UC Berkeley

Graphene is one of the strongest and most electrically and thermally conductive materials in nature; therefore, incorporating even traces of graphene into other materials can significantly enhance their mechanical, electrical, and thermal properties. Such graphene-based materials can be used 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 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.