In this thesis, the behavior of metal thin films on metal-oxide support structures during thermal annealing was investigated with special focus on influences of the substrate as well as alloying effects on the process of solid-state dewetting (SSD). For the former, the first study examined how substrate polarity affects the structural evolution of Au thin films during high-temperature annealing, focusing on SSD, grain growth and interface structure. Therefor Au films were annealed on polar O-ZnO(000-1) and Zn-ZnO(0001) surfaces. A significant difference in thermal stability and texture evolution was found. While both samples showed the same texture dominated by Au(111)110 || ZnO(0001)11-20 orientation relationship (OR2) up to 600 °C, at higher T, the films on O-ZnO underwent SSD, while the Au on Zn-ZnO transitioned to a mazed bicrystal with Au(111)110 || ZnO(0001)10-10 (OR1) microstructure. Combining the experimental results with density functional theory (DFT) calculations, this behaviour could be linked to a decrease of adhesion energy for Au on O-ZnO with increasing T, while on Zn-ZnO the adhesion energy increases with T, stabilizing a closed film. Furthermore, DFT and electron microscopy reveal atomically sharp, energetically stable interfaces for both polarities. OR2 formed a semi-coherent interface with well-separated dislocations, while OR1 leads to an incoherent interface with local reconstructions. However, slight misalignments in OR1 can introduce screw dislocation networks, making the interface effectively semi-coherent. The second study on the influence of the substrate investigated how the substrate topography of conductive fluorine doped tin oxide (FTO) influences Pt nanoparticles (NPs) formation via SSD. Using in situ scanning transmission electron microscopy (STEM) and ex situ rapid thermal annealing (RTA) it was shown, that 5 nm Pt films on FTO dewet into a bimodal size distribution. This is caused by (i) reduced Pt thickness in the valley regions due to shadowing during deposition and (ii) curvature-driven diffusion, where Pt atoms migrate from elevated (positive curvature) to flat or recessed (zero/negative curvature) areas, both effects stemming from the FTO’s topography. Secondly, alloyed structures were prepared via SSD to (i) conduct a systematic study on the effect of alloying on SSD and (ii) tailor the interface between AuNi and c-Al2O3. In (i) bilayer AuNi and AuAg, as well as AuNi films with a chemical gradient were prepared to cover the whole concentration range of the binary alloys. This enabled a systematic study on the influence of alloying on SSD. By performing a quantitative texture analysis, a reduced texture was found for the alloyed particles when compared to the pure elemental particles. Furthermore, covering the whole concentration range revealed that the reduced temperature T/Tm (more precisely: T/Tliquidus) perfectly describes the SSD behavior of binary alloys. In (ii) the AuNi – Sapphire system was used to perform an interface design via controlling the lattice mismatch between AuNi particles and substrate, by controlling the lattice parameter of the alloy particles via the Au concentration. In this context, the lattice parameter was precisely tuned from slightly positive, over near matching to slight negative values. Conducting high resolution integrated differential phase contrast (HR-iDPC) imaging of cross-sectional samples, together with plan-view lamella preparation and interface sensitive in-plane XRD, the successful transformation from a semi-coherent interface (for negative and positive mismatch) to a nearly coherent interface for very small mismatches was demonstrated, proofing that interface engineering with potential applications in catalysis can be performed using SSD.
Martin Dierner (Thu,) studied this question.