Structure and Dynamics of Colloidal Tin Dioxide Nanoparticles

Tin dioxide (SnO2) is a versatile material with functional properties relevant to gas sensing, energy storage and optoelectronics. In these applications structural stability, agglomeration and dispersion behavior, as well as film formation directly influence device performance. Therefore, a comprehensive structural characterization across multiple length scales – from the atomic to the mesoscale – is important for the processing and application of colloidal SnO2 nanoparticles. The aim of this thesis is to investigate the structure of phase-pure SnO2 nanoparticles generated via chemical vapor synthesis. The particles are characterized by a well-defined size, high crystallinity and narrow size distribution. The focus of this study is a detailed structural analysis of the atomic local structure, crystal structure and microstructure. The crystal structure and local structure are characterized by X-ray diffraction and X-ray absorption spectroscopy. Initial atomistic models derived from crystallographic data are refined through reverse Monte Carlo simulations and reveal the high structural stability of the rutile phase of SnO2, even at particle sizes down to 2.3 nm and under modified surface hydration levels. The mesoscopic microstructure, as well as the agglomeration and deagglomeration behavior of colloidal tin dioxide dispersions are investigated using small-angle X-ray scattering (SAXS). Agglomerate size and mass fractal structure are characterized as functions of pH and ionic strength. In situ SAXS studies conducted using custom-built experimental sample setups enable observation of dynamic structural changes during ultrasonic deagglomeration and electrophoretic deposition (EPD). The temporally resolved measurements during ultrasonic agitation reveal the fragmentation mechanisms and structural reorganization of agglomerates under process-relevant ultrasonic conditions. In addition, time- and space-resolved nanofocused SAXS investigations during EPD indicate size-selective particle migration and the formation of particle concentration gradients in the vicinity of the deposition electrode, driven by the interplay of diffusion and electrophoresis. In summary, the combination of synthesis, processing and comprehensive structural characterization across multiple length scales, along with in situ investigations, provides a detailed understanding of the structure and dispersion behavior of colloidal SnO2 nanoparticles.