Metal oxide nanocrystals: Spatial control via polydimethylsiloxane ligands and quantitative composition analysis by XPS

Metal oxide nanoparticles have been widely used as catalysts and sensors because of their unique surface and interface properties. However, because of the scale, it is still a challenge to control the spatial distribution and to characterize the composition of these metal oxide nanoparticles. In the first part of this dissertation, we were able to control and to vary the interparticle spacing among gamma-Fe2O3 nanoparticles on the surface or in the solution by grafting different molecular weight of carboxylic acid terminated polydimethylsiloxane (PDMS-COON) onto the nanoparticles. The phase behavior of the PDMS grafted gamma-Fe2O3 nanoparticles in the bulk PDMS homopolymer blends was also studied. It was found the dispersion of Fe2O3-PDMS colloids in the PDMS homopolymer is strongly depended on the ratio of grafted ligand length to the blend homopolymer length. The Fe2O3-PDMS complexes can be further converted to Fe2O3-SiO x membranes by treating with UV/ozone. These composite oxide membranes were successfully used as the catalysts to grow carbon nanotubes under CVD with several advantages over other techniques. In the second part of this dissertation, we used X-ray Photoelectron Microscopy (XPS) to quantitatively analyze the core-shell structure of Cu2O nanoparticles, i.e. the amorphous CuO shell and the crystalline Cu2O core. Although copper oxides are not stable under the X-ray irradiation, we were able to overcome this difficulty and the CuO shell is estimated to be 0.5 nm by this procedure. This characterization is very important as the catalytic properties of metal oxide nanoparticles are strongly depending on the metal ion state and their composition.