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Unveiling the Far Infrared-to-Ultraviolet Optical Properties of Bismuth for Applications in Plasmonics and Nanophotonics
journal contribution
posted on 2017-01-12, 00:00 authored by Johann Toudert, Rosalia Serna, Iván Camps, Jacek Wojcik, Peter Mascher, Esther Rebollar, Tiberio A. EzquerraFor
years bismuth (Bi) has appealed to a broad community of scientists
due to its peculiar electronic, optical, and more recently plasmonic
and photocatalytic properties, which enable both the understanding
of basic science phenomena and the development of a wide range of
applications. In spite of this interest, a comprehensive spectral
analysis of the dielectric function (ε = ε1 + jε2) of bulk Bi from the far infrared (IR) to
the ultraviolet (UV) region is not available. So far, the data have
been reported in limited spectral ranges and show a wide dispersion
that is especially notorious for the IR region. In this work we report
ε for Bi in a wide spectral range from 0.05 to 4.7 eV (24.8
to 0.3 μm, far IR to UV). ε is extracted from spectroscopic
ellipsometry measurements of excellent quality (dense and smooth)
Bi films by using the transfer matrix formalism and Kramers–Kronig
consistent analysis. The higher quality and accuracy of the obtained
ε compared with the literature data is demonstrated. The analysis
and use of this reference bulk dielectric function provides crucial
information for the exploration and understanding of the optical,
plasmonic, and photocatalytic properties of Bi nanostructures. From
its analysis, it is evidenced that the optical properties of Bi in
the mid wave IR-to-UV are driven only by interband
transitions, which are responsible for the dominant absorption band
peaking at about 0.8 eV. Therefore, the plasmonic behavior and the
photocatalytic performance of Bi nanostructures in the visible and
UV are likely driven by these interband transitions that make ε1 turn negative in this region without the need of exciting
free carriers. Furthermore, classical electrodynamic simulations using
the obtained ε show a strong size dependence for the optical
extinction of Bi nanospheres in the far IR-to-near IR with Mie-like
resonances broadly tunable across this region.