Abstract
In recent years, hybrid nanostructures consisted of plasmonic metals and different dielectric materials have attracted much attention for their intriguing plasmonic properties. Recent studies have also shown that by introducing plasmonic metals, the photocatalytic efficiency of semiconductor can improve via plasmon-enhanced light absorption and plasmonic sensitization. In this thesis, excellent photocatalytic properties for hydrogen production have been demonstrated by utilizing the hexagonal close-packed Au/TiO2 hybrid nanocrystal arrays. By combining colloidal lithography, dewetting process driven by surface energy and atomic layer deposition, a large area of hexagonal close-packed Au/TiO2 hybrid nanocrystal arrays with 100-110 nm single crystalline Au core and 10-40 nm TiO2 shell are prepared with highly ordered periodicity and uniformity. To explore the localized surface plasmon resonance (LSPR) properties of the Au/TiO2 hybrid nanocrystal arrays, the scattering spectra were measured and compared with the simulation by Mie theory. The LSPR wavelength was found to be red-shifting and splitting into two LSPR peaks, correlating exactly to the simulated results based on Mie theory. Under both ultra-violet and visible light, significant increase in the hydrogen production from 20% methanol solution water splitting was achieved with the hybrid Au/TiO2 nanocrystal arrays in comparison with bare TiO2 thin film as well as the randomly distributed Au/TiO2 nanocrystals. From the finite difference time domain simulation, the significant increase in hydrogen production can be correlated to strong and optimum coupling of the enhanced electric field from LSPR in Au/TiO2 nanocrystal arrays. In addition to allowing more accurate measurement of plasmonic enhancement, the ordered nanostructures have been shown to be especially amenable to the systematic analysis of lateral coupling of plasmonically enhanced electric field. As a result, optimal structures with appropriate spacing of core-shell metal-dielectric nanocrystals, metal core size and dielectric shell thickness for maximum enhancement can be designed.