X-ray photoelectron spectroscopy was used to analyze silicon surfaces after some standard cleaning procedures. Buffered hydrofluoric acid (BHF), RCA clean, and back door etch (BDE) result in less than one monolayer of suboxide coverage. RCA clean without BHF, heat treatment in nitrogen ambience, and prolonged explosure to air at room temperature all result in thicker self-passivating suboxides. Wafers with arsenic ion implantation yield thicker oxides even immediately after BHF or BDE clean. Arsenic ion implantation also causes an additional chemical shift of 0.3 eV on the Si 2p peak. The possible causes for these observations are discussed.