Spectroscopic characterization and charging

Abstract

The purpose of this work, is to investigate optical and electrical properties of bimetallic alloy and core-shell Au and Ag nanoparticles by optical spectroscopy and XPS, respectively. Several objectives have been pursued in achievement of the goals. First goal is to investigate the tunability of optical properties of bimetallic Au and Ag alloy and core-shell nanoparticles due to changes in composition and structure. The second goal is to study the possibility of charge-storage on single metal particles, especially on Au and Ag, and bimetallic alloy forms of the corresponding nanoparticles in solution. Within this framework, bimetallic Au-Ag alloy and coreshell particles are synthesized, then their electron-storage capacities in aqueous media by introduction of sodium borohydride is followed by spectral shifts in their surface plasmon resonance bands. Moreover, the parameters like composition, structure, affecting the charging ability of particles are reported by means of optical spectroscopy as well. In addition, electron storing/releasing capacities of Au and Ag nanoparticles and their kinetics are investigated. In the second part, main focus is to investigate optical and electric properties by surface modification through incorporating Au and Ag nanoparticles within dielectric shell (silica and titania). Therefore, small Au@SiO2, Ag@SiO2, and Ag@TiO2 core-shell nanoparticles with the metal core size ca. 5-7.5 nm and the shell size ca. 3-7.5 nm are synthesized and optical properties of these nanoparticles are studied. These nanoparticles are also analyzed by XPS under external biasing to get further understanding of their charging capacities. Additionally, we investigated incorporating metal nanoparticles within titania shell to provide enhanced photoactivity through the metal core by means of increased charging capacity.