Structure of Amorphous Two-Dimensional Materials: Elemental Monolayer Amorphous Carbon versus Binary Monolayer...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• The structure of amorphous materials has been debated since the 1930s, primarily as a dichotomy between Zachariasen continuous random networks (Z-CRNs) and Z-CRNs containing crystallites.
• Recent work showed amorphous diamond can exist in either Z-CRN or crystallite-containing forms, prompting further investigation into other amorphous materials.

Purpose of the Study:

• To determine the structure of single-atom-thick amorphous monolayers, specifically amorphous graphene and amorphous boron nitride (a-BN).
• To reanalyze prior simulation results and conduct new kinetic Monte Carlo simulations to elucidate the structural properties of these 2D amorphous materials.

Main Methods:

• Reanalysis of existing simulation data for amorphous graphene.
• Kinetic Monte Carlo simulations utilizing alternative algorithms to model amorphous monolayer structures.
• Investigating the bonding characteristics and presence of ordered/disordered regions within the amorphous structures.

Main Results:

• Elemental amorphous graphene favors a crystallite-containing Zachariasen continuous random network (Z-CRN) structure.
• Binary monolayer amorphous BN exhibits a novel "pseudo-CRN" structure, distinct from traditional models.
• This pseudo-CRN is characterized by a mix of B-N, B-B, and N-N bonds, and contains "pseudocrystallites" composed of noncanonical hexagonal regions.

Conclusions:

• The structure of amorphous graphene aligns with a crystallite-containing Z-CRN model.
• Amorphous BN monolayers present a new structural paradigm, a pseudo-CRN, challenging the binary classification of amorphous materials.
• These findings have implications for understanding and designing other 2D and bulk amorphous materials.