Critical behavior in the epitaxial growth of two-dimensional tellurium films on SrTiO₃ (001) substrates

Materials’ properties may differ in the thin-film form, especially for epitaxial ultra-thin films, where the substrates play an important role in their deviation from the bulk quality. Here by molecular beam epitaxy (MBE) and scanning tunneling microscopy/spectroscopy, we investigate the growth kinetics of ultra-thin tellurium (Te) films on SrTiO₃ (STO) (001). The MBE growth of Te films usually exhibits Volmer-Weber (VW) island growth mode and no a-few-monolayer film with full coverage has been reported. The absence of wetting-layer formation in the VW growth mode of Te on STO (001) is resulted from its low diffusion barriers as well as its relatively higher surface energy compared with those of the substrate and the interface. Here we circumvent these limiting factors and achieve the growth of ultra-thin β-Te films with near-complete coverages by driving the growth kinetics to the extreme condition. There is a critical thickness (3 monolayer) above which the two-dimensional Te films can form on the STO (001) substrate. In addition, the scanning tunneling spectra on the ultra-thin Te film grown on STO exhibits an enormously large forbidden gap compared with that grown on the graphene substrate. Our work establishes the necessary conditions for the growth of ultra-thin materials with similar kinetics and thermodynamics.