XPS Info - Background

This page provides information on the XPS equipment and on some measurement characteristics:

At each core level peak a rise in the base line (towards higher binding energy) can be observed. The cause is inelastic scattering of electrons. Because of this these electrons will loose some of their kinetic energy. Electrons that have a lower kinetic energy will appear as electrons with a higher binding energy.

The working principle of XPS is that an X-ray will cause core electrons to be emitted. If electrons are removed from the sample, the sample becomes (positively) charged.

An atom that is part of a chemical compound will share one or more electrons with another atom in covalent bonds. Or it will completely 'take' or 'give' one or more electrons from or to another atom in ionic bonds. Chemical bonds will change the electron density of the atoms.

Atoms with a higher electron density will display a lower binding energy. And atoms with a lower electron density will display a higher binding energy.

The electrons in p, d or f orbitals usually split into 2 distinct groups with a different energy level, which looks like this:

p orbital ↑↓ ↑↓ p3/2
d orbital ↑↓ ↑↓ ↑↓ d5/2
f orbital ↑↓ ↑↓ ↑↓ ↑↓ f7/2

↑↓ p1/2
↑↓ ↑↓ d3/2
↑↓ ↑↓ ↑↓ f5/2

These different energy levels will translate into 2 separate peaks in XPS. The 2 peaks have a fixed area ratio of 2:1 for p orbitals, 3:2 for d orbitals and 4:3 for f orbitals, with the larger peak at lower binding energy. This ratio is true for each element and for each level. So it is true for example for Ag3d and Lu4d. The position and distance between the peaks however is element specific.

In Avantage (Peak Fit) the peak area ratio is given as 1:00 for the larger peak and 0.50, 0.67 and 0.75 respectively for the smaller peak in a p, d and f orbital.

For Lu4d this works out as follows:

Lutetium 4d scan

Figure detail scan of lutetium, Lu4d

A peak area ratio of 0.68 was found, with the Lu4d5 peak at 197.24 eV and the Lu4d3 peak at 207.08. The ΔeV thus being 9.84 eV.

XPS info / ChemE / Delft University of Technology
version 20190326
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