Dear Aum,

1. Si 2p has a lower fwhm than Si 2s, that means that Si 2p has better resolution.

2. Because the BE of Si 1s (~1839 eV) is out of range for the conventional XPS sources Al Ka (1486.6 eV) and Mg Ka (1253.6 eV).

In addition to what Jhonatan Rodriguez-Pereira mentioned, there are several groups worldwide using high energy XPS for studying core levels like Cu 1s as well, mostly however using synchrotron radiation as excitation source instead of an x-ray rube. Best regards, Dirk

In principle, you can use any Si peak for quantitation, provided you have the correct RSF applied for your system. A main reason why Si 2p is typically preferred over Si 2s, is that the BE chemical shifts for the 2p are large and quite distinct compared to the 2s. Often, one is interested in the chemical bonding - especially with C, O, N, F, etc - and the shifts of the Si 2p are well known and referenced throughout the literature, so this helps in determining chemical states for your sample.

Dear Aum,

In general you would like to use the outer most orbital of the shell, 1s is the outer most orbital in the first shell and 2p is the outer most orbital in the second shell. The main reasons for this approach is:

As Jhonatan Rodriguez-Pereira pointed out, The excitation energy also determine the possible states you can study. With 1487 eV photon energy as excitation energy for an Aluminum K-alpha source, most common in commercial XPS equipment, you can not access the Si 1s state which is located at about 1840 eV binding energy. If you use a higher excitation energy, e.g. using HAXPES instead of XPS you would go for the Si 1s, as the intensity for the 1s is higher than the 2p in these cases. HAXPES can be measured using synchrotron (as pointed out by Dirk Luetzenkirchen-Hecht) or using Ag L-alpha (about 3000 eV), Cr K-alpha (about 5000 eV) or Ga L-alpha (about 9000 eV).

Best regards,

John

Thank You very much dear Jhonatan Rodriguez-Pereira, Dirk Luetzenkirchen-Hecht , Thomas Tetreault John Åhlund John Åhlund . the comments were very helpful.