Nano Lett., 6 (4), 735 -739, 2006. 10.1021/nl052538e S1530-6984(05)02538-5
Web Release Date: March 15, 2006

Copyright © 2006 American Chemical Society

Ferroelectric Phase Transition in Individual Single-Crystalline BaTiO3 Nanowires

Jonathan E. Spanier, Alexie M. Kolpak, Jeffrey J. Urban, Ilya Grinberg, Lian Ouyang, Wan Soo Yun, Andrew M. Rappe,* and Hongkun Park*

Department of Chemistry and Chemical Biology, Harvard University, Cambridge Massachusetts 02138, Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, and The Makineni Theoretical Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323

Received December 24, 2005

Abstract:

We report scanned probe characterizations of the ferroelectric phase transition in individual barium titanate (BaTiO3) nanowires. Variable-temperature electrostatic force microscopy is used to manipulate, image, and evaluate the diameter-dependent stability of ferroelectric polarizations. These measurements show that the ferroelectric phase transition temperature (TC) is depressed as the nanowire diameter (dnw) decreases, following a 1/dnw scaling. The diameter at which TC falls below room temperature is determined to be ~3 nm, and extrapolation of the data indicates that nanowires with dnw as small as 0.8 nm can support ferroelectricity at lower temperatures. We also present density functional theory (DFT) calculations of bare and molecule-covered BaTiO3 surfaces. These calculations indicate that ferroelectricity in nanowires is stabilized by molecular adsorbates such as OH and carboxylates. These adsorbates are found to passivate polarization charge more effectively than metallic electrodes, explaining the observed stability of ferroelectricity in small-diameter BaTiO3 nanowires.

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