Observation of variable hybridized-band gaps in Eu-intercalated graphene

Abstract

We report europium (Eu)-induced changes in the π-band of graphene (G) formed on the 6H-SiC(0001) surface by a combined study of photoemission measurements and density functional theory (DFT) calculations. Our photoemission data reveal that Eu intercalates upon annealing at 120 °C into the region between the graphene and the buffer layer (BL) to form a G/Eu/BL system, where a band gap of 0.29 eV opens at room temperature. This band gap is found to increase further to 0.48 eV upon cooling down to 60 K. Our DFT calculations suggest that the increased band gap originates from the enhanced hybridization of the graphene π-band with the Eu 4f band due to the increased magnetic ordering upon cooling. These Eu atoms continue to intercalate further down below the BL to produce bilayer graphene (G/BL/Eu) upon annealing at 300 °C. The π-band stemming from the BL then exhibits another band gap of 0.37 eV, which appears to be due to the strong hybridization between the π-band of the BL and the Eu 4f band. The Eu-intercalated graphene thus illustrates an example of versatile band gaps formed under different thermal treatments, which may play a critical role for future applications in graphene-based electronics.

Intercalated europium metal in epitaxial graphene on SiC

“…We note that lower annealing temperatures has been reported in the Ref. [17] (120 C), confining the Eu diffusion between graphene and buffer layer, whereas annealing at 300 C shifts the Eu between the buffer and SiC and transforms the graphene to a bilayer. The annealing temperatures are higher in the current study resulting in a self-organized network of clusters of ∼25 atoms separated by at least 1.8 nm which behave independently in their magnetic response.…”

“…Defect-free and epitaxial monoatomic layer of graphene has long been produced on SiC(0001) forming a continuous membrane over the whole surface including surface steps [9]. With these advances, modifying the electronic properties of graphene has been investigated either by depositing inert metals [10,11] and metaloxides [12] or by intercalating between the graphene and the metal substrate [13][14][15][16] or between graphene and the SiC buffer-layer [17]. Intercalation of metal donors or molecular acceptors into graphite is an old topic that culminated in recipes that enable control of the superstructures (staging phenomena), electrical conduction, superconductivity and even electrical energy storage in batteries (i.e., CF and CLi 6 ) [18].…”

Observation of critical magnetic behavior in 2D carbon based composites

“…Nevertheless, the AFM structure was found to be better at opening a band gap in comparison to the FM structure. 132 Wei et al observed a strong interfacial exchange eld in a graphene/ EuS heterostructure as a consequence of strong Zeeman splitting. 133…”

Intercalated rare-earth metals under graphene on SiC

“…Intercalation of Eu between Ir substrate and graphene (prepared by CVD) reveals that the structure and magnetic properties of the intercalated Eu depend on the coverage which does not seem to affect the graphene electronic structure [6]. However, a recent study shows that Eu intercalation between graphene and the SiC buffer layer modifies the π−band of graphene significantly [9].…”

“…Metal intercalation under graphene on various substrates is by now common practice [1,2,3,4,5,6,7,8,9,10,11]. Indeed, it has been demonstrated that rare earth metals (RE = Nd, Sm, Dy, Er and Yb, and Eu, for example) deposited on graphene grown on SiC or Ir substrate can intercalate under the graphene lattice by annealing pre-deposited metals at elevated temperatures [1,4,9,12]. Adsorbed metals on graphene have also been used to take advantage of special growth or to mutually modify the electronic properties of graphene and the adsorbed metal atoms on it.…”