Microstructure of polycrystalline gold nanoparticles and thin-films from a comparative X-ray line profile analysis

Polycrystalline structures, such as nanoparticles and thin-films, commonly broaden X-ray line profiles due to the presence of dislocation substructures. In this study, the microstructures of gold nanoparticles (AuNPs) and gold thin-films (AuTFs) were analyzed through X-ray line profile analysis according to a series of integral breadth methods. Our estimations suggest, in all cases, a larger crystallite size for AuTFs of about 8.0 +/- 2.0 nm. However, our calculations yielded a very low dislocation density of the order 10(13) (m(-2)) for AuTFs, whereas it is one order higher in AuNPs. The estimated upper limit of strain was calculated as about 0.28 and 0.068 for AuNPs and AuTFs, respectively. With the assumption of the presence of strain, the averaged distances among dislocations are lower in AuNPs (40.8 nm) than AuTFs (163.2 nm). Therefore, it has been suggested that the broadening in AuNPs arises from both small crystallites and microstrain effects, whereas it arises in AuTFs mainly due to size effects. These results allow the identification of reflections with a particular state of strain and outline the presence of anisotropy in the samples. A notorious characteristic is the peak broadening in the (200) and (311) reflections. In particular, the broadening in the plane (200) suggests that the source of the strain is due to dislocations in the a/2<110>{111} primary slip system. Contrast factor calculations indicate that edge-type dislocations contribute to the presence of strain. A qualitative description of the edge/screw characteristics of dislocations is shown using a graphical representation for the displacement field in both edge and screw <110>{111} slip systems. The lattice parameter was extrapolated as about 4.0739 and 4.0746 angstrom for AuNPs and AuTFs, respectively.

Automated summary

X-ray line profile analysis was used to study the microstructures of gold nanoparticles and gold thin-films, revealing larger crystallite size and lower dislocation density in AuTFs compared to AuNPs. The differences in strain, average distances among dislocations, and broadening effects were observed between AuNPs and AuTFs, suggesting different mechanisms contributing to the line broadening in the two types of samples.