In the presented study, we investigated differences in the microstructure of thin gold layers and layers of gold nanoparticles with a focus on their thermal development. Thin films composed of nanoparticles are interesting for applications because of their inherent high porosity, which is essential for gas sensing, efficient batteries, catalysis or hydrogen storage applications. The thermal stability of nanoparticle layers depends on chemical and phase composition, the configuration of nanoparticles or the atmosphere in which they are heated up and it is critical for multiple applications of gold nanoparticles.
The homogeneous gold nanoparticles in our study were prepared by magnetron sputtering from pure metal targets followed by aggregation of fragments to the metallic clusters, by so-called gas aggregation cluster sources. The gold thin films for comparison were prepared by evaporation and by sputtering. A Series of samples with various thicknesses deposited on silicon substrates were characterized after preparation and also under annealing up to 1000 °C in the air atmosphere.
Size distribution and morphology of nanoparticles were determined by small angle x-ray scattering (SAXS), atomic force microscopy (AFM) and confirmed by scanning electron microscopy measurements (SEM) for ex-situ annealed samples. In-situ measurements of x-ray diffraction were used to characterize the thermal evolution of lattice parameters, microstructural defects and sizes of crystallites.
The as-deposited gold nanoparticles contain a large amount of stacking faults (up to 6 %) and also significant microstrain in the crystal structure. During annealing, ordering of the structure is observed together with the step-like increase of the sizes of crystallites following the increase of the sizes of whole nanoparticles. The occurrence of the holes in the substrates after heating to the highest temperatures was successfully explained.