Wafer-Scale Synthesis of Graphene on Sapphire: Toward Fab-Compatible Graphene.

The adoption of graphene in electronics, optoelectronics, and photonics is hindered by the difficulty in obtaining high-quality material on technologically relevant substrates, over wafer-scale sizes, and with metal contamination levels compatible with industrial requirements. To date, the direct growth of graphene on insulating substrates has proved to be challenging, usually requiring metal-catalysts or yielding defective graphene. In this work, a metal-free approach implemented in commercially available reactors to obtain high-quality monolayer graphene on c-plane sapphire substrates via chemical vapor deposition is demonstrated. Low energy electron diffraction, low energy electron microscopy, and scanning tunneling microscopy measurements identify the Al-rich reconstruction 31 × 31 R ± 9 ° of sapphire to be crucial for obtaining epitaxial graphene. Raman spectroscopy and electrical transport measurements reveal high-quality graphene with mobilities consistently above 2000 cm2 V-1 s-1 . The process is scaled up to 4 and 6 in. wafers sizes and metal contamination levels are retrieved to be within the limits for back-end-of-line integration. The growth process introduced here establishes a method for the synthesis of wafer-scale graphene films on a technologically viable basis.

Nanopattering in CeOx/Cu(111): A New Type of Surface Reconstruction and Enhancement of Catalytic Activity.

Our results indicate that small amounts of an oxide deposited on a stable metal surface can trigger a massive surface reconstruction under reaction conditions. In low-energy electron microscopy (LEEM) experiments, no reconstruction of Cu(111) is observed after chemisorbing oxygen or after reducing O/Cu(111) in a CO atmosphere. On the other hand, LEEM images taken in situ during the reduction of CeO2/CuO1-x/Cu(111) show a complex nonuniform transformation of the surface morphology. Ceria particles act as nucleation sites for the growth of copper microterraces once CuO1-x is reduced. Can this reconstructed surface be used to enhance the catalytic activity of inverse oxide/metal catalysts? Indeed, CeOx on reconstructed Cu(111) is an extremely active catalyst for the water-gas shift process (CO + H2O → H2 + CO2), with the Cu microterraces providing very efficient sites for the dissociation of water and subsequent reaction with CO.