Sulfur‐to‐Metal Single‐Atom Editing of a Thiourea Self‐Assembled Monolayer into an Adatom‐Bound N‐Heterocyclic Carbene Monolayer on Coinage Metal Surfaces

N‐Heterocyclic carbene (NHC) self‐assembled monolayers (SAMs) are emerging as robust and versatile surface ligands, yet their direct on‐surface construction with atomic precision remains elusive. Here, we report a reagent‐free, thermally driven on‐surface strategy for single‐atom editing, providing an alternative to convert a heteroatom‐anchored SAM into a functional NHC layer. N‐Heterocyclic thiourea (NHT) with carefully chosen substituents undergoes a S‐to‐metal adatom exchange, yielding adatom‐bound NHC on coinage metal surfaces. Using low‐temperature scanning tunneling microscopy (LT‐STM), synchrotron‐radiation X‐ray photoelectron spectroscopy (SR‐XPS), time of flight secondary ion mass spectrometry (ToF‐SIMS) and density functional theory (DFT), we identify two distinct classes of SAMs: (i) NHT‐SAM, in which sulfur coordinates to the metal surface and (ii) NHC‐SAM, characterized by M─C σ ‐bonds between the carbene center and a surface adatom. NHT undergoes a clean SAM‐to‐SAM conversion, achieving covalent single‐atom editing within an intact monolayer. DFT calculations show this transformation is energetically favorable and highly tunable by substrates and N‐substituents, establishing a general framework for atom‐precise molecular editing at surfaces.