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Highlights Surface Science Lab

Fine tuning of graphene-metal adhesion by surface alloys  

 Controlling the graphene adhesion to the substrate requires a thorough understanding of the physical mechanisms underlying the graphene-metal interaction.This is a key step towards the establishment of graphene-based technologies and the development of graphene heterostructures in novel electrical and mechanical devices. It is well known, in fact, that the coupling between supported graphene (GR) and the substrate affects a number of properties of GR-based devices, such as the electromechanical, thermal and optical properties, as well as  the electronic transport and the contact resistance. Several methods, such as the choice of the substrate, the intercalation of adspecies or the creation of an oxide buffer layer, have proven effective in manipulating the graphene–metal interaction, but not to a precisely controllable extent.Moreover, these methods come with some significant drawbacks. Here we show that bimetallic surface alloying provides a viable route for governing the GR-metal interaction by selectively choosing  the elemental composition of the surface alloy. This concept is illustrated by characterising the properties of graphene on a model PtRu surface alloy on Ru(0001), with Pt concentrations ranging from 0 to 50%. Pt and Ru traditionally stand out as two model examples of weakly and strongly interacting substrates, respectively. In fact, while GR interacts very weakly with Pt -as reflected in the almost flat morphology of the C layer-, a strong coupling has been observed for GR/Ru(0001), leading to a significant corrugation of the moiré superstructure.

 Our study was conducted via a multidisciplinary approach, combining a range of experimental techniques (high-energy resolution core level Photoemission Spectroscopy, Low Energy Electron Diffraction and Low Energy Electron Microscopy) and state-of-the-art DFT calculations.Our results show that the progressive increase of the Pt content in the surface alloy is associated with a gradual lifting of graphene from the substrate, which results from the Pt-induced carbon orbital rehybridization. Alloying is also found to affect the growth mode and the morphology of graphene, which is strongly corrugated on bare Ru but becomes flat at a Pt coverage of 50%. Our work is the proof of concept that the employment of binary surface alloys, which are used in many areas of materials science, can provide an unprecedented tool to selectively manipulate the GR-metal adhesion. The proposed method can be readily extended to a range of supports, thus opening the way to a full tunability of the graphene-substrate interaction.

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Fine-tuning of graphene metal adhesion by surface alloys;
D. Alfe', M. Pozzo, E. Miniussi, S. Gunther, P. Lacovig, S. Lizzit, R. Larciprete, B. Santos Burgos, T.O. Menteş¸ M.Á. Niño, A. Locatelli, and A. Baraldi;
Sci. Rep. in press.

Last Updated on Saturday, 10 August 2013 15:41