ISO/TR 18394:2016

TECHNICAL ISO/TR
REPORT 18394
Second edition
2016-05-01
Surface chemical analysis — Auger
electron spectroscopy — Derivation of
chemical information
Analyse chimique des surfaces — Spectroscopie des électrons Auger
— Déduction de l’information chimique
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 1
5 Types of chemical and solid-state effects in Auger-electron spectra .1
6 Chemical effects arising from core-level Auger-electron transitions .3
6.1 General . 3
6.2 Chemical shifts of Auger-electron energies . 3
6.3 Chemical shifts of Auger parameters . 4
6.4 Chemical-state plots . 6
6.5 Databases of chemical shifts of Auger-electron energies and Auger parameters . 7
6.6 Chemical effects on Auger-electron satellite structures . 7
6.7 Chemical effects on the relative intensities and line shapes of CCC Auger-electron lines . 8
6.8 Chemical effects on the inelastic region of CCC Auger-electron spectra . 9
7 Chemical effects on Auger-electron transitions involving valence electrons .10
7.1 General .10
7.2 Chemical-state-dependent line shapes of CCV and CVV Auger-electron spectra .10
7.3 Information on local electronic structure from analysis of CCV and CVV Auger-
electron line shapes .15
7.4 Novel techniques for obtaining information on chemical bonding from Auger processes 16
Bibliography .21
Foreword
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The committee responsible for this document is ISO/TC 201, Surface chemical analysis, Subcommittee
SC 7, Electron spectroscopies.
This second edition cancels and replaces the first edition (ISO/TR 18394:2006), which has been
technically revised.
iv © ISO 2016 – All rights reserved

Introduction
This Technical Report provides guidelines for the identification of chemical effects on X-ray or electron-
excited Auger-electron spectra and for using these effects in chemical characterization.
Auger-electron spectra contain information on surface/interface elemental composition as well as
[1][2][3][4][5]
on the environment local to the atom with the initial core hole . Changes in Auger-electron
spectra due to alterations of the atomic environment are called chemical (or solid-state) effects.
Recognition of chemical effects is very important in proper quantitative applications of Auger-electron
spectroscopy and can be very helpful in identification of surface chemical species and of the chemical
state of constituent atoms in surface or interface layers.
TECHNICAL REPORT ISO/TR 18394:2016(E)
Surface chemical analysis — Auger electron spectroscopy
— Derivation of chemical information
1 Scope
This Technical Report provides guidelines for identifying chemical effects in X-ray or electron-excited
Auger-electron spectra and for using these effects in chemical characterization.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 18115 (all parts), Surface chemical analysis — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18115 (all parts) apply.
4 Abbreviated terms
CCC core-core-core (Auger-electron transition)
CCV core-core-valence (Auger-electron transition)
CK Coster-Kronig
c-BN cubic boron nitride
CVV core-valence-valence (Auger-electron transition)
DEAR-APECS Dichroic Effect in Angle Resolved Auger-Photoelectron Coincidence Spectroscopy
h-BN hexagonal boron nitride
IAE Interatomic Auger Emission
ICD Interatomic Coulomb Decay
PAES Positron-Annihilation-induced Auger Electron Spectroscopy
REELS Reflection Electron Energy-Loss Spectroscopy
5 Types of chemical and solid-state effects in Auger-electron spectra
[1][2][3][4][5]
Many types of chemical or solid-state effects can be observed in Auger-electron spectra .
Changes in the atomic environment of an atom ionized in its inner shell can result in a shift of the kinetic
energy of the emitted Auger electron. In the case of X-ray-excited Auger-electron spectra, energy shifts of
Auger parameters (i.e. kinetic-energy differences between Auger-electron peaks and the photoelectron
peaks corresponding to the core levels involved in the Auger-electron process) can be detected as well.
Furthermore, the line shape, the relative intensity and the satellite structure (induced by the intrinsic
excitation processes) of the Auger-electron lines can be considerably influenced by chemical effects,
as can the structure of the energy-loss region (induced by extrinsic, electron-scattering processes)
accompanying the intrinsic peaks. Strong chemical effects on the Auger-electron spectral shapes offer
ways of identification of chemical species using the “fingerprint” approach.
In the case of electron-excited Auger-electron spectra, the Auger peaks are generally weak features
superimposed on an intense background caused to a large extent by the primary electrons scattered
inelastically within the solid sample. As a consequence, the differential Auger-electron spectrum is
often recorded (or calculated from the measured spectrum) rather than the direct energy spectrum,
facilitating the observation and identification of the Auger-electron peaks and the measurement of the
respective Auger transition energies. Differentiation can, however, enhance the visibility of random
fluctuations in recorded intensities, as shown in Figure 1. If chemical-state information is needed from
a direct energy spectrum, then the relative energy resolution of the electron spectrometer should be
better than 0,15 % (e.g. 0,05 % or 0,02 %). A poorer energy resolution causes a significant broadening
of the Auger-electron peaks and prevents observation of small changes of spectral line shapes or peak
energies as chemical-state effects in the spectra. A great advantage of electron-excited Auger-electron
spectroscopy over X-ray excitation with laboratory X-ray source, however, is the possibility of using
high lateral resolution and obtaining chemical-state maps of surface nanostructures.
NOTE 1 Auger-electron spectra can be reported with the energy scale referenced either to the Fermi level or
to the vacuum level. Kinetic energies with the latter reference are typically 4,5 eV less than those referenced to
the Fermi level, but the difference in energies for these two references can vary from 4,0 eV to 5,0 eV since the
position of the vacuum level depends on the condition of the spectrometer and may, in practice, vary with respect
to the Fermi level. When energy shifts are determined from spectra recorded on different instruments, use of
different energy references should be taken into account.
NOTE 2 While the visibility of noise features in a differential spectrum can be reduced by use of a larger
number of channels in the calculation of the derivative, there may also be distortion of the resulting differential
spectrum and loss of fine details associated with chemical-state effects.
Key
X kinetic energy, eV
Y intensity
1 differential spectrum
2 direct spectrum
NOTE This figure is reproduced from Figure 2.8 of Reference [1].
Figure 1 — Comparison of direct and differentiated Auger-electron spectra for copper (Cu
LMM peaks)
2 © ISO 2016 – All rights reserved

6 Chemical effects arising from core-level Auger-electron transitions
6.1 General
Core-level (or core-core-core, CCC) Auger-electron transitions occur when all of the levels involved in
the Auger transition belong to the atomic core for the atom of interest.
6.2 Chemical shifts of Auger-electron energies
The main effect of any change in the solid-state environment on Auger-electron spectra for Auger
transitions involving core levels is a shift of the Auger energies. This shift results from a change in the
core atomic potential due to the changed environment and from a contribution due to the response of
the local electronic structure to the appearance of core holes. Auger chemical shifts are generally larger
than the binding-energy shifts of the atomic levels involved in the Auger-electron process because the
two-hole final state of the process is more strongly influenced by relaxation effects. This phenomenon is
[6]
illustrated by the example of aluminium and its oxide in Figure 2 . Large chemical shifts in the energy
positions of the Auger-electron lines provide possibilities for chemical-state identification even in the
case of electron-excited Auger-electron spectroscopy with, in this case, moderate energy resolution. In
X-ray-excited Auger-electron spectra, the peak-to-background intensity ratios are usually larger than
those in electron-excited spectra, facilitating accurate determination of peak energies. Recommended
[7]
Auger electron energies are available for 42 elemental solids . Information on Auger chemical shifts of
[8][9][10][11] [12][13]
particular elements can be obtained
...