The paper is a review of surface plasmon resonance (SPR)
structures containing amorphous chalcogenide (ChG) films as plasmonic
waveguides. The transfer matrix method was used for calculation of light
intensity reflected from SPR structure. The method permits the calculation of
reflectance for arbitrary number of layers. Specific characteristics of a
four-layer SPR structures containing prism, metal, thin dielectric film and
ambient medium were obtained by using a software realized in MATLAB. The
results are presented for structures containing amorphous As2S3 and As2Se3 thin
films characterized by a high refractive index and a metallic layer made of
gold. The requirements to the metallic
films are the same as in the case of widely known three-layer structures with
SPR. The paper is mainly based on our previously obtained and published
scattered results, to which a generalized point of view was applied.
The analysis shows that with the correct choice of film
thickness and of refractive index, it is possible to control the resonance
angles, the sharpness of the SPR resonance curve, the penetration depth, and
the sensitivity to the refractive index of the analyte. Aspects regarding the
choice of the coupling prism are studied. It was shown that in the case of GaP
prisms with a refractive index greater than that of the waveguide, the entire
spectrum of modes can be excited, which is generally understandable. However,
it was found that at a certain waveguide thickness, the excitation of one
selected mode is also possible with a prism having the refractive index lower
than waveguide film material. This case is very important for practice, since
it allows us to make a prism from ordinary materials, like of BK7 glass. The
gold film thickness must be optimized in order to obtain near zero value of the
resonant reflectance. It corresponds to 40 nm in the near IR spectrum and 50 nm
in VIS spectrum for which R~0 can be obtained. The waveguide thin film
thickness permits the adjustment of SPR sensor’s sensitivity.
Optical hysteresis was detected and explained in SPR
resonance structure containing an amorphous As2S3 film, which have self-induced
changes of the refractive index. Although such changes are small under normal
conditions, the resonant conditions greatly enhance the effect, allowing for a
transition to practical application. The four-layer structure of the SPR makes
it possible to identify alcohols and hydrocarbons even with small differences
in refractive index. The numerical model viability was experimentally
demonstrated by identification of E. coli bacteria. The usefulness of other
materials with high refractive index were discussed. However, the As-S-Se
materials have the advantage of producing thin films with smooth surfaces due
to their amorphous state.
Author(s)details:-
Aurelian
Popescu
National Institute of R&D for Optoelectronics INOE 2000, Romania.
Dan
Savastru
National Institute of R&D for Optoelectronics INOE 2000, Romania.
Mihai Stafe
Department of Physics, University Politehnica of Bucharest, Romania.
Nicolae
Puscas
Department of Physics, University Politehnica of Bucharest, Romania.
Please See
the book here :- https://doi.org/10.9734/bpi/cmsdi/v1/11917F
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