Germany *email: [email protected]
Ferroelectric materials are heavily used in electro-mechanics and electronics. Interfaces called
domain-walls separate regions, domains, inside the ferroelectric, in which the spontaneous
polarization is differently oriented. The thickness of domain walls is typically 1-5 nm. Recent
improvements of electron microscopes and force microscopes allow the investigation of the internal
structure and properties of individual domain walls. Research worldwide, e.g. (1), revealed that
domain wall properties can differ from those of the domains themselves, leading to new, potentially
exploitable phenomena. This is attractive, particularly in light of the possibility to create, displace,
annihilate, and recreate domain walls by applied voltage. We are studying how to control domain wall
patterns and are exploring their properties. Among the obtained results are dense patterns of arrays
of domains having <10nm width (2), controlled movements of domain walls (3), domain walls with
quasi-2DG metallic conductivity inside the insulating matrix (4,5), and their controlled density (6) and
demonstrated reconfigurability (7). In addition, ferroelectric boundaries are evidenced experimentally
in centro-symmetric, non-ferroelectric materials (8) and elastic interaction between non-ferroelastic
domain walls is shown, theoretically, to exist (9), promising new dimensions in domain-wall control.
1. J. Seidel et al., Nat. Mater. 8, 229 (2009)
2. L. Feigl et al., Nat. Commun. 5, 4677(2014)
3. L. McGilly et al., Nat. Nanotech. 10, 145 (2015)
4. T. Sluka et al., Nat. Commun.4, 2389 (2013)
5. I. Stolichnov et al. (Sbumitted)
6. P. Bednyakov et al. (submitted)
7. A. Crassous et al. (submitted)
8. X.-K. Wei et al., Nat. Commun 5, 3031(2014)
9. K. Shapovalov et al. PRL113, 207601(2014).
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Cornelius Thomas IM2NP (UMR 7334) CNRS Marseille France [email protected]
In situ X-ray diffraction studies on PZT thin films
T.W. Cornelius (a), A. Davydok (a), C. Mocuta (b), E.B. Araujo (c), E.C. Lima (d), I.K. Bidikin (e), A.L.
Kholkin (e), O. Thomas (a)
(a) Aix-Marseille Université, CNRS, IM2NP (UMR 7334), Marseille, France
(b) DiffAbs beamline, Synchrotron SOLEIL, France
(c) Departamento de Fisica et Quimica, Universidade Estadual Paulista, Ilha Solteira, SP, Brazil
(d) Universidade Federal do Tocantins, Porto Nacional, TO, Brazil (e) Universidade de Aveiro,
Portugal
Within the last decade, the properties of ferroelectrics have been extensively studied. Several
important devices, such as Ferroelectric Random Access Memories (FeRAMs) and Dynamic Random
Access Memory (DRAM) are manufactured based on ferroelectric thin films [1, 2]. With the increasing
and continuous demand for portability in consumer electronics, the understanding of the effects of
miniaturization on the properties of ferroelectric thin films becomes increasingly important. Although
continuous improvements in conventional semiconductor designs are implemented, the basic physics
of the size effects is, however, poorly understood. It is well known that the crystallite size plays an
important role in tailoring ferroelectric properties. For studying the piezoelectric properties of
Pb(Zr0.5Ti0.5)O3 (PZT) thin films with a thickness of few hundred nanometers consisting of few tens
of nanometer sized grains, in situ X-ray diffraction has been performed at the DiffAbs beamline at
Synchrotron SOLEIL. For this purpose, gold electrodes of 0.3 mm in diameter were deposited on top
of the thin film. One electrode was contacted electrically and the diffraction signal from an area under
the electrode (beam size: 5 x 8 µm2) was monitored as a function of the applied electric field. Twotheta curves of the PZT110 and PZT100 Bragg reflections were extracted from the recorded XPAD
(X-ray hybrid pixel area detector) images showing a shift of the Bragg peaks to lower 2theta values for
an applied voltage of 9 V, i.e. a piezoelectric extension. The piezoelectric strain as a function of the
applied voltage revealed butterfly loops [3]. The asymmetry and the fact that the loops were not
closed most probably originate from a self-polarization of the thin film. These findings are supported
by asymmetries on the macroscale P-E hysteresis loops and local piezoresponse hysteresis loops,
which are a clear signature of a self-polarization effect in the studied PZT films.
[1] J.F. Scott and C.A. Araujo, Science 246, 1400 (1989). [2] J.F. Scott, Ferroelectric Memories
(Springer, Heidelberg, Germany, 2000). [3] M.C. Ehmke. J. Glaum, M. Hoffman, J.E. Blendell, K.J.
Bowman, J. Am. Ceram. Soc. 96, 2913 (2013).
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Denneulin Thibaud CEMES CNRS Toulouse France [email protected]
Structural characterization of
transmission electron microscopy
piezoelectric
materials
by
T. Denneulin (a), N. Wollschläger (b), W. Österle (b), C. Magén (c), and M.J. Hÿtch (a)
(a) CEMES CNRS, 29 rue Jeanne Marvig, 31055 Toulouse, France.
(b) BAM, Unter den Eichen 87, 12205 Berlin, Germany. (c) Transpyrenean Associated Laboratory for
Electron Microscopy (TALEM), CEMES-INA, CNRS-Universidad de Zaragoza, Spain.
Piezoelectric materials have a large number of applications in ferroelectric memories and
microelectronics devices [1]. In particular, piezoelectronic transistors are foreseen as a new
alternative to metal-oxide-semiconductor devices [2]. They exhibit high speed and low power
consumption thanks to the combination of a piezoelectric and a piezoresistive material. Consequently
there is a growing need for the characterization of piezoelectric thin films at the nanometer scale.
Here, we have investigated Pb(Zr,Ti)O3 (PZT) and (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) thin
films grown by epitaxy using transmission electron microscopy (TEM). We will mainly discuss strain
measurements performed by aberration-corrected high-resolution TEM and dark-field electron
holography [3] using the I2TEM-Toulouse microscope. Strain maps with a large field of view (up to
500nm) and nanometer resolution (3-6nm) were obtained after processing the images by geometrical
phase analysis (GPA) [4]. Samples of different structures, either tetragonal or rhombohedral, will be
discussed. In particular, we will describe strain and rotation gradients induced by the distribution of
needle-shaped 90° ferroelectric domains (a-domains) in tetragonal PZT. Nano-indentation tests were
carried out inside the microscope in order to evidence the movements of domain walls. As an
example we will show the extension of a partial 90° domain under compression of the film using a
small diamond probe. Finally we will show some polarization measurements in ferroelectric domains
using high-resolution scanning TEM (STEM) images.
Acknowledgments This work was funded
through the European Metrology Research Programme (EMRP) Project IND54 Nanostrain. The
EMRP is jointly funded by the EMRP participating countries within EURAMET and the European
Union. The authors acknowledge the European Union under the Seventh Framework Programme
under a contract for an Integrated Infrastructure Initiative Reference 312483-ESTEEM2.
[1]
[2]
[3]
[4]
M. Dawber et al., Rev. Mod. Phys. 77, 1083-1130 (2005)
D.M. Newns et al., Adv. Mater. 24, 3672-677 (2012)
M.J. Hÿtch et al., Nature 453, 1086-1089 (2008)
M.J. Hÿtch et al.,Ultramicroscopy 74, 13-146 (1998)
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Schamm-Chardon Sylvie CEMES-CNRS Toulouse cedex4 France [email protected]
Strain at the nanoscale in epitaxial BaTiO3 films on silicon
S. Schamm-Chardon (a, c), C. Magen (b, c), L. Mazet (d), R. Cours (a), R. Bachelet (d), G. SaintGirons (d), M. Hÿtch (a, c), and C. Dubourdieu (d)
(a) CEMES-CNRS, Université de Toulouse, 31055 Toulouse, France
(b) LMA-INA, Universidad de Zaragoza and Fundación ARAID, 50018 Zaragoza, Spain
(c) Transpyrenean Associated Laboratory for Electron Microscopy, CEMES –INA, CNRS -University
of Zaragoza, Spain
(d) INL, UMR CNRS 5270, Ecole Centrale de Lyon, 69134 Ecully, France
Integration of ferroelectrics on semiconductors would offer the opportunity to add novel functionalities
1,2
on chips (logic, memory, sensors…) . For such a purpose, molecular beam epitaxy provides unique
advantages to precisely construct the oxide/semiconductor interface, which plays a major role in
nanoelectronic devices. However, the direct epitaxy on silicon of an oxide such as BaTiO3 is
challenging due to the oxidation of the silicon surface and due to the large lattice mismatch and
thermal expansion mismatch between the oxide and the semiconductor. One solution is Interface
engineering using Sr- passivation and epitaxial growth of SrTiO3 templates on Si substrates. Then
subsequent epitaxial growth of a perovskite oxide like BaTiO3 can be explored. In this study, a
quantitative analysis of high-resolution transmission electron microscopy (HR(S)TEM) images using
3
the geometric phase analysis (GPA) is proposed in order to support the growth strategy of epitaxial
BaTiO3 films with the desired orientation, i.e. with the c-axis of the tetragonal structure perpendicular
to the Si substrate. With GPA, maps of the strain in the BaTiO3 films with respect to the Si substrate
are determined with a high precision (0.1%) at the nanometric scale (1-2nm). From these maps, the
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local lattice parameters and thus the tetragonality (c/a ratio) of the BaTiO3 films can be evidenced .
HRTEM work is performed on an image corrected Hitachi HF3300S microscope (I2TEM-Toulouse)
and HR(S)TEM on a FEI Titan Low-Base 60-300 (Zaragoza). Different process parameters like the
growth temperature, oxygen pressure and cooling conditions were explored to optimize the quality of
15-20 nm thick BaTiO3 films and to minimize the SiO2 interfacial layer regrowth between Si and the
SrTiO3 buffer.
1. J. Scott, Ferroelectric memories (Berlin: Springer), chapter 2 and 12 (2000)
2. S. Salahuddin et al., Nano Lett. 8(2), 405 (2008)
3. M.J. Hytch et al., Ultramicroscopy 74, 131 (1998)
4. C. Dubourdieu et al., Nature Nanotechnology 8, 748 (2013) This work has been supported by the
French National Research Agency under the reference No. ANR-10-EQPX-38-01. The authors
acknowledge the "Conseil Regional Midi-Pyrénées" and the European FEDER for financial support
within the CPER program.
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Faurie Damien LSPM-CNRS Villetaneuse France [email protected] (invited lecture)
Strains in thin films on flexible substrates and associated effects
on magnetic properties
Fatih Zighem (a), Damien Faurie (a), Mouhamadou Gueye (a), Silvana Mercone (a), Mohamed
Belmeguenai (a)
(a) LSPM-CNRS Villetaneuse France
Devices fabricated on a flexible substrates (polymers such as Kapton®, PET, PDMS, PVDF, ….)
have been widely studied because of their remarkable potential for new applications requiring nonplanar functional systems. During last years, several electronic devices, such as flexible organic solar
cells, light-emitting diodes , and transistors , have been realized on top of various polymeric
substrates and even on paper. Obviously, when a thin film is deposited on a flexible substrate, it is
usually submitted to mechanical stresses due to the curvature of the whole system. These stresses
may have an important effect on the static and dynamic magnetic properties, especially on the
resulting magnetic anisotropy. Indeed, the realization of functional, transparent, flexible, and
stretchable magnetic micro- and nano-structures could lead to the development of novel magnetic
materials for sensing and recording as well as magneto-optical and magneto-photonic devices, all
applications that have been highly successful with more traditional substrate technologies. In the
present work, the strain effects on magnetic thin films on Kapton® are experimentally studied by two
kinds of mechanical testing coupled with ferromagnetic resonance technique: tensile and bending.
Tensile tests (nearly uniaxial) are made using piezoelectric actuators while bending tests are made
thanks to curved aluminum blocks of different radii. First, we will show the development of a
methodology combining the microstrip ferromagnetic resonance technique and digital image
correlation in order to simultaneously measure applied strains and the magnetic resonance in thin
films. This methodology can be applied to system for which the strains are well transmitted at the
different interfaces (thin film adherent to a substrate, artificial magnetoelectric systems). Indeed, the
strain transmission is crucial and is demonstrated through elastic strains measurements. Second, the
effect of strains on magnetic anisotropy will be discussed and we will show how the effective
magnetostriction coefficient of the magnetic films can be simply estimated. Finally, we will give a few
perspectives in this field.
(1) M. Gueye, B.M. Wague, F. Zighem, M. Belmeguenai, M.S. Gabor, T. Petrisor Jr, C. Tiusan, S.
Mercone, D. Faurie. “Bending strain‐tunable magnetic anisotropy in Co2FeAl Heusler thin film on
Kapton®”, Applied Physics Letters 105 (6), 062409 (2014)
(2) M. Gueye, F. Zighem, D. Faurie, M. Belmeguenai, S. Mercone. “Optimization of indirect
magnetoelectric effect in (thin film/substrate/piezoelectric actuator) heterostructure using polymer
substrate”, Applied Physics Letters 105 (5), 052411 (2014)
(3) F. Zighem, M. Belmeguenai, D. Faurie, H. Haddadi, J. Moulin. “Combining ferromagnetic
resonator and digital image correlation to study the strain induced resonance tunability in
magnetoelectric heterostructures”. Review of Scientific Instruments 85 (10), 103905 (2014)
(4) F. Zighem, A. El Bahoui, J. Moulin, D. Faurie, M. Belmeguenai, S. Mercone, H. Haddadi.
“Microstrip ferromagnetic resonance study of strain‐induced anisotropy in amorphous FeCuNbSiB film
on flexible substrate” J. Appl. Phys. 116, 123903 (2014)
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Agnus Guillaume IEF / Université Paris-Sud Orsay France [email protected]
Strain analysis in manganites integrated on silicon
Le Bourdais, D. (a), Agnus, G. (a), Matzen, S. (a), Maroutian, T. (a), Largeau, L. (b), T. Lecoeur,
Ph. (a)
(a) Institut d’Electronique Fondamentale, Univ. Paris-Sud, CNRS UMR 8622, Orsay, France
(b) LPN-UPR20-CNRS, route de Nozay, 91460 Marcoussis, France
Functionnal oxides with perovskite ABO3 structure exhibit a broad range of physical properties
depending on the nature of the A and B atoms, and eventually dopant. Ferromagnetism,
ferroelectricity,, superconductivity are some examples of the properties of those alloys. The
characteristics of this class of material are closely related to their atomic structure, and then very
sensitive to strain. Examples can be found in the literature where modulation of thin films properties
can be obtained by growth on different substrate that lead to a fixed strained state. Other option
consists in the use of piezo-electric actuator to get the modulation on demand. Examples can be
found where magnetism/conductivity of manganites are tuned by means of those approaches.
However, only a few examples of strain-based devices can be found in the literature because (i) it
requires mastering the growth of all the required materials as thin films on substrate and (ii) it has to
face the clamping effect of the substrate. Actually, the response of the piezo-electric material is
intrinsically limitated by the elastic response of the substrate where it is epitaxialy grown, mainly
characterized by the substrate Young modulus. Freestanding devices based on MEMS are of
particular interest to avoid clamping. A few examples of MEMS fabricated using sacrifice layers on
STO substrate exist but mastering the growth of oxides on silicon allow to use all the mature
technologies developed for the micro-electronic industry and now also used for MEMS technology.
We used STO and YSZ buffer to epitaxialy grow manganites on silicon. We analyze by means of
optical profilometry the modification of the shape of the microstructures during the liberation process
to obtain a freestanding microdevices that allow us to extract the initial strain and the strain relief. We
characterize the device properties during the different steps of the process.
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Sakai Joe GREMAN, Univ. Tours Tours France [email protected]
Strain effect on transport properties of pulsed laser - deposited
V2O3 thin films
Joe Sakai (a) and Hiroshi Funakubo (b)
(a) GREMAN, UMR 7347 CNRS, Université François Rabelais de Tours, Parc de Grandmont 37200
Tours, France
(b) Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259
Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan
Corundum-structured vanadium sesquioxide, V2O3, being metallic under the standard condition,
demonstrates metal-insulator (MI) transition when the material is cooled or doped with another
element such as Cr. It has been reported that discontinuous lattice deformation occurs through MI
phase transition of V2O3.[1,2] Previous results on evolution of a- and c-axes lengths of V2O3 by Crdoping or pressure application lead one to assume that metallic / insulating nature of V2O3-based
materials is governed by their c/a ratio. In this work we prepared V2O3 thin films by a pulsed laser
deposition (PLD) method, and studied the relationship between lattice strain and transport properties
of these films.
VOx films were deposited on c- or r-plane of sapphire (Al2O3) substrates heated at 600˚C in the
ambient of 2 x 10-2 mbar of Ar gas. A KrF excimer laser beam with a frequency of 5 Hz was focused
on a V2O5 bulk target with fluence of 0.7 – 2.0 J/cm2. 1800 sec of deposition resulted in a film
thickness of ~ 80 nm in cases of 1.5 – 2.0 J/cm2. X-ray diffraction analysis confirmed that single
oriented V2O3 films were epitaxially grown on both c- and r-planes of sapphire substrates.
Depending on the laser fluence or thickness, we have obtained (0001)-oriented V2O3 films of various
c/a ratios ranging in 2.801 – 2.827 on c-plane Al2O3. Moreover, resistance – temperature (R-T)
measurements have revealed that V2O3 films of higher (lower) c/a ratio are accompanied by more
metallic (insulating) properties, as expected. It is noteworthy that films with steep MI transition on R-T
curves are obtained easier on r-plane sapphire substrates than on c-plane. We speculate that
clamping (1 -1 0 2) plane of V2O3 lattice imposes less restriction on its MI phase transition, which is
accompanied by expansion of a-axis and shrinkage of c-axis.
Thus the lattice strain, c/a, of PLD V2O3 thin films under the standard condition can be controlled to
smaller values than that of the bulk (2.828) by modifying the deposition conditions. The present
results suggest that selecting a proper substrate, a buffer layer or thickness of films may introduce
more strain onto pure V2O3 films as c/a ≤ 2.79, which we predict is accompanied by the insulating
nature.
[1] McWhan & Remeika, Phys. Rev. B 2 (1970) 3734.
[2] Rodolakis et al., Phys. Rev. B 84 (2011) 245113.
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Catalan Gustau ICREA and ICN2 Barcelona España [email protected] (invited lecture)
Flexoelectricity and Strain Gradient Engineering in Oxides
Gustau Catalan1,2, Jackeline Narvaez2, Kumara Cordero2, Umesh Bhaskar2, Amir Abdollahi2,3,
Marino Arroyo3, Irene Arias3
1 ICREA-Institucio Catalana de Recerca i Estudis Avançats, Barcelona, Spain
2 ICN2-Insitut Catala de Nanociencia i Nanotecnologia, Campus UAB, Bellaterra, Barcelona, Spain
3 LaCaN-Laboratori de Calcul Numeric, Universitat Politecnica de Catalunya (UPC), Barcelona, Spain
Flexoelectricity is the generation of polarization by strain gradients. It is a universal property of all
dielectrics irrespective of their symmetry, and it is therefore naturally most tempting to exploit it in
order to elicit polarization out of non-polar materials. On the other hand, the best flexoelectric
materials tend to be polar (ferroelectric) materials. Because flexoelectricity and piezoelectricity are not
mutually exclusive, they will coexist in these materials, and their coexistence can enhance their
performance or even enable new physical properties. Exploring and exploiting flexoelectricity,
however, requires careful consideration of a device’s shape and size. Shape, because asymmetric
deformations must be introduced in order to generate any flexoelectricity. And size, because strain
gradients –and thus also flexoelectric effects- grow in inverse proportion to device size, being biggest
at the nanoscale. The engineering of asymmetry at the nanoscale in order to exploit flexoelectricity
constitutes a new design paradigm that one might term “strain gradient engineering”. In this talk, I will
give a general overview of the field of flexoelectricity, with a focus on how strain gradient engineering
can be used to substitute or enhance piezoelectricity, or to generate new functionalities not possible
by piezoelectricity or homogeneous strain alone.
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Infante Ingrid C UMR8580 CNRS & CentraleSupélec, SPMS lab Chatenay Malabry France
[email protected]
Ultrafast photoinduced strain in ferroelectric BiFeO3 and its
mechanisms
M. Lejman (a), G. Vaudel (a), I. C. Infante (b), P. Gemeiner (b), V. Gusev (c), B. Dkhil (b), P. Ruello
(a)
(a) Institut des Molécules et Matériaux du Mans UMR6283 CNRS-Université du Maine, Le Mans,
France,
(b) SPMS lab. UMR8580 CNRS-CentraleSupélec, Chatenay Malabry, France,
(c) Laboratoire d’Acoustique de l’Université du Maine UMR6613 CNRS-Université du Maine, Le
Mans, France
Generation of strain using light is a key issue for future development of GHz-THz ultrasonic devices.
Up to now, photo-induced GHz-THz acoustic phonons have been mainly explored in metals and
semiconductors as well as in artificial nanostructures. However, despite their inherent strong
polarization (providing natural asymmetry) and superior piezoelectric properties, ferroelectric oxides
have been regarded only recently [1-4]. Here by using ultrafast pump-probe optical measurements,
we report that photo-generation/photo-detection of small band-gap BiFeO3 ferroelectric leads, at
room temperature, to spectacular larger GHz coherent shear acoustic wave signal (TA mode) than
that coming from longitudinal mode (LA mode) [5]. The detailed analysis of the data indicates that the
major mechanism involved corresponds to screening of the internal electric fields in BFO by lightinduced separation of charges, which in turn induces stress by indirect piezoelectric effect. We also
show that the ordinary to extraordinary (and vice-versa) optical mode conversion through photoelastic
interactions is efficient in BFO compared to classical anisotropic media like CaCO3 [6]. All these
scattering mechanisms at the picosecond time scale will be described and discussed in details and
we hope it will push the ferroelectric oxides community to further consider the strategy to induce strain
using light to tune the ferroic properties.
[1] P. Ruello, T. Pezeril, S. Avanesyan, G. Vaudel, V. Gusev, I. C. Infante, and B. Dkhil, Appl. Phys.
Lett. 100, 212906 (2012)
[2] L. Y. Chen, J. C. Yang, C. W. Luo, C. W. Laing, K. H. Wu, J.-Y. Lin, T. M. Uen, J. Y. Juang, Y. H.
Chu, and T. Kobayashi, Appl. Phys. Lett. 101, 041902 (2012)
[3] Z. Jin, Y. Xu, Z. Zhang, X. Lin, G. Ma, Z. Cheng, and X. Wang, Appl. Phys. Lett., 101, 242902
(2012)
[4] H. Wen, P. Chen, M. P. Cosgri, D. A. Walko, J. H. Lee, C. Adamo, R. D. Schaller, J. F. Ihlefeld, E.
M. Dufresne, D. G. Schlom, P. G. Evans, J. W. Freeland, and Y. Li, Phys. Rev. Lett. 110, 037601
(2013)
[5] M. Lejman, G. Vaudel, I. C. Infante, P. Gemeiner, V. E. Gusev, B. Dkhil, and P. Ruello, Nature
Comm. 5, 4301 (2014)
[6] M. Lejman et al., to be published
14
Bhaskar Umesh Kumar ICN2 Bellaterra España [email protected]
Flexoelectric MEMS on silicon
U.K.Bhaskar1*, Nirupam Banerjee2, Amir Abdollahi1, Guus Rijnders2, and G.C. Catalan1
1 ICN2 – Institut Catala de Nanociencia i Nanotecnologia, Campus UAB, 08193 Bellaterra
(Barcelona), Spain Street, City, State, Postal Code
2 Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente,
P.O. Box 217, 7500 AE Enschede, The Netherlands
Flexoelectricity 1 can be conceived as a non-local piezoelectric effect 2, wherein the magnitude of the
dielectric polarization generated under an external force is insensitive to the absolute magnitude of
deformation (𝜖), but is determined rather by the non-uniformity of the applied deformation (∂ϵ/∂x).
Flexoelectricity, when compared to piezoelectricity, is a weak effect of little practical significance in
bulk materials. However, the roles can be reversed at the nanoscale and in this paper we present
experimental results to stake the claim of flexoelectricity as a route to lead-free piezoelectric MEMS
applications. We report here on flexoelectricity-based electromechanical performance observed in
non-piezoelectric cantilevers, fabricated from epitaxial (100) STO thin films grown on Si substrates.
These results establish a paradigm in microelectromechanical systems (MEMS) whereby the
functionality of bimorph piezoelectric cantilevers can be replicated with single-layer centrosymmetric
dielectric materials.
15
Ardila Gustavo IMEP-LaHC Grenoble France [email protected] (invited lecture)
Semiconductor piezoelectric nanowires for mechanical energy
harvesters and sensors
G. Ardila, T. Rao, R. Hinchet, L. Montès, M. Mouis IMEP-LaHC, MINATEC, 3 rue Parvis Louis Neel,
38016 Grenoble, France
Piezoelectric thin films have been widely used in applications ranging from micro and nano actuators
to resonators [1] Other applications include mechanical sensors and energy harvesters used typically
for Wireless Sensors Networks (WSN), with the objective to monitor human health, environment or
structures such as airplanes or buildings [2]. The most used materials in these applications are PZT
and AlN thin films [1]. At the nanoscale, the most studied materials are ZnO and GaN nanowires (NW)
because they are relatively easy to fabricate and because of their electromechanical properties:
higher flexibility and higher piezoelectric coefficients compared to their thin film counterparts [3]. In
this presentation, our main activities on semiconductor piezoelectric nanowires will be presented,
ranging from individual NW characterizations using near-field techniques [4, 5], multiphysics modeling
[6, 7] and the fabrication of proof of concept devices [8]. The advantages of these nano structures will
be discussed when used in two example applications: mechanical energy harvesters and mechanical
sensors. For instance composite materials can be fabricated integrating vertically grown NWs into an
insulating matrix theoretically presenting better performances compared to piezoelectric thin films [6,
7]. This can be observed as an increase in the produced voltage or electrical energy (or power) when
used in mechanical energy harvesters or the increase on the sensibility when used in mechanical
sensors for a given mechanical input.
[1] C-B. Eom and S. Trolier-McKinstry, MRS bull. 37 1007 (2012)
[2] W. J. Choi et al., J. Electroceram. 17 543 (2006)
[3] H.D. Espinosa et al., Adv. Mater. 24 4656 (2012)
[4] X. Xu et al., Nanotechnology, 22(10), 105704. (2011)
[5] Y. Zhou et al., Adv. Mat., 25(6), 883 (2013)
[6] R. Hinchet et al., Adv. Func. Mat., 24(7), 971 (2014)
[7] R. Tao et al., Nano Energy, (2014) http://dx.doi.org/10.1016/j.nanoen.2014.11.035.
[8] S. Lee et al., Adv. Func. Mat., 24(8), 1163-1168 (2014).
16
Amodeo Jonathan INSA-Lyon/MATEIS laboratory France Lyon France [email protected]
Small-scale simulations of MgO mechanical properties
Jonathan Amodeo (a), Inas Issa (a,b), Karine Masenelli-Varlot (a), Julien Morthomas (a), Michel
Perez (a), Jérome Chevalier (a)
(a) Laboratoire MATEIS, INSA-Lyon, Villeurbanne, France
(b) Laboratoire LAMCOS, INSA-Lyon, Villeurbanne, France
Nanometer-sized structures such as nanopillars, nanowires, nanoparticles and thin films have
attracted substantial interest due to their special mechanical behaviour: they generally show an
increased yield strength compared with the bulk material as well as a size-dependent elastic
response. While these size effects have been widely studied in face centered cubic metals, few
studies, especially on semi-conductors and metallic alloys, show they could have a broader
scope.Indeed, the way ceramic particles behave at the nanometer scale has recently gained more
interest, especially in the field of modern surgery where metallic alloys used for implants and
prosthesis are progressively replaced by bio-compatible ceramics to increase their lifetime and reduce
ion release presumed to be responsible for inflammatory reactions. Based on this framework, we will
present here an investigation of the mechanical behaviour of ionic MgO nanoparticles using statics
and molecular dynamics simulations. MgO has been widely studied in the past decades for its
mechanical properties under compression at the macroscopic scale (e.g., elastic properties, slip
systems, dislocation characterization and flow behaviour). Using numerical nano-mechanical tests at
300 K , here we show that MgO nanoparticles deform under high stress and up to large deformation
without any sign of damage compared to what is observed in bulk experiments and mesoscopic
discrete dislocation dynamics simulations. Deformation proceeds by ½<110>{110} dislocation
nucleation and multiplication. Results are discussed in terms of stacking fault energies and interpreted
within the framework of small-scale plasticity. Finally, these findings enable the interpretation of recent
in situ TEM compression tests performed on MgO <100>-oriented nanocubes at scale of about
100nm.
17
 Poster communications
CHALUVADI SANDEEP KUMAR GREYC- UMR 6072, CNRS-ENSICAEN, Caen , France
Substrate strain induced effects in La0.7Sr0.3MnO3 thin films
GARCIA-SANCHEZ Alexis LSPM-CNRS Villetaneuse France
Local study of mechanical and physical properties in oxide nanostructures by using Scanning Probe Microscopy under
strain/magnetic and/or electric fields.
GUEYE Mouhamadou LSPM-CNRS Villetaneuse France
Effective 90-degree switching of magnetization in strained Co2FeAl thin film probed byferromagnetic resonance.
LECOUTRE Gautier Institut FEMTO-ST Besancon France
Preliminary steps towards computation of carbon nanotubes flexoelectric tensor by atomistic simulation
MERCONE Silvana LSPM Villetaneuse France
Magnetic domain-wall motion in thin films with perpendicular anisotropy: a magnetic force microscopy study of the magnetoelasto-electric coupling
SA Pedro Institute of Condensed Matter and Nanosciences (IMCN) Louvain la Neuve Belgium
Hybrid Magnetoelectric Nanocomposites
SAHOO TAPAS RANJAN POLITECNICO DI TORINO TORINO ITALY
Co/ZrO2 and Fe/ZrO2: Structural and Magnetic studies
TUYAERTS Romain Université catholique de Louvain / Division of Materials and Process Engineering Louvain-la-Neuve
Belgium
Strain engineering of oxides thin films
VAN OVERMEERE Quentin Université catholique de Louvain / iMMC Louvain-la-Neuve Belgique
Ultrathin oxide films in electrochemical energy conversion devices: controlling the internal stress for improved reliability and
performance
Chaluvadi Sandeep Kumar Groupe de Recherche en Informatique, Image, Automatique et
Instrumentation de Caen, (GREYC- UMR 6072), CNRS-ENSICAEN CAEN France [email protected]
 POSTER COMMUNICATIONS
18
Substrate strain induced effects in La0.7Sr0.3MnO3 thin films
S.K.Chaluvadi, M.Rioult, C.Jorel, L.Méchin
Groupe de Recherche en Informatique, Image, Automatique et Instrumentation de Caen, (GREYCUMR 6072), CNRS-ENSICAEN-Universite de Caen Basse-Normandie, 6 boulevard Marechal Juin,
14050 Caen Cedex, France.
La0.7Sr0.3MnO3 (LSMO) belongs to the manganite family and shows a perovskite structure. It has
got attention due to its properties like colossal magnetoresistance (CMR), room temperature
ferromagnetism and metallic state that can be useful in many applications. The properties of
manganite materials are very sensitive to external parameters such as strain1, crystalline quality and
oxygen stoichiometry. Here, we deposited LSMO thin films by Pulsed Laser Deposition (PLD) on
different lattice mismatched single crystal substrates inducing in-plane compressive strain on LaAlO3
(001), nearly matched on La0.3Sr0.7Al0.65Ta0.35O3 (001) and NdGaO3 (110), or in-plane tensile
strain on SrTiO3 (001), MgO (001), and SrTiO3 buffered MgO (001). The out-of-plane X-Ray
Diffraction (XRD) studies were performed on the samples to measure the strain induced in the thin
films by the different substrates. All LSMO films were (001) oriented, and showed different values of
the FWHM of the rocking curve around (002) LSMO peak in the 0.08°-1.3° range. The film
morphology was studied by Atomic Force Microscopy. Electrical and magnetic transport properties
will be presented. Substrate induced epitaxial strain in LSMO thin films have significant effects on
metal-insulator transition temperature (Tp) and magnetic anisotropy. Depending upon the biaxial inplane strain in films, the transition temperature could be either lower or higher. As the strain in thin
film increases, we have observed the Tp tend to decrease from > 420K on nearly matched substrates
to 310K with highly strained films.
19
Garcia-Sanchez Alexis Laboratoire des Sciences des Procédés et Matériaux (LSPM) - UPR 3407 du
C.N.R.S. Villetaneuse France [email protected]
Local study of mechanical and physical properties in oxide
nanostructures by using Scanning Probe Microscopy under
strain/magnetic and/or electric fields.
Garcia-Sanchez Alexis
Université Paris 13, Sorbonne Paris Cité, LSPM (UPR 3407) CNRS, 99 Avenue J.-B. Clément, 93430
Villetaneuse, France
In the last two decades, scanning probe microscopy (SPM) became a very interesting tool for
studying surface structural, electronic and mechanical properties at a nanometer and atomic scale in
a large variety of materials. Oxide surfaces offer a rich combination of structures and surface physical
phenomena that are exploitable for a wide range of applications. Here we present several examples
of local studies that have been realized by SPM (i.e. AFM, MFM and PFM) in order to characterize the
local control of these physical interesting phenomena. 1) Using a nanometric tip at the edge of a
flexible cantilever in AFM, we determined useful surface parameters that can be critical for the optic
applications of nanostructured ZnO thin films. 2) In situ dynamic observations of mechanical
properties have been performed under a local deformation applied by an in situ stress micro-machine.
The dislocations behavior has been followed and locally imaged in bulk composite. 3) We
successfully locally control the polarization of a piezoelectric thin film PZT and a micro-structured
BaTiO3 piezoelectric ceramics by applying a local voltage with a conductive-coated tip (PFM). The
local polarization is then read using an electro-mechanical coupling between the tip and the sample
surface. Quantitate property like the perpendicular piezoelectric coefficient (d33) is thus accessible by
PFM in the low frequency range (u<100 KHz). 4) Using a magnetic tip near the surface that interacts
with the magnetic stray field coming from the sample, a magnetic domains map is also shown (MFM).
The evolution of this map under local strain/voltage and magnetic field applied is also locally imaged.
The in situ experimental developments of our SPM under local controlled in-plane strain induced by
an electric field and/or a stress machine simultaneously to the application of an in-plane magnetic
field, is widely presented in order to open discussions and encourage collaborations.
20
Gueye Mouhamadou LSPM-CNRS Villetanuese France [email protected]
Effective 90-degree switching of magnetization
in
Co2FeAl thin film probed by ferromagnetic resonance.
strained
M. Gueye1, F. Zighem1, M. Belmeguenai1, M. S. Gabor2, C. Tuisan2, H. Haddadi3 and D. Faurie1
1 LSPM, CNRS-Université Paris 13-Sorbonne Paris Cité, Villetaneuse, France
2 Center for Superconductivity, Spintronics and Surface Science, Technical University of ClujNapoca, Cluj-Napoca, Romania
3 Laboratoire MSMP – Carnot Arts, ENSAM ParisTech, Châlons-en-Champagne, France
In recent decades, an unrestrained race has launched on the conquest of multiferroic materials.
Multiferroic heterostructures based on a stacking of ferroelectric (FE) and ferromagnetic (FM) media
offer an electric control of magnetism via the magnetoelectric coupling (ME) and are promising for
spintronic applications. We have studied the electric control of the magnetic properties in a strainmediated magnetoelectric system composed of a 25 nm Co2FeAl magnetostrictive thin film glued
onto a lead zirconate titane (PZT) actuator. For this purpose, ferromagnetic resonance (FMR) has
been employed in sweeping-field and sweeping-frequency regimes. From the sweeping-field FMR
experiments, we observe an increase of the voltage-induced anisotropy field from 30 Oe to around
360 Oe when applying electric field inside the PZT actuator. A positive shift of the FMR spectra with
the applied voltage is observed which is consistent with a positive magnetostriction coefficient at
saturation (~17ppm) of the Co2FeAl. The sweeping-frequency FMR experiments allows to directly
probe the magnetization direction as function of the applied voltage since the FMR-intensity spectra is
related to the angle in between the magnetization direction and the voltage-induced anisotropy field.
This approach is used to demonstrate a 90-degree switching of the magnetization direction.
21
Lecoutre Gautier Institut FEMTO-ST Besancon France [email protected]
Preliminary steps towards computation of carbon nanotubes
flexoelectric tensor by atomistic simulation
Gautier Lecoutre, Michel Devel, Naoum Daher, Laurent Hirsinger,
Institut FEMTO-ST 15B avenue des Montboucons, 25030 Besançon Cedex
Najib
Kacem
In this preliminary work, we elaborate on a previous work using atomistic simulations to study the
mechanical response of a Single Wall Carbon Nanotube (SWCNT) to an external electric field [1], [2].
Our goal is to compute the flexoelectric tensor of nanosystems by imposing a possibly
inhomogeneous external electric field and recording the deformation, complementary to a more
common method that imposes the deformation and computes the resulting polarization (see e.g.
[3],[4]). The flexoelectric coefficient will then be studied as a function of the characteristics of the
nanosystem in order to optimize it. In our atomistic simulations, a cantilevered clamped-free
semiconducting SWCNT deforms under the action of an external oblique field. We record this
deformation and the torques on rings of atoms from the torques on the self-consistent dipoles
associated to these atoms. Then, we calculate the deformation from the torques by the Finite Element
Method (FEM) and compare our results with those given by the atomistic simulation. We first checked
that the nanotube verifies all Bernoulli hypotheses for a beam and used them to simplify the equations
obtained by taking into account the polarization and deformation gradients. Our next work aims at
constructing a theory using the principle of virtual power, adapted to semi-conductors which would
allow us to extract the flexoelectric coefficients and take into account dissipation and surface effects
[5].
[1] “Electrostatic deflections of cantilevered semiconducting single-walled carbon nanotubes”, Z.
Wang, M. Devel, R. Langlet, B. Dulmet, Phys. Rev. B, 75, 205414 (2007)
[2] “Electrostatic deﬂections of cantilevered metallic carbon nanotubes via charge-dipole model”, Z.
Wang, M. Devel, Phys. Rev. B, 76, 195434 (2007)
[3] “Electronic flexoelectricity in low-dimensional systems“, S. V. Kalinin and V. Meunier, Phys. Rev.
B, 77, 033403 (2008)
[4] “First-principles theory and calculation of flexoelectricity”, J. Hong and D. Vanderbilt, Phys. Rev.
B, 88, 174107 (2013)
[5] “DEFORMABLE SEMICONDUCTORS WITH INTERFACES - BASIC CONTINUUM EQUATIONS”,
N. Daher and G. A. Maugin, Int. J. Eng. Science, 25, 1093-1129 (1987)
22
Mercone Silvana LSPM Villetaneuse France [email protected]
Magnetic domain-wall motion in thin films with perpendicular
anisotropy: a magnetic force microscopy study of the magnetoelasto-electric coupling
C. Ibrhaim(a), A. Garcia-Sanchez (a), N. Thi Lan (a), J. Moulin (b), D. Faurie (a), F. Zighem (a), M.
Belmeguenai (a) and S. Mercone(a)
(a) LSPM, CNRS UPR 3407, Université Paris 13, Sorbonne Paris Cité, 99 Av. J.-B. Clément 93430
Villetaneuse, France
(b) IEF Institut d'Electronique Fondamentale, UMR 8622 Université Paris Sud / CNRS, Orsay, France
Artificial multiferroïc (MF) materials have attracted a great attention due to their potential applications
in new smart nanotechnology. Coupling between ferroelectric (FE) phase and ferromagnetic (FM) one
via elastic strains can provide additional degrees of freedom to control the polarization
or
magnetization by a magnetic field or an electric field . Using, in this artificial MF media, FM thin film
with perpendicular magnetic anisotropy can provide the possibility of perpendicular magnetic
recording. They can be also an option for domain walls based device in logic applications and data
storage. The feasibility of these devices depends on the DWs response to a magnetic and/or electric
fields and thus on the efficiency of the magneto-elasto-electric coupling between the two previous
orders (FE (piezoelectric) and FM (magnetostrictive)) at room temperature. A laminate artificial
hetero-structure, based on multi-layered system (FM thin film/flexible substrate/piezoelectric actuator),
has been studied in order to determine the influence of an applied in-plane elastic strain/voltage on
the magnetic properties. The in-plane strain is induced via the application of a voltage in a
piezoelectric actuator on the top of which the film/flexible substrate system is glued. The local static
study under the electric field/voltage application performed by MFM has been compared to the
magnetic DWs behavior under the application of an in-plane magnetic field and discussed in terms of
magneto-electric coupling control of the magnetic perpendicular anisotropy.
23
SA Pedro Institute of Condensed Matter and Nanosciences (IMCN) Louvain la Neuve Belgium
[email protected]
Hybrid Magnetoelectric Nanocomposites
Pedro Sá (a), Alain Jonas (a), Luc Piraux (a)
(a) Institute of Condensed Matter and Nanosciences (IMCN), Place Croix du Sud, 1 bte L7.04.01;
Bât. Boltzmann (a1) B-1348 Louvain-la-Neuve Belgium
The development of a simple but controlled preparation method of multiferroic materials in which
ferroelectricity and ferromagnetism coexist at room temperature would be a technological and
scientific milestone. Produce and characterize hybrid (organic/inorganic) structures with optimized
coupling interfaces is one alternative to provide such magnetoelectric coupling. The challenge here is
to couple efficiently the ferromagnetic properties of inorganic nanostructures with the ferroelectric
properties of organic polymers. The design of these materials consists of organic-inorganic thin films
built from ferromagnetic vertically-aligned nanowires (NWs) inside an organic ferroelectric matrix. To
do that, we combined piezo- and ferro-electric poly(vinylidene fluoride) (PVDF) or poly(vinylidene
fluoride-ran-trifluoroethylene) random copolymer (P(VDF-TrFE)) and ferromagnetic CoFe2O4
nanowires. In this context CoFe2O4 nanowires arrays were fabricated by electrodeposition of Fe2+
and Co2+ into supported anodic aluminum oxide (AAO) templates and further oxidization. Vertically
aligned Nws were obtained on top a solid substrate. The effect of heating treatment on the oxidation
of CoFe2 nanowire arrays was investigated. The M(H) curves and the magnetic properties of the
ferromagnetic nanowires (coercive field, saturation magnetization, saturation field) was investigated
using an Alternating Gradient Magnetometer (AGM). Finally, first attempts were made to cover the
nanowires with a layer of P(VDF-TrFE). Different strategies are currently developed for embedding
the array of magnetic nanowires.
24
Sahoo Tapas Ranjan Politecnico Di Torino Torino Italy [email protected]
Co/ZrO2 and Fe/ZrO2: Structural and Magnetic studies
Tapas Ranjan Sahoo (a,b,*), Marco Armandi (b), Barbara Bonelli (b)
(a) Chemistry Department, School of Applied Sciences, KIIT University, Bhubaneswar-751024,
Odisha, India
(b) Applied Science and Technology Department, Politecnico di Torino, Corso Duca degli Abruzzi,
10129 Turin, Italy
The important features of the present work relates to the uniqueness of our synthetic approach
followed by some concrete microscopic (SAED & TEM), magnetic and spectroscopic (Mössbauer)
evidences. We highlight the essential features underlying our investigation.
Synthetic approach: The non-conventional technique like microwave-assisted combustion method
has been employed to realize this high temperature cubic phase of ZrO2. The major advantages of
this method are: Low processing time, Uniform heating and Better product quality with less impurity.
Microwave combustion method is a high temperature fast quenching route. As a result of which, cubic
phase of ZrO2 can be realized as a metastable phase despite its high temperature stability
(>23700C).
Magnetism: The foremost data on the parent ZrO2 sample forms the basis of our interpretation.
Parent ZrO2 shows a diamagnetic signal and for Co substituted ZrO2 samples, two linear behavior
exists in the composition range of 0 to 40% of ferromagnetic dopants. There is a distinct linearity for
compositions from 0 up to 10% doping and the other linearity exists from 10 to 40% of saturation
magnetization as a function of doping concentration. This provides scope to conclude that substitution
induced ferromagnetism might be possible only in the lean compositions, say up to 10% of dopants.
Beyond which clustering of metallic particles severely influence the saturation magnetization. This is
highlighted in the magnetic phase diagram. Further, for Fe/ZrO2 systems, the M vs. H plots at room
temperature show typical hysteresis loops indicating that, they are room temperature ferromagnetic.
And the magnetic behavior shows an increase in moment, with an increase in Fe concentration.
Microscopy: Microscopic techniques give clue to such substitutional phase. (a) For sample
concentration < 10% Co, in selected area diffraction (SAED) pattern only ZrO2 phase is observed,
suggesting that doping of metal ion is achieved. (b) For sample > 40% of Co, impurity phase such as
CoO phase is observed along with the cubic ZrO2 phase. (c) For samples of 50% of Co/ZrO2, clear
CoO grains are observed as impurity phases in TEM micrograph. Spectroscopy: Fe-doped ZrO2
samples were synthesized to probe the local magnetic environment prevailing around the Fe sites,
employing Mössbauer spectroscopy. (a) The spectrum of 3% Fe sample shows a characteristic
doublet, confirming the ferromagnetism originating from Fe occupying Zr sites. (b) The presence of
additional sextet signal in 6% Fe spectra is due to the existence of interacting Fe3+ ions, as a result
of the evolution of Fe3O4, as an impurity phase. (c) The 9% Fe-doped sample shows well resolved
sextets corresponding to the Fe3O4 phase in the sample.
25
Tuyaerts Romain Université catholique de Louvain / Division of Materials and Process Engineering
Louvain-la-Neuve Belgium [email protected]
Strain engineering of oxides thin films
R. Tuyaerts (a), J.-P. Raskin (b) and J. Proost (a)
(a) Division of Materials and Process Engineering , Université Catholique de Louvain, 1348, Louvainla-Neuve, Belgium
(b) Institute of Information and Communication Technologies, Electronics and Applied Mathematics,
Université Catholique de Louvain, 1348, Louvain-la-Neuve, Belgium
When a material is strained its unit cells are deformed which may influence in turn a number of
functional properties. This effect is often significant at large deformations and can be used to improve
the properties of a material if the deformations are sufficient. A limiting factor for the application of
large strains on thin films is often the fracture of the substrate. The lab-on-chip technique allows
performing uniaxial tensile tests on free-standing thin films, from zero strain up to the fracture strain.
Another possibility to apply strain to a thin film is to tune the deposition parameters. This technique
allows having a large range of strain, in tension as well as in compression, but changes not only the
strain but the microstructure too, making interpretation of the results less straightforward. This strain
engineering is possible on many materials since in general, all properties will change when the unit
cell is varied. Two different materials were used to study this strain engineering: zinc oxide (ZnO) and
vanadium dioxide (VO2). There is growing experimental evidence that in the case of ZnO thin films,
this strain-effect can be significant on properties such as resistivity, electronic mobility, or transition
energies of excitons [1]. Moreover there are theoretical predictions that confirm the strong effect of
strain on the ZnO electronic band structure, and therefore also on its dielectric function and bandgap
[2]. Recently, it has also been shown by ab initio calculations that non-linearities in the piezoelectric
coefficients are non-negligible and should be taken into account at large deformations [3]. If these
non-linearities can be experimentally confirmed, this could lead to interesting novel applications, like a
decrease in Schottky barrier in contact with transparent electrodes. By in-situ measurements of the
stress during deposition we were also able to investigate the growth process and to correlate the
growth-induced stress with the observed functional properties of the ZnO thin films. For instance, by
changing the temperature from 25°C to 250°C, the stress in the film could be changed from 200 MPa
in tension to 400 MPa in compression. At the same time, the measured band gap decreased from
3.32 to 3.24 eV. Vanadium dioxide (VO2) is interesting because of its phase transition between an
insulating state at room temperature and a metallic state above 67°C. This phase transition goes
along with a lot of variations: from monoclinic to rutile structure, a decrease of resistivity of three to
five orders of magnitude and a drop in the transmission of infra-red are examples. This could be used
in various applications such as MEMS actuators, RF switches, or optical switches. The transition can
be activated with a change of temperature, but with charge injection and application of a strain as
well. The lab-on-chip technique is thus especially handy to characterize the influence of a tensile
stress on the transition temperature.
[1] T. Gosh, et al., Mater. Res. Bull. 46, 1039 (2011).
[2] Y. Q. Gai, et al., Phys. Lett. A. 372, 72 (2007).
[3] S. Gravier, et al., Nano Energy. 2, 1214 (2013).
26
Van Overmeere Quentin Université catholique de Louvain / iMMC Louvain-la-Neuve Belgique
[email protected]
Ultrathin oxide films in electrochemical energy conversion devices:
controlling the internal stress for improved reliability and
performance
Q. Van Overmeere (a), R. Castadot (a), J. Proost (a), S. Ramanathan (b)
(a) Institute of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, B-1348
Louvain-la-Neuve, Belgium
(b) School of Engineering and Applied Sciences, Harvard University, Cambridge MA 02138, USA
Various electrochemical energy conversion devices could benefit from decreasing the thickness of
their constituting parts. We focus here on solid oxide fuel cells (SOFCs) and solar water splitting cells.
In the case of SOFCs, decreasing the electrolyte thickness to ~100 nm allows to decrease the
operating temperature. In the case of solar water splitting, using ultrathin films (<10 nm) for
electrocatalysts and passivation layers allows to decrease losses associated with light absorbtion and
transport of charges through the device. An increase of the internal stress in the GPa range can be
expected for such ultrathin films, and could affect the performance as well. We study the effect of
internal stress in yttria-stabilized zirconia thin film electrolytes on the reliability of SOFCs. Varying the
synthesis conditions modified the internal stress from –1400 (compression) to +100 MPa (tension).
The open circuit potential of the cells, an indication of their reliability, varies with the internal stress
and is higher for moderate compressive stress. The effect of internal stress in ultrathin passivating
oxide layers on the performance of photoanodes for solar water splitting is also explored. The oxide
prevents the degradation of the photovoltaic material by oxidation. The microstructure of the oxide
thin film, associated with variations of its internal stress, affects the losses associated with charge
transfer between the photovoltaic and the electrocatalyst layer.
27

Joint Workshop GDRi CNRS mecano and GDR CNRS

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