ASTM E995-16
(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
5.1 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.
5.2 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.
5.3 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 elsewhere (1-5).6
5.4 Background subtraction is commonly performed prior to peak fitting, although it can be assessed (fitted) during peak fitting (active approach (6, 7)). Some commercial data analysis packages require background removal before peak fitting. 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 applying peak functions for each component with parameters for each one determined in a single least-squares fit. The choice of the background to be removed, if required or desired, before or during peak fitting is suggested by the experience of the analysts, the capabilities of the peak fitting software, and the p...
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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This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
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Designation: E995 − 16
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 3. Terminology
1.1 The purpose of this guide is to familiarize the analyst 3.1 Definitions—Since Terminology E673 was withdrawn
with the principal background subtraction techniques presently in 2012, for definitions of terms used in this guide, refer to ISO
5
in use together with the nature of their application to data 18115-1.
acquisition and manipulation.
4. Summary of Guide
1.2 This guide is intended to apply to background subtrac-
4.1 Relevance to AES and XPS:
tion in electron, X-ray, and ion-excited Auger electron spec-
4.1.1 AES—The production ofAuger electrons by bombard-
troscopy (AES), and X-ray photoelectron spectroscopy (XPS).
ment of surfaces with electron beams is also accompanied by
1.3 The values stated in SI units are to be regarded as
emission of secondary and backscattered electrons. These
standard. No other units of measurement are included in this
secondary and backscattered electrons create a background
standard.
signal. This background signal covers the complete energy
spectrum and has a maximum (near 10 eV for true
1.4 This standard does not purport to address all of the
secondaries), and a second maximum for elastically backscat-
safety concerns, if any, associated with its use. It is the
tered electrons at the energy of the incident electron beam.An
responsibility of the user of this standard to establish appro-
additional source of background is associated with Auger
priate safety and health practices and determine the applica-
electrons, which are inelastically scattered while traveling
bility of regulatory limitations prior to use.
through the specimen. Auger electron excitation may also
2. Referenced Documents occur by X-ray and ion bombardment of surfaces.
2 4.1.2 XPS—The production of electrons from X-ray excita-
2.1 ASTM Standards:
tion of surfaces may be grouped into two categories—
E673 Terminology Relating to SurfaceAnalysis (Withdrawn
3 photoemission of electrons and the production of Auger
2012)
electrons from the decay of the resultant core hole states. The
4
2.2 ISO Standard:
source of the background signal observed in the XPS spectrum
ISO 18115–1 Surface chemical analysis—Vocabulary—Part
includes a contribution from inelastic scattering processes, and
1: General terms and terms used in spectroscopy
for non-monochromatic X-ray sources, electrons produced by
Bremsstrahlung radiation.
1
4.2 Various background subtraction techniques have been
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
employed to diminish or remove the influence of these back-
Spectroscopy and X-Ray Photoelectron Spectroscopy.
ground electrons from the shape and intensity of Auger
Current edition approved Nov. 1, 2016. Published December 2016. Originally
electron and photoelectron features. Relevance to a particular
approved in 1984. Last previous edition approved in 2011 as E995-11. DOI:
10.1520/E0995-16. analytical technique (AES or XPS) will be indicated in the title
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
of the procedure.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
4.3 Implementation of any of the various background sub-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
traction techniques that are described in this guide may depend
3
The last approved version of this historical standard is referenced on
on available instrumentation and software as well as the
www.astm.org.
4
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
5
4th Floor, New York, NY 10036, http://www.ansi.org. https://www.iso.org/obp/ui/#iso:std:iso:18115:-1:ed-2:v1:en.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
E995 − 16
method of acquisition of the original signal. These subtraction among them depending on the shape of the spectrum. As
methods fall into two general categories: (1) real-time back- showninaRoundRobinstudy,differentgroupschosed
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM 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 − 11 E995 − 16
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
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.
2. Referenced Documents
2
2.1 ASTM Standards:
3
E673 Terminology Relating to Surface Analysis (Withdrawn 2012)
4
2.2 ISO Standard:
ISO 18115–1 Surface chemical analysis—Vocabulary—Part 1: General terms and terms used in spectroscopy
3. Terminology
3.1 Definitions—For —Since Terminology E673 was withdrawn in 2012, for definitions of terms used in this guide, refer to
5
TerminologyISO E673. 18115-1.
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
is associated with Auger electrons, which are inelastically scattered while traveling through the specimen. Auger electron excitation
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 of Auger electrons from the decay of the resultant core hole states. The source of the background
signal observed in the XPS spectrum includes a contribution from inelastic scattering processes, and for non-monochromatic X-ray
sources, electrons produced by Bremsstrahlung radiation.
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 X-Ray Photoelectron Spectroscopy.
Current edition approved Oct. 15, 2011Nov. 1, 2016. Published October 2011December 2016. Originally approved in 1984. Last previous edition approved in 20042011
as E995 – 04.E995-11. DOI: 10.1520/E0995-11.10.1520/E0995-16.
2
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 Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
3
The last approved version of this historical standard is referenced on www.astm.org.
4
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
5
https://www.iso.org/obp/ui/#iso:std:iso:18115:-1:ed-2:v1:en.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
E995 − 16
4.2 Various background subtraction techniques have been employed to diminish or remove the influence of these background
electrons from the shape and intensity of Auger 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 o
...
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