Browsing by Subject "Grating Coupled Surface Plasmon Resonance"

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Open Access
Design, fabrication and characterization of surface plasmon resonance based MEMS displacement sensors
(2009) Güner, Hasan
Strong dependence of surface plasmon resonance (SPR) on coupling parameters offers new varieties of sensing mechanisms in nano and micro-scale engineering fields. In this study, design, fabrication and characterization of MEMS displacement sensors that utilize angular dependence of grating coupled SPR condition are explored. Several surface plasmon polariton (SPP) excitation mechanisms are reported in the academic literature. One of them which is quite adaptable to microelectromechanical systems is grating coupling scheme. In this scheme, thin metallized grating structures are particularly designed depending on the desired wavelength and the angle of incidence of the SPP excitation light. Geometric parameters like periodicity, surface profile, depth and duty cycle of the grooves and material parameters like dispersion and thickness of the top metal layer have to be chosen with care in order to reach sharp SPR curves in the reflected intensity spectra with respect to either wavelength or angle of incidence. As the first step, geometric and material parameters of SPR gratings are numerically optimized using rigorous coupled-wave analysis (RCWA). Angular quality factors on the order of tens are shown to be achievable. Various lithographic techniques (nanoimprint, electron beam and optical lithography) are used to nanofabricate those certainly defined gratings. It is observed that p-polarized reflected intensity measurements using spectroscopic ellipsometry are in quite good agreement with those numerically calculated. Spectroscopic scan measurements are also provided to show the polarization dependence of SPP excitation. All effort to obtain high angular Q-factor grating structures is aimed at enhancing the sensitivity of angular displacement detection scheme. In this scheme, angular position of the grating structure in the polarization plane is detected through the reflected intensity response of the photodetector. Dependence of sensitivity on excitation light source wavefront parameters and photodetector noise are analyzed. MEMS displacement sensor designs relying on the principle of angular displacement detection scheme are developed. Simply, SPR grating structures are transferred on conventional micromembranes. Two types of such particular designed micromembranes are introduced: corrugated microcantilevers (singly clamped) and corrugated microbridges (doubly clamped). They are fabricated through well-known surface micromachining processes in addition to SPR grating nanofabrication procedures. Mechanical resonance frequencies, flexural mode shapes and effective spring constants are analytically, numerically and experimentally obtained. In addition, a MEMS accelerometer design with plasmonic readout with nano-G noise floor is presented. An experimental configuration for micromechanical displacement sensing is investigated. According to the results of this work, novel arrayed sensors combining the sensitivities of plasmon resonance and micromembrane type sensors may provide unprecedented performance.
Open Access
Electrochemically swithable plasmonic surfaces
(2014) Karayalçın, Nihat Serkan
In this study, we design and produce grating coupled surface plasmon surfaces which are switched by electrochemistry. Grating structures are fabricated using digital versatile discs (DVDs) which are commercially available. According to atomic force microscopy (AFM) results, we categorize the different grating structures in two groups, namely shallow and deep gratings. Plasmonic properties of the surfaces are investigated using numerical simulations. Gold and silver are used as plasmon supporting metallic layers on gratings. Refractive index sensitivity of the plasmon resonances are studied using deionized water, air and glycerol solutions as the dielectric media and results are compared with simulations. Experimental results are coherent with the simulations in terms of reflection spectra. Electrochemical switching of plasmonic properties may have applications in tunable and switchable filters, as well as enhanced colorimetric sensing. We deposit ultrathin films of copper on plasmonic surfaces and investigate reversible changes in the plasmonic properties. Copper sulfate is selected as the electrolyte. Cyclic voltammetry is performed on plasmonic surfaces while monitoring optical reflectance. Copper is observed to deposit in the form of nanoislands on silver and gold films rather than uniform thin films. The effect of copper deposition on the plasmonic properties of the grating structure is simulated by Lumerical software and is seen to be two fold. For small effective thickness of copper nanoislands, the plasmon resonance condition shifts, whereas for thicker copper deposition plasmonic resonances are eliminated. Finally, copper's oxidation and reduction reactions are controlled by changing applied voltage thus shifting the resonance wavelength. Resonances are switched reversibly multiple times not only for different molarities but also for different grating sructures and plasmon supporting metallic layers . In summary, we demonstrate that plasmonic properties of nanostructured metallic surfaces can be controlled by electrochemistry. Switchable resonance surfaces can be used as dynamic filters or may enhanced contrast in plasmon resonance imaging applications.