New approaches to the fabrication of ferroelectric nanostructures onto substrates are critical for the development of competitive functional devices that successfully integrate at nanoscale ferroelectrics as alternative materials in the microelectronic industry. These approaches have to meet reliability and utilization requirements to realize a cost-effective production of an increasing demand for ultra-high-density memories or nanometric electromechanical systems. An important challenge in the fabrication of ferroelectric nanomaterials supported onto substrates is the ability to fabricate an organized arrangement of the nanostructures. This is a key point for the applications of ferroelectrics in nanoelectronic devices.

Recently, scientists from the Institute of Materials Science of Madrid (CSIC) and the Centre for the Research of Advanced Materials in Chihuaha, in collaboration with Apurva Mehta of SSRL, used grazing incidence scattering experiments to determine the crystal structure and texture of ferroelectric nanostructures onto SrTiO₃ single crystal substrates.

For the preparation of these nanostructures, a novel preparation method was used, which involves the use of microemulsions, sol-gel chemistry and chemical solution deposition. A transparent solution was first prepared by mixing a PbTiO₃ precursor sol and a microemulsion formed by water, cyclohexane and the surfactant Brij 30 (Polyoxyethylene(4) lauryl ether). The solution was deposited onto the substrates by spin-coating and dried under controlled conditions. After a rapid thermal treatment of crystallisation at 650ºC, nanostructures with uniform sizes of ~40 nm diameter and showing periodicity in some zones of the substrate were obtained.

The analysis of these nanostructures by grazing incidence x-ray synchrotron radiation indicates that they have a perovskite PbTiO₃ structure with a <100> preferred orientation and that are under strained conditions. Thermal treatments at higher temperatures produce the collapse of the ordered nanoparticles network and the formation of larger isolated particles of PbTiO₃ with a truncated-pyramid morphology. Piezoresponse Force Microscopy studies demonstrate that these PbTiO₃ nanostructures can be switched and that they have piezoelectric activity. These results support the potentiality of a fabrication strategy for the preparation of nanoferroelectrics onto substrates of interest in future nanoelectronic devices.

M. L. Calzada, M. Torres, L. E. Fuentes-Cobas, A. Mehta, J. Ricote and L. Pardo. "Ferroelectric self-assembled PbTiO₃ perovskite nanostructures onto (100)SrTiO₃ substrates from a novel microemulsion aided sol-gel preparation". Nanotechnology, 2007, 18, 375603.

To learn more about this research see the full scientific highlight at:
http://www- ssrl.slac.stanford.edu/research/highlights_archive/fuentes.html