Synthesis, Mass Spectrometry, and Atomic Structural Analysis of Au_â2000(SR)_â290 Nanoparticles

Metallic nanoparticles display unique optical, electronic, and chemical properties compared to their bulk counterparts. These properties are influenced by the internal structure of nanoparticles. Therefore, atomic structural characterization of nanoparticles is of paramount importance in nanotechnology. In this work, we present the synthesis, mass spectrometry, and structural characterization of highly monodisperse thiolate-protected gold nanoparticles (∼3.8 nm) using aberration-corrected scanning transmission electron microscopy (STEM). Mass spectrometry reveals the composition to be Au_∼2000(SC₆H₁₃)_∼290. The images registered in the high-angle annular dark field detector (HAADF-STEM) showed the presence of decahedral and single-crystal face-centered cubic (fcc) nanoparticles as well as fcc structures with multiple planar defects. We also observed nanoparticles with an inner grain boundary corresponding to a high-angle grain boundary classified as Σ9 under the coincidence site lattice notation. Experimental structural analysis and characterization of grain boundaries were correlated with simulated HAADF-STEM images of structural models for Σ9. The present report demonstrates the coexistence of two crystallites within thiolate-protected nanoparticles separated by high-angle grain boundaries.