Discovering atomistic pathways for supply of metal atoms to graphene surface from methyl-based precursors

TL;DR

This study uses molecular dynamics simulations to uncover atomic-scale pathways by which methyl-based precursors deliver metal atoms to graphene surfaces, aiding the development of 2D heterostructures.

Contribution

It provides detailed atomic-level insights into the dissociation and reaction mechanisms of trimethylindium on graphene, a previously unclear aspect of MOCVD processes.

Findings

Revealed how hydrogen collisions facilitate precursor dissociation.

Identified reaction pathways leading to hydrocarbon and hydrogen formation.

Demonstrated mechanisms for metal atom delivery to graphene surfaces.

Abstract

Conceptual 2D group III nitrides and oxides (e.g., 2D InN and 2D InO) in heterostructures with graphene have been realized by metalorganic chemical vapor deposition (MOCVD). MOCVD is credited with being central to fabrication of established semiconductor materials and by purpose for an advance in emergent semiconductor materials at the 2D limit. A defining characteristic of MOCVD is the employment of metalorganic precursors such as trimethyl-indium, -gallium, and -aluminum, which contain (strong) metal-carbon bonds. Mechanisms that regulate MOCVD processes at the atomic scale are largely unknown. Here, we employ density-functional molecular dynamics -- accounting for van der Waals interactions -- to locate reaction pathways responsible for dissociation of trimethylindium (TMIn) precursor in the gas phase as well as on top-layer and zero-layer graphene. The simulations reveal how collisions with hydrogen molecules, intramolecular or surface-mediated proton transfer, and direct TMIn/graphene reactions assist TMIn transformations, which ultimately enables delivery of In monomers, or InH and CH3In admolecules, on graphene. Results presented also show how TMIn/H2 reactions on graphene, or in the gas phase, lead to formation of methane, ethane, propane, ethene hydrocarbons, and atomic hydrogen. This work provides knowledge for understanding thin-film nucleation and intercalation mechanisms at the atomic scale and for overcoming challenges in integration of 2D materials and graphene heterostructures in technology.