Oxygen Switching of the Epitaxial Graphene–Metal Interaction

Abstract

Using photoemission spectroscopy techniques, we show that oxygen intercalation is achieved on an extended layer of epitaxial graphene on Ir(111), which results in the "lifting" of the graphene layer and in its decoupling from the metal substrate. The oxygen adsorption below graphene proceeds as on clean Ir(111), giving only a slightly higher oxygen coverage. Upon lifting, the C 1s signal shows a downshift in binding energy, due to the charge transfer to graphene from the oxygen-covered metal surface. Moreover, the characteristic spectral signatures of the graphene-substrate interaction in the valence band are removed, and the spectrum of strongly hole-doped, quasi free-standing graphene with a single Dirac cone around the K point is observed. The oxygen can be deintercalated by annealing, and this process takes place at around T = 600 K, in a rather abrupt way. A small amount of carbon atoms is lost, implying that graphene has been etched. After deintercalation graphene restores its interaction with the Ir(111) substrate. Additional intercalation/deintercalation cycles readily occur at lower oxygen doses and temperatures, consistently with an increasingly defective lattice. Our findings demonstrate that oxygen intercalation is an efficient method for fully decoupling an extended layer of graphene from a metal substrate, such as Ir(111). They pave the way for the fundamental research on graphene, where extended, ordered layers of free-standing graphene are important and, due to the stability of the intercalated system in a wide temperature range, also for the advancement of next-generation graphene-based electronics.

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

“…After Gr growth, the Gr-alloy interface was exposed to a high flux of molecular oxygen (pressure ¼ 3 Â 10 À 3 torr) at 520 K. Following this procedure, it is possible to intercalate oxygen underneath the Gr layer and to selectively oxidize only the Al atoms at the metal interface. In fact, the intercalation of noble or light atoms has already proven to be an effective method to create an interface nanosheet between Gr and the substrate [21][22][23][24] . Figure 3a,b shows a set of high-resolution photoemission spectra acquired after different oxygen exposures, for the C1s and Al2p levels, respectively.…”

“…It is important to underline the absence of any interfacial buffer layer between Gr and alumina, which would give rise to a feature at 281.5 eV (the BE corresponding to the Al-C bonds) and 282.5 eV (Al-O-C bond) 28,29 and also to C-O bonds characteristic of epoxy, ethers, quinones and lactones, which typically show up in the C1s spectrum at binding energies4284.2 eV (ref. 22). In addition, we can safely rule out the formation of a high density of Gr defects such as single-and double-vacancies or Stone-Wales defects.…”

Variation of the character of spin-orbit interaction by Pt intercalation underneath graphene on Ir(111)

“…First of all, in Ref. [37] authors showed that intercalation of oxygen leads to decoupling of graphene from the substrate with the shift of the Dirac point by 0.57 eV above the Fermi level. On the other hand, Cu intercalated graphene on Ir(111) is characterized by a gap between the π and π * states, opened by lifting the sublattice symmetry due to hybridization of the Cu and graphene bands [38].…”

Enhanced reactivity of graphene wrinkles and their function as nanosized gas inlets for reactions under graphene

“…27,[32][33][34] The intercalated oxygen atoms directly attack carbon atoms inside graphene islands with high oxidation rate. 27 On graphene/Ir(111) surfaces oxygen intercalation is also feasible in low pressure O 2 , 30,35 and the mechanism of direct attack by the intercalated oxygen atoms is active for the graphene oxidation. Moreover, wrinkles are present at the graphene/Ir(111) surfaces, 14,15 which probably make the oxygen intercalation easier and enhance the oxidation as well.…”