Epitaxial BiFeO3 nanostructures fabricated by differential etching of BiFeO3 films

We report on differential etching behavior of the different orientations of the polarization in BiFeO3 (BFO), similar to other ferroelectrics, such as LiNbO3. We show how this effect can be used to fabricate epitaxial BiFeO3 nanostructures. By means of piezoresponse force microscopy (PFM) domains of arbitrary shape and size can be poled in an epitaxial BiFeO3 film, which are then reproduced in the film morphology by differential etching. Structures with a lateral size smaller than 200 nm were fabricated and very good retention properties as well as a highly increased piezoelectric response were detected by PFM. (C) 2011 American Institute of Physics. [doi:10.1063/1.3630027]

Ferroelectric nanostructures fabricated by focused-ion-beam milling in epitaxial BiFeO3 thin films

We studied a suitable route to fabricate ferroelectric islands by focused-ion-beam milling in bismuth ferrite epitaxial thin films. Piezoresponse force microscopy shows that the damage induced by the milling process is extended to 1 mu m away from the edge of the focused-ion-beam patterned islands. After a combined vacuum and oxygen atmosphere annealing procedure, ferroelectricity is fully recovered in structures with sizes down to 500 nm, while for 250 nm islands the defects at the interfaces induce polarization direction pinning.

Monodomain strained ferroelectric PbTiO(3) thin films: Phase transition and critical thickness study

This work demonstrates that instead of paraelectric PbTiO(3), completely c-oriented ferroelectric PbTiO(3) thin films were directly grown on (001)-SrTiO(3) substrates by pulsed-laser deposition with thickness up to 340 nm at a temperature well above the Curie temperature of bulk PbTiO(3). The influence of laser-pulse frequency, substrate-surface termination on growth, and functional properties were studied using x-ray diffraction, transmission electron microscopy, and piezoresponse force microscopy. At low growth rates (frequency 8 Hz) a domains were formed for film thickness above 20-100 nm. Due to coherency strains the Curie temperature (T(c)) of the monodomain films was increased approximately by 350 degrees C with respect to the T(c) of bulk PbTiO(3) even for 280-nm-thick films. Nonetheless, up to now this type of growth mode has been considered unlikely to occur since the Matthews-Blakeslee (MB) model already predicts strain relaxation for films having a thickness of only similar to 10 nm. However, the present work disputes the applicability of the MB model. It clarifies the physical reasons for the large increase in T(c) for thick films, and it is shown that the experimental results are in good agreement with the predictions based on the monodomain model of Pertsev et al. [Phys. Rev. Lett. 80, 1988 (1998)].