Abstract
We report the use of a novel atomic carbon source for the molecular beam epitaxy (MBE) of graphene layers on hBN flakes and on sapphire wafers at substrate growth temperatures of ~1400 °C. The source produces a flux of predominantly atomic carbon, which diffuses through the walls of a Joule-heated tantalum tube filled with graphite powder. We demonstrate deposition of carbon on sapphire with carbon deposition rates up to 12 nm/h. Atomic force microscopy measurements reveal the formation of hexagonal moiré patterns when graphene monolayers are grown on hBN flakes. The Raman spectra of the graphene layers grown on hBN and sapphire with the sublimation carbon source and the atomic carbon source are similar, whilst the nature of the carbon aggregates is different - graphitic with the sublimation carbon source and amorphous with the atomic carbon source. At MBE growth temperatures we observe etching of the sapphire wafer surface by the flux from the atomic carbon source, which we have not observed in the MBE growth of graphene with the sublimation carbon source.
Highlights
Our AFM measurements reveal the formation of hexagonal moiré patterns on the surface of graphene monolayers on hBN flakes
The amount of non-graphene carbon on the surface is reduced for the layers grown with the atomic carbon source when compared with a carbon sublimation source
Overall our work shows that it is possible to form graphene/BN heterostructures by MBE using this new atomic carbon source
Summary
To test whether the novel source could produce a flux of carbon and to measure the potential carbon deposition rates we first grew carbon layers on unheated sapphire substrates at approximately room temperature. Both graphene layers were grown at the same substrate temperatures of approximately 1400 °C, the growth times differed to ensure a comparable overall coverage of carbon. AFM images of the carbon layer grown on sapphire with the atomic carbon source at a room substrate temperature and the sapphire surface where the carbon has been removed after the growth are given in the SI. We are performing more studies on the epitaxy of graphene with both atomic and standard sublimation carbon sources to establish the influence of the source design on the properties of graphene layers and results will be published in due course
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