Electromagnetic fields around silver nanoparticles and dimers

Abstract

We use the discrete dipole approximation to investigate the electromagnetic fields induced by optical excitation of localized surface plasmon resonances of silver nanoparticles, including monomers and dimers, with emphasis on what size, shape, and arrangement leads to the largest local electric field (E-field) enhancement near the particle surfaces. The results are used to determine what conditions are most favorable for producing enhancements large enough to observe single molecule surface enhanced Raman spectroscopy. Most of the calculations refer to triangular prisms, which exhibit distinct dipole and quadrupole resonances that can easily be controlled by varying particle size. In addition, for the dimer calculations we study the influence of dimer separation and orientation, especially for dimers that are separated by a few nanometers. We find that the largest /E/2 values for dimers are about a factor of 10 larger than those for all the monomers examined. For all particles and particle orientations, the plasmon resonances which lead to the largest E-fields are those with the longest wavelength dipolar excitation. The spacing of the particles in the dimer plays a crucial role, and we find that the spacing needed to achieve a given /E/2 is proportional to nanoparticle size for particles below 100 nm in size. Particle shape and curvature are of lesser importance, with a head to tail configuration of two triangles giving enhanced fields comparable to head to head, or rounded head to tail. The largest /E/2 values we have calculated for spacings of 2 nm or more is approximately 10(5).

Surface-Enhanced Raman Spectroscopy

“…In this body of work, field enhancement has been studied as a function of nanoparticle aspect ratio and shape (20,21), extremely large SERS enhancement has been predicted in small nanoparticle assemblies (22,23), and interesting optical phenomena that occur in extended arrays of nanoparticles have been uncovered (24,25).…”

Plasmon-enhanced photocurrent generation and water oxidation from visible to near-infrared wavelengths

“…Moreover, LSPR gives rise to an optical antenna effect, which efficiently harvests light and localizes electromagnetic waves at the nanoscale. [15][16][17][18][19] Therefore, it is understood that metallic nanostructures act as photoelectric conversion systems that enable the effective utilization of photons, having a role similar to that of chlorophyll in photosynthesis. [20][21][22][23] Although many photoelectric conversion systems using LSPR have been previously reported, the wavelengths at which photoelectric conversion occurs did not extend beyond 700 nm, [24][25][26][27][28][29][30][31] creating a need to explore photoelectric conversion at infrared wavelengths past 800 nm.…”

Dark Modes and Fano Resonances in Plasmonic Clusters Excited by Cylindrical Vector Beams

“…44 In order to get a deeper insight on the characteristics of dark plasmon modes excited by CVB, the near field intensity maps at the photon energy where the average field enhancement is maximal are shown in Figure 2. For a focused x polarized plane wave there is a strong field enhancement at center of the dimer, i.e., a hot spot is formed due to the large accumulation of charges with opposite signs at the regions of the particle surface facing the dimer gap 45,46 (see Supporting Information for movies of the surface charge distribution oscillations). The y polarized plane wave does not induce significant enhancement as no large charge gradients are generated.…”