Two Particle Enhanced Nano Raman Microscopy and Spectroscopy

Abstract

The distance- and polarization-dependent near-field enhancement of two coupling metal nanoparticles (MNPs) is analyzed by means of the novel scanning particle enhanced Raman spectroscopy (SPRM) technique. In contrast to single MNP Raman experiments, the near-field coupling between two dissimilar MNPs as followed here leads to a Raman hot spot yielding an extra enhancement factor of 17.6 and 20, as proven here both in experiment and in theory. Three-dimensional electric field calculations for our two-particle arrangements were performed using the semianalytical multiple-multipole method. An excellent agreement is found to our experiments, in which we inspect the interaction between a "scanning" 30 nm gold MNP (Au30) and a "fixed" 80 nm Au MNP (Au80). The Au80 MNP is attached to the apex of an optical fiber manipulator and exposed to the Gaussian focus of a high NA = 1.45 objective at lambda = 532 nm. A monolayer of 1-octanethiol molecules covering the Au80 MNP serves as the electric field prober when scanning the Au30 MNP through the optical focus. This constellation allows recording the Raman signatures from a very low number of well-confined molecules. Moreover, also the spectral and spatial dependence could be explored with a superb sensitivity and very low integration time.

Shaping light beams in the nanometer scale: A Yagi-Uda nanoantenna in the optical domain

“…6͒, and with the outer diameter we use in the former description ͑124 nm͒, a particle with core/ shell radii ratio of 0.851 gives a scattering peak at 634 nm, longer than the operating wavelength of 620 nm, while the particle with 0.834 radii ratio resonate at 605 nm, shorter than the operating wavelength. By testing the particles one by one using modern near-field technology, [17][18][19] one can, in principle, find the desired reflector and directors. We also point out that although the scattering property of the concentric particles may change rapidly with the ratio of radii due to their small size, the radiated power pattern of the entire array may maintain its general shape over a certain range of operating wavelengths ͑620-674 nm͒.…”

Gold Nanoparticles on Polarizable Surfaces as Raman Scattering Antennas

“…However, in these systems, SERS is strongly sensitive to junction width. 18,19,24 Furthermore, quantitative excitation and enhancement requires not only control of junction width but usually also alignment of the SERS substrate relative to the polarization direction of the incident field. We previously have reported quantitative SERS at the ensemble level from solution phase assemblies that used molecular tethers to control junction width.…”

Nanoparticles On A String – Fiber Probes as "Invisible" Positioners for Nanostructures

“…Depending on the actual setup and experiment, various mechanisms and realisations are imaginable, Fig. 2, and most of them were successfully applied for particle decoration experiments (Kalkbrenner et al, 2001;Olk et al, 2007;Uhlig et al, 2007). For mid-IR and THz applications, even silicon is more or less transparent, so the SNOM tip may be replaced by a slightly modified AFM cantilever .…”

“…For optical antenna applications, e.g., using a metal nanostructure as a concentrator of the incident field in order to produce a high intensity, say, for Raman scattering experiments, multiple particles turn out to be advantageous, (Fleischer et al, 2008;Jiang et al, 2003;Li et al, 2003;Nie & Emory, 1997;Olk et al, 2007). For this reason, it may seem attractive to obtain particle decorated probes consisting of two (or even more) particles.…”

“…sputtered metal coagulated to islands, which we consider as nanoparticles here) are used. Aside from the simple fact that attaching a pre-selected particle, as demonstrated here, came later into being (Olk et al, 2007), each experimentalist needs to consider the advantages and disadvantages of the two approaches: price, availability of tools, reproducibility, expected and desired local enhancement, and experimental skills play roles.…”