ASTM E984-95
(Guide)Standard Guide for Identifying Chemical Effects and Matrix Effects in Auger Electron Spectroscopy
Standard Guide for Identifying Chemical Effects and Matrix Effects in Auger Electron Spectroscopy
SCOPE
1.1 This guide outlines the types of chemical effects and matrix effects which are observed in Auger electron spectroscopy.
1.2 Guidelines are given for the reporting of chemical and matrix effects in Auger spectra.
1.3 Guidelines are given for utilizing Auger chemical effects for identification or characterization.
1.4 This guide is applicable to both electron excited and X-ray excited Auger electron spectroscopy.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E 984 – 95
Standard Guide for
Identifying Chemical Effects and Matrix Effects in Auger
Electron Spectroscopy
This standard is issued under the fixed designation E 984; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope is in some reference form. The differences in the two spectra
are said to be due to a “chemical effect” or a “matrix effect.”
1.1 This guide outlines the types of chemical effects and
Despite sometimes making elemental identification and quan-
matrix effects which are observed in Auger electron spectros-
titative measurements more difficult, these effects in the Auger
copy.
spectrum are considered valuable tools for characterizing the
1.2 Guidelines are given for the reporting of chemical and
environment of the near-surface atoms in a solid.
matrix effects in Auger spectra.
1.3 Guidelines are given for utilizing Auger chemical effects
5. Defining Auger Chemical Effects and Matrix Effects
for identification or characterization.
5.1 In general, Auger chemical and matrix effects may result
1.4 This guide is applicable to both electron excited and
in (a) a shift in the energy of an Auger peak, (b) a change in the
X-ray excited Auger electron spectroscopy.
shape of an Auger electron energy distribution, (c) a change in
1.5 This standard does not purport to address all of the
the shape of the electron energy loss distribution associated
safety concerns, if any, associated with its use. It is the
with an Auger peak, or (d) a change in the Auger signal
responsibility of the user of this standard to establish appro-
strengths of an Auger transition. The above changes may be
priate safety and health practices and determine the applica-
due to the bonding or chemical environment of the element
bility of regulatory limitations prior to use.
(chemical effect) or to the distribution of the element or
2. Referenced Documents compound within the specimen (matrix effect).
5.2 The Auger chemical shift is one of the most commonly
2.1 ASTM Standards:
2 observed chemical effects. A comparison can be made to the
E 673 Terminology Relating to Surface Analysis
more familiar chemical shifts in XPS (X-ray photoelectron
E 827 Practice for Elemental Identification by Auger Elec-
spectroscopy) photoelectron lines, where energy shifts are
tron Spectroscopy
caused by changes in the ionic charge on an atom, the lattice
E 983 Guide for Minimizing Unwanted Electron Beam
potential at that atomic site, and the final-state relaxation
Effects In Auger Electron Spectroscopy
energy contributed by adjacent atoms (1 and 2 ). Coverage by
E 996 Practice for Reporting Data in Auger Electron Spec-
gas adsorbates on metal surfaces may also cause shifts in the
troscopy
metal Auger peak energies (3). The magnitude of the Auger
3. Terminology chemical shift will usually be different from the XPS photo-
electron shift because the Auger process involves a two-hole
3.1 Terms used in Auger electron spectroscopy are defined
final state for the atom which is more strongly influenced by
in Terminology E 673.
extra-atomic relaxation. Frequently an Auger chemical shift is
4. Significance and Use
larger than an XPS chemical shift (see Fig. 1).
5.2.1 Related to chemical shifts is the (modified) Auger
4.1 Auger electron spectroscopy is often capable of yielding
parameter, defined as the sum of the photoelectron binding
information concerning the chemical and physical environment
energy and the Auger electron kinetic energy (4). Because the
of atoms in the near-surface region of a solid as well as giving
Auger parameter is the difference between two line energies of
elemental and quantitative information. This information is
the same element of the same specimen, it is independent of
manifested as changes in the observed Auger electron spectrum
any electrical charging of the specimen and spectrometer
for a particular element in the specimen under study compared
energy reference level, making it easier to identify chemical
to the Auger spectrum produced by the same element when it
states of elements in insulating specimens. Naturally, since
both photoelectron lines and Auger lines must be measured, the
This guide is under the jurisdiction of ASTM Committee E-42 on Surface
Auger parameter can only be used with X-ray excited spectra.
Analysis and is the direct responsibility of Subcommittee E42.03 on Auger Electron
Spectroscopy and XPS.
Current edition approved Sept. 10, 1995. Published November 1995. Originally
published as E 984 – 84. Last previous edition E 984 – 89. The boldface numbers in parentheses refer to the references at the end of this
Annual Book of ASTM Standards, Vol 03.06. standard.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 984
(a) Almost no Oxidation (b) Partial Oxidation (c) After Oxidation has
Reached a Satura-
tion Stage
FIG. 3 Changes in the Aluminum LVV Auger spectrum as
Oxygen is Absorbed on the Surface (Ref 15)
FIG. 1 Comparison of X-ray Excited Cd MNN Auger and 3d
peaks in the Auger spectrum to transitions from particular
Photoelectron Energy Shifts for Cd Metal, CdO, and CdF (Ref 13)
bands in the density of states (for solids) or to particular
molecular orbitals (for molecules) (5), this is not an easy task.
The large number of possible two-hole final states, taken
5.3 The second category of chemical information from
together with shake-up and shake-off transitions and uncer-
Auger spectroscopy is the Auger lineshapes observed for
tainty on all their final energies and intensities make the job of
transitions involving valence electron orbitals. Shown in Fig. 2
constructing a valence orbital density map from the Auger
and Fig. 3 are selected lineshapes for carbon KLL and
spectrum next to impossible for all but the simplest systems.
aluminum LVV Auger transitions for different chemical states
Further, some spectra exhibit a quasiatomic character (6).
of those elements. While it is possible to relate the prominent
Accordingly, most studies use the “fingerprint” approach when
attempting to identify unknown species based on their Auger
lineshape. Of course reference spectra are necessary in this
approach for a positive identification.
5.4 Other effects besides energy shifts and valence line-
shapes may be classified as chemical effects in Auger spectros-
copy. For instance, many body effects in metals, such as
plasmons, may make the lineshapes of Auger transitions of
atoms in the metallic state very different from the Auger
lineshapes for other chemical states, even for transitions
involving only core-type electrons, Al and Mg (7). In single
crystals, diffraction effects will produce different lineshapes
(8). Relative intensities of several Auger transitions may
change, either from attenuation of overlayers (9), or from
different chemical states resulting in different Auger transition
...
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