Templating of arrays of Ru nanoclusters by monolayer graphene/Ru Moirés with different periodicities

Mechanism of Corrugated Graphene Moiré Superstructures on Transition-Metal Surfaces

A graphene layer on a transition-metal (TM) surface can be either corrugated or flat, depending on the type of the substrate and its rotation angle with respect to the substrate. It was broadly observed that the degree of corrugation generally decreases with the increase of rotation angle or the decrease of Moiré pattern size. In contrast to a flat graphene on a TM surface, a corrugated graphene layer has an increased binding energy to the substrate and a concomitant elastic energy. Here, we developed a theoretical model about the competition between the binding energy increase and the elastic energy of corrugated graphene layers on TM surfaces in which all the parameters can be calculated by density functional theory (DFT) calculations. The agreement between the theoretical model and the experimental observations of graphene on various TM surfaces, for example, Ru(0001), Rh(111), Pt(111), and Ir(111), substantiated the applicability of this model for graphene on other TM surfaces. Moreover, the morphology of a graphene layer on an arbitrary TM surface can be theoretically predicted through simple DFT calculations based on the model. Our work thus provides a theoretical framework for the intelligent design of graphene/TM superstructures with the desired structure.

Graphene Layer Morphology as an Indicator of the Metal Alloy Formation at the Interface

The intercalation of different species in graphene-metal interfaces is widely used to stabilize the artificial phases of different materials, which in some cases leads to the formation of the surface alloys between atoms of the guest metal and the substrate. Here, the interfaces of graphene with Ru(0001) and Ir(111) were modified using intercalation of a thin Mn layer and investigated by means of scanning tunneling microscopy (STM) accompanied by density functional theory (DFT) calculations. It is found that Mn forms a pseudomorphic layer on Ru(0001) under a strongly buckled graphene layer. In the case of Mn intercalation in graphene/Ir(111), a buried thin layer of MnIr alloy is formed beneath the first Ir layer under a flat graphene layer. This unexpected observation is explained on the basis of phase diagram pictures for the Mn-Ru and Mn-Ir systems as well as via comparison of calculated total energies for the respective interfaces.

Growth of Pd Nanoclusters on Single-Layer Graphene on Cu(111)

We report scanning tunneling microscopy results on the nucleation and growth of Pd nanoclusters on a single layer of graphene on the Cu(111) surface. The shape, organization, and structural evolution of the Pd nanoclusters were investigated using two different growth methods, continuous and stepwise. The size and shape of the formed nanoclusters were found to greatly depend on the growth technique used. The size and density of spherical Pd nanoclusters increased with increasing coverage during stepwise deposition as a result of coarsening of existing clusters and continued nucleation of new clusters. In contrast, continuous deposition gave rise to well-defined triangular Pd clusters as a result of anisotropic growth on the graphene surface. Exposure to ethylene caused a decrease in the size of the Pd clusters. This is attributed to the exothermic formation of ethylidyne on the cluster surfaces and an accompanying weakening of the Pd-Pd bonding.

Templating ultra-small manganese isomers with preference for adsorption sites and narrow distribution tuned by different moiré periodicities of monolayer graphene on Ru(0001)

The process of templating a manganese nanocluster with the 12 × 12 moiré and other two slightly distorted graphene/Ru(0001) moirés was investigated by scanning tunneling microscopy (STM). At the initial stage of nucleation, different adsorption modes for Mn monomer, dimer and trimer guided by various moiré periodicities were observed. Upon Mn coverage increasing, STM measurements revealed that Mn clusters exhibit a detectable preference for adsorption sites on all the three different moirés. The most favorable adsorption sites for Mn clusters are the fcc regions, where ordering of Mn clusters was observable, and the lateral size of the clusters are tunable with coverage. A density functional theory calculation also showed that magnetism appears with a magnetic moment of 3.79μ(B) for Mn monomer on MLG/Ru(0001).