Ions Adsorbed at Amorphous Solid/Solution Interfaces Form Wigner Crystal-like Structures

Area of Science:

• Surface Science
• Physical Chemistry
• Nanotechnology

Background:

• Electrical double layers form at interfaces, with the Stern layer comprising directly adsorbed ions.
• Previous studies lacked insight into the lateral organization of Stern layer ions due to instrumental limits.
• Understanding Stern layer structure is crucial for interfacial phenomena.

Purpose of the Study:

• To visualize and characterize the *in situ* lateral structure of Stern layer ions on different surfaces.
• To investigate the conditions leading to ordered ion arrangements within the Stern layer.
• To explore the influence of surface properties and electrolyte parameters on Stern layer organization.

Main Methods:

• High-resolution amplitude modulated atomic force microscopy (AFM) for *in situ* imaging.
• Utilized polycrystalline gold, amorphous silica, and gallium nitride (GaN) substrates.
• Molecular dynamics (MD) simulations were employed for gold surfaces.

Main Results:

• Observed formation of Wigner crystal-like structures (hexagonal, cubic, worm-like) in the Stern layer above an ion density threshold.
• Demonstrated that electrolyte concentration, ion species/valence, and surface properties influence these structures.
• Found that below the threshold, the Stern layer remains unstructured.
• MD simulations on gold showed ion cluster formation correlating with AFM observations.

Conclusions:

• The lateral organization of Stern layer ions can form ordered, Wigner crystal-like structures under specific conditions.
• These findings provide new insights into interfacial ion behavior.
• The discovered structures have potential implications for diverse applications in chemistry, energy, and medicine.