ASTM E1523-03
(Guide)Standard Guide to Charge Control and Charge Referencing Techniques in X-Ray Photoelectron Spectroscopy
Standard Guide to Charge Control and Charge Referencing Techniques in X-Ray Photoelectron Spectroscopy
SIGNIFICANCE AND USE
The acquisition of chemical information from variations in the energy position of peaks in the XPS spectrum is of primary interest in the use of XPS as a surface analytical tool. Surface charging acts to shift spectral peaks independent of their chemical relationship to other elements on the same surface. The desire to eliminate the influence of surface charging on the peak positions and peak shapes has resulted in the development of several empirical methods designed to assist in the interpretation of the XPS peak positions, determine surface chemistry, and allow comparison of spectra of conducting and nonconducting systems of the same element. It is assumed that the spectrometer is generally working properly for non-insulating specimens (see Practice E 902).
No ideal method has been developed to deal with surface charging (3, 4). For insulators, an appropriate choice of any control or referencing system will depend on the nature of the specimen, the instruments, and the information needed. The appropriate use of charge control and referencing techniques will result in more consistent, reproducible data. Researchers are strongly urged to report both the control and referencing techniques that have been used, the specific peaks and binding energies used as standards (if any), and the criteria applied in determining optimum results so that the appropriate comparisons may be made.
SCOPE
1.1 This guide covers the acquainting of the XPS user with the various charge control and charge shift referencing techniques that are and have been used in the acquisition and interpretation of X-ray photoelectron spectroscopy (XPS) data from surfaces of insulating specimens.
1.2 This guide is intended to apply to charge control and charge referencing techniques in XPS and is not necessarily applicable to electron-excited systems.
1.3 SI units are standard unless otherwise noted.
1.4 This standard does not purport to address all of the safety problems, 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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Standards Content (Sample)
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Designation:E1523–03
Standard Guide to
Charge Control and Charge Referencing Techniques in
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X-Ray Photoelectron Spectroscopy
This standard is issued under the fixed designation E1523; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
BE Reference binding energy, in
ref
eV
1.1 This guide acquaints the XPS user with the various
BE Measured Binding energy, in
meas,
charge control and charge shift referencing techniques that are
ref eV, of a reference line
and have been used in the acquisition and interpretation of
FWHM Full width at half maximum
amplitude of a peak in the pho-
X-ray photoelectron spectroscopy (XPS) data from surfaces of
toelectron spectrum above the
insulating specimens and provides information needed for
background, in eV
reporting the methods used to customers or in the literature.
XPS X-ray photoelectron spectros-
copy
1.2 This guide is intended to apply to charge control and
D Correction energy, to be added
corr
charge referencing techniques in XPS and is not necessarily
to measured binding energies
applicable to electron-excited systems.
for charge correction, in eV
1.3 SI units are standard unless otherwise noted.
4. Overview of Charging Effects
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 4.1 For insulating specimen surfaces, the emission of pho-
responsibility of the user of this standard to establish appro-
toelectrons following X-ray excitation may result in a buildup
priate safety and health practices and determine the applica- of a positive surface charge. This positive surface charge
bility of regulatory limitations prior to use.
changes the surface potential thereby shifting the measured
energies of the photoelectron peaks to higher binding energy.
2. Referenced Documents
Thisbindingenergyshiftmayreachanearlysteady-statevalue
2.1 ASTM Standards:
of between 2 and 5 eV for spectrometers equipped with
2
E673 Terminology Relating to Surface Analysis
nonmonochromatic X-ray sources. The surface potential
E902 Practice for Checking the Operating Characteristics
charge and the resulting binding energy shift is, generally,
2
of X-Ray Photoelectron Spectrometers
larger for spectrometers equipped with monochromatic X-ray
E1078 Guide for Specimen Handling in Auger Electron
sources because of the, generally, lower flux of low-energy
Spectroscopy, X-Ray Photoelectron Spectroscopy, and
electrons impinging on the specimen surface. This lower flux
2
Secondary Ion Mass Spectrometry
arises because focused, monochromatic X-ray beams irradiate
E 1829 Guide for Specimen Preparation and Mounting in
only a portion of the specimen and not other nearby surfaces
2
Surface Analysis
(for example, the specimen holder) that are sources of low-
energy electrons. The absence of an X-ray window in many
3. Terminology
monochromatic X-ray sources (or a greater distance of the
3.1 Definitions:
specimen from the X-ray window) also eliminates another
3.1.1 SeeTerminologyE673fordefinitionsoftermsusedin
source of low-energy electrons.
X-ray photoelectron spectroscopy.
4.2 The amount of induced surface charge, its distribution
3.1.2 Symbols
acrossthespecimensurface,anditsdependenceonexperimen-
BE Binding energy, in eV tal conditions are determined by several factors including
BE Corrected binding energy, in eV
corr specimen composition, homogeneity, magnitude of surface
BE Measured binding energy, in eV
meas
conductivity, total photoionization cross-section, surface to-
pography, spacial distribution of the exciting X-rays, and
availability of neutralizing electrons. Charge buildup is a
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This guide is under the jurisdiction of ASTM Committee E42 on Surface
3
well-studied(1,2) ,threedimensionalphenomenonthatoccurs
AnalysisandisthedirectresponsibilityofSubcommitteeE42.03onAugerElectron
Spectroscopy and X-ray Photoelectron Spectroscopy.
Current edition approved May 10, 2003. Published July 2003. Originally
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approved in 1993. Last previous edition approved in 1997 as E 1523 – 97. The boldface numbers given in parentheses refer to a list of references at the
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Annual Book of ASTM Standards, Vol 03.06. end of the text.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E1523–03
alongthesamplesurfaceandintothematerial.Thepresenceof reduce the amount of surface charge buildup. This and other
particles on or different phases in the specimen surface may methods of specimen mounting to reduce static charge are
result in an un
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