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Abstract

This thesis deals with the liquid cell transmission electron microscopy (LCTEM) technique. LCTEM is currently at the frontier of the research into nanomaterials, since it enables in situ in-liquid nanoparticle-synthesis experiments at a sub-nanometer spatial resolution. LCTEM allowed us to make observations of the nucleation, growth/dissolution, and movement of nanoparticles in situ in a liquid. For this purpose, three different synthesis systems were applied: gold-based, yttrium-based, and iron-based.
It was found that for all the selected systems, radiolysis, induced by the 200-kV electron beam of a transmission electron microscope (TEM), has the predominant effect on the nanoparticle synthesis. In order to mitigate the radiolysis effects and produce reliable data about in situ nanoparticle synthesis, the kinetic radiolysis model was built. For the case of gold nanoparticle synthesis from a gold(III) chloride trihydrate solution, we could predict the gold nanoparticle precipitation/dissolution in relation to the induced dose rate and the temperature parameters. Kinetic radiolysis model predictions were matched with LCTEM in situ experiments, proving the model is valid for this experimental system and that it can be further expanded to other technologically important material systems. In the thesis, procedures for obtaining quantitative and replicable data with the LCTEM technique are thoroughly discussed.
In the case of the yttrium-based system as a model phosphor material, ex situ synthesis of the nanoparticles was performed from urea and a yttrium acetate hydrate solution. The experiments were replicated under the same conditions using the LCTEM technique. Both methods yielded the same result - amorphous yttria nanoparticles. In the second step, nanoparticles were annealed, which transformed them into crystalline yttrium hydroxide that could be used in the future in photonics. This is believed to be one the first reports of the synthesis of hydroxide powders using the LCTEM technique.
Iron nanoparticles were synthesized from Iron(II) sulfate heptahydrate, sodium citrate, and sodium sulfate solution using the electrochemical approach. First, a cyclic voltammetry study inside the LCTEM was used to investigate the electrochemical behavior of the studied Fe-based system. Based on these studies, the conditions for potentiostatic Fe deposition were determined, and the Fe deposition was performed for E= -1.1 V vs Pt quasi reference electrode in situ under dynamic conditions. Experiments were replicated under the same conditions using LCTEM. The synthesized nanoparticles were γ-iron, which is a material with interesting ferromagnetic properties.
Finally, artifacts resulting from radiolysis are shown and procedures for its mitigation are discussed.