Paper NS+BI+EM-MoM8
Engineering Multimodal Localized Surface Plasmon Resonances in Silicon Nanowires

Monday, October 28, 2013, 10:40 am, Room 203 B

Semiconductors, as a result of their widely tunable carrier density (10¹⁹ - 10²¹ cm^-3), are emerging as promising plasmonic materials for applications in the infrared and near-infrared. Silicon, in particular, is inexpensive relative to the noble metals and benefits from a robust suite of processing tools due to its extensive use in the semiconductor industry. To this end, we recently reported that phosphorus-doped Si nanowires can support mid-infrared localized surface plasmon resonances (LSPRs) with quality factors comparable to those of the noble metals [1]. Herein, we demonstrate that axial control of dopant profile in individual nanowires permits complex, user-programmable, multimodal spectral responses. Highly aligned Si nanowire arrays are synthesized via the vapor-liquid-solid (VLS) technique with a combination of Si- and P-containing precursors. In-situ infrared absorption spectroscopy measurements reveal intense absorption bands (5 – 10 um) with dopant concentration and shape-dependent spectral shifts consistent with longitudinal LSPRs. Discrete dipole approximation (DDA) calculations confirm that the observed spectral response results from resonant absorption and free carrier concentrations on the order of 10²⁰ cm^-3. We also observe near-field coupling between neighboring plasmonic domains, which varies as a function of intrinsic spacer length and can be described with hybridization theory. Our results highlight the utility of VLS synthesis for surface plasmon engineering in semiconductors, create new opportunities to study basic surface plasmon physics, and pave the way for applications including ultra-sensitive molecular detection and thermal energy harvesting.

[1] Chou, L.-W.; Shin, N.; Sivaram, S. V.; Filler, M. A. J. Am. Chem. Soc. 2012, 134, 16155.