Graphene films for corrosion protection of gold coated cuprous substrates in view of an application to electrical contacts

Corrosion of gold coated electrical contacts remains a problem often avoided by keeping the final gold coating thicknesses over 1 mu m. Graphene has recently been shown to be an outstanding material: among its astonishing properties are the theoretical carrier mobility at room temperature (200 000 cm(2)/V(-1)s(-1)) and the Young modulus (1.5 TPa). Graphene is a one-atom thick two-dimensional carbon crystal and has been first produced by mechanical exfoliation to obtain high purity defect free sheets. Chemical vapour deposition (CVD) is another method producing larger areas of graphene. Much work has been dedicated to graphene oxide (GO) deposition and reduction processes for applications ranging from electronics to sensors. In this work we describe briefly how a method of liquid exfoliation and spray deposition can be used to produce nanometric films of graphene flakes which can be more or less uniform and continuous according to the tuning of the process. Films were sprayed in different conditions on various substrates: laboratory substrates such as evaporated gold on glass, Si wafers and metallic coupons. The coupons under study were cut from cuprous alloy strips with a 2 mu m Ni underlayer and a 0.8 mu m Au layer. The coupons were coated with graphene films; they were then submitted to a four gas corrosion environmental test of the GR-1217-CORE Nov. 1995 type. A significant protection effect was observed for the sprayed graphene films. The deposition method by means of a spraying device was difficult to characterise but Raman spectroscopy and SEM images of the sprayed films showed evidence of the film formation. Contact resistance measurements and friction tests in a ball plane configuration were performed; low values of resistance and very low friction coefficients were measured. These first results show the very strong potential of graphene films deposited by a spraying method for electrical contacts applications and particularly for corrosion protection.