Low-friction, wear-resistant, and electrically homogeneous multilayer graphene grown by chemical vapor deposition on molybdenum

Abstract

Chemical vapour deposition (CVD) is a promising method for producing largescale graphene (Gr). Nevertheless, microscopic inhomogeneity of Gr grown on traditional metal substrates such as copper or nickel results in a spatial variation of Gr properties due to long wrinkles formed when the metal substrate shrinks during the cooling part of the production cycle. Recently, molybdenum (Mo) has emerged as an alternative substrate for CVD growth of Gr, mainly due to a better matching of the thermal expansion coefficient of the substrate and Gr. We investigate the quality of multilayer Gr grown on Mo and the relation between Gr morphology and nanoscale mechanical and electrical properties, and spatial homogeneity of these parameters. With atomic force microscopy (AFM) based scratching, Kelvin probe force microscopy, and conductive AFM, we measure friction and wear, surface potential, and local conductivity, respectively. We find that Gr grown on Mo is free of large wrinkles that are common with growth on other metals, although it contains a dense network of small wrinkles. We demonstrate that as a result of this unique and favorable morphology, the Gr studied here has low friction, high wear resistance, and excellent homogeneity * Corresponding author Email address: bvasic@ipb.ac.rs (Borislav Vasić) of electrical surface potential and conductivity. 1

Multilayer CVD graphene electrodes using a transfer-free process for the next generation of optically transparent and MRI-compatible neural interfaces

“…Mo is chosen as a catalyst layer due to the possibility of growing thin and uniform layers of graphene because of its extremely low carbon solubility, thus creating a self-limiting growth process 55 . Moreover, the thermal expansion coefficient (CTE) of Mo in comparison with Cu and Ni is much closer to the one of Si, hence, Mo is less prone to wrinkle creation during high temperature graphene growth 56 , 57 . Additionally, catalyst residues are an important concern in an implantable device.…”

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“…Wrinkles inevitably form during the chemical vapor deposition (CVD) and wet transfer process of graphene attributed to the different thermal expansion coefficients between materials (graphene and typical catalysts) and the draining of liquid. − These wrinkles are believed to exhibit significant influences on the nanotribological properties of graphene . In the literature, researchers find that except when the probe scanning direction aligns with wrinkle orientation, the friction of wrinkled regions is always higher than that of wrinkle-free areas. , Besides, the graphene wear in the interior region initiates exactly from the wrinkled structures in both micro- and macrotribological tests, , and the presence of graphene wrinkles (GWs) can significantly drop the load-bearing capacity (the critical load for the graphene failure) by nearly 1 order of magnitude …”

“…6 In the literature, researchers find that except when the probe scanning direction aligns with wrinkle orientation, the friction of wrinkled regions is always higher than that of wrinkle-free areas. 6,7 Besides, the graphene wear in the interior region initiates exactly from the wrinkled structures in both micro-and macrotribological tests, 8,9 and the presence of graphene wrinkles (GWs) can significantly drop the load-bearing capacity (the critical load for the graphene failure) by nearly 1 order of magnitude. 10 From the observed phenomena, the mechanisms behind the high friction and easier failure of wrinkles remain controversial.…”

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