Effects of hydrogen exposure on monolayer graphene on SiC(0001)

The influence of hydrogen exposures on a high quality monolayer graphene grown on SiC(0001) is investigated using photoelectron spectroscopy (PES), low-energy electron microscopy (LEEM) and micro low energy electron diffraction ($\mu $-LEED). We observe significant changes in the C1s core level, electron reflectivity curve, and electron diffraction after hydrogenation. Collected LEEM and $\mu $-LEED data after atomic hydrogen exposures demonstrate unambiguously a transformation from monolayer graphene plus carbon buffer layer to bi-layer graphene with no carbon buffer layer. This is novel since the preparation of either homogenous large area bi-layer graphene or bi-layer graphene without the carbon buffer (interface) layer on SiC(0001) has earlier not been reported. Our findings therefore open up new possibilities and opportunities for graphene-SiC based electronic devices and hydrogen storage.