Growth morphology and properties of metals on graphene

Abstract

a b s t r a c tGraphene, a single atomic layer of graphite, has been the focus of recent intensive studies due to its novel electronic and structural properties. Metals grown on graphene also have been of interest because of their potential use as metal contacts in graphene devices, for spintronics applications, and for catalysis. All of these applications require good understanding and control of the metal growth morphology, which in part reflects the strength of the metal-graphene bond. Also of importance is whether the interaction between graphene and metal is sufficiently strong to modify the electronic structure of graphene. In this review, we will discuss recent experimental and computational studies related to deposition of metals on graphene supported on various substrates (SiC, SiO 2 , and hexagonal close-packed metal surfaces). Of specific interest are the metal-graphene interactions (adsorption energies and diffusion barriers of metal adatoms), and the crystal structures and thermal stability of the metal nanoclusters.

Formation and morphological evolution of self-similar 3D nanostructures on weakly interacting substrates

“…Moreover, the island height increases, compared to those at lower T s , to seven atomic layers. Similar island morphologies have been experimentally reported in STM studies of Pb and Dy growth on graphene [4].…”

“…A notable example is the deposition of metal films on twodimensional (2D) crystals (e.g., graphene and MoS 2 ) [4][5][6] for which the tendency toward the formation of 3D agglomerates imposes technological obstacles for the use of 2D materials in a wide range of switching and, in some cases, catalytic devices [4][5][6][7][8][9][10][11][12][13][14]. Thus, understanding atomistic mechanisms that govern 3D island formation and shape evolution is a key step toward controlling film morphology and, by extension, the functionality of devices based on weakly interacting film/substrate materials systems.…”

“…Currently, the most detailed atomistic * kostas.sarakinos@liu.se description of far-from-equilibrium 3D island formation is based on homoepitaxial systems in which 3D islands (mounds) form by deposition onto existing small islands, followed by atomic-step descent limited by the Ehlrich-Schwöbel barrier [15][16][17][18][19]. However, for weakly interacting film/substrate systems-including Ag/SiO 2 [20][21][22][23][24], Pd/TiO 2 [25], Cu/ZnO [26,27], and Dy/graphene [4,28]-3D islands develop before the initially formed one-atom-high islands are large enough to efficiently capture vapor-phase deposition flux. Moreover, 3D island formation is also known to occur in the absence of deposition flux due to surface restructuring via dewetting [29].…”

“…Following the early categorization and description of 3D (Volmer-Weber) film growth by Bauer [31], recent studies of metal-film and nanostructure growth on graphite [32], graphene [4], and other 2D materials [5,6] have explained experimentally observed growth morphologies as a function of the ratio between the adsorption energy (E ads ) of metal atoms on the substrate and the bulk-metal cohesive energy (E coh ); the lower the E ads /E coh ratio, the stronger the tendency toward 3D growth. Intuitively, this can be understood as the metal atoms being more weakly bound to the substrate, which facilitates their ascent onto the first layer of an island by either direct hopping or an exchange mechanism [33].…”

“…These facets have been suggested to facilitate growth of AlSn alloy films on weakly interacting substratesincluding amorphous-C, SiO 2 , NaCl, and mica [3,[45][46][47]-by providing pathways for accelerated mass transport between the base and the upper layer of 3D atomic islands. Moreover, facet formation has been experimentally observed during the deposition of metal films on graphene and graphite surfaces [4,32]. Hence, in the context of 3D growth beyond the second layer, the absence of steps may allow adatoms to ascend multiple layers by encountering a terrace diffusion barrier [E s in Fig.…”