Charge neutrality of quasi-free-standing monolayer graphene induced by the intercalated Sn layer

Abstract

It has been confirmed by angle-resolved photoemission spectroscopy that decoupled quasi-free-standing monolayer graphene (QFMLG), obtained by Sn intercalation between the buffer layer and the 6H-SiC(0 0 0 1) substrate, is charge-neutral, i.e. the Dirac point matches with the Fermi level. By combined studies of scanning tunneling microscopy/spectroscopy and core-level/valence-band photoemission spectroscopy on this system, it has been found that the intercalated Sn atoms, bonding with the Si atoms of the top Si-C bilayer on the substrate comprise a hexagonal layer, which turns out to be metallic. Such a metallic character, which has never been found in intercalation using different elements, is a major cause of charge neutrality of QFMLG, since conduction electrons of the Sn layer compensate completely spontaneous polarization charges of 6H-SiC(0 0 0 1). This charge-neutral QFMLG is stable at a high temperature of 850 °C.