Interface effects of Pb films on TlBiSe2 and Bi2Se3 topological insulators and Bi 2 Se 3 topological insulators

We present an experimental investigation of the Pb-induced changes on the electronic structure of selected topological insulators, namely, TlBiSe2 and Bi2Se3. Using spatially resolved and surface-sensitive techniques, including micro-angle-resolved photoemission (μ-ARPES) and micro-core-level photoemission (μ-PES), we track the evolution of the electronic states during adsorbate growth. For low Pb coverage on TlBiSe2, we identify the formation of a disordered interface. For thicker films, μ-ARPES measurements clearly resolve well-defined electron confinement (quantum well) states within the metallic Pb layers and no migration of the topological surface state onto the Pb film is observed. Furthermore, μ-PES results on both Pb/TlBiSe2 and Pb/Bi2Se3 heterostructures can be rationalized in terms of a significant chemical interaction between Pb and Se, leading to substantial surface degradation and Bi atom segregation. The ab initio modeling performed on the adsorption of lead on topological insulator surfaces, which includes the consideration of the swapping of Pb adsorbates with Bi substrate atoms, validates the scenario derived from experimental observations. It also suggests that the development of a disordered interface is due to the formation of PbSe nuclei, whose size is constrained by the compressive stresses exerted by the TI substrate.