Localized surface plasmons in structures with linear Au nanoantennas on a SiO₂/Si surface

Abstract

The study of infrared absorption by linear gold nanoantennas fabricated on a Si surface with underlying SiO2 layers of various thicknesses allowed the penetration depth of localized surface plasmons into SiO2 to be determined. The value of the penetration depth derived experimentally (20 ± 10 nm) corresponds to that obtained from electromagnetic simulations (12.9–30.0 nm). Coupling between plasmonic excitations of gold nanoantennas and optical phonons in SiO2 leads to the appearance of new plasmon–phonon modes observed in the infrared transmission spectra the frequencies of which are well predicted by the simulations.

Nanoantenna structures for the detection of phonons in nanocrystals

“…The lower curve (black, labeled as ×5) shows the magnified IR spectrum (blue) to emphasize the higher-order plasmon modes. b) Normalized IR transmission spectra of linear antennas with different lengths (adopted from [ 12 ]). c) LSPR energy in nanoantenna arrays fabricated on bare Si surfaces as a function of the nanoantenna length (adopted from [ 12 ]).…”

“…b) Normalized IR transmission spectra of linear antennas with different lengths (adopted from [ 12 ]). c) LSPR energy in nanoantenna arrays fabricated on bare Si surfaces as a function of the nanoantenna length (adopted from [ 12 ]). d) Normalized IR transmission spectra of the fabricated microantennas with different lengths (14.7; 16.4; 17.8; 20.2; 24.3; 30.6 µm).…”

“…The linear nanoantennas effectively couple to the incident electromagnetic waves once their wavelength coincides with the doubled antenna length [ 36 ]. This coupling also depends on the dielectric function of the surrounding medium that causes an increase in the LSPR energy when a thin SiO 2 layer (with a thickness of 0.5–100 nm) is introduced beneath the nanoantennas [ 12 ].…”

“…However, stochastical distribution of metal nanoclusters in terms of size, shape, and orientation reduces the IR enhancement and impedes the study of SEIRA regularities. Further progress was achieved with the development of nanolithography techniques which made possible the fabrication of arrays of metal nanoantennas with structural parameters that were well-controlled at the nanometer scale [ 12 – 13 ]. The most common, linear-shaped nanoantennas exhibit two LSPR modes polarized parallel and perpendicular to the nanoantenna axis (herein, referred to as the longitudinal and transverse modes, respectively).…”

“…In our earlier papers we demonstrated SEIRA in the mid- and far-infrared for both organic molecules and inorganic NCs deposited on Au linear nanoantenna arrays fabricated on Si substrates by nanolithography [ 22 – 23 ]. The influence of a thin SiO 2 layer (0–100 nm) beneath the nanoantenna arrays on the LSPR energy, as well as the LSP penetration depth into SiO 2 were established [ 12 ]. We also showed that diffraction modes in linear Au nanoantenna arrays propagating along the Si surface and perpendicular to the nanoantennas [ 24 ] can be effectively employed for further enhancement of SEIRA by optical phonons in semiconductor NCs [ 23 ].…”