Role of the Pinning Points in epitaxial Graphene Moiré Superstructures on the Pt(111) Surface

Chemical Changes of Graphene Oxide Thin Films Induced by Thermal Treatment under Vacuum Conditions

Reduction of graphene oxide is one of the most promising strategies for obtaining bulk quantities of graphene-like materials. In this study, graphene oxide was deposited on SiO2 and reduced by annealing at 500 K under vacuum conditions (5 × 10−1 Pa). Here, graphene oxide films as well as their chemical changes upon heating were characterized in depth by X-ray photoelectron spectroscopy, Raman spectroscopy, and scanning electron and atomic force microscopies. From the chemical point of view, the as prepared graphene oxide films presented a large quantity of oxidized functional groups that were reduced to a large extent upon heating. Moreover, residual oxidized sulfur species that originated during the synthesis of graphene oxide (GO) were almost completely removed by heating while nitrogen traces were integrated into the carbon framework. On the other hand, regarding structural considerations, reduced graphene oxide films showed more homogeneity and lower roughness than graphene oxide films.

Chemistry below graphene: decoupling epitaxial graphene from metals by potential-controlled electrochemical oxidation

While high-quality defect-free epitaxial graphene can be efficiently grown on metal substrates, strong interaction with the supporting metal quenches its outstanding properties. Thus, protocols to transfer graphene to insulating substrates are obligatory, and these often severely impair graphene properties by the introduction of structural or chemical defects. Here we describe a simple and easily scalable general methodology to structurally and electronically decouple epitaxial graphene from Pt(111) and Ir(111) metal surfaces. A multi-technique characterization combined with ab-initio calculations was employed to fully explain the different steps involved in the process. It was shown that, after a controlled electrochemical oxidation process, a single-atom thick metal-hydroxide layer intercalates below graphene, decoupling it from the metal substrate. This decoupling process occurs without disrupting the morphology and electronic properties of graphene. The results suggest that suitably optimized electrochemical treatments may provide effective alternatives to current transfer protocols for graphene and other 2D materials on diverse metal surfaces.

High-quality PVD graphene growth by fullerene decomposition on Cu foils

We present a new protocol to grow large-area, high-quality single-layer graphene on Cu foils at relatively low temperatures. We use C₆₀ molecules evaporated in ultra high vacuum conditions as carbon source. This clean environment results in a strong reduction of oxygen-containing groups as depicted by X-ray photoelectron spectroscopy (XPS). Unzipping of C₆₀ is thermally promoted by annealing the substrate at 800ºC during evaporation. The graphene layer extends over areas larger than the Cu crystallite size, although it is changing its orientation with respect to the surface in the wrinkles and grain boundaries, producing a modulated ring in the low energy electron diffraction (LEED) pattern. This protocol is a self-limiting process leading exclusively to one single graphene layer. Raman spectroscopy confirms the high quality of the grown graphene. This layer exhibits an unperturbed Dirac-cone with a clear n-doping of 0.77 eV, which is caused by the interaction between graphene and substrate. Density functional theory (DFT) calculations show that this interaction can be induced by a coupling between graphene and substrate at specific points of the structure leading to a local sp³ configuration, which also contribute to the D-band in the Raman spectra.

Influence of interface interaction on the moiré superstructures of graphene on transition-metal substrates

The formation of moiré superstructures between graphene and its underlying substrate has attracted significant attention because it significantly influences the morphology and properties of graphene.