Surface modification of a silicate glass during XPS experiments

The surface chemistry of a commercial soda‐lime silicate glass is shown to change during a long‐duration XPS experiment wherein the glass surface was exposed to the monochromatic x‐rays and low‐energy electrons (0.2–5 eV) that compensate for the charging of the surface. The atomic percentage of sodium increases and that of oxygen decreases with increasing time of the experiment. The separate influence of x‐rays and the low‐energy electrons on the glass surface is also measured. The results show that diffusion of the sodium ions is enhanced more in the presence of x‐rays than in the presence of low‐energy electrons. All observations can be explained well by a model that considers the breaking of the bridging and non‐bridging oxygen bonds, and the trapping of photoelectrons and the externally supplied electrons. Although long‐duration XPS experiments show significant changes on the exposed surface, the chemical composition of the bulk glass obtained during a short experiment agrees well with that obtained from the chemical analysis.