No abstract

Molecular adsorption on noble‐metal surfaces influences the Rashba effect in the Shockley surface state (SS), but the underlying mechanism remains unclear. Melamine is a simple molecule with a symmetric backbone consisting of a heterocyclic ring. It self‐assembles into a rosette‐like superstructures on Au(111) via double intermolecular hydrogen bonds. In this study, the growth process and structure of this hydrogen‐bonded organic framework (HOF) using low‐energy electron diffraction and X‐ray photoemission spectroscopy is revealed. Above room temperature, it is impossible for melamine to be adsorbed on Au(111) as a monomer, but it is adsorbed collectively as a hydrogen‐bonding network. The melamine HOF has a characteristic hexagonal honeycomb structure (MHC), which significantly affects both the structure and electronic states of Au(111). A theoretical approach reveals that MHC induces a hexagonal periodic deformation in the structure of Au(111) and introduces a new periodic potential in the surface electronic system. Angle‐resolved photoemission spectroscopy measurements of MHC/Au(111) indicate that the bulk sp band is strongly folded back, enhancing the Rashba splitting of the SS of Au(111). Furthermore, spin‐ and angle‐resolved photoemission spectroscopy reveals that the enhanced Rashba splitting of the SS by the MHC is the largest reported to date for the adsorption system on Au(111).

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, Bi 2 Se 3 , in which the interaction between the molecule and TSS is the weakest one possible. Angle-resolved photo-emission 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 Bi 2 Se 3 . The amount of energy reduction is consistent with the reduction in vacuum level at the TTC/Bi 2 Se 3 interface, valence states of Bi 2 Se 3 and the core levels of Bi 2 Se 3 observed by ultravioletand X-ray photoemission spectroscopy. Therefore, no chemical interactions, such as charge transfer, occur at the TTC/ Bi 2 Se 3 interface, but only a redistribution of charge density on the Bi 2 Se 3 surface occurs due to the Pauli repulsion between the electrons of the adsorbed TTC molecule and TSS.