Anomalous field enhancement from the superfocusing of surface plasmons at contacting silver surfaces

Abstract

We demonstrate, both theoretically and experimentally, that an anomalous field enhancement occurs in the vicinity of contact points between two plasmon-resonant surfaces. The theoretical model involves two spheres in contact, and the enhancement is shown to result from the localization of surface plasmon polaritons in the vicinity of the contact point brought on by a decrease of the wavelength and an enhancement of the field of plasmons propagating toward the tip. This model is applied to experiments involving silver films having mesoscopic surface protrusions which are irradiated by intense laser pulses: films in close contact (where the protrusions touch) suffer laser-induced damage which is absent in separately irradiated films. This is interpreted as arising from the additional field enhancement, relative to the well-known enhancement occurring at isolated silver surface protrusions, brought on by the contacts.

Manipulating the confinement of electromagnetic field in size-specific gold nanoparticles dimers and trimers

“…Khlebtsov group 52 systematically compared the plasmon spectra of dimers with various interparticle distances obtained using dipolar approximation or full electrodynamic calculations, including all multipole orders, and demonstrated the significance of the multipole orders for an accurate description of the plasmon fields. Nerkararyan and co-workers 61 solved the wave equation for two conductive spheres in the immediate vicinity, predicting huge enhancement of the electromagnetic energy at the exact point of contact. Nijhuis and colleagues 62 directly observed the charge transfer plasmon mode in the electron energy loss spectra of a silver nanoparticle dimer with the nanogap narrowed by electron beams or molecular linkers, revealing quantum plasmon interactions.…”

Identifying plasmonic modes in a circular paraboloidal geometry by quasi-separation of variables

“…1/2 ( ) , and the incoming wave, H 1 (2) 2!" 1/2 ( ) , as shown in (21). In this case, the unified radial function !…”

Plasmons in nearly touching metallic nanoparticles: singular response in the limit of touching dimers

“…Control over the plasmon frequencies has been gained by playing with particle shapes, as recently shown for nanoshells [4], nanorings [5], and nanorods [6]. Furthermore, mixing, splitting, and frequency shifting of the plasmon modes of individual particles have been experimentally [7][8][9][10][11][12][13] and theoretically [9,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] addressed in particle dimers, giving rise to the concept of plasmon chemistry [25,28]. In particular, coupling particle dipole modes have been observed to yield a strongly red-shifted dipole-active mode for external fields oriented along the inter-particle axis and a blue shifted mode for perpendicular orientations [10][11][12].…”

“…Dimers in the near-touching limit present a challenging situation that is accompanied by (i) dramatic enhancement of the induced electric field at the point of maximum proximity [23,29], (ii) shift of plasmon resonances towards the infrared [9,11,12], (iii) the possibility of a singular transition when the particles touch, 11 and (iv) modes appearing and disappearing near touching [11]. Several theoretical studies have focused on the interaction between neighboring separated spheres both in the non-retarded limit [14][15][16][17][18][19]26] and including full retardation effects [20,21,[23][24][25]27]. However, particles in the nearly-touching limit deserve further consideration to understand the singular transition observed in recent experiments [11], which includes strong mode shifts towards the infrared before touching and shifts away from the infrared as the particles overlap, with a discontinuous change in the evolution of the response when the particles are just touching.…”