title: Anisotropy contrast in phonon-enhanced apertureless near-field microscopy using a free-electron laser.
abstract: We demonstrate the imaging of ferroelectric domains in BaTiO3, using an infrared-emitting free-electron laser as a tunable optical source for scattering scanning near-field optical microscopy and spectroscopy. When the laser is tuned into the spectral vicinity of a phonon resonance, ferroelectric domains can be resolved due to the anisotropy of the dielectric properties of the material. Slight detuning of the wavelength gives rise to a contrast reversal clearly evidencing the resonant character of the excitation. The near-field domain contrast shows that the orientation of the dielectric tensor with respect to the sample surface has a clear influence on the near-field signal.
authors.affiliation: Institute of Applied Photophysics, Technische Universität Dresden, D-01062 Dresden, Germany.
authors.forename: S C
authors.initials: SC
authors.lastname: Kehr
authors.forename: M
authors.initials: M
authors.lastname: Cebula
authors.forename: O
authors.initials: O
authors.lastname: Mieth
authors.forename: T
authors.initials: T
authors.lastname: Härtling
authors.forename: J
authors.initials: J
authors.lastname: Seidel
authors.forename: S
authors.initials: S
authors.lastname: Grafström
authors.forename: L M
authors.initials: LM
authors.lastname: Eng
authors.forename: S
authors.initials: S
authors.lastname: Winnerl
authors.forename: D
authors.initials: D
authors.lastname: Stehr
authors.forename: M
authors.initials: M
authors.lastname: Helm