Plasmon wavelength

Recently, a new class of chemical and biological sensors has been developed based on the shift of the plasmon resonance wavelength that arises when the analyte of interest binds to the surface of the nanoparticle [9,38]. The effect is very much like that considered in Fig. 4.5, except that the particles considered are anisotropic (truncated tetrahedron shape), the particles are on a surface (glass or mica, typically) and the analyte layer thickness can be varied. Fig. 4.7 shows an example of the type of information studied, here showing the plasmon wavelength shift associated with binding many layers of molecules on the surface of the particle as a function of the layer thickness. The curves labeled B and D show results obtained in experimental studies for particles with dimensions 100 nm (in-plane) and 30 or 50 nm (out of plane), while curves A and C show calculated results for the same two structures. The molecules on the particle surface were... 

One reason for the behavior in Fig. 4.7 can be inferred from Figs. 4.8 and 4.9, in which we examine the electric fields near the particle surfaces. Fig. 4.8 shows contours of the field for the truncated tetrahedron particle, for light polarized along the z-axis in the figure. We see that the bottom tips of the particle are hot compared to the top and sides, with lEp being 12,000 at the tips, and only 6 on the cool sidewalls. Since the plasmon wavelength... 

We are interested here in resonant interaction between incident EW and plasma oscillations in the 2D electron system. As it is well-known [5], the plasmon wavelengths in 2D electron system are several orders of magnitude shorter than the wavelength of the EW of the same fi equency. To ensure a resonant coupling between the EW and plasma oscillations, the period of the structure has to be of the order o f the plasmon wavelength, which means that L 2n/ko. In this case, only transmitted and reflected EWs of the zero diffraction order survive at distances much longer than the EW wavelength away from 2D electron system. 

Figure 2. Plasmon wavelength for a layer of silver dipole nanoparticles as a function of packing density (d=5 nm nm=1.5).

Figure 3. Plasmon wavelength of a silver nanospheres layer as a function of diameter at different values of packing density ( , =l.5). Solid lines correspond to the data calculated in the QCA, dashed lines show approximation by Eq. (2).

W. Ni et al.. Tailoring longitudinal surface plasmon wavelengths, scattering and absorption cross sections of gold nanorods, ACS Nano, 2(4), 677-686 (2008). 

Michaelis and Henglein [131] prepared Pd-core/Ag-shell bimetallic nanoparticles by the successive reduction of Ag ions on the surface of Pd nanoparticles (mean radius 4.6 nm) with formaldehyde. The core/shell nanoparticles, however, became larger and deviated from spherical with an increase in the shell thickness. The Pd/Ag bimetallic nanoparticles had a surface plasmon absorption band close to 380 nm when more than 10-atomic layer of Ag are deposited. When the shell thickness is less than 10-atomic layer, the absorption band is located at shorter wavelengths and the band disappears below about three-atomic layer. 

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