Subsurface Carbon Incorporation Controls Graphene Nucleation on Ir(111)

The growth of two-dimensional materials by chemical vapor deposition is governed by a complex interplay of adsorption, surface diffusion, and nucleation processes. For growth on transition metal surfaces, dissolution into the bulk adds an additional parameter. Using low-energy electron microscopy, we analyze temperature- and dosing-pressure-dependent nucleation of graphene islands on Ir(111). Depending on dosing conditions, the island nucleation density follows two distinct regimes, described within Venables' nucleation theory. At low dosing pressure, nucleation is strongly suppressed, the island density is small, and it follows scaling characteristics of initially incomplete condensation. Increasing dosing pressure renders bulk-mediated adatom loss negligible, leading to a higher nucleation density and a strongly reduced scaling exponent. Kinetic Monte Carlo simulations that explicitly consider bulk dissolution reveal a universal, temperature-independent scaling law with a crossover from steep to shallow scaling, reflecting generic nucleation behavior for 2D materials with finite solubility.