Direct Selenization Growth and Electronic Properties of Ultrathin Fe(Te,Se) on a van der Waals Ferromagnet

Fe(Te,Se) is a prototypical iron-based superconductor and a promising platform for exploring topological superconductivity. However, growing high-quality ultrathin Fe(Te,Se) films on magnetic substrates remains challenging. Here, we demonstrate epitaxial growth of monolayer-to-trilayer Fe(Te,Se) on the van der Waals itinerant ferromagnet Fe3GeTe2 (FGT) via direct selenization of the substrate, without external Fe or Te deposition. Combined scanning tunneling microscopy/spectroscopy (STM/STS), low-energy electron diffraction (LEED), scanning transmission electron microscopy (STEM), and energy-dispersive spectroscopy (EDS) characterizations reveal large-area, atomically flat tetragonal films with well-defined rotational alignment to the hexagonal FGT lattice. Cross-sectional STEM-EDS confirms Se incorporation and interfacial elemental redistribution. Thickness-dependent spectroscopy reveals evolving electronic structures and progressive decoupling from the ferromagnetic substrate. Measurements across lateral monolayer–bilayer interfaces further uncover asymmetric band bending and charge redistribution driven by Fermi-level equilibration. These findings establish substrate-mediated selenization as a versatile route to ultrathin superconducting heterostructures and magnetic quantum platforms.