Single-step metal-catalyzed synthesis of hybrid planar graphene–orbicular graphitic carbon structures using an amorphous carbon thin film as a precursor

Abstract Graphene is one of the strongest and most electrically and thermally conductive materials in nature; therefore, incorporating even traces of graphene to other materials can significantly enhance their mechanical, electrical, and thermal properties. Such graphene-based materials can find uses in many applications, including flexible displays, batteries, supercapacitors, solar panels, and mobile devices. However, developing graphene-based 2D materials is challenging. In this study, a facile single-step synthesis method for fabricating thin layers of amorphous carbon (a-C) containing planar graphene (PG) and orbicular graphitic carbon (OGC) nanostructures was developed by thermal annealing in inert atmosphere using an sp3-rich a-C thin film as a precursor. By annealing thin-film stacks of Si/NiFe/a-C, a thin layer with a hybrid a-C-PG-OGC structure was produced with OGC nanostructures forming on top of PG nanostructures and pyramidal NiSix nanocrystals extending into the Si substrate due to the diffusion of nickel into the silicon substrate during elevated-temperature annealing. Raman spectroscopy and cross-sectional transmission electron microscopy confirmed the transformation from amorphous to graphitic structure in the a-C film during thermal annealing. The obtained results demonstrate that the development of this 2D material with a hybrid a-C-PG-OGC microstructure is due to a metal-catalyzed PG nucleation mechanism and a mismatch-induced OGC growth mechanism. The present method for synthesizing graphene-containing thin-film structures paves the way toward the fabrication of complex micro-assemblies where high strength and good thermoelectric properties are of paramount importance.