Carbodicarbene Monolayers on Au(111) Enable Strong Carbon(0)-Metal Binding and Work-Function Modulation

Carbodicarbenes (CDCs), featuring a formally zero-valent carbon atom coordinated by two N-heterocyclic carbene (NHC) units, are exceptionally strong σ-donor ligands in molecular chemistry, yet their ability to functionalize and electronically modulate solid surfaces has remained unexplored. Here, we introduce CDCs as a new class of molecular surface ligands for nanoscale interface engineering and demonstrate their assembly into robust monolayers on Au(111). Scanning tunneling microscopy (STM) imaging, supported by simulations, resolve the nanoscale organization and adsorption geometry of the CDC monolayers, showing that CDCs adsorb predominantly in a tilted configuration and transform upon annealing into a flat-lying geometry without long-range surface diffusion. This behavior is consistent with strong ligand-surface coupling and a high degree of interfacial stability. X-ray photoelectron spectroscopy (XPS) and polarized near-edge X-ray absorption fine structure (NEXAFS) measurements further confirm the formation of chemically anchored, thermally stable CDC monolayers and the thermally-induced shift in their adsorption geometry. Ultraviolet photoelectron spectroscopy (UPS) reveals that CDC adsorption decreases the Au work function by up to 1 eV, demonstrating substantial electronic modulation of the metal surface. These experimental findings, supported by Density functional theory (DFT) calculations, establish CDC as a surface- ligand for molecularly controlled work-function modulation and interface engineering.