Kinetically Controlled Epitaxial Growth of Fe3GeTe2 van der Waals Ferromagnetic Films

We demonstrate that kinetics play an important role in the epitaxial growth\nof Fe$_3$GeTe$_2$ (FGT) van der Waals (vdW) ferromagnetic films by molecular\nbeam epitaxy. By varying the deposition rate, we control the formation or\nsuppression of an initial tellurium-deficient non-van der Waals phase\n(Fe$_3$Ge$_2$) prior to realizing epitaxial growth of the vdW FGT phase. Using\ncross-sectional scanning transmission electron microscopy and scanning\ntunneling microscopy, we optimize the FGT films to have atomically smooth\nsurfaces and abrupt interfaces with the Ge(111) substrate. The magnetic\nproperties of our high quality material are confirmed through magneto-optic,\nmagnetotransport, and spin-polarized STM studies. Importantly, this\ndemonstrates how the interplay of energetics and kinetics can help tune the\nre-evaporation rate of chalcogen atoms and interdiffusion from the underlayer,\nwhich paves the way for future studies of van der Waals epitaxy.\n