Silicon carbide (SiC) is one of the hardest known materials. Its exceptional mechanical properties combined with its high thermal conductivity make it a very attractive material for a variety of technological applications. Recently, it is discovered that two-layer epitaxial graphene films on SiC can undergo a pressure activated phase transition into a sp3 diamene structure at room temperature. Here, it is shown that epitaxial graphene films grown on SiC can increase the hardness of SiC up to 100% at low loads (up to 900 µN), and up to 30% at high loads (10 mN). By using a Berkovich diamond indenter and nanoindentation experiments, it is demonstrated that the 30% increase in hardness is present even for indentations depths of 175 nm, almost three hundred times larger than the graphene film thickness. The experiments also show that the yield point of SiC increases up to 77% when the SiC surface is coated with epitaxial graphene. These improved mechanical properties are explained with the formation of diamene under the indenter's pressure.

Charles University Faculty of Mathematics and Physics Institute of Physics Ke Karlovu 5 Prague 2 Prague CZ 121 16 Czech Republic

Department of Chemical and Biomolecular Engineering Tandon School of Engineering New York University Brooklyn NY 11201 USA

Department of Physics New York University Brooklyn NY 11201 USA

Division of Biomaterials Department of Molecular Pathobiology New York University College of Dentistry New York NY USA

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