ASTM E1217-00
(Practice)Standard Practice for Determination of the Specimen Area Contributing to the Detected Signal in Auger Electron Spectrometers and Some X-Ray Photoelectron Spectrometers
Standard Practice for Determination of the Specimen Area Contributing to the Detected Signal in Auger Electron Spectrometers and Some X-Ray Photoelectron Spectrometers
SCOPE
1.1 This practice describes methods for determining the specimen area contributing to the detected signal in X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) when this area is defined by the electron collection lens/aperture system. It is recommended as a useful means of determining the observed specimen area for different conditions of spectrometer operation, verifying adequate specimen alignment, and characterizing the imaging properties of the electron energy analyzer.
1.2 This practice is intended only for spectrometers in which the specimen area excited by X-ray or electron beams is or can be made larger than the specimen area viewed by the analyzer. It is assumed that, under normal conditions of operation, the specimen is excited by a beam of X rays or electrons that can be considered to have a uniform intensity over the specimen area viewed by the analyzer, and the specimen is homogeneous and uniform over the observed area.
1.3 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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Designation:E1217–00
Standard Practice for
Determination of the Specimen Area Contributing to the
Detected Signal in Auger Electron Spectrometers and Some
X-Ray Photoelectron Spectrometers
This standard is issued under the fixed designation E 1217; 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 3. Terminology
1.1 This practice describes methods for determining the 3.1 Definitions—See Terminology E 673 for terms used in
specimen area contributing to the detected signal in Auger AugerelectronspectroscopyandX-rayphotoelectronspectros-
electron spectrometers and some types of X-ray photoelectron copy.
spectrometers when this area is defined by the electron
4. Summary of Practice
collection lens and aperture system of the electron energy
4.1 An electron beam with a selected energy is scanned
analyzer. The practice is applicable only to those X-ray
photoelectron spectrometers in which the specimen area ex- across the surface of a test specimen. The beam may be
scanned once, that is, a line scan, or in a pattern, that is,
cited by the incident X-ray beam is larger than the specimen
area viewed by the analyzer, in which the photoelectrons travel rastered.As the electron beam is deflected across the specimen
surface, measurements are made of the intensities detected by
in a field-free region from the specimen to the analyzer
entrance, and in which an auxiliary electron gun can be the electron energy analyzer as a function of the beam position
for selected conditions of analyzer operation. The measured
mounted to produce an electron beam of variable energy on the
specimen. intensities may be due to electrons elastically scattered by the
specimen surface, to electrons inelastically scattered by the
1.2 This practice is recommended as a useful means for
determining the specimen area viewed by the analyzer for specimen, or to Auger electrons emitted by the specimen. The
intensity distributions for a particular detected electron energy
different conditions of spectrometer operation, for verifying
adequate specimen and beam alignment, and for characterizing can be plotted as a function of beam position in several ways
the imaging properties of the electron energy analyzer. and can be utilized to obtain information on the specimen area
contributing to the detected signal and on analyzer perfor-
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the mance for the particular conditions of operation. This informa-
tion can be used to determine the analysis area (see Terminol-
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- ogy E 673 or ISO 18115).
bility of regulatory limitations prior to use.
5. Significance and Use
2. Referenced Documents
5.1 Auger electron spectroscopy and X-ray photoelectron
spectroscopy are used extensively for the surface analysis of
2.1 ASTM Standards:
E 673 Terminology Relating to Surface Analysis materials. This practice summarizes methods for determining
the specimen area contributing to the detected signal for
E 1016 Practice for Describing and Specifying the Proper-
ties of Electrostatic Electron Spectrometers instruments in which a focused electron beam can be scanned
over a region with dimensions greater than the dimensions of
2.2 ISO Standards:
ISO/DIS 18115 Surface Chemical Analysis—Vocabulary the specimen area viewed by the analyzer.
5.2 This practice is intended as a means for determining the
(in ballot)
observed specimen area for selected conditions of operation of
This practice is under the jurisdiction of ASTM Committee E-42 on Surface
Analysis and is the direct responsibility of Subcommittee E42.03 onAuger Electron
Spectroscopy and X-ray Photoelectron Spectroscopy.
Current edition approved April 10, 2000. Published June 2000. Originally
published as E 1217 – 87. Last previous edition E 1217 – 87 (1992).
Annual Book of ASTM Standards, Vol 03.06.
Available from American National Standards Institute, 11 W. 42nd St., 13th
Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1217–00
the electron energy analyzer. The observed specimen area used to scan the electron beam across the test specimen
depends on whether or not the electrons are retarded before surface, either on a selected line or on a raster pattern with
energy analysis, the analyzer pass energy or retarding ratio if selected dimensions. The selected analyzer signals may be
the electrons are retarded before energy analysis, the size of recorded in a computer system or be displayed directly on an
selected slits or apertures, and the value of the electron energy oscilloscope or X-Y recorder.
to be measured. The observed specimen area depends on these 6.3.2 Unequipped Spectrometer—If the spectrometer is not
selected conditions of operation and also can depend on the equipped with instrumentation for scanning the electron beam,
adequacy of alignment of the specimen with respect to the this instrumentation will have to be provided. A line scan can
electron energy analyzer. be accomplished with a suitable wave-form generator (either
5.3 Any changes in the observed specimen area as a triangular or sawtooth) or a programmable power supply.
function of measurement conditions, for example, electron Anotherdcsupplymayberequiredtodefinethepositionofthe
energy or analyzer pass energy, may need to be known if the line on the specimen, that is, in the direction orthogonal to the
specimen materials in regular use have lateral inhomogeneities scan. Raster scans can be made with two waveform generators
withdimensionscomparabletothedimensionsofthespecimen or two programmable power supplies.
area viewed by the analyzer.
7. Procedure
5.4 Thispracticecangiveusefulinformationontheimaging
7.1 Choose the energy of the electron beam incident on the
properties of the electron energy analyzer for particular con-
surface of the test specimen. This choice should be made
ditions of operation. This information can be helpful in
depending on the nature of the tests to be made. For example,
comparing analyzer performance with manufacturer’s specifi-
electron energies between 100 eV and 2000 eV may be chosen
cations.
forAuger electron experiments with specific choices related to
5.5 Examples of the application of the methods described in
the energies of Auger electron peaks of particular interest. In
this practice have been published (1-6).
X-ray photoelectron spectroscopy experiments with magne-
6. Apparatus
sium characteristic X-rays, electron energies between approxi-
mately 254 eV and 1254 eV might be chosen to determine the
6.1 Test Specimen, preferably a conductor, is required and is
analyzer performance for the binding-energy range between 0
mounted in the Auger electron or X-ray photoelectron spec-
eV and 1000 eV.
trometer in the usual position for surface analysis. It is
7.2 Choosethetypeofscanfortheelectronbeamonthetest
recommended that the test specimen be a metallic foil with
surface, either line scan or raster scan (6.3). If a line scan is
lateral dimensions larger than the dimensions of the field of
selected, choose the position of the line on the specimen.
view of the electron energy analyzer. The test specimen should
7.2.1 Aline scan is a relatively simple procedure and can be
be polycrystalline and have grain dimensions much less than
made for two orthogonal directions.This method for determin-
the expected spatial resolution of the analyzer or the width of
ing the active area of the analyzer may suffice for many
the incident beam on the specimen in order to avoid artifacts
applications but has the disadvantage that the active area may
due to channeling or diffraction effects. The specimen surface
not be symmetrical about the two scan lines (1, 2). The raster
should be smooth and be free of scratches and similar defects
scan method allows convenient observation of any instrumen-
that are observable with the unaided eye (see 8.6). It is
tal asymmetries.
desirablethatthesurfaceofthetestspecimenbecleanedbyion
7.2.2 The following suggestions are made if the instrument
sputtering or other means to remove surface impurities such as
is not already equipped with instrumentation to scan the
oxides and adsorbed hydrocarbons; the degree of surface
electron beam. The specific suggestions are made to generate a
cleanliness can be checked with AES or XPS measurements.
raster scan for an electron gun equipped with deflection plates.
6.2 Electron Gun—An electron gun must be available on
Line scans can be made in a similar way. An analogous
the spectrometer to provide a beam of electrons incident on the
procedure would be used for an electron gun operated with an
test specimen surface with energy typically between 100 eV
electromagnetic deflection system.
and2000eV(thenormalrangeofdetectedenergiesinAESand
7.2.2.1 Use of Waveform Generators—In this approach, use
XPS). The gun must be equipped with a deflection system so
two waveform generators to generate triangular waveforms at
that the electron beam can be deflected to different regions of
frequencies typically in the range of 0.5 kHz to 1 kHz. The
thespecimensurface.Thewidthoftheelectronbeam(FWHM)
waveforms are amplified and coupled through a transformer to
at the test specimen should be less than the spatial resolution
the deflection plates of the electron gun, one output being
desired in the following measurements.
designated for horizontal deflection and the other for vertical
6.3 Electronic Equipment, is required to scan the electron
deflection. A resistive center-tap is connected across each
beam on the surface of the test specimen and to record and
transformer output with the midpoints grounded. The wave-
display the selected signals.
formsarealsoconnectedtothehorizontalandverticalinputsof
6.3.1 Equipped Spectrometer—Some commercial spec-
anoscilloscope.Adjustthefrequenciesoftheoscillatorssothat
trometers, particularly those designed for scanning Auger
there is a uniform intensity distribution on the oscilloscope,
microscopy, have electronic instrumentation, which can be
thatis,absenceofanyLissajou’sfigures.Selectthegainsofthe
amplifiers to deflect the electron beam across the test specimen
by amounts corresponding at least to the anticipated analyzer
The boldface numbers in parentheses refer to the list of references at the end of
this practice. field of view; for a desired deflection on the test specimen, the
E1217–00
maximum deflection-plate voltage will scale with the selected 7.5.2 Inelastically Scattered Electrons—The electron en-
electron energy. Make a line scan with a single waveform ergy analyzer can be adjusted to detect electrons inelastically
scattered by the specimen surface. The electron energy being
generator and with the scan voltage applied to either the
horizontal or the vertical deflection plates. Apply a dc voltage detected may be between zero and the energy of the incident
beam.
totheotherdeflectionplatestoselectthepositionofthelineon
the specimen. 7.5.2.1 This choice is recommended for avoiding the pos-
sible artifact described in 7.5.1. It is suggested that the region
7.2.2.2 Use of Programmable Power Supplies—Program a
of the scattered-electron energy distribution about 100 eV
computer to control the output voltages of two programmable
below the elastic peak be utilized because the intensity is
power supplies. Connect the outputs of the power supplies to
relatively high. The actual electron energy should be chosen to
the deflection plates of the electron gun. Make these connec-
avoid any structure that may be present in this region due to
tions as in 7.2.1; connect center taps across each power supply,
excitations of inner-shell electrons.
also as in 7.2.1. At a given vertical position, step the electron
7.5.2.2 A consideration in the choice of signals due to
beam horizontally across the test specimen surface. The beam
elastically or inelastically scattered electrons is the energy
then can be stepped vertically prior to the next horizontal
widths(FWHM)oftheAESorXPSpeaksusuallymeasuredby
sweep, and so on. Make measurements for each horizontal
the analyzer. If these widths are less than about 2 eV, it is
sweep and for equally spaced horizontal lines within the
recommended that the elastic-peak signal be used; if these
vertical sweep range. The interval between the positions of the
widths are greater than about 2 eV, it is recommended that the
electron beam on the specimen surface together with the width
inelastically-scattered-electron signal be used. The reason for
of the beam at the surface will determine the spatial resolution
these recommendations is that there is a coupling for any
in the measurement of the specimen area contributing to each
analyzerbetweenthedetectedsignalandsourceposition,angle
detected signal.
of emission for the source, and electron energy (Practice
7.2.3 The maximum amount of deflection of the electron
E 1016). As a result, the active specimen area measured with
beam on the test specimen should be less than that which
inelastically scattered electrons can be greater than that mea-
would cause significant (>5 %) reduction of incident electron-
sured with elastically scattered electrons under otherwise
beam current, for example, reduction due to interception of the
identical conditions. More accurate characterization of the
beam by electrodes of the electron gun.
analyzer will be obtained if the energy width of the scattered-
7.3 The amount of deflection of the electron beam on the
electron signal approximates the energy widths of the AES or
test specimen can be determined from electron intensity
XPS peaks encountered in practice.
measurements with test objects, for example, grids or holes, of
7.5.3 Auger Electrons—It may be conveniently possible,
known dimensions (1). The test object is mounted on the test
particularly with instruments intended for scanning Auger
specimen and features of known shape and size are located in
electron microscopy, to adjust the electron energy analyzer to
the recorded data (see 7.7). Alternatively, a feature can be
detect Auger electrons emitted from the surface of the test
located in plots of absorbed current (see 7.4) due to, for
specimen. Even if there is no significantAuger-electron signal
example, specimen roughness or a specimen mounting clip (3).
from the test specimen at the e
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