Fundamentals and applications of surface plasmon resonance using non-uniform gratings in azobenzene materials

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Optical nanostructures can be photo-inscribed as surface relief in azobenzene-containing solid thin-films due to the unique photomechanical behaviour of the azobenzene chromophores. In the simplest case, uniform sinusoidal surface relief diffraction gratings are inscribed in azobenzene films upon exposure to a collimated laser interference pattern from a Lloyd mirror interferometer. Compared to other nanofabrication techniques, the inscription of nanostructures in azobenzene films is relatively inexpensive, can be done in under a minute and consists of a single fabrication step with no post-exposure processing. These uniform surface relief gratings have been widely used in the past in photonics applications, such as planar optical waveguides, beam splitters, couplers and light filters useful in optical communications. Futuristic applications based on this class of materials would ultimately include light-activated nano-switches and motors, as well as transport of nanoparticles by light. In recent years, my group and I researched the fundamentals of the photomechanical effect in azobenzene materials, as well as harnessed their potential by developing novel photonics devices, such as non-uniform diffraction gratings, including constant- and chirped-pitch circular gratings over 1 cm in diameter. Upon coating our gratings with a thin metal layer, surface plasmons can be generated at the boundary between the metal layer and an adjacent dielectric medium. Plasmon resonance is currently a hot research topic because it enables significant enhancements in the performance of high-priority technological applications such as solar cells, light emitting diodes, imagers and sensors. When a plasmon is excited, the local electromagnetic fields at the metal-dielectric boundary are highly amplified in a narrow wavelength range, which provides an excellent opportunity for sensing and for light entrapment. My group and I published research papers on the use of non-uniform chirped gratings to widen the surface plasmon excitation bandwidth, on the active control of plasmon signals using an electrostrictive material, on the use of azobenzene nanostructures for photocurrent enhancements in thin-film solar cells, and on the development of plasmonic biosensors for detecting proteins and bacteria in water. Interestingly, we obtained an increase of over 300% in the power conversion efficiency from organic solar cells, achieved an impressive biosensing bulk sensitivity of over 778 nm per refractive index unit, and successfully detected E. coli bacteria for diagnosing urinary tract infections. The objectives of this proposal are to continue exploring the photomechanical effect in azobenzene materials and to fabricate novel plasmonic devices useful in optical communications, imaging and microscopy, microfluidics and planar photonics circuits, biosensing of bacteria in water solutions, air quality remote monitoring, as well as efficiency enhancements in thin-film solar cells.