Silica-coated Anisotropic Semiconductor Nanocrystals as Building Blocks for Plastic Crystals

Abstract

In this thesis, 1D and 2D anisotropic semiconductor nanocrystals are coated with silica in a reverse microemulsion to obtain water-soluble nanoparticles that are protected towards oxidation and photo-degradation. An extensive study on the effect of ammonia (which plays a catalytic role in the silica shell formation) on the resulting silica shell leads to a versatile method that can be widely used to coat anisotropic nanocrystals with a uniform and size-tunable silica shell. Furthermore, modification steps are explored to use these silica-coated semiconductor nanocrystals as building blocks for long-range liquid crystals, better known as plastic crystals. In this respect, it is essential to obtain long-range interparticle repulsion, which can be achieved by charge-stabilization of the nanoparticles. Therefore, the silica-coated nanocrystals are functionalized with an organic ligand and consequently transferred to a nonpolar solvent. The challenge however remains to measure these nanometer-sized objects when these are dispersed in a liquid medium, which is needed to detect plastic crystal phases.