Formation and self-assembly of graphene nanoribbons and nanosheets in metals*

Composites consisting of carbon nanostructures, such as graphene and carbon nanotubes, and metals are desirable for power transmission lines, interconnects and heat transfer applications due to the combination of excellent charge carrier mobility, thermal conductivity and mechanical strength of the carbon nanostructures and the high density of electrons in the metal. Metal/nanocarbon composites made by chemical vapor deposition, friction stir, ball milling, and plasma spraying have yielded materials with enhanced hardness and tensile strength but their electrical and thermal conductivities usually deteriorate. We use an electrocharging assisted process which consists of the application of a high DC current to a mixture of liquid metal and carbon particles to form crystalline graphitic nanoribbons in the liquid metal. The solid composites have shown 5% higher electrical conductivity and enhanced local stiffness, measured by nanoindentation, compared to the pure Al alloys. Molecular dynamic simulations of nanoindentation tests into the nanocarbon metal composite show how the graphene nanoribbons impede dislocation motion and increase hardness. Conductive AFM shows an increase in the local conductivity from these samples compared to the parent aluminum alloy.