Highly Sensitive Plasmonic Structures Utilizing a Silicon Dioxide Overlayer

Abstract

In this paper, simple and highly sensitive plasmonic structures are analyzed theoretically and experimentally. A structure comprising a glass substrate with a gold layer, two adhesion layers of chromium, and a silicon dioxide overlayer is employed in liquid analyte sensing. The sensing properties of two structures with distinct protective layer thicknesses are derived based on a wavelength interrogation method. Spectral reflectance responses in the Kretschmann configuration with a coupling BK7 prism are presented, using the thicknesses of individual layers obtained by a method of spectral ellipsometry. In the measured spectral reflectance, a pronounced dip is resolved, which is strongly red-shifted as the refractive index (RI) of the analyte increases. Consequently, a sensitivity of 15,785 nm per RI unit (RIU) and a figure of merit (FOM) of 37.9 RIU−1 are reached for the silicon dioxide overlayer thickness of 147.5 nm. These results are in agreement with the theoretical ones, confirming that both the sensitivity and FOM can be enhanced using a thicker silicon dioxide overlayer. The designed structures prove to be advantageous as their durable design ensures the repeatability of measurement and extends their employment compared to regularly used structures for aqueous analyte sensing.

Optical Processes behind Plasmonic Applications

“…The position of the resonance peak depends on the size and shape of the nanoparticle, as well as the refractive index of the surrounding medium [ 136 , 137 , 138 ]. Plasmonic sensors operate by monitoring changes in the resonance wavelength that occur when analyte molecules bind to the surface of the nanoparticle, altering the local refractive index.…”

Optical and Mechanical Properties of Layered Infrared Interference Filters

“…The paper [ 9 ] describes measures aimed at improving the performance of a non-dispersive infrared methane gas sensor by using multilayer thin-film bandpass filters containing germanium (Ge) and niobium pentoxide (Nb 2 O 5 ) and based on alternating layers with a high and low refractive index, respectively. The researchers [ 10 ] developed a highly sensitive plasmonic layered structure containing layers of chromium, gold, chromium, and silicon dioxide deposited on a BK7 base for measuring a liquid analyte.…”