Design and preparation of nanostructures for applications

Abstract

The synthesis and properties of several nanomaterials such as PbS and PbS/CdS QDs are studied. In particular, several synthesis methodologies for the formation of single layer and multi layer polystyrene or poly(methylmethacrylate) thin films uniformly embedded with CdS or PbS nanoparticles are developed. The absorption, PL and nonlinear optical (NLO) properties of the PbS QDs dispersed in either hexane or in polystyrene polymer films are studied. Interesting size-dependent NLO properties were revealed by using the Z scan technique. Next, we have successfully prepared a series of different-sized core-shell PbS/CdS QDs and studied their optical and NLO properties using PL, transient absorption and/or Z-scan technique. We established the effect of free surface ligands and thickness of the polymer film on their optical limiting properties. Transient absorption pump-probe spectroscopy revealed that the relaxation kinetics of the PbS and core-shell PbS/CdS QDs are dependent on the excitation intensity, pump wavelength and probe delay time. We have also developed synthesis methodologies for the formation of PbS nanowires by using potentiostatic or cyclic electrochemical deposition using a commercial AAO template. Different segmented and core-shell metal/PbS nanowires are fabricated by using a step-wise pore widening deposition method and an investigation on the mechanism of formation is carried out. The conductivity of the PbS nanowires are studied using conductive AFM analysis. Lastly, a series of different phases of nanocrystalline MnOx are prepared for their applications as catalyst in the removal of CO. We explored in depth the crystal growth of MnO and Mn3O4 nanocrystals.