Investigations of ultrathin nanocrystalline metal films generated at the liquid-liquid interface

Abstract

The thesis presents the results of investigations on the preparation, characterization and organization of metal nanocrystals at the liquid-liquid interface, and exploring the formation of their mesoscopic assemblies. Section 1 contains a brief overview of nanocrystals and their mesoscopic organization. Section 2 contains the scope of investigations as well as the results and discussion. Section 3 covers other studies undertaken by the candidate. The Liquid-liquid interface serves as an excellent nanoreactor where the interaction among the reacting species from the two immiscible layers is confined due to the interface. Synthesis of nanocrystalline filM.S. of Au, Ag, Pd and Cu metals and their alloys using the liquid-liquid interface has been carried out by this elegant, yet simple technique. Control parameters such as type of solvent, solution concentration, temperature, viscosity and mechanical vibrations-all influence the nanocrystal formation. Thus, it has been possible to achieve good control over the particle size and the extent of packing in mesoscopic assemblies. Nanocrystalline Au filM.S. so prepared have been investigated for their optical and electrical properties. The course of growth of Au nanocrystalline filM.S. at the interface has been studied using small angle X-ray scattering. Rheological properties of Ag filM.S. at the interface have also been examined. Besides monometallic filM.S., nanocrystalline alloy filM.S. of Au-Ag, Au-Cu and Au-Ag-Cu have been prepared by suitably mixing metal precursors in the top organic phase. By adding surfactants to either of the layers, the formation of dendritic structures and fractal assemblies has been observed. The nanocrystalline filM.S. of Au have been chemically modified by adsorbing thiols of various types, such as alkane thiols of different chain lengths as well as conjugated dithiols. The modified filM.S. have been examined for their structural, optical and electrical properties. This aspect of the study has enabled to understand the dependence of the surface plasmon band and other characteristics on the interparticle separation. Apart from above studies, a small electrode system was designed and fabricated to study single molecular properties using two identical palladium nanocrystals, and scanning tunneling microscopy to study molecular properties.