Síntese, modificação superficial e propriedades de nanoestruturas de semicondutores

resumo

This thesis describes new research on the synthesis, surface chemical modification and properties of several semiconductor nanostructures. In particular metal chalcogenide nanoparticles such as ZnE (E= O, S, Se) and LnS (Ln= Eu and Er) have been investigated. The first chapter consists on a literature review of recent work on the chemistry and fundamental properties of semiconductor nanostructures. This introduction has privileged work directly related to the systems described in the following chapters. The chemistry of ZnO nanoparticles and their transition metal doped analogues was investigated in chapter 2. Subsequent studies were made on surface modification methods, such as the synthesis of polymer based nanocomposites by in situ miniemulsion polymerization. These studies, together with the optical and magnetic characterization, have been relevant to understand the localization of the dopant ions on the ZnO host. In chapter 3, complexes of bis-dialkyldithiocarbamato and bisdialkyldisselenocarbamato of tris-aminozinc (II) were prepared with the aim of being used as single-source precursors for the synthesis of ZnS and ZnSe nanostructures. This research was conducted to obtain nanostructures using a method that allows control over their crystalline phases and, morphological and optical properties. In chapter 4 various lanthanide dithiocarbamate complexes were investigated as single-molecule precursors for the preparation of lanthanide sulfide nanoparticles, specifically for EuS and ErS materials. The insertion of EuS nanoparticles into various polymer matrices was investigated. Miniemulsion in situ polymerization was used to form stable emulsions composed of composite nanoparticles containing a semiconductor phase and a polymer. The influence of various experimental parameters was investigated on the final characteristics of the nanoparticles, particularly on the morphological and magnetic properties. The research described in chapter 5 has focused on the use of vegetable oils as solvents to produce ZnSe and ZnS-capped ZnSe nanoparticles. The aim of this work was to develop an alternative green method to synthesize core/shell semiconductor nanoparticles. The nanostructures obtained by this method were characterized and their properties were compared to those obtained in conventional high-boiling point solvents. The as prepared ZnSe nanoparticles were then modified with a second semiconductor phase (ZnS) and the photoluminescence and surface nature, before and after surface modification, were investigated.

autores

Angela Sofia Santos Pereira

nossos autores

orientadores

Tito da Silva Trindade

Grupos

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