Dresden 2014 – wissenschaftliches Programm
O 71.7: Vortrag
Donnerstag, 3. April 2014, 12:00–12:15, GER 38
Low-temperature scattering scanning near-field optical microscopy — •Jonathan Döring, Susanne C. Kehr, and Lukas M. Eng — IAPP, George-Bähr-Straße 1, 01069 Dresden
We present a fully operating low-temperature scattering scanning near-field optical microscope (LT-s-SNOM) with access to a tunable free-electron laser (FEL) source. The light scattered off an AFM tip strongly depends on the tip-sample near-field interaction, and thus enables mapping of optical properties with a resolution ways below the diffraction limit. The FEL provides spectrally narrow laser radiation in the regime from 4 to 250 µ m at a high power density. By the novel and unique combination of LT-s-SNOM and FEL, optical properties of materials can be measured at specific wavelengths as well as at temperatures down to 4 K. Our device is therefore perfectly suited for investigating phase transitions of sample materials featuring phonon resonances in the mid-to-far-infrared regime.
We present measurements of the tetragonal-to-orthorhombic phase transition of barium titanate (BTO), a prototype perovskite ferroelectric material. At room temperature BTO features a characteristic domain pattern, which changes dramatically below the transition temperature of 253 K as the alteration of the crystal structure is accompanied by a realignment of the spontaneous polarisation axes. We imaged the anisotropy contrast between such ferroelectric domains by LT-s-SNOM  above and below the phase transition temperature and confirmed our results by piezo-response force microscopy (PFM).
 Kehr et al., Phys. Rev. Lett. 100, 256403 (2008)