Enhanced Rashba Splitting of Au(111) Surface States with Hydrogen-Bonded Melamine-Based Organic Framework

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).

Automated summary

This study reveals that molecular adsorption on noble-metal surfaces influences the Rashba effect in the Shockley surface state, with melamine self-assembling into a characteristic hexagonal honeycomb structure on Au(111), significantly affecting the structure and electronic states.