TY - JOUR
KW - Thin films
KW - Resonance
KW - Electrons
KW - Iron compounds
KW - Multiferroics
KW - Phonons
KW - Bismuth compounds
KW - Free electron lasers
KW - Lattice vibrations
KW - Photons
KW - Single crystals
KW - Bfo thin films
KW - BiFeO3 thin film
KW - Enhanced sensitivity
KW - Local material properties
KW - Optical signals
KW - Phonon polaritons
KW - Scattering-type scanning near-field optical microscopy (s-SNOM)
KW - Tip-sample distance
KW - Near-field scanning optical microscopy
AU - L Wehmeier
AU - T Nörenberg
AU - T.V.A.G De Oliveira
AU - J.M Klopf
AU - S.-Y Yang
AU - L.W Martin
AU - Ramamoorthy Ramesh
AU - L.M Eng
AU - S.C Kehr
AB - Multiferroic BiFeO3 (BFO) shows several phonon modes at infrared (IR) to THz energies, which are expected to carry information on any sample property coupled to crystal lattice vibrations. While macroscopic IR studies of BFO are often limited by single-crystal size, scattering-type scanning near-field optical microscopy (s-SNOM) allows for IR thin film spectroscopy of nanoscopic probing volumes with negligible direct substrate contribution to the optical signal. In fact, polaritons such as phonon polaritons of BFO introduce a resonant tip-sample coupling in s-SNOM, leading to both stronger signals and enhanced sensitivity to local material properties. Here, we explore the near-field response of BFO thin films at three consecutive resonances (centered around 5 THz, 13 THz, and 16 THz), by combining s-SNOM with a free-electron laser. We study the dependence of these near-field resonances on both the wavelength and tip-sample distance. Enabled by the broad spectral range of the measurement, we probe phonon modes connected to the predominant motion of either the bismuth or oxygen ions. Therefore, we propose s-SNOM at multiple near-field resonances as a versatile and very sensitive tool for the simultaneous investigation of various sample properties. © 2020 Author(s).
BT - Applied Physics Letters
DO - 10.1063/1.5133116
LA - eng
M1 - 7
N1 - cited By 0
N2 - Multiferroic BiFeO3 (BFO) shows several phonon modes at infrared (IR) to THz energies, which are expected to carry information on any sample property coupled to crystal lattice vibrations. While macroscopic IR studies of BFO are often limited by single-crystal size, scattering-type scanning near-field optical microscopy (s-SNOM) allows for IR thin film spectroscopy of nanoscopic probing volumes with negligible direct substrate contribution to the optical signal. In fact, polaritons such as phonon polaritons of BFO introduce a resonant tip-sample coupling in s-SNOM, leading to both stronger signals and enhanced sensitivity to local material properties. Here, we explore the near-field response of BFO thin films at three consecutive resonances (centered around 5 THz, 13 THz, and 16 THz), by combining s-SNOM with a free-electron laser. We study the dependence of these near-field resonances on both the wavelength and tip-sample distance. Enabled by the broad spectral range of the measurement, we probe phonon modes connected to the predominant motion of either the bismuth or oxygen ions. Therefore, we propose s-SNOM at multiple near-field resonances as a versatile and very sensitive tool for the simultaneous investigation of various sample properties. © 2020 Author(s).
PB - American Institute of Physics Inc.
PY - 2020
T2 - Applied Physics Letters
TI - Phonon-induced near-field resonances in multiferroic BiFeO3 thin films at infrared and THz wavelengths
VL - 116
SN - 00036951
ER -