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

Quasi-free-standing monolayer graphene(QFMLG) formed by Gd intercalation hosts considerable electronic density of states compared with regular epitaxialmonolayer graphene (EMLG) on the SiC(0001) substrate. Here, we revealed that Gd-intercalated QFMLG with heavy electrondoping exhibited a stronger interface adsorption energy than that of EMLG, which is beneficial for the growth of quasi-monolayerSnSe2films. Combining the in situ reflection high-energy electron diffraction, scanning tunneling microscopy, and X-ray photo-electron spectroscopy, we systematically investigated the morphol-ogy and chemical bonding states of the monolayer SnSe2filmsgrown 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 SnSe2grown on the EMLG substrate (SnSe2/EMLG) presentsan island growth mode with a mixture of different thicknesses. Further angle-resolved photoelectron spectroscopic measurementsallow us to observe that the monolayer SnSe2films on Gd-intercalated QFMLG exhibit an indirect band gap of similar to 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 monolayerSnSe2and significant information in understanding the fundamental physical properties of monolayer SnSe2as a 2D semiconductor