Structure of gold thin films grown on Ir(111)

STM Study of the Initial Stage of Gold Intercalation of Graphene on Ir(111)

In this paper, we present a study of the sub-monolayer gold intercalation of graphene on Ir(111) using scanning tunnelling microscopy (STM). We found that Au islands grow following different kinetics than growth on Ir(111) without graphene. Graphene appears to increase the mobility of Au atoms by shifting the growth kinetics of Au islands from dendritic to a more compact shape. Graphene on top of intercalated gold exhibits a moiré superstructure, with parameters significantly different from graphene on Au(111) but almost identical to graphene on Ir(111). The intercalated Au monolayer shows a quasi-herringbone reconstruction with similar structural parameters as on Au(111).

Understanding the origin of band gap formation in graphene on metals: graphene on Cu/Ir(111)

Understanding the nature of the interaction at the graphene/metal interfaces is the basis for graphene-based electron- and spin-transport devices. Here we investigate the hybridization between graphene- and metal-derived electronic states by studying the changes induced through intercalation of a pseudomorphic monolayer of Cu in between graphene and Ir(111), using scanning tunnelling microscopy and photoelectron spectroscopy in combination with density functional theory calculations. We observe the modifications in the band structure by the intercalation process and its concomitant changes in the charge distribution at the interface. Through a state-selective analysis of band hybridization, we are able to determine their contributions to the valence band of graphene giving rise to the gap opening. Our methodology reveals the mechanisms that are responsible for the modification of the electronic structure of graphene at the Dirac point, and permits to predict the electronic structure of other graphene-metal interfaces.

Interlayer diffusion of Au atoms in a heteroepitaxial system

In heteroepitaxy, thin-film growth proceeds in two-dimensional layer-by-layer, three-dimensional island, or layer-plus-island modes depending on the growth conditions. Interlayer mass transport plays a crucial role in determining the growth mode. We investigate interlayer diffusion of Au atoms from Au islands grown on Ir(111) by scanning tunneling microscopy (STM) and kinetic Monte Carlo (KMC) simulations. STM measurements reveal that the first Au layer on Ir(111) grows in a complete layer at 100 K, whereas the Au layer grows in a three-dimensional fashion from the second Au layer at this temperature. Annealing these surfaces to 300 K reduces the higher-layer islands, indicating that Au atoms undergo step-down diffusion. By measuring the density of the top-layer islands and comparing them with the KMC simulation results, the additional step-down diffusion barrier for Au atoms to descend from the Au islands is estimated to be 0.02 eV on the first Au layer and 0.04 eV on the second Au layer. The layer dependence of the additional step-down diffusion barrier is explained in terms of the lattice mismatch between Au and underlying layers.