 Material properties are inferred from the measurement of the kinetic energy and the number of the ejected electrons.XPS requires high vacuum (residual gas pressure "p" ~ 10−6 Pa) or ultra-high vacuum (p < 10−7 Pa) conditions, although a current area of development is ambient-pressure XPS, in which samples are analyzed at pressures of a few tens of millibar.When laboratory X-ray sources are used, XPS easily detects all elements except hydrogen and helium.