Role of local structural variation in x-ray photoelectron spectrum of silicon oxide interfaces

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 SiO$_2$ reproduce the full extent of this broadening, reaching 5 eV for SiO$_{1.0}$ , in quantitative agreement with 0.23 nm layer-resolved spectra reconstructed from 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.