PhD Thesis Arne Lüker final version V4 - Cranfield University

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Characterisation of Ferroelectric Thin Films
photon in order to go down to the K-shell position vacated by the ejected electron. The
photon released by the second electron will either get lost or eject yet another electron
from a different level, say, L2. Auger electrons are electrons ejected in this manner, such
as the third electron from L2 in the example. Thus, the generation of an Auger electron
requires at least three electrons, which in the example above are the K, L1, and L2
electrons. In this example, the emitted Auger electron is referred to as a KLL Auger
electron. Hydrogen and Helium atoms have less than three electrons, and are therefore
undetectable by AES.
The energy content of the emitted Auger electron is unique to the atom where it came
from. Thus, AES works by quantifying the energy content of each of the Auger electrons
collected and matching it with the right element.
Fig. 3.7: The VG ESCAlab Mk 2 AES-Lab in Cranfield
The energy of Auger electrons is
usually between 20 and 2000 eV. The
depths from which Auger electrons are
able to escape from the sample without
losing too much energy are low,
usually less than 50 Å. Thus, Auger
electrons collected by the AES come
from the surface or just beneath the
surface. As such, AES can only provide
compositional information about the
surface of the sample. In order to use
AES for compositional analysis of matter deep into the sample, a crater must first be
milled onto the sample at the correct depth by ion-sputtering.
AES has the ability to provide excellent lateral resolution, allowing reliable analysis of
very small areas (less than 1 micron). It also offers satisfactory sensitivity, detecting
elements that are less than 1% of the atomic composition of the sample.
The output of AES is referred to as an Auger spectrum. This spectrum would show
peaks at Auger electron energy levels corresponding to the atoms from which the auger
electrons were released [1] (sometimes called binding energy).