Breaking of atomic terrace equivalence demonstrated via room temperature Sn growth on Pt(111)

Single-crystal substrates used for epitaxial growth are generally assumed to provide spatially equivalent terraces, implying that homogeneous deposition conditions should produce uniform self-organization across the surface. Here, spatial symmetry breaking under homogeneous atomic flux deposition onto single crystal Pt(111) is demonstrated using in situ low-energy electron microscopy (LEEM) supported by scanning tunneling microscopy (STM) and ab initio calculations. Sn atoms, characterized by exceptionally high surface diffusivity, are deposited on Pt(111) at room temperature. In the coverage range between 0.3 and 0.5 monolayers, pronounced terrace-dependent differentiation is observed, manifested by distinct Sn cluster populations. We propose that small stochastic differences in the onset of nucleation on neighboring terraces may be amplified by atomic step-limited inter-terrace transport, while rapid intra-terrace diffusion and repulsive interactions between clusters, which may originate from local surface electric dipoles arising from electron transfer from Sn to Pt(111), may promote their self-organization. This study demonstrates that epitaxial self-organization on stepped surfaces can lead to the coexistence of distinct ordered states under identical external growth conditions.