The graphene growth and its interaction with the metal support are interesting both from a fundamental and technological point of view. In particular, graphene on ferromagnets has the potential to be used for the realization of spintronic devices, acting as a conductive channel, into which spin-polarized electrons are injected from the ferromagnet support. For this reason, the study of the growth and the electronic structure of the graphene-metal interface is the prerequisite for any practical application.
Here, we follow the temperature-dependent growth of graphene on Co/W(110) by means of low energy electron and photoemission electron microscopy (LEEM/PEEM). LEEM studies show that a highly ordered graphene layer with single azimuthal orientation can be only grown within a certain temperature range (>500°C). At lower temperatures, graphene grows predominantly with misoriented domains. This was confirmed using different techniques: LEED shows a (1x1) structure with an additional blurred ring indicating graphene domains rotated relative to the Co lattice. In addition, the C 1s XPS spectra indicate the presence of defects in the graphene network along with carbide components at lower binding energy.
At higher temperatures, the low quality graphene transforms into a (1x1) epitaxial graphene with better structural quality, as monitored by LEEM and μ-LEED. In this case, the diffraction ring due to azimuthally misoriented domains disappears and the LEED pattern is composed only by a (1x1) structure in registry with the Co substrate, indicating the presence of an epitaxial graphene overlayer. Moreover, the C 1s XPS spectrum presents a sharp single-component feature centered at 284.8 eV binding energy, characteristic in graphene-cobalt complexes.