We report on the structural and chemical evolution of submonolayer \(\hbox{Sn}\) on \({\hbox{Au}(111)}\) up to the formation of the striped \({\hbox {Au}_{2}\hbox {Sn}}\) surface alloy. Using Low-Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM), we identify a previously unobserved hexagonal \((2\times 2)\) -reconstruction at a \(\hbox{Sn}\) film thickness of \(\approx 0.28\) monolayers (ML). X-ray Photoelectron Spectroscopy (XPS) analysis reveals that the \((2\times 2)\) -structure is not chemically bonded to the \({\hbox{Au}(111)}\) substrate. With increasing \(\hbox{Sn}\) coverage, the \((2\times 2)\) -reconstruction performs a structural transition into a mixed phase before forming a local \((\sqrt{3} \times \sqrt{3})\text {R}{30}^{\circ }\) -reconstruction at a \(\hbox{Sn}\) film thickness of \(0.33\,\textrm{ML}\) . This reconstruction is superimposed by a larger periodicity resembling the herringbone reconstruction of clean \({\hbox{Au}(111)}\) . Our XPS analysis identifies this phase as an \({\hbox {Au}_{2}\hbox {Sn}}\) -alloy. By combining high-resolution x-ray photoelectron diffraction (XPD) measurements of \(\hbox{Au}\,\hbox{4f}\) and \(\hbox{Sn}\,\hbox{4d}\) 4d core levels with simulations based on a genetic algorithm, we propose a structural model for the \({\hbox {Au}_{2}\hbox {Sn}}\) -supercell, revealing an unusually large unit cell with \(\text {Rec}(26\times \sqrt{3})\) -periodicity. This study advances the understanding of the structural evolution of \(\hbox{Sn}\) surface reconstructions on \({\hbox{Au}(111)}\) up to the formation of the \({\hbox {Au}_{2}\hbox {Sn}}\) surface alloy. Furthermore, it provides insights into the structural arrangements emerging at higher submonolayer \(\hbox{Sn}\) coverages on \({\hbox{Au}(111)}\) , offering potential pathways towards realizing freestanding stanene.
