Ferroelectric Phase Transition in Individual Single-Crystalline BaTiO3 Nanowires

by Jonathan E. Spanier et al. Nano Letters, 15 Mar 2006 (web release) We report scanned probe characterizations of the ferroelectric phase transition in individual barium titanate 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 calculations of bare and molecule-covered barium titanate 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 barium titanate nanowires. Read more