Surface-Enhanced Infrared Spectroscopy Using Nanometer-Sized Gaps

Abstract

We report on the near-field coupling of individual gold nanoantennas arranged in tip-to-tip dimer configuration, leading to strong electromagnetic field enhancements in the infrared, which is of great interest for sensing applications such as surface-enhanced infrared spectroscopy. We quantitatively evaluated the enhancement of vibrational excitations of a 5 nm thick test layer of 4,4'-bis(N-carbazolyl)-1,1'-biphenyl as a function of different gap sizes. The dimers with the smallest gaps under investigation (∼3 nm) lead to more than 1 order of magnitude higher signal enhancement with respect to gaps of 50 nm width. The comparison of experimental data and finite-difference time-domain simulations reveals a nonperfect filling of the gaps with sizes below 10 nm, which means that morphological information on the nanoscale is obtained additionally to chemical information.

Multifunctional Fe3O4@SiO2–Au Satellite Structured SERS Probe for Charge Selective Detection of Food Dyes

“…The FDTD results show that, in agreement with our SERS observations, the decrease in the Au NP gap from 60 to 5 nm was accompanied by elevation of the localized electromagnetic field (Figure 1C and 1D) because of effectively confined light in the Au cavities. 41 If the wavelength of incident light matches the localized surface plasmon resonance of a metal nanostructure, a strong localized electromagnetic field will be excited in the vicinity of the nanogaps. 42,43 Our FDTD model also predicts that the optimal SERS excitation wavelength for sub-10 nm gaps on FA satellite structures would lie in the red and near-infrared spectral region, such as 633 and 785 nm ( Figure S4).…”

Plasmonic Chiral Nanostructures: Chiroptical Effects and Applications

“…[18][19][20] Surface plasmons (SPs), as the collective electrons oscillation at the dielectric and metal interface, [21][22][23] present the capacity of light confine ment and field enhancement, which significantly improve the strength of lightmatter interactions. [24][25][26][27][28] With the uptodate nanofabrication technology, the study field of chirality has been extended from traditional chiral molecules to 3D metallic nanostructures. [29][30][31][32] Chiroptical responses of metallic meta molecules have been widely investigated, [33][34][35] and applied in various fields, such as biosensing, [36] chiral catalysis, [37] polari zation tuning, [38] and chiral photo detection.…”

Highly doped semiconductor plasmonic nanoantenna arrays for polarization selective broadband surface-enhanced infrared absorption spectroscopy of vanillin

“…They benefit furthermore from the lightning rod effect, the geometrical electric field enhancement at highly curved surfaces [30]. Antenna dimers with nanometer size gaps have been employed to further increase the electric field enhancement and focus incident light into small hot spots [12,16,31,32]. The use of HDSC allows us to deviate from these design schemes, owing to the material properties, as the elongated shape or the interaction through a gap to decrease the resonance frequency is not necessarily needed to reach resonance frequencies in the mid-IR.…”

“…The original approach in this article is to cover a large spectral range by the polarization switchable plasmonic resonances in simple, gap-free rectangular nanoantennas. This is particularly interesting for sensing applications, like resonant surface-enhanced infrared absorption (SEIRA) spectroscopy, which ideally requires a good spectral overlap between the plasmonic resonance and the narrow IR-active molecular vibrations [15,32]. The spectral overlap can easily be achieved by selecting the spectral band of interest by the polarization of the incident light, offering a new degree of freedom for the tuning of the resonances.…”