Size to density coupling of supported metallic clusters.

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Controlling metallic nano-cluster size and density simultaneously on oxide substrates is a significant challenge for model catalyst development.
• Existing methods often exhibit strong coupling between cluster size and density, limiting precise fabrication.
• Understanding and overcoming this coupling is crucial for designing efficient nano-structured materials.

Purpose of the Study:

• To demonstrate a method for decoupling the size and density of metallic nano-clusters during growth.
• To investigate the effect of multiple amorphous solid water-buffer layer assisted growth (ASW-BLAG) cycles on cluster characteristics.
• To explore the potential of ASW-BLAG for creating tailored model catalysts and bimetallic films.

Main Methods:

• Utilized amorphous solid water (ASW) as a buffer layer for assisted growth of gold clusters on SiO2/Si(100) substrates in ultra-high vacuum (UHV).
• Employed a multiple ASW-BLAG procedure, repeating growth cycles up to 10 times to influence cluster density.
• Characterized cluster morphology and density using tapping mode atomic force microscopy (AFM) and high-resolution scanning electron microscopy (HR-SEM).
• Quantified gold coverage using in situ Auger electron spectroscopy (AES).

Main Results:

• The ASW-BLAG procedure successfully increased nano-cluster density by over fivefold without altering cluster size in initial cycles.
• Beyond a saturation point, further cycles led to increased cluster size and a lower saturation density, attributed to cluster-cluster attraction.
• Achieved control over inter-cluster distances, with larger clusters (≥4 nm) maintaining distances of at least 20 nm.
• Demonstrated the ability to create bimodal size distributions and co-adsorbed bimetallic (Au and Pd) cluster films with controlled density and size.

Conclusions:

• The ASW-BLAG technique effectively decouples metallic nano-cluster size and density under specific conditions.
• This method offers a versatile pathway for fabricating precisely controlled model catalysts and nano-structured materials.
• The findings open new possibilities for designing advanced catalysts with tailored properties.