Stability of Two-Dimensional Iron-Carbides Suspended across Graphene Pores: First-principles Particle Swarm Optimization

TL;DR

This study uses first-principles particle swarm optimization to identify stable two-dimensional iron-carbide structures on graphene, revealing that experimentally observed square-lattices are likely iron-carbides rather than pure iron, with implications for their electronic properties.

Contribution

The paper introduces a computational approach to discover stable 2D Fe-C structures on graphene, clarifying the nature of experimentally observed square-lattices as iron-carbides and predicting their stability and electronic features.

Findings

Identified a stable ML Fe2C2 structure with distorted square lattices.

Proposed that observed square-lattices are iron-carbides, not pure Fe.

Predicted high spin polarization due to orbital hybridization.

Abstract

Inspired by recent experimental realizations of two-dimensional (2D) metals and alloys, we theoretically investigate the stability and electronic properties of monolayer (ML) Fe-C compounds and pure Fe. According to our and others theoretical results, the experiment [Science 343, 1228 (2014)] proposed ML pure Fe square-lattices embedded in graphene (Gr) pores are energetically unstable compared to that of the Fe triangular-lattices in Gr. To solve the above contradiction, we search for the stable structures of ML Fe-C with various Fe to C ratios (as a generalization of ML Fe in Gr) using ab initio particle swarm optimization technique. A Fe1C1 square-lattice embedded in Gr is found. We propose and demonstrate that the square-lattices observed in the experiment were iron-carbides (Fe-C) but not pure Fe from the square-lattice shape, Fe-Fe lattice constant and energetic considerations. Note that the coexistence of C with Fe cannot be excluded from the experiment. More importantly, we find a lowest energy and dynamically stable structure, ML Fe2C2 with Fe atoms form distorted square lattices. High spin polarization around the Fermi level is predicted for different 2D Fe-C structures due to significant orbital hybridization between C and Fe.