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Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P318
Strain & domain formation in thin films of PbTiO3
A. Vlooswijk 1 , A. Janssens 2 , G. Rispens 1 , G. Catalan 1 , O. Seeck 3 , G.
Rijnders 2 , D.H.A. Blank 2 , B. Noheda 1
1 Materials Science Center, University of Groningen, Nijenborgh 4, 9747 AG Groningen,
The Netherlands – 2 Mesa+ Institute for Nanotechnology, University of Twente, P.O.
box 217, 7500 AE Enschede, The Netherlands – 3 HASYLAB- DESY, Notkestr. 85,
D-22603 Hamburg, Germany
PbTiO3 is a classical ferroelectric perovskite. In bulk form, it distorts tetragonally
with ct > at below TC = 490 ◦ C and the ferroelectric polarization lies along the [001]
direction. In thin film form, the polarization is preferred along the surface normal to
facilitate the switching geometry, so substrates, such are SrTiO3, are commonly chosen
with lattice parameters close to at. Grazing Incidence Diffraction (GID) performed
at the DORIS W1 beamline (HASYLAB) on thin layers of ferroelectric PbTiO3 has
revealed that, on a well-chosen substrate with tensile misfit values, and for sufficiently
thin (fully-strained) films, the polarization can tilt from the surface normal[1] without
reaching the in-plane orientation. This is not only of fundamental interest since it has
been predicted that this lowering of symmetry can improve functional properties like
the piezoelectric and dielectric responses of the films[2].
The underlying substrate and the film thickness are the main parameters to control
the strain state and orientation of an epitaxial thin film [3-5]. These effects can be
used to tune and improve the physical properties of the film. Due to the presence of a
high-symmetry phase at the growth temperatures, films of ferroelectric perovskites can
release strain in the ferroelectric phase by forming periodic 90 ◦ domain patterns (with
alternating in-plane and out-of-plane polarizations)[5]. Although this mechanism is
known, a detailed characterization is still missing, in particular for weak tensile strain.
Here we investigate the strain tunability and strain relaxation of thin films of ferroelectric
PbTiO3 on different substrates and with different thickness. The films have been
prepared using RHEED-assisted PLD (Reflection High-Energy Electron Diffraction assisted
Pulsed Laser Deposition). The structural properties of the PbTiO3 films have
been studied by x-ray diffraction. Reciprocal space maps have been measured around
several main reflections, both in reflection and GID geometry at a lab diffractometer
and at the DORIS W1 beamline at HASYLAB. Dielectric and Piezoelectric Force Microscopy
(PFM) measurements have also been performed. Preliminary results indicate
that tensile strain improves the piezoelectric response, as expected for a tilted polar
phase[2,4].
[1] G. Catalan et al., Phys. Rev. Lett. 96 (2006) 127602 [2] E. Almahmoud, Phys.
Rev. B 70 (2004) 220102(R) [3] N.A. Pertsev et al., Phys.Rev. Lett. 80 (1998) 1988
[4] C. Bungaro and K. M. Rabe, Phys. Rev. B 69 (2004) 184101 [5] W. Pompe et al.,
J. Appl. Phys. 74 (1993) 6012