Page "Auger electron spectroscopy" Paragraph 5

The types of state-to-state transitions available to electrons during an Auger event are dependent on several factors, ranging from initial excitation energy to relative interaction rates, yet are often dominated by a few characteristic transitions.

Because of the interaction between an electron's spin and orbital angular momentum ( spin-orbit coupling ) and the concomitant energy level splitting for various shells in an atom, there are a variety of transition pathways for filling a core hole.

Energy levels are labeled using a number of different schemes such as the j-j coupling method for heavy elements ( Z ≥ 75 ), the Russell-Saunders L-S method for lighter elements ( Z < 20 ), and a combination of both for intermediate elements.

The j-j coupling method, which is historically linked to X-ray notation, is almost always used to denote Auger transitions.

Thus for a transition, K represents the core level hole, the relaxing electron's initial state, and the emitted electron's initial energy state.

Figure 1 ( b ) illustrates this transition with the corresponding spectroscopic notation.

The energy level of the core hole will often determine which transition types will be favored.

For single energy levels, i. e. K, transitions can occur from the L levels, giving rise to strong KLL type peaks in an Auger spectrum.

Higher level transitions can also occur, but are less probable.

For multi-level shells, transitions are available from higher energy orbitals ( different n, ℓ quantum numbers ) or energy levels within the same shell ( same n, different ℓ number ).

The result are transitions of the type LMM and KLL along with faster Coster – Kronig transitions such as LLM.

while Coster – Kronig transitions are faster, they are also less energetic and thus harder to locate on an Auger spectrum.

As the atomic number Z increases, so too does the number of potential Auger transitions.

Fortunately, the strongest electron-electron interactions are between levels which are close together, giving rise to characteristic peaks in an Auger spectrum.

KLL and LMM peaks are some of the most commonly identified transitions during surface analysis.

Finally, valence band electrons can also fill core holes or be emitted during KVV-type transitions.