Plasmonic particles

Alu, A. and Engheta, N. (2006) Theory of linear chains of metamaterial/plasmonic particles as subdiffraction optical nanotransmission lines. Physical Review B - Condensed Matter, 74, 205436. 

The plasmonic ELISA links the color of plasmonic nanoparticles to the presence or absence of the analyte. The assay uses enzymes to control the particle synthesis for generating plasmonic particles with different sizes [65,66], which exhibit distinct solution colors caused by different localized SPR. In one of the demonstrations that utilize p24 as the target analyte, the assay incorporates catalase to regulate the hydrogen peroxide concentration. 

The inclusion of other materials within structurally coloured CNC films is of huge importance for the production of structurally coloured films. Of particular interest is the inclusion of plasmonic particles,whose directed inclusion has been especially studied, as well as latex nanoparticles.There has also been significant interest in the inclusion of polymers in the films to improve their mechanical flexibility. The inclusion of these molecules... 

Figure 5.6 Pictorial representation of geometrical and frequency-related effects on the relative orientation of the molecular dipole and the induced dipole in the plasmonics particle. For frequencies far from the absorption edge [left panel], molecular transition dipoles tangential to the surface induces antiparallel dipole in the nanoparticle. For frequencies just above the surface plasmon excitation, the opposite may be true. Note that the magnitude of the induced dipole and the exact position where the inversion takes place depend on the dielectric function and the shape of the metal nanoparticle.

The inclusion of sub-wavelength plasmonic particles and other plasmonic structures in solar cells has been shown to reduce notably the required thickness of the photoactive layer and to expand greatly the pool of its usable absorber materials. For most plasmon-enhanced solar cells, fabrication only involves... 

CuNPs) in Fig. 7 shows the monodisperse and uniformly distributed spherical particles of 10+5 nm diameter. The solution containing nanoparticles of silver was found to be transparent and stable for 6 months with no significant change in the surface plasmon and average particle size. However, in the absence of starch, the nanoparticles formed were observed to be immediately aggregated into black precipitate. The hydroxyl groups of the starch polymer act as passivation contacts for the stabilization of the metallic nanoparticles in the aqueous solution. The method can be extended for synthesis of various other metallic and bimetallic particles as well. 

When the silver nanocrystals are organized in a 2D superlattice, the plasmon peak is shifted toward an energy lower than that obtained in solution (Fig. 6). The covered support is washed with hexane, and the nanoparticles are dispersed again in the solvent. The absorption spectrum of the latter solution is similar to that used to cover the support (free particles in hexane). This clearly indicates that the shift in the absorption spectrum of nanosized silver particles is due to their self-organization on the support. The bandwidth of the plasmon peak (1.3 eV) obtained after deposition is larger than that in solution (0.9 eV). This can be attributed to a change in the dielectric constant of the composite medium. Similar behavior is observed for various nanocrystal sizes (from 3 to 8 nm). 

Under i-polarization light, the optical spectra of 5-nm nanoparticles (Fig. 7A), recorded at various incident angles 0 do not change with increasing 0. They are characterized by a maximum centered at 2.9 cV, which is similar to that observed for isolated particles (Fig. 5B). Flowever, the plasmon resonance peak remains asymmetrical, as observed under nonpolarized light (Fig. 6). 

Inset Figure 8 shows that the sizes of most of the particles remain similar. However, it can be observed that, in part of the TEM pattern, some particles form chains, which are either close together or coalesced. The presence of the two plasmon modes (Fig. 8B) indicates an optical anisotropy due to the nonspherical shape of the particles, as shown on the TEM grid (inset Fig. 8). 

The UV-visible spectrum (Fig. 6) of the aggregates described earlier shows a 0.25-eV shift toward lower energy of the plasmon peak with a slight decrease in the bandwidth (0.8 eV) compared to that observed in solution (0.9 eV). As observed earlier with monolayers, by washing the support, the particles are redispersed in hexane and the absorption spectrum remains similar to that of the colloidal solution used to make the self-assemblies. 

The last problem of this series concerns femtosecond laser ablation from gold nanoparticles [87]. In this process, solid material transforms into a volatile phase initiated by rapid deposition of energy. This ablation is nonthermal in nature. Material ejection is induced by the enhancement of the electric field close to the curved nanoparticle surface. This ablation is achievable for laser excitation powers far below the onset of general catastrophic material deterioration, such as plasma formation or laser-induced explosive boiling. Anisotropy in the ablation pattern was observed. It coincides with a reduction of the surface barrier from water vaporization and particle melting. This effect limits any high-power manipulation of nanostructured surfaces such as surface-enhanced Raman measurements or plasmonics with femtosecond pulses. 

Rendell, R., Scalapino, D. and Miihlschlegel, B. (1978) Role of local plasmon modes in light emission from small-particle tunnel junctions. Rhys. Rev. Lett., 41, 1746-1750. 

Eischer, U. Ch. and Pohl, D. W. (1989) Observation of single-particle plasmons by near-field optical microscopy. Phys. Rev. Lett., 62, 458-461. 

---