XPS measurements on glass surfaces

Surfaces of a 74SiO2, 16 Na2O, 10 CaO(wt%) glass were prepared by mechanical, chemical and fire polishing as well as fracture and investigated by XPS. A strong influence of surface preparation on the Na concentration was found. The same holds true for depth profiling of the surfaces, where highly mobile Na ions are created by Ar+ sputtering ions. These na ions can easily be displaced by surface charges, thus changing the apparent composition. During sputtering we observed a strong correlation between the concentration of network modifying ions and the fraction of nonbridging oxygens as measured by the splitting of the O 1s signal.