Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 29: Near-Field Microscopy

O 29.7: Vortrag

Dienstag, 17. März 2015, 15:30–15:45, MA 042

Low-temperature scattering scanning near-field optical microscopy — •Jonathan Döring, Kehr Susanne C., and Eng Lukas M. — IAPP, Technische Universität 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 several orders of magnitude 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 ferroelectric phase transitions of barium titanate (BTO). We use this unique setup to investigate the two ferroelectric phase transitions of barium titanate single crystals below room temperature at 253 K and 173 K. The first constitutes a structural phase transition from tetragonal to orthorhombic, which reflects in both a different domain arrangement and significant phonon resonance shifts, as probed near-field optically [1]. The second transition changes the pattern to rhombohedral, again reflected in both altered micrographs and spectra.

[1] Döring et al., Appl. Phys. Lett. 105, 053109 (2014)