Phonon-induced near-field resonances in multiferroic BiFeO3 thin films at infrared and THz wavelengths
- Technische Univ. Dresden (Germany). Institute of Applied Physics
- Technische Univ. Dresden (Germany). Institute of Applied Physics; Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany). Institute of Radiation Physics
- Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany). Institute of Radiation Physics
- SanDisk, Western Digital Technologies Inc., Milpitas, CA (United States)
- Univ. of California, Berkeley, CA (United States)
- Technische Univ. Dresden (Germany). Institute of Applied Physics and Dresden-Wurzburg Cluster of Excellence-EXC 2147
Multiferroic BiFeO$$_3$$ (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 in this paper, 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.
- Research Organization:
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- German Federal Ministry of Education and Research (BMBF); German Research Foundation (DFG); USDOE Office of Science (SC)
- Grant/Contract Number:
- AC02-05CH11231
- OSTI ID:
- 1633262
- Journal Information:
- Applied Physics Letters, Journal Name: Applied Physics Letters Journal Issue: 7 Vol. 116; ISSN 0003-6951
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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