2008 NSTI Nanotechnology Conference and Trade Show - Nanotech 2008 - 11th Annual

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TechConnect Summit
Clean Technology 2008

Polar distortion in ultra-thin BaTiO3 films studied by in situ LEED-IV characterization

V.B. Nascimento, J-S Shin, A.Y. Borisevich, A.P. Baddorf, S.V. Kalinin, E.W. Plummer
University of Tennessee, US

Keywords:
ferroelectrics, LEED-IV, thin films, structure determination

Abstract:
Ferroelectric phase stability in nanoscale ferroelectrics is governed by the interplay of electrostatic depolarization energy and domain formation, adsorption, or surface band bending. Predictions for the minimum critical film thickness for ferroelectricity have continuously decreased. For BaTiO3, ferroelectricity has previously been observed experimentally down to 12 layers and predicted by first-principles calculations in 6 layer films. Using in situ low energy electron diffraction (LEED) I-V, we have characterized the structure of 4 and 10 ML BaTiO3 films, grown using laser molecular beam epitaxy with fully compressive strain on a SrRuO3/SrTiO3 substrate. LEED-IV reveals a single surface dead layer with a single-domain vertically polarized state (upward -out of surface) below. The existence of single orientation is attributed to the intrinsic asymmetry and the stability to compensation of depolarizing charges by dipoles induced by surface stress. This research reveals that the true minimum film thickness for ferroelectric or ferroic behavior is still unknown. Loss of symmetry at the surface allows reconstructions that can compensate surface charge and the associated depolarizing field.


Nanotech 2008 Conference Program Abstract