Ultrahard carbon film from epitaxial two-layer graphene

Abstract

Atomically thin graphene exhibits fascinating mechanical properties, although its hardness and transverse stiffness are inferior to those of diamond. To date, there hasn't been any practical demonstration of the transformation of multi-layer graphene into diamond-like ultra-hard structures. Here we show that at room temperature and after nano-indentation, two-layer graphene on SiC(0001) exhibits a transverse stiffness and hardness comparable to diamond, resisting to perforation with a diamond indenter, and showing a reversible drop in electrical conductivity upon indentation. Density functional theory calculations suggest that upon compression, the two-layer graphene film transforms into a diamond-like film, producing both elastic deformations and sp2-to-sp3 chemical changes. Experiments and calculations show that this reversible phase change is not observed for a single buffer layer on SiC or graphene films thicker than 3 to 5 layers. Indeed, calculations show that whereas in two-layer graphene layer-stacking configuration controls the conformation of the diamond-like film, in a multilayer film it hinders the phase transformation.

arXiv commentPublished online on Nature Nanotechnology on December 18, 2017

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• Evidence for temporary and local transition of sp2 graphite-type to sp3 diamond-type bonding induced by the tip of an atomic force microscope
• Elastic properties and mechanical stability of bilayer graphene: Molecular dynamics simulations
• Nuclear quantum effects in graphene bilayers
• Evidence for a pressure-induced phase transition of few-layer graphene to 2D diamond
• Designable ductility of a nano-network from few-layered graphene bonded with benzene: A molecular dynamics study
• Driving carbon nanotube to rotate by diamond wedges at room temperature