Structure and Light Emission in Germanium Nanoparticles

PhDIn this study, advanced techniques in the synthesis of germanium nanoparticles have been investigated. Based on physical and chemical production methods, including stain etching, liquid-phase pulsed laser ablation, sol-gel synthesis and two benchtop colloidal synthesis techniques, germanium nanoparticles with various surface terminations were formed. Out of those, colloidal synthesis by benchtop chemistry (named CS1) were found to be the most promising synthesis route in terms of yield and stability of the as-prepared Ge qdots and its luminescence with almost no oxides present. For the characterisation of Ge nanoparticles, Raman spectroscopy, Photoluminescence (PL) spectroscopy, Transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDX) and selective area electron diffraction (SAED) techniques were utilised before conducting X-ray absorption spectroscopy (XAS) measurements. The structure and morphology of Ge quantum dots formed using colloidal synthesis routes were found to fit best to the model of a nanocrystalline core surrounded by disordered Ge layers. Optically-detected X-ray absorption studies have enabled us to establish a direct link between nanoparticles structure and the source of the luminescence. The most important outcome of this study is that it provides a direct experimental route linking synthesis conditions and properties of nanosized Ge quantum dots. Furthermore, using annealing, we can control surface termination even further, as well as change particle size and possibly produce metastable phases.School of Physics and Astronomy, Queen Mary University of Londo