Chee Cheong Wong

SENSITIVITY OF PLASMONIC CRYSTAL WITH ACTIVE SOL–GEL THIN FILM

Plasmonic crystal or gratings with periodicity and amplitudes suitable for plasmon coupling can be fabricated using interference lithography technique. The grating structure is holographically formed in a photoresist film. This technique offers an easy way to control the vertical and horizontal ratio of the corrugated profile. Since surface polaritons are extremely sensitive to the changes at the metallic and dielectric interface, one can expect that by controlling this refractive index, an effective control of the SPP can be realized. Different diffracted orders can be explored by controlling the dielectric medium, in this case hybrid materials. A comprehensive simulation that models the effect of dielectric medium to the changes of SPP coupling condition has been undertaken for the reflectivity and azimuthal angle dependence. An active porous thin film, which is hybrid organic–inorganic materials synthesized by sol–gel techniques, starting from bridged polysilsesquioxanes with phenol red, is coupled on plasmonic crystals in order to exploit enhanced effective refractive index sensitivity for sensing purposes; in this case, we use hydrochloric acid as analyte. The porosity of film increases reacting surface area and chemical reactivity of the plasmonic crystal. This film will change color from yellow to orange red when exposed to the acid. The change of optical characteristic after matrix wetting in HCl 0.01 molar solution has also been characterized. The activity of the film is determined by the dielectric properties depending on an applied external electric and magnetic field. They constitute molecular-engineered materials that exhibit a fine control in porosity in order to control the permittivity of the dielectric medium. The optical, thermal, and structural characterizations of these films are investigated by ellipsometry, DTA, and FTIR measurements. We present this configuration as a sensitive architecture for plasmonic-based sensor application.

Sensitivity enhancement in 2D plasmonic crystals

In this paper, the author shows that a self-assembled monolayer of decanethiol (C10-SAM) molecules, which is only ∼1.3 nm in optical thickness, can be easily detected using 2D plasmonic crystal (PCL) with an angular shift as large as 2.86° which is more than one order of magnitude higher than conventional prism-based SPR and an estimated sensitivity larger than 900°/RIU is possible. The experimental data are accompanied by a model description that explains the principle of sensitivity enhancement. However the field enhancement of 2D PCL will be further improved when the optimum SPP excitation conditions are met.

Exploring the negative diffraction order in plasmonic crystals by refractive index engineering

In this paper an engineered dielectric material is used to introduce porosities which will change the plasmonic crystals (PCL) refractive index profile, its excitation conditions, electromagnetic (EM) characteristics and propagations. SPP excitation is moved from positive diffraction order (m=1) to negative diffraction order range (m=−1); hence the increment in wavelength will decrease the resonant angle. The m=−1 opens the possibility to control and manipulate the preferred excitation conditions of SPP for different purposes such as optical devices and sensors.