ASTM E995-11
(Guide)Standard Guide for Background Subtraction Techniques in Auger Electron Spectroscopy and X-Ray Photoelectron Spectroscopy
Standard Guide for Background Subtraction Techniques in Auger Electron Spectroscopy and X-Ray Photoelectron Spectroscopy
SIGNIFICANCE AND USE
Background subtraction techniques in AES were originally employed as a method of enhancement of the relatively weak Auger signals to distinguish them from the slowly varying background of secondary and backscattered electrons. Interest in obtaining useful information from the Auger peak line shape, concern for greater quantitative accuracy from Auger spectra, and improvements in data gathering techniques, have led to the development of various background subtraction techniques.
Similarly, the use of background subtraction techniques in XPS has evolved mainly from the interest in the determination of chemical states (from the binding-energy values for component peaks that may often overlap), greater quantitative accuracy from the XPS spectra, and improvements in data acquisition. Post-acquisition background subtraction is normally applied to XPS data.
The procedures outlined in Section 7 are popular in XPS and AES; less popular procedures and rarely used procedures are described in Sections 8 and 9, respectively. General reviews of background subtraction methods and curve-fitting techniques have been published (1-5).
Background subtraction is usually done before peak fitting. Some commercial systems require background removal. Nevertheless, a measured spectral region consisting of one or more peaks and background intensities due to inelastic scattering, Bremsstrahlung (for XPS with unmonochromated X-ray sources), and scattered primary electrons (for AES) can often be satisfactorily represented by choosing functions for each intensity component with parameters for each component determined in a single least-squares fit. The choice of the background to be removed if required or desired before peak fitting is suggested by the experience of the analysts and the peak complexity as noted above.
SCOPE
1.1 The purpose of this guide is to familiarize the analyst with the principal background subtraction techniques presently in use together with the nature of their application to data acquisition and manipulation.
1.2 This guide is intended to apply to background subtraction in electron, X-ray, and ion-excited Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS).
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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: E995 − 11
Standard Guide for
Background Subtraction Techniques in Auger Electron
1
Spectroscopy and X-Ray Photoelectron Spectroscopy
This standard is issued under the fixed designation E995; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope emission of secondary and backscattered electrons. These
secondary and backscattered electrons create a background
1.1 The purpose of this guide is to familiarize the analyst
signal. This background signal covers the complete energy
with the principal background subtraction techniques presently
spectrum and has a maximum (near 10 eV for true
in use together with the nature of their application to data
secondaries), and a second maximum for elastically backscat-
acquisition and manipulation.
tered electrons at the energy of the incident electron beam.An
1.2 This guide is intended to apply to background subtrac-
additional source of background is associated with Auger
tion in electron, X-ray, and ion-excited Auger electron spec-
electrons, which are inelastically scattered while traveling
troscopy (AES), and X-ray photoelectron spectroscopy (XPS).
through the specimen. Auger electron excitation may also
occur by X-ray and ion bombardment of surfaces.
1.3 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this 4.1.2 XPS—The production of electrons from X-ray excita-
tion of surfaces may be grouped into two categories—
standard.
photoemission of electrons and the production of Auger
1.4 This standard does not purport to address all of the
electrons from the decay of the resultant core hole states. The
safety concerns, if any, associated with its use. It is the
source of the background signal observed in the XPS spectrum
responsibility of the user of this standard to establish appro-
includes a contribution from inelastic scattering processes, and
priate safety and health practices and determine the applica-
for non-monochromatic X-ray sources, electrons produced by
bility of regulatory limitations prior to use.
Bremsstrahlung radiation.
2. Referenced Documents
4.2 Various background subtraction techniques have been
2
employed to diminish or remove the influence of these back-
2.1 ASTM Standards:
ground electrons from the shape and intensity of Auger
E673 Terminology Relating to SurfaceAnalysis (Withdrawn
3
electron and photoelectron features. Relevance to a particular
2012)
analytical technique (AES or XPS) will be indicated in the title
3. Terminology
of the procedure.
3.1 Definitions—For definitions of terms used in this guide,
4.3 Implementation of any of the various background sub-
refer to Terminology E673.
traction techniques that are described in this guide may depend
on available instrumentation and software as well as the
4. Summary of Guide
method of acquisition of the original signal. These subtraction
4.1 Relevance to AES and XPS: methods fall into two general categories: (1) real-time back-
4.1.1 AES—The production ofAuger electrons by bombard- ground subtraction; and (2) post-acquisition background sub-
ment of surfaces with electron beams is also accompanied by traction.
5. Significance and Use
1
This guide is under the jurisdiction of ASTM Committee E42 on Surface
5.1 Background subtraction techniques in AES were origi-
Analysis and is the direct responsibility of Subcommittee E42.03 on Auger Electron
Spectroscopy and X-Ray Photoelectron Spectroscopy.
nally employed as a method of enhancement of the relatively
Current edition approved Oct. 15, 2011. Published October 2011. Originally
weak Auger signals to distinguish them from the slowly
approved in 1984. Last previous edition approved in 2004 as E995 – 04. DOI:
varying background of secondary and backscattered electrons.
10.1520/E0995-11.
2
Interest in obtaining useful information from the Auger peak
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
line shape, concern for greater quantitative accuracy from
Standards volume information, refer to the standard’s Document Summary page on
Auger spectra, and improvements in data gathering techniques,
the ASTM website.
3
have led to the development of various background subtraction
The last approved version of this historical standard is referenced on
www.astm.org. techniques.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E995 − 11
5.2 Similarly, the use of bac
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This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:E995–04 Designation:E995–11
Standard Guide for
Background Subtraction Techniques in Auger Electron
1
Spectroscopy and X-rayX-Ray Photoelectron Spectroscopy
This standard is issued under the fixed designation E995; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 The purpose of this guide is to familiarize the analyst with the principal background subtraction techniques presently in use
together with the nature of their application to data acquisition and manipulation.
1.2 This guide is intended to apply to background subtraction in electron, X-ray, and ion-excited Auger electron spectroscopy
(AES), and X-ray photoelectron spectroscopy (XPS).
1.3
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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.
2. Referenced Documents
2
2.1 ASTM Standards:
E673 Terminology Relating to Surface Analysis
E996Practice for Reporting Data inAuger Electron Spectroscopy and X-ray Photoelectron Spectroscopy Terminology Relating
to Surface Analysis
3. Terminology
3.1 Definitions—For definitions of terms used in this guide, refer to Terminology E673.
4. Summary of Guide
4.1 Relevance to AES and XPS:
4.1.1 AES—The production of Auger electrons by bombardment of surfaces with electron beams is also accompanied by
emission of secondary and backscattered electrons. These secondary and backscattered electrons create a background signal. This
background signal covers the complete energy spectrum and has a maximum (near 10 eV for true secondaries), and a second
maximum for elastically backscattered electrons at the energy of the incident electron beam.An additional source of background
isassociatedwithAugerelectrons,whichareinelasticallyscatteredwhiletravelingthroughthespecimen.Augerelectronexcitation
may also occur by X-ray and ion bombardment of surfaces.
4.1.2 XPS—The production of electrons from X-ray excitation of surfaces may be grouped into two categories—photoemission
of electrons and the production ofAuger electrons from the decay of the resultant core hole states. The source of the background
signalobservedintheXPSspectrumincludesacontributionfrominelasticscatteringprocesses,andfornon-monochromaticX-ray
sources, electrons produced by Bremsstrahlung radiation.
4.2 Various background subtraction techniques have been employed to diminish or remove the influence of these background
electrons from the shape and intensity ofAuger electron and photoelectron features. Relevance to a particular analytical technique
(AES or XPS) will be indicated in the title of the procedure.
4.3 Implementation of any of the various background subtraction techniques that are described in this guide may depend on
available instrumentation and software as well as the method of acquisition of the original signal. These subtraction methods fall
1
This guide is under the jurisdiction of ASTM Committee E42 on Surface Analysis and is the direct responsibility of Subcommittee E42.03 on Auger Electron
Spectroscopy and XPS.
Current edition approved July 1, 2004. Published August 2004. Originally approved in 1984. Last previous edition approved in 1997 as E995–97. DOI:
10.1520/E0995-04.on Auger Electron Spectroscopy and X-Ray Photoelectron Spectroscopy.
Current edition approved Oct. 15, 2011. Published October 2011. Originally approved in 1984. Last previous edition approved in 2004 as E995 – 04. DOI:
10.1520/E0995-11.
2
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1
---------------------- Page: 1 ----------------------
E995–11
into two general categories: (1) real-time background subtraction; and (2) post-acquisition background subtraction.
5. Significance and Use
5.1 Background subtraction technique
...
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