XPS is used to determine the chemical structure and the phases present within the sample. XPS can be used to investigate many aspects of materials with the most basic being the surface composition. XPS is a useful technique for obtaining information about the surface of a sample due to its surface sensitivity. Although x-rays can penetrate far into the sample, it is only the ones produced from the near surface region (approx 1-5nm depth) which will contribute to useful peaks.
