Laboratoire Charles Coulomb UMR 5221 CNRS/UM2 (L2C)

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Passivation properties of a coating of graphene on copper

par Christelle EVE - publié le

Rigorously speaking, graphene refers to a single layer of sp2 carbon atoms covalently-bonded on a bidimensional hexagonal array, ie the elementary sublayer of graphite. However, nowadays, the term graphene is commonly used to designate a packing of a few (typically 1 to 10) layers. Several effective techniques have been developed for preparing graphene and chemically derived graphene sheets : i) the costly bottom-up synthesis of large and high quality graphene single sheets [1], ii) dispersion of graphene oxide in water [2], iii) solubilization of graphene intercalation compounds (GICs) in organic polar solvents [3], followed by a transfer in degassed water [4]. The second class of graphene is much less defined than the two others : it is highly dispersed in size and properties with a large number of defects present into the graphene sheets due to the formation of oxygen-containing groups. On the other hand, the size of the flakes is smaller in the third method. The wet routes have nevertheless the advantage of being easily scalable for industrial applications concerning inks, coatings and composites but the deposition processes still need to be optimized. This is one of the goal of the ANR project GAELIC (“Graphene Liquid Crystals” [5]). In this framework, the L2C and its partners prepare aqueous graphene and graphene oxide inks and develop processes to deposit thin layers on various surfaces.

Graphene presents many promising properties for future industrial developments. It is especially highly impermeable to gases, and highly resistant to oxidation, and it is therefore expected to be a good candidate for passivation barriers [6]. However, some studies showed that even though graphene protects copper from thermal oxidation at low temperature and short term, a coating of graphene can promote galvanic corrosion over long time scales because of diffusion and trapping of oxidizing species under the graphene coating [7,8]. The origin of the oxidizing agents is still in debate : Shriver et al suggested that O2 and H2O molecules diffuse from the atmosphere through defects in the graphene flakes [7], while de Andres et al proposed that the oxygen retained in the grain boundaries of copper progressively diffuses toward the surface where it gets trapped under the graphene layer [8]. However, the influence of the microstructure of graphene was not investigated so far and no detailed study of the oxidation kinetics in a controlled atmosphere was carried out.
A setup and method based on coupled Raman/photoluminescence spectroscopy was recently developed in our group for in situ studies of copper oxidation at controlled temperatures in a controlled atmosphere [9].

The master degree project will focus on the deposition of ultrathin films of graphene or graphene oxide (from a monolayer to 10 nm) on various copper-based materials (single crystals, copper foils, electroless thin layers) and on the spectroscopic study of the oxidation kinetics of the coated copper as a function of the thickness, structural (flake size, defects) and chemical (functionalization rate) properties of graphene, as well as the microstructure and oxygen content of the copper substrates.

[1] K.S. Novoselov et al, ‘‘Electric field effect in atomically thin carbon films’’, Science 306, 666-669 (2004)
[2] D.R. Dreyer et al, ‘‘The chemistry of graphene oxide’’, Chemical Society Reviews 39, 228-240 (2010)
[3] A. Pénicaud, C. Drummond, ‘‘Deconstructing graphite : Graphenide solutions’’, Accounts of chemical research 46,
129-137 (2012)
[4] G. Bepete et al, ‘‘Surfactant-free single-layer graphene in water’’, Nature Chemistry 9, 347 (2017)
[5] http://www.agence-nationale-recherche.fr/Project-ANR-15-CE09-0011
[6] S. Chen et al, ‘‘Oxidation resistance of graphene-coated Cu and Cu/Ni alloy’’, ACS nano 5, 1321-1327 (2011)
[7] M. Schriver, ‘‘Graphene as a long-term metal oxidation barrier : worse than nothing’’, ACS nano 7, 5763-5768
(2013)
[8] L. Álvarez-Fraga, ‘‘Oxidation mechanisms of copper under graphene : the role of oxygen encapsulation’’, Chemistry
of Materials 29, 3257-3264 (2017)
[9] PhD Deniz Cakir, ‘‘Enhanced Raman spectroscopy of copper-based materials’’, Université de Montpellier (2017)

Encadrants :
Eric Anglaret, Nanomaterials team : eric.anglaret@umontpellier.fr

Christophe Blanc, Soft Matter team : christophe.blanc@umontpellier.fr


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