Electron Backscatter Diffraction of Gold Nanoparticles

Abstract

Electron Backscatter Diffraction (EBSD) is a well-developed technique used to perform quantitative microstructure analysis in the Scanning Electron Microscope (SEM); however, it has not been widely applied towards studying nanostructures. This work focuses on the use and limitations of EBSD in the characterization of Au nanoparticles on an MgAl2O4 substrate. Samples under investigation are prepared by depositing a thin film of Au on an MgAl2O4 substrate, and then finally heated in a furnace to induce dewetting and cluster formation. The challenges of obtaining crystallographic information from nanoparticles using EBSD are qualitatively and quantitatively described through an evaluation of the quality of the diffraction pattern at various locations of the primary electron beam on the nanoparticle. It is determined that for a high quality Electron Backscatter Diffraction Pattern (EBSP), the production of diffracted backscattered electrons travelling towards the detector must be high and the depth of the source point must be low. The top of the nanoparticle, where the local geometry of the system is similar to the geometry of a macroscopically flat sample, is found to produce diffraction patterns of the highest quality. On the other hand, reversed-contrast EBSPs are observed when the beam is positioned near the bottom of the nanoparticle. In addition, crystallographic information for each individual nanoparticle is gathered using EBSD. Each individual AuNP is observed to be single crystalline. Finally, the complete ensemble of crystalline orientations for individual nanoparticles is then compared to the global averaged crystallinity of the sample, as measured by X-ray diffraction. These results show that EBSD promises to be a powerful and robust technique in the characterization of nanoparticles.