In Situ Observations of the Atomistic Mechanisms of Ni Catalyzed Low Temperature Graphene Growth

Abstract

The key atomistic mechanisms of graphene formation on Ni for technologically relevant hydrocarbon exposures below 600 °C are directly revealed via complementary in situ scanning tunneling microscopy and X-ray photoelectron spectroscopy. For clean Ni(111) below 500 °C, two different surface carbide (Ni2C) conversion mechanisms are dominant which both yield epitaxial graphene, whereas above 500 °C, graphene predominantly grows directly on Ni(111) via replacement mechanisms leading to embedded epitaxial and/or rotated graphene domains. Upon cooling, additional carbon structures form exclusively underneath rotated graphene domains. The dominant graphene growth mechanism also critically depends on the near-surface carbon concentration and hence is intimately linked to the full history of the catalyst and all possible sources of contamination. The detailed XPS fingerprinting of these processes allows a direct link to high pressure XPS measurements of a wide range of growth conditions, including polycrystalline Ni catalysts and recipes commonly used in industrial reactors for graphene and carbon nanotube CVD. This enables an unambiguous and consistent interpretation of prior literature and an assessment of how the quality/structure of as-grown carbon nanostructures relates to the growth modes.

Bottom-up approach for the low-cost synthesis of graphene-alumina nanosheet interfaces using bimetallic alloys

“…At low exposure we observe a peak at B283.5 eV binding energy (BE), most probably due to C 2 H 4 fragments and carbides, while at larger carbon coverage a new component appears at higher BE (284.84 eV), attributed to Gr by comparison with Gr on Ni(111) (ref. 17). The integrated intensity of this peak shows a saturating behaviour, indicating a self-limiting growth process.…”

Redox dynamics of Ni catalysts in CO2 reforming of methane

“…The growth mode of carbon on Ni also depends on the particle size. Only small enough particles, which are present in both catalysts, will favor fiber or tube growth, while highly ordered graphene growth and graphite crystallization was observed predominantly on Ni111 terraces [27] that can be expected to a greater extent on larger particles. According to these considerations, a design goal for high-temperature Ni DRM catalysts is the formation of particles that are too large to trigger fiber growth, but at the same time exhibit a low fraction of Ni111 terraces and/or a blocking of carbon dissolution into the bulk by modifications of the surface, e.g.…”

Chemical vapour deposition of freestanding sub-60 nm graphene gyroids

“…40 These graphitic deposits are expected to exhibit a strong interaction with Ni, as a result of hybridisation between the graphene π and Ni 3d orbitals, thus helping to stabilise the template. 41 Additionally, nickel surface carbides are known to readily form on Ni at temperatures below 500 o C, 42 which may also assist in stabilising the template. As the process temperature continues to increase, amorphous and highly defective regions of the C coating are graphitised, which may involve defect healing as well as a re-dissolution process, as the C solubility in Ni increases with temperature.…”