Aluminum Nanostructures For Surface Enhanced Spectroscopy

The novel and burgeoning technique of localized surface plasmon resonance （LSPR） has tremendous potential in molecular detection, bioimaging and photocatalysis. Aluminum is a potential plasmonic material besides noble materials with an extended response into the deep UV region. The key for plasmonic materials hinges on the development and fabrication of patterned nanostructures with tunable size and shape to adjust their plasmonic modes with the incident light, which is key in this dissertation. Our study is outlined as follows:1. Detection of multiple analytes by surface enhanced spectroscopy is a challenge due to the compromise between the high enhancing efficiency and broad response bandwidth. A facile way to fabricate and synthesize functionalized aluminum based nano-islands by metal ion implantation is demonstrated by embedding silver in an aluminum film. In this technique, the ion energy and fluence can be tailored to control the subsurface location of the fabricated metal nanostructures and the resulting bimetallic structure with a broad plasmon band ranging from deep UV to visible is demonstrated ideal for optical detection of multiple analytes. This technique greatly promotes the applications of aluminum plasmonics.2. The fluorescence signal depends on the distance between the emitter and substrate, which have a great effect on the excitation and emission process. Distance dependent phenomenon is studied by adjusting the thickness of a protective layer between the substrate and fluorescent molecules. It is found that the fluorescence intensities increases at first but then diminishes with distance due to the combined action of enhancement and quenching. It is demonstrated that the ideal distance is 10 nm for the protective layer in surface enhanced fluorescence and the result is convinced by our simulation results.3. Template based methods for the fabrication of precisely controlled aluminum nano-arrays are illustrated. It is observed that the LSPR modes of aluminum nanovoids can be smoothly tuned to overlap the TiO2 bandgap, which promotes the plasmonic photocatalytic properties of TiO2/Al nanoarrays by photovoltaic conversion. An enhanced decay rate of more than 7.2 folds is observed from the Rhodamine B degradation process by analyzing the UV-vis spectra. The experimental results are in consistent with our simulation results from the finite-difference time-domain method.4. Al/TiO2 plasmonic material for photocatalytic applications is studied to reveal the involved mechanisms. The underlying mechanisms concerning the radiative energy transfer and interface energy transfer processes which occur at the TiO2/Al interface are discussed and their contributions to photocatalysis are evaluated. Our results show that photocurrent still exists without external voltage, meaning that the native Al2O3 oxide layer cannot totally hamper the hot charge transfer process formed by the Schottky barrier at the TiO₂/Al interface.