Local electric and magnetic fields in semicontinuous metal films: Beyond the quasistatic approximation

Abstract

A theory of optical, infrared, and microwave response of metal-dielectric inhomogeneous films is developed. The generalized Ohm's law is formulated for the important case, when the inhomogeneity length scale is comparable with or larger than the skin ͑penetration͒ depth in metal grains. In this approach electric and magnetic fields outside a film can be related to the currents inside the film. Our computer simulations, with the use of the generalized Ohm's law approximation, reproduce the experimentally observed prominent absorption band near the percolation threshold. Calculations show that the local electric and magnetic fields experience giant spatial fluctuations. The fields are localized in small spatially separated peaks: electric and magnetic hot spots. In these hot spots the local fields ͑both electric and magnetic͒ exceed the applied field by several orders of magnitude. It is also shown that transmittance of a regular array of small holes in a metal film is strongly enhanced when the incident wave is in resonance with surface polaritons in the film. In addition, there is a skin resonance in transmission, which is of a purely geometrical nature.

Surface-enhanced Raman spectroscopy at single-molecule scale and its implications in biology

“…To achieve this EF, nanostructures with hot spots are the prerequisite as demonstrated since the first observation of SM-SERS in 1997 [18,19]. A class of silver and gold nanostructures that has provided large EFs is colloidal aggregates [55], as well as metal evaporated films [56] and, most recently, modified scanning tunnelling microscopy (STM) tips [57]. Although the easiest route to achieve SM-SERS is to use the aggregated metal colloid, which could be obtained by simply changing the solvent and the ionic strength, the aggregation state is hard to control because signals from randomly aggregated nanoparticles often suffer from uncertainty in the size of aggregates and geometry.…”

Tuning Gold Nanorod-Nanoparticle Hybrids into Plasmonic Fano Resonance for Dramatically Enhanced Light Emission and Transmission

“…28,29 Semicontinuous gold films support both localized and delocalized surface plasmon modes and have a much stronger local field enhancement than continuous thin film. 30 Both the metallic nanorod array and semicontinuous film are commonly used as SERS substrates due to large local field enhancements, [31][32][33][34][35][36][37][38][39] so the plasmon coupling in our nanorod-film hybrid is also expected to further enhance the local field and improve the sensitivity of SERS. In our studies, the long-axis SPR of the Au nanorod array is tuned by adjusting the rod length and the SPR of the semicontinuous Au film is tuned by controlling the sputtering deposition time.…”

“…30 Both the metallic nanorod array and semicontinuous film are commonly used as SERS substrates due to large local field enhancements, [31][32][33][34][35][36][37][38][39] …”

Radar absorbing materials based on titanium thin film obtained by sputtering technique

“…Based on such equation, it is possible to estimate that titanium films with thickness values near 4.0 nm attenuate nearby 100% of the incident electromagnetic wave. This behavior is explained by the increase of defects in the crystalline structure of the nanofilm as the thickness decreases, which favors the losses in the metallic film, as cited in the literature (Bosman, Lau and Gilgenbach, 2003;Shubin et al, 2000).…”

“…The variation of this parameter (δ) depends on the characteristics of the metallic material used in the film production, mainly its electric conductivity, and also on the incident radiation wavelength that interacts with the film (Ohring, 1991). When the metallic layer thickness is adequate, the resulting electric current becomes confined into the film (Salmon, 1993) and losses occur (Bosman, Lau and Gilgenbach, 2003;Shubin, et al, 2000).…”