Topological Surface State of Bi2Se3 Modified by Physisorption of n-Alkane

Recently, the interface between an organic molecular layer and a topological insulator (TI) surface (Org./TI interface) has been studied to explore the possibility of multifunctional TI devices with organic molecules. Nevertheless, understanding of the electronic structure of Org./TI interfaces is insufficient. Especially, little is known about physisorption systems, where the interaction between adsorbed molecules and topological surface state (TSS) is weak. Here, we discuss an ideal physisorption system of an n-alkane molecule, n-tetratertacontane (TTC), and prototypical TI, Bi2Se3, in which the interaction between the molecule and TSS is the weakest one possible. Angle-resolved photoemission spectroscopy results show that the energy of the Dirac cone (DC) energy band decreases by approximately 60 meV when the TTC layer is formed on Bi2Se3. The amount of energy reduction is consistent with the reduction in vacuum level at the TTC/Bi2Se3 interface, valence states of Bi2Se3 and the core levels of Bi2Se3 observed by ultraviolet- and X-ray photoemission spectroscopy. Therefore, no chemical interactions, such as charge transfer, occur at the TTC/Bi2Se3 interface, but only a redistribution of charge density on the Bi2Se3 surface occurs due to the Pauli repulsion between the electrons of the adsorbed TTC molecule and TSS.