Surface Structure and Acoustic Phonon Dynamics of graphene on Ni(111)
1Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Spain
2Instituto de Ciencia de Materiales "Nicolás Cabrera", Universidad Autónoma de Madrid, Spain
3Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Spain
The structure and acoustic phonon modes of graphene grown on Ni(111) have been measured by helium atom scattering (HAS). The data are discussed in comparison with earlier HREELS measurements [1,2]. The HAS diffraction spectra reveal that the graphene layer has a three-fold symmetry. The He-specular reflectivity at low temperatures is very high (~20% of incident beam) with a FWHM = 0.07˚, which is the limit of our apparatus resolution. This makes this system an excellent candidate to be used as a mirror for He-microscopy. Thermal attenuation measurements give information on the Debye-Waller factor, which were compared to results reported for graphene/Ru(0001) and HOPG. The acoustic phonon modes were determined by time-of-flight measurements. The HAS data are consistent with previous HREELS measurements, and reveal more information on the nature of the graphene-Ni(111) interaction. Surprisingly, the Rayleigh mode observed for graphene/Ni(111) is almost identical to the one measured on clean Ni(111). Our data suggest what appears to be an anomaly in the ZA mode in the middle of the Brillouin zone, as well as a pronounced asymmetry of the ZA mode along both GM and GK directions.
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