We show that the broad x-ray photoelectron lines of silicon oxide on silicon arise from a continuous statistical distribution of core-level binding energies. Statistical simulations spanning compositions from Si to ${\mathrm{SiO}}_2$ reproduce the full extent of this broadening, reaching $\sim 5\mathrm{eV}$ for ${\mathrm{SiO}}_{1.0}$, in quantitative agreement with 0.23-nm layer-resolved spectra reconstructed from ${\mathrm{Ar}}^{+}$ sputtering data. This continuous distribution blurs distinct spectral fingerprints of local structural motifs, thereby challenging conventional chemical state assignment in oxide x-ray photoelectron spectra.

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• Interfaces
• Oxides
• Density functional calculations
• Machine learning models
• X-ray photoelectron spectroscopy