Abstract
Using helium atom scattering, we have studied the structure and dynamics of a graphene layer prepared in situ on a Ni(111) surface. Graphene/Ni(111) exhibits a helium reflectivity of ∼20% for a thermal helium atom beam and a particularly small surface electron density corrugation ((0.06 ± 0.02) Å peak to peak height). The Debye–Waller attenuation of the elastic diffraction peaks of graphene/Ni(111) and Ni(111) was measured at surface temperatures between 150 and 740 K. A surface Debye temperature of θD = (784 ± 14) K is determined for the graphene/Ni(111) system and θD = (388 ± 7) K for Ni(111), suggesting that the interlayer interaction between graphene and the Ni substrate is intermediary between those for strongly interacting systems like graphene/Ru(0001) and weakly interacting systems like graphene/Pt(111). In addition we present measurements of low frequency surface phonon modes on graphene/Ni(111) where the phonon modes of the Ni(111) substrate can be clearly observed. The similarity of these findings with the graphene/Ru(0001) system indicates that the bonding of graphene to a metal substrate alters the dynamic properties of the graphene surface strongly and is responsible for the high helium reflectivity of these systems.
Highlights
Metal−graphene interfaces are attracting much attention due to the possibility of synthesizing large area graphene films on metals by chemical vapor deposition.[1]
The quality of graphene layers grown in this way is in general very high allowing us to investigate the elastic properties of these systems and the interaction strength between the graphene layer and the metallic substrate.[2,3]
helium atom scattering (HAS) can be used to obtain information about the weak interactions between substrates and a molecular overlayer: As recently shown by Shichibe et al.,[4] by measuring the surface Debye temperature the interlayer bonding can be quantified, which is rather difficult to probe with other conventional techniques
Summary
Metal−graphene interfaces are attracting much attention due to the possibility of synthesizing large area graphene films on metals by chemical vapor deposition.[1]. The quality of graphene layers grown in this way is in general very high allowing us to investigate the elastic properties of these systems and the interaction strength between the graphene layer and the metallic substrate.[2,3] graphene−metal systems are excellent model systems in order to understand the interaction between organic semiconductors and metal electrodes which is vital in organic electronics.[4] Since the interaction between an organic molecule and the substrate is weak compared with conventional metallic or covalent bonding, techniques such as X-ray scattering and high-energy electron diffraction can often turn out to be destructive Neutral He atom beams with energies of typically 10 meV are perfectly suited to probe these systems in an inert, completely nondestructive manner.[4−6] In addition, helium atom scattering (HAS) provides an accurate description of the surface charge density corrugation as seen by He atoms at thermal energies and the excellent surface sensitivity of this technique has been used to determine structural and vibrational properties of molecular adsorbates.[4,5] More importantly, HAS can be used to obtain information about the weak interactions between substrates and a molecular overlayer: As recently shown by Shichibe et al.,[4] by measuring the surface Debye temperature the interlayer bonding can be quantified, which is rather difficult to probe with other conventional techniques.
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