Early stage of CVD graphene synthesis on Ge(001) substrate

In this work we shed light on the early stage of the chemical vapor deposition of graphene on Ge(001) surfaces. By a combined use of microRaman and x-ray photoelectron spectroscopies, and scanning tunneling microscopy and spectroscopy, we were able to individuate a carbon precursor phase to graphene nucleation which coexists with small graphene domains. This precursor phase is made of C aggregates with different size, shape and local ordering which are not fully sp2 hybridized. In some atomic size regions these aggregates show a linear arrangement of atoms as well as the first signature of the hexagonal structure of graphene. The carbon precursor phase evolves in graphene domains through an ordering process, associated to a re-arrangement of the Ge surface morphology. This surface structuring represents the embryo stage of the hills-and-valleys faceting featured by the Ge(001) surface for longer deposition times, when the graphene domains coalesce to form a single layer graphene film

Driving with temperature the synthesis of graphene films on Ge(110)

We systematically investigate the chemical vapor deposition growth of graphene on Ge(110) as a function of the deposition temperature close to the Ge melting point. By merging spectroscopic and morphological information, we find that the quality of graphene films depends critically on the growth temperature improving significantly by increasing this temperature in the 910-930 {\deg}C range. We correlate the abrupt improvement of the graphene quality to the formation of a quasi-liquid Ge surface occurring in the same temperature range, which determines increased atom diffusivity and sublimation rate. Being observed for diverse Ge orientations, this process is of general relevance for graphene synthesis on Ge

Abrupt changes in the graphene on Ge(001) system at the onset of surface melting

By combining scanning probe microscopy with Raman and x-ray photoelectron spectroscopies, we investigate the evolution of CVD-grown graphene/Ge(001) as a function of the deposition temperature in close proximity to the Ge melting point, highlighting an abrupt change of the graphene's quality, morphology, electronic properties and growth mode at 930 degrees. We attribute this discontinuity to the incomplete surface melting of the Ge substrate and show how incomplete melting explains a variety of diverse and long-debated peculiar features of the graphene/Ge(001), including the characteristic nanostructuring of the Ge substrate induced by graphene overgrowth. We find that the quasi-liquid Ge layer formed close to 930 degrees is fundamental to obtain high-quality graphene, while a temperature decrease of 10 degrees already results in a wrinkled and defective graphene film.Comment: in pres

Don Giovanni raccontato e cantato dai Comici dell’Arte

Preceduta da un articolo introduttivo, l'edizione comprende il testo dello spettacolo andato in scena con la regia di M. Scaparro nel 2001 al Teatro Olimpico di Vicenza e, successivamente, per tre anni, nei principali teatri italiani, a Parigi per due stagioni e, in Spagna, al Festival di Almagro

Effectiveness of Co intercalation between Graphene and Ir(1 1 1)

Graphene can be used to avoid the oxidation of metallic films. This work explores the effectiveness of such stabilizing effect on Cobalt (Co) films intercalated between Graphene and Ir(1 1 1). After intercalation at 300 °C, two Co films are exposed to ambient pressure and investigated using Co-K edge X-ray Absorption Near Edge Spectroscopy. The formation of a disordered oxide phase is observed, and associated to the presence of some non-intercalated Co. Further annealing at 500 °C causes the oxide reduction to metallic Co which further intercalates below the Graphene. Once the intercalation is completed, Graphene prevents the Co from oxidation under ambient pressure conditions

Co-Ir interface alloying induced by thermal annealing

Using angular resolved X-ray Photoelectron Spectroscopy (XPS), Magneto Optic Kerr Effect (MOKE) and X-ray Absorption Spectroscopy (XAS), we characterize the structural and magnetic evolution upon annealing of two thin Co films (8 and 9 Monolayers) deposited on Ir(111). The XAS data collected in the near Co K edge region (XANES), interpreted with ab-initio simulations, show that intermixing takes place at the Co-Ir interface. Using a linear combination analysis, we follow the intermixing during the thermally driven diffusion process. At 500 °C, the interface between Co and Ir(111) roughens slightly, but no alloy formation is detected. At 600 °C, the Co film loses integrity and MOKE data show a rearrangement of the magnetic domains. Annealing to higher temperatures results in CoxIr1 −  x alloy formation and Ir segregation on the surface