Intercalation from the Depths: Growth of a Metastable Chromium Carbide between Epitaxial Graphene and Ni(111) by Carbon Segregation from the Bulk

Abstract

The intercalation of atoms or small molecules underneath graphene epitaxially grown on single metal surfaces is a widely exploited method for modifying the interaction between the carbon monolayer and the substrate. Despite it would be highly desirable to expand the class of the intercalants by including also metal compounds such as oxides, nitrides, or carbides, their use as decoupling layers is a much more challenging task. Here, we demonstrate that it is possible to intercalate an ultrathin layer of Cr-carbide at the graphene/Ni(111) interface by using the carbon dissolved in the bulk of the substrate as a reservoir. Auger electron spectroscopy reveals that Cr deposition on the graphene/Ni(111) interface triggers C segregation from the Ni bulk, while the graphene layer floats on top of the growing film. Scanning tunneling microscopy shows the presence of a periodic superstructure on the surface, due to a coincidence lattice at the graphene/carbide boundary or alternatively to a dislocation network developing at the carbide/Ni(111) interface. Scanning tunneling spectra normalized to the total conductance indicate that the density of states around the Fermi level depends linearly on the energy, suggesting that the graphene layer is electronically decoupled from the Cr-carbide film

Spin‐Resolved PES and IPES Investigation of the Graphene/Ni(111) Interface

“…Our LEED and XPS analysis ensure the quality of the Gr/Ni(111) interface, also confirmed by comparing the scanning tunneling microscopy (STM) image reported in Figure 3 with the available literature. [14,39] According to the literature, Gr may adsorb on Ni(111) in line with the topbridge, top-fcc, and top-hcp registries, the last two being the most stable configurations. [40] The differences between the two cases, however, are too subtle to allow for an unambiguous determination of the adsorption registry in our STM images.…”

Graphene as an Ideal Buffer Layer for the Growth of High-Quality Ultrathin Cr2O3Layers on Ni(111)

“…After C 2 H 4 was dosed, the sample was further kept at 500 °C in UHV conditions for 5 min. This procedure induces the stabilization of a high-quality epitaxial layer of graphene on the Ni(111) surface with the hollow site of the honeycomb residing on the top site …”

“…This procedure induces the stabilization of a high-quality epitaxial layer of graphene on the Ni(111) surface with the hollow site of the honeycomb residing on the top site. 51 Chromium oxide (Cr 2 O 3 ) was grown by reactive molecular beam epitaxy in an oxygen atmosphere with pressure p O 2 = 1 × 10 −6 mbar. The growth was performed by keeping the sample at 300 °C.…”

Interface Characterization and Control of 2D Materials and Heterostructures

“…This process transforms the buffer layer into quasi‐free standing graphene with recovered electronic properties . In addition to hydrogen, other intercalants have been explored including alkali metals (e.g., Li, Na, K, Cs,), Ca, Cu, Bi, Cr, Ge, and Si . Specifically, Li and Ca induce superconductivity in graphene, while Ge leads to interfacial ambipolar doping of graphene depending on local Ge coverage, allowing for the creation of 2D lateral p–n junctions .…”

“…Similar intercalation strategies have been applied to grow other 2D compounds at the graphene/substrate interface. For example, 2D FeO and Cr‐carbide form after Fe and Cr intercalated graphene reacts with O 2 gas and C segregated from the metal substrate, respectively. In the case of graphene‐capped water molecules, the formed 2D lattices exhibit a rich phase space with multiple polymorphs.…”