Robust Plasmon Waveguides in Strongly Interacting Nanowire Arrays

Abstract

Arrays of parallel metallic nanowires are shown to provide a tunable, robust, and versatile platform for plasmon interconnects, including high-curvature turns with minimum signal loss. The proposed guiding mechanism relies on gap plasmons existing in the region between adjacent nanowires of dimers and multi-wire arrays. We focus on square and circular silver nanowires in silica, for which excellent agreement between both boundary element method and multiple multipolar expansion calculations is obtained. Our work provides the tools for designing plasmon-based interconnects and achieving high degree of integration with minimum cross talk between adjacent plasmon guides.PACS numbers: 73.20. Mf,84.40.Az,42.82.Gw Electromagnetic modes in metal surfaces known as plasmons can propagate along millimeters in metallic structures at near-infrared frequencies [1], thus providing a plausible substitute for the electrical impulses used in current electronic circuits operating at microwave clock frequencies [2,3]. Several designs of plasmon interconnects have been prototyped in recent years, including metallic waveguides of finite cross section in symmetric [4,5] and asymmetric [6] environments, channels cut into flat surfaces [7], plasmon-band-gap structures based upon periodic corrugations [8], and plasmon hopping in arrays of nanoparticles [9,10]. Plasmon modes can be tuned in frequency, and their spatial distribution molded, by tailoring the geometry of metallic structures on the nanometer scale. In particular, extreme plasmon confinement has been achieved in narrow insulator films buried inside metal [11]. Actually, buried structures provide a natural but technologically challenging approach to compact integration. In contrast to that, open plasmonic geometries involve electromagnetic fields extending significantly away from the metal [5,6,7,8,9,10], and consequently producing a substantial degree of cross-talk between neighboring waveguides [12].In this Letter, arrays of parallel metallic nanowires are shown to provide a versatile and tunable platform for highly-integrated plasmon interconnects. The propagation distance and degree of confinement of the plasmon guided modes depend strongly on the separation between wires. Individual wire modes are recovered at large separations, while mode hybridization is observed when the spacing is reduced. Gap modes are observed at small separations, highly localized in the regions between two adjacent wires. We use both the boundary element method (BEM) [13] and a two-dimensional multipleelastic-scattering multipolar expansion of the fields for straight cylinders (2D-MESME) [14], with the two approaches resulting in complete agreement on the scale of the plots. These methods provide rigorous solutions of Maxwell's equations in frequency space for materials described by local dielectric functions and separated by abrupt interfaces. We focus on silver nanowires of circular and square cross sections embedded in silica. The dielectric functions of silver [15] and silica [16] have been...

Optical and electrical properties of gold nanowires synthesized by electrochemical deposition

“…Individual wire modes are recovered at large separations, while mode hybridization is observed when the spacing is reduced. 32 Previous studies have demonstrated that, in an array of nanorods, the SPR of the individual nanorods can be viewed as harmonic oscillators that couple to each other, leading to a resonance shift as well as a changed near-field distribution. 33 In the present work, the mean distances between the wire surfaces facing each other decreases from 470 to 370 nm with the nanowires diameters increasing from 30 to 130 nm at the certain area density of 1 Â 10 8 wires/cm 2 (with the assumption of all nanopores in the templates being filled).…”

“…The observed peak broadening can be ascribed to the polydispersity in the nanowires distance and overlap of the gap mode with the metal. 32 The absorbance properties of gold nanowire arrays with different incident angle a were also investigated [ Fig. 3(b)].…”

Controllable excitation of gap plasmons by electron beams in metallic nanowire pairs

“…[12][13][14][15][16][17] Propagating gap plasmons are well understood from a theoretical point of view. 7 Notice that these plasmons are quite different from the resonances that one obtains associated to the excitation of wire pairs using light incident normal to the wires. In particular, retardation in the response of the system is required to have a realistic description of trapped propagating modes.…”

“…1,2 Their potential application for on-chip communication and signal processing has stimulated recent investigations of different geometries for plasmon waveguiding intended to optimize the compromise between propagation distance, degree of confinement, and electric field enhancement. Among these structures, interesting results have been reported for particle chains, 3,4 grooves, 5 and wedges 6 carved in planar surfaces, gaps between metallic nanowires, 7 and metallodielectric structures. 8 In particular, gap plasmons have been shown to be excellent candidates to minimize crosstalk between neighboring waveguides, thus allowing a high degree of spatial integration.…”

Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths

“…In theoretical models, strong subwavelength field enhancements are observed indicating the relevance of imaging on a spatial scale far below the free-space wavelength of the light. Many Ag and Au nanostructures, which are the common model structures for plasmonic studies, have localized plasmonic resonances at these wavelengths with field concentration at wedges or crescents [20][21][22][23].…”