The localized surface plasmon resonance (LSPR) position in tip-enhanced Raman spectroscopy (TERS) is of great importance to the understanding and interpretation of the relative intensity of different enhanced Raman modes....
We introduce a simple, fast, efficient and non-destructive method to study the optical near-field properties of plasmonic nanotriangles prepared by nanosphere lithography. Using a rectangular Fourier filter on the blurred signal together with filtering of the lower spatial frequencies to remove the far-field contribution, the pure near-field contributions of the optical images were extracted. We performed measurements using two excitation wavelengths (532.1 nm and 632.8 nm) and two different polarizations. After the processing of the optical images, the distribution of hot spots can be correlated with the topography of the structures, as indicated by the presence of brighter spots at the apexes of the nanostructures. This technique is validated by comparison of the results to numerical simulations, where agreement is obtained, thereby confirming the near-field nature of the images. Our approach does not require any advanced equipment and we suggest that it could be applied to any type of sample, while keeping the measurement times reasonably short.
Herein, we propose a facile fabrication procedure for platinum (Pt) nanoprobes. Our approach consists in performing a one-step electrochemical etching using a mixture of DI water, acetone, and CaCl2. Our technique is self-terminated and thus does not necessitate a cut-off circuit nor other sophisticated equipment or set-up commonly used in the fabrication process of Pt nanoprobes. The Pt nanoprobes thereby manufactured demonstrate small tip radii, a high aspect-ratio, no detectable surface contamination, and good reproducibility.
Plasmonic nanoantennas are at the core of various optical near-field scanning techniques such as tip-enhanced Raman spectroscopy as they provide the amplification and confinement of the electromagnetic field, which ultimately provides sensitivity and spatial resolution. With a cornucopia of different fabrication methods available, the actual performance of a nanoantenna is often only assessed by whether or not near-field imaging is possible, implying the complete alignment and landing procedure of the scanning probe. We present a semi-quantitative approach to assess the plasmonic enhancement of gold tips via localized surface plasmon resonance (LSPR) enhancement of intrinsic gold photoluminescence without the need for interaction with the sample. As the intensity of the plasmon at the apex decreases, a significant change in the shape of the tip signal spectrum is observed, reflecting itself as a decrease in the R2 value (fit quality) for numerical fitting with a Lorentzian, which also provides an approximation for the LSPR wavelength. Our findings suggest that the potential of a tip to perform well as an optical near field antenna may already be assessed in an early stage of the experiment.
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