Epitaxial Growth of Monolayer SnSe₂ Films on Gd-Intercalated Quasi-Free-Standing Monolayer Graphene with Enhanced Interface Adsorption

Abstract

Quasi-free-standing monolayer graphene (QFMLG) formed by Gd intercalation hosts considerable electronic density of states compared with regular epitaxial monolayer graphene (EMLG) on the SiC(0001) substrate. Here, we revealed that Gd-intercalated QFMLG with heavy electron doping exhibited a stronger interface adsorption energy than that of EMLG, which is beneficial for the growth of quasi-monolayer SnSe2 films. Combining the in situ reflection high-energy electron diffraction, scanning tunneling microscopy, and X-ray photoelectron spectroscopy, we systematically investigated the morphology and chemical bonding states of the monolayer SnSe2 films grown on the Gd-intercalated QFMLG substrate (SnSe2/QFMLG). We found that the SnSe2/QFMLG presents a quasi-layered growth mode with less bilayer islands formed; in contrast, the SnSe2 grown on the EMLG substrate (SnSe2/EMLG) presents an island growth mode with a mixture of different thicknesses. Further angle-resolved photoelectron spectroscopic measurements allow us to observe that the monolayer SnSe2 films on Gd-intercalated QFMLG exhibit an indirect band gap of ∼1.47 eV due to the pronounced charge transfer at SnSe2/QFMLG interfaces. In addition, we extracted the effective mass of holes located at the valence band maximum. Our results provide an effective way to improve the controlling of thickness in van der Waals growth of monolayer SnSe2 and significant information in understanding the fundamental physical properties of monolayer SnSe2 as a 2D semiconductor.

Observation of a Folded Dirac Cone in Heavily Doped Graphene

“…The Gd-intercalated graphene was prepared by evaporating Gd at 1130 °C. The temperature of the substrate was kept at 800 °C during the process of intercalation. , Then, the sample flashing was annealed at 1200 °C for 10 s to obtain homogeneous Gd intercalation film. In situ ARPES and X-ray photoelectron spectroscopy (XPS) measurements were performed in an UHV better than 2 × 10 –10 mbar using a Scienta-Omicron DA30 analyzer spectrometer with a monochromatized He lamp (21.22 eV) and Al K α radiation (1486.6 eV), respectively.…”