An x-ray photoemission electron microscope (X-PEEM) equipped with a hemispherical energy analyzer is capable of fast acquisition of momentum-resolved photoelectron angular distribution patterns in a complete cone. We have applied this technique to observe the 3-D electronic band structure of zero-, one-, and two-monolayer (ML) graphene grown ex situ on 6H-SiC(0001) substrates where a carbon buffer layer (zero ML) forms underneath the graphene layer(s). We demonstrate that the interfacial buffer layer can be converted into quasi-free-standing graphene upon intercalation of Li atoms at the interface and that such a graphene is structurally and electronically decoupled from the SiC substrate. High energy and momentum resolution of the X-PEEM, along with short data acquisition times from submicrometer areas on the surface demonstrates the uniqueness and the versatility of the technique and broadens its impact and applicability within surface science and nanotechnology.
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