Surface Shape Resonances in Lamellar Metallic Gratings

Abstract

The specular reflectivity of lamellar gratings of gold with grooves 0.5 microns wide separated by a distance of 3.5 microns was measured on the 2000 cm −1 -7000 cm −1 spectral range for p-polarized light. For the first time, experimental evidence of the excitation of electromagnetic surface shape resonances for optical frequencies is given. In these resonances the electric field is highly localized inside the grooves and is almost zero in all other regions. For grooves of depth equal to 0.6 microns, we have analyzed one of these modes whose wavelength (3.3 microns) is much greater than the lateral dimension of the grooves.PACS numbers: 71.36.+c, 73.20.Mf, 78.66.Bz Metallic gratings can exhibit absorption anomalies [1]. One of these anomalies which is particularly remarkable is observed for p-polarized light only, and is due to surface plasmon polariton (SPP) excitations. SPP excitation induces a minimum on the specular reflectance spectra which is indicative of the amount of energy flowing parallel to the surface. In a first order approximation, the spectral position of the minimum does not depend on the shape or the amplitude of the grooves but depends only on the dielectric constant and period of the grating. One interesting problem which has been raised long time ago and which is still of interest today is the near field dependence of these modes on the grating shape [2]. Linked to this problem is the possible existence of modes localized in grooves of prominent shape and their relation with non-linear optical effects observed in certain rough metal surfaces [3][4][5][6][7][8].At the beginning of the century Rayleigh pointed out that flat rigid surfaces with cylindrical holes can present acoustic resonances for well defined depths of the holes [9]. Rayleigh showed that under these resonant conditions the acoustic energy is concentrated in the holes and he suggested that similar effects could occur with light. More recently Rendell and Scalapino [10] suggested the possible existence of localized plasmons in order to explain light emission in metal-oxide-metal structures. These plasmon modes are qualitatively different from propagative SPPs on a flat surface excited by attenuated total reflection or by a gentle surface corrugation. Despite the conceptual and practical interest of these surface shape resonances and well documented theoretical predictions, till now no experimental evidence of these electromagnetic resonances has been reported for optical frequencies.In this letter we show that for lamellar gratings with deep rectangular cross sections, localized waveguide resonances which are equivalent to the acoustic resonances described by Rayleigh, can be excited in the channels when the impinging light has an electric field component perpendicular to the grooves direction. The experiments here presented also illustrate the existence of hybrid modes, combination of standing waves localized in the grooves with propagating SPPs.Measured samples consist in periodic arrays of metallic grooves of nominal width ...

Hydrogen concentration and bonding configuration in polycrystalline diamond films: From micro-to nanometric grain size

“…Surface to volume atom ratio of fcc crystallite with the same crystalline size. 44 that these peaks are associated with 1 and 3 vibration modes of trans-polyacetylene ͑t-PA͒ codeposited with diamond phase. The 1140 cm −1 Raman peak is associated most likely with a C u H bending mode of hydrogenated sp 2 carbon bonded to diamond grain internal surfaces and boundaries.…”

“…It was shown in the works of many authors, 36,37,43,44 including us, 20 that the 1140 cm −1 Raman peak is attributed to C u H bending mode of sp 2 carbon and positioned most likely in the diamond grain boundary. Both peaks ͑Raman 1140 cm −1 and HR-EELS ϳ375 meV mode͒ are attributed to ͑sp 2 ͒-carbon-hydrogen vibration.…”

Surface plasmon-related resonances on deep and asymmetric gold gratings

“…The impact of an increased grating amplitude on the optical response of the grating has been theoretically modeled by various authors. [11][12][13][14][15][16] In addition to the enhanced plasmon-plasmon interaction on deeper gratings that can be expected intuitively, new types of surface plasmon-related resonances have been predicted on deep grating structures. The main focus of this paper lies with an experimental investigation of these effects on deep grating structures of different degrees of asymmetry.…”

Surface plasmon polaritons on narrow-ridged short-pitch metal gratings

“…The SPP bands observed on gratings consisting of very deep (dϾ g ) and narrow (wӶ g ) grooves have been shown to be very flat-banded across all available wave vectors. 5,6 Through modeling it has also been shown that it is possible to excite these flat-banded SPP's on zero-order gratings where SPP excitation would not be possible on lower aspect ratio structures. [7][8][9] However, the resonant absorption bands are found to be very broad and shallow.…”