XPS spectra of modified silicon wafers and cover slips. (A) Survey spectra of piranha treated wafer (black) and PEGylated wafer (red) were used to verify the spectra-alignment of the piranha treated cover slip (yellow) and the PEGylated cover slip (blue). Oxygen and silicon are the only distinct peaks after piranha treatment both for the wafer and the cover slip. After PEGylation, there is an additional carbon peak arising. (B) Scanning the C 1s range in higher resolution, nearly no carbon is detected on the cover slips without PEGylation, both after the HCl step (green) and after the piranha treatment (yellow). A distinct peak is measureable after the addition of the PEG layer (blue). (C) The silicon dioxide peak at 103.3 eV is the only peak in the Si 2p range. Due to the piranha treatment (yellow), the peak amplitude rises relative to the HCl treated surface (green) slightly. The amplitude decreases considerably due to the attenuation effect from the PEG layer after PEGylation (blue).