Coverage–Dependent Structural Evolution of CoBr2 at the Au(111) Interface

CoBr2 grown on Au(111) initially forms a surface‐stabilized molecular precursor phase is composed of ordered three‐molecule clusters that lie flat on the surface and have a periodic coincidence with the substrate. As coverage increases, the precursor phase transforms into the bulk‐like van der Waals 1T trilayer, with subsequent layers adopting the same bulk‐like structure, challenging conventional views of direct van der Waals layer formation. Abstract Unraveling the growth mechanism of van der Waals materials is crucial for their device implementation, as this improves the overall film quality, allowing precise control of their electronic and magnetic properties in nanoscale applications. The initial structure formed on the substrate during growth is often assumed to be bulk‐like, thereby neglecting the role of the surface in the assembly. Here, the coverage–dependent growth of CoBr2 on Au(111) from a stoichiometric molecular powder is studied using a combination of experimental techniques, machine–learning‐driven molecular dynamics simulations and density functional theory calculations. It is found that CoBr2 molecules initially form a molecular precursor phase characterized by three‐molecule clusters arranged in a surface–stabilized structure with long‐range order and a periodic coincidence with Au(111). As the surface coverage is increased, this phase subsequently undergoes a transition to form the equilibrium van der Waals crystal layered structure observed for the bulk material. These findings challenge conventional views of direct van der Waals layer formation and provide new insight into the role of the substrate during the growth process. CoBr 2 grown on Au(111) initially forms a surface-stabilized molecular precursor phase is composed of ordered three-molecule clusters that lie flat on the surface and have a periodic coincidence with the substrate. As coverage increases, the precursor phase transforms into the bulk-like van der Waals 1T trilayer, with subsequent layers adopting the same bulk-like structure, challenging conventional views of direct van der Waals layer formation. Abstract Unraveling the growth mechanism of van der Waals materials is crucial for their device implementation, as this improves the overall film quality, allowing precise control of their electronic and magnetic properties in nanoscale applications. The initial structure formed on the substrate during growth is often assumed to be bulk-like, thereby neglecting the role of the surface in the assembly. Here, the coverage–dependent growth of CoBr 2 on Au(111) from a stoichiometric molecular powder is studied using a combination of experimental techniques, machine–learning-driven molecular dynamics simulations and density functional theory calculations. It is found that CoBr 2 molecules initially form a molecular precursor phase characterized by three-molecule clusters arranged in a surface–stabilized structure with long-range order and a periodic coincidence with Au(111). As the surface coverage is increased, this phase subsequently undergoes a transition to form the equilibrium van der Waals crystal layered structure observed for the bulk material. These findings challenge conventional views of direct van der Waals layer formation and provide new insight into the role of the substrate during the growth process. Advanced Science, EarlyView.