Photonic Crystal-Supported Long-Range Surface Plasmon-Polaritons Propagating Along High-Quality Silver Nanofilms

Sergey Sekatskii,Anton Smirnov,Giovanni Dietler,Mohammad Nur E Alam,Kamal Alameh,Mikhail Vasiliev

doi:10.3390/app8020248

Abstract

Long-range surface plasmon-polaritons (LRSPP) with a propagation length equal to 180 microns at the wavelength of 633 nm have been observed at the interface of 12.5 nm-thick silver nanofilm, coated by a 20 nm-thick protective ZnS layer, with air. Their propagation has been supported by a specially prepared 40-layer 1D Photonic Crystal designed in such a manner that silver layer has been deposited directly onto thin ZnS layer, earlier shown to be a non-oxide material most suitable for the preparation of high-quality thin silver nanofilms.

Highlights

This is well known that thin metal layers sandwiched between two dielectrics having the same refraction indices (RI) support the propagation of long-range surface plasmon polaritons (LRSPP) appearing as a result of the interference of SPP pertinent to the two neighboring metal-dielectric interfaces [1,2,3]. (For brevity, below we will usually omit the word polariton speaking about surface plasmons)
Standard p-polarized He-Ne laser light has been focused on the structure studied with 10 cm focal length lens, and the angular structure of the reflected light has been recorded observing the light spots at distances of 162 and/or 405 cm (both recordings of the light intensity with CMOS camera and processing of color digital photographs of the corresponding light spots were used leading to essentially the same results)
Surface plasmon excitation has been observed for conditions quite close to the normal incidence of the incoming light beam onto the prism entrance face: the corresponding angle was equal to 0.3◦ which results in the incidence angle onto the prism hypotenuse θ = 44.80 giving the propagation parameter ρ = 1.04

Summary

Introduction

This is well known that thin (no thicker than a few tens of nanometers) metal layers sandwiched between two dielectrics having the same refraction indices (RI) support the propagation of long-range surface plasmon polaritons (LRSPP) appearing as a result of the interference of SPP pertinent to the two neighboring metal-dielectric interfaces [1,2,3]. (For brevity, below we will usually omit the word polariton speaking about surface plasmons). Besides fundamental researches, during previous years this effect has been used for sensing purposes, somewhat analogously (but with certain advantages caused by the long propagation distances in the case) to more standard surface plasmon resonance (SPR)-based sensors (see e.g., [4,5] for general reviews of the field) Both (almost) free-standing thin metal layers, and such layers working in water and deposited onto an appropriate substratum made from material having the same RI as the water (e.g., particular Teflon) were exploited [6,7]. Sci. 2018, 8, 248 speaking about surface plasmons at all: their propagation distances would be just of the order of the wavelength Another big topic is the use of PC-supported surface electromagnetic waves without any metal layer, which has numerous implications in sensorics, electromagnetic field control at the surface and so forth. Detailed discussion of this point is given

Photon Crystal Design

Experimental Results and Discussion

Conclusions