Structural analysis of [Formula: see text] on [Formula: see text] at low coverages: Towards the [Formula: see text]...

We report on the structural and chemical evolution of submonolayer [Formula: see text] on [Formula: see text] up to the formation of the striped [Formula: see text] surface alloy. Using Low-Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM), we identify a previously unobserved hexagonal [Formula: see text]-reconstruction at a [Formula: see text] film thickness of [Formula: see text] monolayers (ML). X-ray Photoelectron Spectroscopy (XPS) analysis reveals that the [Formula: see text]-structure is not chemically bonded to the [Formula: see text] substrate. With increasing [Formula: see text] coverage, the [Formula: see text]-reconstruction performs a structural transition into a mixed phase before forming a local [Formula: see text]-reconstruction at a [Formula: see text] film thickness of [Formula: see text]. This reconstruction is superimposed by a larger periodicity resembling the herringbone reconstruction of clean [Formula: see text]. Our XPS analysis identifies this phase as an [Formula: see text]-alloy. By combining high-resolution x-ray photoelectron diffraction (XPD) measurements of [Formula: see text] and [Formula: see text] 4d core levels with simulations based on a genetic algorithm, we propose a structural model for the [Formula: see text]-supercell, revealing an unusually large unit cell with [Formula: see text]-periodicity. This study advances the understanding of the structural evolution of [Formula: see text] surface reconstructions on [Formula: see text] up to the formation of the [Formula: see text] surface alloy. Furthermore, it provides insights into the structural arrangements emerging at higher submonolayer [Formula: see text] coverages on [Formula: see text], offering potential pathways towards realizing freestanding stanene.