I was reading a paper and found this elemental XPS analysis of an unmodified microscope glass slide surface.
C (1s): 17.7%
Si (2p): 28.47%
O (1s): 53.83%
It seems strange for a piece of normal glass to have almost 20% of Carbon, since most of it is silicon dioxide and other metal oxides in smaller amounts. I am not used to XPS analysis so there might be something I am overlooking (maybe adsorbed CO2 on the surface ?), can someone tell me if this is a normal result for an XPS analysis of glass, and if it is, where does the carbon come from?