Photoemission studies of interface properties of thin Bi overlayers on two-dimensional crystals of ${\mathrm{Bi}}_x{\mathrm{Sb}}_{2-x}{\mathrm{Te}}_3$ semiconductors using synchrotron radiation

Bonding between cleavage planes of layered ${\mathrm{Bi}}_2{\mathrm{Sb}}_{2-x}{\mathrm{Te}}_3$ solids and in situ deposited Bi overlayers has been investigated by ultraviolet photoelectron spectroscopy. The use of synchrotron radiation allows us to study the changes of electronic structure of both initial (occupied) as well as final (empty) states during interface formation. While Bi adatoms do not become a chemical part of the substrate, interfacial bonds of intermediate strength are proposed to occur at the well-defined Bi-layered solid interface. These intermediate bonds, considerably stronger than the Van der Waals bonds expected from the inert character of the cleavage plane of ${\mathrm{Bi}}_2$ ${\mathrm{Te}}_3$, are associated with an adatom-induced charge redistribution of the valence-band states of the substrate. This results in modification of the type of substrate interlayer bonds from nonbonding into chemically active ones, and to (presumed) weakening of the intralayer bonds.