Growth, structure, and morphology of ultra-thin tin oxide phases forming on Pt <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si48.svg" display="inline" id="d1e352"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <

Here we report an investigation of ultrathin tin oxide films on Pt 3 Sn(111) using low-energy electron microscopy (LEEM), microspot low-energy electron diffraction ( μ -LEED), scanning tunneling microscopy (STM), surface X-ray diffraction (SXRD), and high-resolution X-ray photoelectron spectroscopy (XPS). Oxidation at ∼ 390–410 ° C produces triangular, two-dimensional oxide islands that nucleate rapidly and exhibit self-limited lateral growth, attributed to limited Sn diffusion from the subsurface of the crystal. μ -LEED shows that the initially formed ( 4 × 4 ) Sn oxide is subsequently converted to a more oxygen-rich ( 2 × 2 n ) “stripe” phase. At 630 ° C , enhanced Sn mobility enables a closed ( 4 × 4 ) film. The ( 2 × 2 n ) phase is shown to consist of a ( 2 × 2 ) Sn lattice modulated by 1D stripe defects with spacings of n = 4 –6 atomic rows; LEED and SXRD measurements show diffraction features corresponding to this striped superstructure. The two oxides can be distinguished in XPS by their O 1s lineshapes: the ( 4 × 4 ) phase shows a clear doublet attributable to distinct O species, whereas the ( 2 × 2 n ) phase exhibits a broader envelope consistent with a distribution of O coordination environments. The Sn 3d 5 / 2 spectra are similar for both phases, reflecting closely related Sn bonding motifs. The spectra are consistent with those of previous near-ambient-pressure XPS measurements, suggesting that the surface oxides forming under CO oxidation conditions are similar to those studied here. • Several experimental techniques have been applied to study the oxidation behavior of Pt 3 Sn(111) by O 2 under low-pressure conditions. • Oxidation of Pt 3 Sn(111) shows strong temperature dependence, both in terms of morphology and in atomic structure of surface oxides formed. • Self-limited growth of small islands at low temperature is caused by restricted diffusion of tin, while the difference in atomic structure is caused by differences in oxygen content. • The low-temperature “(2×2n)” surface oxide exhibits a complex structure that can be described as a reconstruction of a simpler (2×2) oxide motif.