Ultra-Low Atomic Diffusion Barrier on Two-Dimensional Materials: The Case of Pt on Epitaxial Graphene

Understanding the energetics of atomic diffusion on graphene and two-dimensional (2D) materials is critical for advancing ultraminiaturized nanodevices, where even single-atom dynamics can significantly impact their functionality and performance, and for designing next-generation catalysts with superior activity and selectivity. In this work, we demonstrate that the combination of fast, high-resolution X-ray photoelectron spectroscopy (HR-XPS) and density functional theory (DFT) simulations provides a powerful approach to probe Pt atoms diffusion on epitaxial graphene. HR-XPS with its high chemical sensitivity and temporal resolution allows in situ tracking of Pt 4f_7/2 spectral components associated with monomers, dimers, and larger clusters at low temperature. This capability enabled us to monitor the rapid decay of monomer coverage and the subsequent aggregation into larger clusters. By fitting the time evolution of the different Pt species using a kinetic model, we extracted a diffusion barrier of 128 ± 6 meV, in excellent agreement with the 130 meV value obtained by nudged elastic band (NEB) calculations. These findings establish fast HR-XPS as a noninvasive, high surface-sensitive, and chemically specific technique for quantifying ultralow diffusion barriers of atoms on weakly interacting two-dimensional materials. This approach provides a practical framework for exploring surface dynamics and for guiding the controlled assembly of small atomic clusters or ordered superlattices on 2D templates.