Homo- und Heterometallische Alkoxide der Gruppe 13 zum Einsatz in der Materialsynthese: Einfluß des Vorstufendesigns auf die Materialzusammensetzung

Abstract

A series of homoleptic aminoalcoholates of aluminium, gallium and indium was synthesised and characterised. The monomeric nature of all alkoxides was indicated by NMR spectroscopy in solution and was confirmed for the solid state via single-crystal XRD. These monomeric derivatives are the first structurally characterised homoleptic alkoxides of these metals, which was achieved by a combination of coordinative saturation via the amine donor functionality and steric shielding. Additionally, novel thioether functionalised gallium and indium alkoxides are presented. NMR spectroscopic investigations propose a monomeric state for these alkoxides with a weak interaction of the thioether moiety with the metal centre. In case of asymmetrically functionalised alcoholates featuring amine or ether donors alongside the thioether functionality, coordination of the latter is suppressed and only the stronger amine or ether donor interacts with the metal centre. These findings have been confirmed for the solid state via single-crystal XRD for a limited number of derivatives. Applying these thioether functionalised alkoxides in molecule-to-material conversion processes showed their potency to act as single-source precursors for the formation of oxysulphide materials, which are typically prepared via multi-step or multi-source procedures. Employing LPCVD, gallium alkoxides were converted to amorphous Ga2O3-xSx thin films with strong dependence of the sulphide content of temperature and precursor species. Sulphide contents reached a maximum of x = 1.17 at low temperatures (400 °C) as obtained via EDX analysis. XPS measurements showed that thin films grown at low temperatures incorporated thioether fragments from incomplete decomposition. Pure sulphide containing oxide coatings could be obtained at temperatures >500 °C with sulphide contents up to 12 at%. Impedance spectroscopy of selected thin films deposited on interdigitated electrodes showed drastically increased electrical conductivity accompanied by lower activation energy upon oxysulphide formation when compared to a Ga2O3 reference. Investigations of the mechanism of sulphide incorporation via TGA-MS revealed a strong supportive role of the amino functionality in asymmetric aminoalcoholates leading to in situ formation of H2S as a potent sulphidisation agent. Using hot-injection methods all alkoxides could be converted into oxysulphide sub-micron particles exhibiting high sulphide contents. Indium based materials showed particularly high sulphide contents with pure In2S3 phases found in XRD analysis, most likely because of lowered In-O bond strength and hence facilitated conversion to the sulphide. AACVD processes using indium based alkoxides showed the formation of sulphide rich In2O3-xSx thin films and 1D nanostructures. Lastly, a series of transition metal gallates [MIIGa2(OtBu)8] was prepared and characterised via single-crystal XRD showing the expected spirocyclic arrangement. Using them in sol-gel and LPCVD processes led to the formation of the respective MIIGa2O4 spinels for M=Co, Ni. In contrast, for M=Fe, non-stoichiometric deposits and phase separation was observed, most likely caused by susceptibility of the precursor towards oxidation. Copper gallates exhibited thermal instability and increased reactivity leading to copper deficient thin film deposits and phase separation upon sol-gel processing.