Modification of the van der Waals interaction at the Bi2Te3 and Ge(111) interface

We present a structural and density-functional theory study of the interface of the quasi-twin-free grown three-dimensional topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ on Ge(111). Aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy in combination with first-principles calculations show that the weak van der Waals adhesion between the ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ quintuple layer and Ge can be overcome by forming an additional Te layer at their interface. The first-principles calculations of the formation energy of the additional Te layer show it to be energetically favorable as a result of the strong hybridization between the Te and Ge.