Counting the atoms in supported, monolayer-protected gold clusters

Area of Science:

• Materials Science
• Nanotechnology
• Analytical Chemistry

Background:

• Accurate characterization of atomic composition in nanomaterials is crucial for understanding their properties.
• Monolayer-protected gold clusters (MP-Au) are important in catalysis and electronics.
• Existing methods for cluster quantification have limitations.

Purpose of the Study:

• To develop and validate a quantitative method for determining the exact number of gold atoms in supported monolayer-protected gold clusters.
• To assess the aggregation state of nanoparticles using the developed technique.

Main Methods:

• Quantitative High Angle Annular Dark Field-Scanning Transmission Electron Microscopy (HAADF-STEM) was employed.
• Size-selected gold clusters (Au(N), N = 25, 38, 55) were used as mass calibration standards.
• The contribution of thiolate ligands to the electron scattering intensity was accounted for.

Main Results:

• The method accurately determined the atomic composition of nominally Au(38) clusters to be 38 ± 2 gold atoms.
• The electron scattering intensity was correlated with the number of gold atoms.
• The technique demonstrated potential for assessing nanoparticle aggregation.

Conclusions:

• Quantitative HAADF-STEM provides a reliable method for precise atomic quantification of supported gold clusters.
• This technique offers a valuable tool for nanoparticle characterization and aggregation analysis.
• The findings advance the understanding and application of gold nanoclusters.