Resolving the Chemically Discrete Structure of Synthetic Borophene Polymorphs

Area of Science:

• Materials Science
• Condensed Matter Physics
• Surface Science

Background:

• Two-dimensional (2D) materials possess unique properties determined by their atomic structure.
• Current 2D materials are derived from bulk crystals, limiting their potential.
• Synthetic 2D materials, without bulk counterparts, could unlock new properties.

Purpose of the Study:

• To investigate the structural and chemical nature of synthetic borophene grown on Ag(111).
• To determine if borophene forms distinct layers with van der Waals (vdW) interactions.
• To explore the potential for engineering novel 2D materials beyond those from bulk crystals.

Main Methods:

• Growth of atomically thin boron sheets on a silver (Ag(111)) surface.
• X-ray standing wave-excited X-ray photoelectron spectroscopy (XSW-XPS).
• Sub-angstrom spatial resolution analysis of boron atomic positions and chemical states.

Main Results:

• Atomically thin borophene was successfully synthesized on Ag(111) without a bulk allotrope.
• Borophene formed a single, planar layer with vdW-like structural characteristics.
• Multiple borophene phases were observed, exhibiting polymorphism.
• Boron layers were found to be chemically distinct from the Ag(111) substrate.

Conclusions:

• Synthetic borophene exists as a distinct 2D material with vdW-like bonding.
• The synthesis of borophene demonstrates the feasibility of creating synthetic 2D materials.
• This work significantly expands the accessible phase space for 2D material discovery and engineering.