Graphene is a unique 2D system of confined electrons with an unusual electronic structure of two inverted Dirac cones touching at a single point, with high electron mobility and promising microelectronics applications. The clean system has been studied extensively, but metal adsorption studies in controlled experiments have been limited; such experiments are important to grow uniform metallic films, metal contacts, carrier doping, etc. Two non-free-electron-like metals (rare earth Gd and transition metal Fe) were grown epitaxially on graphene as a function of temperature T and coverage θ. By measuring the nucleated island density and its variation with growth conditions, information about the metal-graphene interaction (terrace diffusion, detachment energy) is extracted. The nucleated island densities at room temperature (RT) are stable and do not coarsen, at least up to 400 °C, which shows an unusually strong metal-graphene bond; most likely it is a result of C atom rebonding from the pure graphene sp(2) C-C configuration to one of lower energy.

No abstract

It has been puzzling why for Pb/Si͑111͒, oscillations have been observed at temperatures as low as 18 K and were found to improve with decreasing temperature. With scanning tunneling microscope we have directly observed this ideal layer by layer growth. A dramatic dependence of the second layer island morphology on island height, expected from quantum size effects ͑QSE͒, is also found. Low density of fractal islands on stable vs high density on unstable Pb islands on a mixed height island confirms the role of QSE in kinetics. The low diffusion barrier and the fractal island morphology can explain the unusual layer by layer growth.