Dire - XPS

• surface technique with 2nm penetration depth

• based on photoelectric effect

• information about chem. composition of the surface (qualitative and quantitative)

• information on chemical enviroment (nearest neighbors, bonds, oxidation)

• depth concentration profile (with sputtering)

The Xray photons give the electrons the energy to leave the binding of the atom. These Electron are evaluated.

X-ray photoelectron spectroscopy

2nm=1-2 atom layers

The kinetic energy of the photoejected electrons.

XPS measurements rely on the photoelectric effect.

For a measurement X-ray photons are shot at the surface, which leads to an ejection of electrons. By measuring the kinetic energy of those electrons, one can calculate the binding energy.

The Energy difference of the electron moving to a lower energy level is applied to another outer electron, which leads to it ejecting. These electrons are measured.

The chemical shift is a change in binding energy due to the chemical influence on the atoms.

• the binding energy increases with the oxidation state of the element

• the binding energy increases with the electronegativity of its neares neighbour

Mg K alpha with hv=1253,6 eV

Al K alpha with hv=1486,6 eV

Changing the angle between analyser and surface. (take off angle)

• stability (due to ultra high vacuum conditions and X-ray influence)

• Conductivity (if charge accumulation, results will be greatly distorted)

• X-rays may cause damage to the samples

• Sensitive samples may decompose: damage to the instrument

• charge up of electrically insulated materials due to x-rays

• different charges in different regions: Differential charging leads to peak broadening

• Analysis of the purety of semicondutors

• in combination with sputtering for determination of a oxide surface layer thickness

• XPS: Composition, oxidation state, dispersion

• AES: Surface composition, depth profiles

• UPS: Chemical bonding, work function

By removing the surface via sputtering