Probing interlayer interactions between graphene and metal substrates by supersonic rare-gas atom scattering

Abstract

We demonstrate that highly surface-sensitive supersonic rare-gas (He, Ar, and Xe) atom scattering, in both the quantum and classical regimes, can probe and quantify the interlayer interactions between graphene monolayers and metal substrates in terms of the Debye temperature corresponding to the surface normal vibration, and the surface effective mass. As models of the strongly and weakly interacting graphene, we investigated two systems, graphene on Ru(0001) and Pt (111), respectively. The experimental data for Ar and Xe are compared with the results from theoretical simulations based on the classical smooth surface model. For gr/Pt(111) we find that the scattering pattern of the rare-gas beam, including the Debye-Waller attenuation of the He beam, are quite similar to that from highly oriented pyrolytic graphite (HOPG); this suggests that the graphene-Pt (111) interaction is much like a van der Waals interaction. On the contrary, for the gr/Ru(0001) system, we find a smaller Debye-Waller attenuation and a larger surface effective mass, indicating that graphene on Ru(0001) is tightly bonded to the substrate. Furthermore, asymmetrical spectral shapes in the Ar and Xe scattering spectra from gr/Ru(0001) are interpreted as a result of the lateral distribution of the interlayer interaction corresponding to the moiré pattern. It is found that the "valley" region of the moiré pattern has high effective mass reflecting stronger bonding to the substrate, contributing to the high reflectivity of the He beam reported for this system. On the other hand, the effective mass of the "hill" region is found to be similar to that of HOPG, indicating that this region is well decoupled from the substrate. These results demonstrate a unique capability of atom scattering to probe and evaluate the molecule-substrate interaction and its spatial distributions.

Helium diffraction on SiC grown graphene: Qualitative and quantitative descriptions with the hard-corrugated-wall model

“…A more significant difference between GIFAD and HAS lies in the ability of HAS to measure phonon modes of the graphene surface by inelastic scattering [4][5][6][7][8]. In the present case some modes specific to quasi-free standing graphene were identified [4] providing a very interesting link with dynamical behavior of the graphene layer as probed by Atomic Force Microscopy [43].…”

“…On the one hand, a few meV resolution on top of few hundred eV projectiles does not seem realistic. On the other hand, Shichibe et al [8] have shown that this inelastic behavior also has specific signatures in the scattering profile perpendicular to the surface plane. Provided that topological defects are under control, these aspects could probably be investigated at grazing incidences as well.…”

“…This anchoring is visible both in the detailed topography and in the local conductivity, measured in STM experiments where individual contributions are difficult to disentangle. In contrast, AFM or helium diffraction (HAS) are techniques that probe only the topography of the electronic density of the topmost layer [1][2][3][4][5][6][7][8], and are only perturbed by weak polarization effects. This is also the case of grazing incidence fast atom diffraction (GIFAD or FAD) which uses helium atoms with an energy E 0 in the keV range but at such a low incidence angle θ, that the energy E ⊥ = E 0 sin 2 θ of the movement normal to the surface is in the sub-eV range.…”

Insights on the Excitation Spectrum of Graphene Contacted with a Pt Skin

“…The intensity and dispersion relations of electronic excitations in supported graphene depend on the strength of the graphene interaction with the substrate [1][2][3][4][5][6][7][8]. Plasmonic excitations of graphene on different metallic surfaces, such as Ir(111), Cu(111) and Ni(111), have been studied in many experimental and theoretical reports [9][10][11][12][13][14][15][16][17][18][19][20]. The goal of most investigations on graphene/metal interfaces is to achieve a graphene sheet electronically decoupled from the substrate, with its electronic structure as similar as possible to the structure of free-standing graphene.…”

Unified quantum theory of elastic and inelastic atomic scattering from a physisorbed monolayer solid

“…However, much quantitative analysis of diffraction intensities for beams of energy E i < 10 meV relies on elementary Debye-Waller attenuation approximations [12]. Similar approximations are used in analyzing specular helium reflection for information on graphene-metal bonding [13]. There has been progress in the calculation of diffraction intensities with explicit coupling to inelastic channels [14] and with multichannel elastic scattering theory for heavier atoms [15].…”