Grant: Discovery Grants Program - Individual

Holographic nanostructures can be photo-induced as surface-relief in azobenzene-containing solid thin-films due to the reversible trans-cis photo-isomerization of the azobenzene chromophores. In the simplest case, linear surface-relief diffraction gratings are inscribed on azo thin-films upon exposure to a collimated laser interference pattern. The inscription of nanostructures on azo films can be done in a few minutes and consists of a single fabrication step. This makes them highly advantageous compared to other nanofabrication techniques. The resulting nanostructures are stable over time and can be coated with other materials, depending on the application. My group has recently developed new experimental techniques to inscribe non-linear surface-relief structures on azo films. For example, we successfully inscribed holographic representations of cylindrical and spherical lenses as chirped-pitch diffraction gratings. These gratings focalized a probing light beam just like a real physical lens. We also designed and fabricated a novel conical fixture that enabled the production of both constant-pitch and chirped-pitch circular surface-relief gratings. Upon coating these novel non-linear nanostructures with a thin metallic layer, surface plasmons could be generated. These plasmons are resonant electromagnetic waves that propagate at the boundary between the metal layer and an adjacent dielectric medium. Upon excitation of the plasmon, the local electromagnetic fields at the boundary are highly amplified. These fields could extend up to 200 nanometers above and below the interface and this results in light entrapment and enhanced transmission throughout the dielectric layer. Surface plasmons are normally generated if several parameters are simultaneously satisfied. This allows them to be equally used as sensors. The objective of this proposal is to study and optimize the generation of surface plasmons in those novel non-linear nanostructures which where inscribed on azo thin-films. We will study the various parameters required to excite the strongest plasmons in circular gratings. We will also optimize the chirped-pitch gratings for optimal light bandwidth excitations, as well as utilize them as plasmonic energy concentrators. These gratings will be incorporated in thin-film solar cells and organic light emitting diodes, which will act as the dielectric media. The goal is to achieve substantial and controllable surface plasmon enhancements over a wide light bandwidth as well as in all light polarizations. This will be done by methodical studies on the nanostructures' shape and their influence on the plasmon excitation. These nanostructures will also be studied for their potential use in sensing applications, particularly biosensors.