Tunable Mid-Infrared Localized
Surface Plasmon Resonances
in Silicon Nanowires
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Abstract
We observe and systematically tune an intense mid-infrared
absorption
mode that results from phosphorus doping in silicon nanowires synthesized
via the vapor–liquid–solid technique. The angle- and
shape-dependence of this spectral feature, as determined via <i>in-situ</i> transmission infrared spectroscopy, supports its
assignment as a longitudinal localized surface plasmon resonance (LSPR).
Modulation of resonant frequency (740–1620 cm<sup>–1</sup>) is accomplished by varying nanowire length (135–1160 nm).
The observed frequency shift is consistent with Mie–Gans theory,
which indicates electrically active dopant concentrations between
10<sup>19</sup> and 10<sup>20</sup> cm<sup>–3</sup>. Our findings
suggest new opportunities to confine light in this ubiquitous semiconductor
and engineer the optical properties of nontraditional plasmonic materials