Core-shell structure disclosed in self-assembled Cu-Ag nanoalloy particles

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Self-assembled nanoparticles offer unique properties for various applications.
• Understanding the elemental distribution in bimetallic nanoparticles is crucial for controlling their behavior.
• Copper-silver (Cu-Ag) alloys are of interest due to their plasmonic and catalytic potential.

Purpose of the Study:

• To investigate the core-shell segregation of copper and silver in free nanoparticles.
• To analyze the influence of relative Cu-Ag concentrations on nanoparticle surface composition and electronic structure.
• To compare findings with existing data on Cu-Ag macroscopic and surface alloys.

Main Methods:

• Formation of mixed Cu-Ag nanoparticles using magnetron sputtering and a gas-aggregation cluster source.
• Analysis of nanoparticle composition and electronic structure via photoelectron spectroscopy.
• Photon-energy-dependent measurements of Cu 3d and Ag 4d photoelectron spectra.

Main Results:

• Core-shell segregation of Cu and Ag was confirmed across a broad range of compositions.
• Silver predominantly forms the surface layer of the nanoparticles, even with similar initial vapor fractions.
• Copper segregation to the surface was observed only at low silver concentrations.
• A significant threefold decrease in Ag 4d spin-orbit splitting was detected when copper was present on the surface.

Conclusions:

• The study establishes distinct core-shell segregation in self-assembled Cu-Ag nanoparticles.
• Surface composition is strongly influenced by the relative Cu-Ag concentrations, favoring silver.
• The observed changes in electronic structure, particularly the reduced spin-orbit splitting, provide insights into metal-metal interactions at the nanoscale.