Anisotropy contrast in phonon-enhanced apertureless near-field microscopy using a free-electron laser

Phys Rev Lett. 2008 Jun 27;100(25):256403. doi: 10.1103/PhysRevLett.100.256403. Epub 2008 Jun 24.


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.