Strongly localized plasmon oscillations in a cluster of two metallic nanospheres and their influence on spontaneous emission of an atom

Abstract

The plasmon oscillations in a cluster of two metallic nanospheres are studied theoretically. Particular attention is paid to the case of nearly touching spheres. Simple analytical expressions have been found for the spectra of plasmon oscillations of different symmetry in this case. A new type of the plasmon oscillations, which are strongly localized between the spheres, and which totally disappear at separation of the spheres, has been discovered. The found plasmon oscillations have a dramatic effect on optical properties of an atom localized between the spheres.Much attention has been paid, of late, to the experimental and theoretical study of optical properties of the metallic nanoparticles. This interest is mainly due to a considerable enhancement of local fields near the nanoparticles. An especially high increase occurs in the case of plasmon polariton resonances ("plasmons") [1,2] or phonon polariton resonances ("phonons") [3]. On the basis of this effect one considers quite a number of possible applications. One of the most developed is the use of large local fields for enhancement of the Raman scattering cross-section [4]. Recent experiments have shown that such an increase may achieve 10-14 orders of magnitude, which may help to resolve separate molecules [5]- [7]. The local enhancement of the fields can also be used to increase the fluorescence intensity and to determine the structure of a single DNA strand without using the fluorescent labels [8,9]. By using the nanoparticles of complex configuration one can provide enhancement of both the absorption and the emission of light by natural and artificial fluorophores [10]. Of particular interest and promise are the studies of optical properties of the clusters of two and more metallic nanoparticles, because by changing the cluster's geometry one can effectively control the spectra of the plasmon oscillations. This effect makes it possible to produce, for example, new types of biosensors [11]-[13]. A whole series of experimental [14]-[17] and theoretical [18]-[27] studies have been devoted to the two-particle clusters.

Control of surface plasmon resonances in dielectrically coated proximate gold nanoparticles immobilized on a substrate

“…We note that similar features observed in the extinction spectra of metal nanoparticle arrays have been explained by propagating surface plasmon modes, 12 increase in size effects, 35 or bound states. 36 These, however, do not explain the experimental results described below.…”

“…Therefore, we do not attribute this peak to the formation of bound states between the two nanoparticles. 36 The bottom left and right spectra of Fig. 3 show the calculated plasmon resonance shifts for bare and coated nanoparticles, respectively, as a function of interparticle separation in an aqueous medium.…”

Van der Waals Forces Between Plasmonic Nanoparticles

“…Plasmonic oscillations in this system have a very complicated spatial and spectral structure [1,2]. We will show that both recently predicted [1,2] and previously known [20][21][22] plasmon oscillations give contributions to the van der Waals energy that are approximately equal in amplitude but opposite in sign. As a result, the van der Waals energy turns out to be very sensitive to geometry and materials of the interface and the nanoparticles.…”

Plasmonic atoms and plasmonic molecules

“…The evidence for the existence of bound states of the plasmonic atoms was first provided in [18,19] by the example of a cluster of two closely sitiated spherical nanoparticles (Fig. 5).…”

“…Such an approach seems to be efficient and useful as it follows from the strongly localized plasmonic oscillations recently discovered in the clusters of spherical nanoparticles [18,19,20]. These oscillations, being localized and of short-range, represent the plasmonic molecules, and on their basis it is possible to create different kinds of plasmonic nanostructures and to develop new nanodevices (optical nanosensors of single molecules, nanoelectromechanical systems (NEMS [21]), and even plasmonic computers).…”