ASTM E983-94(1999)
(Guide)Standard Guide for Minimizing Unwanted Electron Beam Effects in Auger Electron Spectroscopy
Standard Guide for Minimizing Unwanted Electron Beam Effects in Auger Electron Spectroscopy
SCOPE
1.1 This guide outlines the origins and manifestations of unwanted electron beam effects in Auger electron spectroscopy (AES).
1.2 Some general guidelines are provided concerning the electron beam parameters which are most likely to produce these effects.
1.3 General classes of materials are identified which are most likely to exhibit unwanted electron beam effects. In addition, a tabulation of some specific materials which have been observed to undergo electron damage effects is provided.
1.4 A simple method is outlined for establishing the existence and extent of these effects during routine AES analysis.
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:E983–94 (Reapproved 1999)
Standard Guide for
Minimizing Unwanted Electron Beam Effects in Auger
Electron Spectroscopy
This standard is issued under the fixed designation E 983; 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 causing physical and chemical changes. In general, these
effects are a hindrance to AES analysis because they cause
1.1 This guide outlines the origins and manifestations of
localized specimen modification (1, 2, 3).
unwanted electron beam effects inAuger electron spectroscopy
4.2 With specimens that have poor electrical conductivity
(AES).
the electron beam can stimulate the development of localized
1.2 Some general guidelines are provided concerning the
charge on the specimen surface. This effect is a hindrance to
electron beam parameters which are most likely to produce
AES analysis because the potentials associated with the charge
these effects.
can either adversely affect the integrity of Auger data or make
1.3 General classes of materials are identified which are
Auger data collection difficult.
most likely to exhibit unwanted electron beam effects. In
addition, a tabulation of some specific materials which have
5. Origins of Electron Beam Effects
been observed to undergo electron damage effects is provided.
5.1 Electron beam effects inAES may originate from one or
1.4 A simple method is outlined for establishing the exist-
more distinct processes.
ence and extent of these effects during routine AES analysis.
5.1.1 Charge accumulation in materials with poor electrical
1.5 This standard does not purport to address all of the
conductivityleadingtopotentialsthatcausedistortionofAuger
safety concerns, if any, associated with its use. It is the
data or make AES data collection difficult by virtue of:
responsibility of the user of this standard to establish appro-
5.1.1.1 Auger peak shift on energy scale.
priate safety and health practices and determine the applica-
5.1.1.2 Auger peak shape and size distortion.
bility of regulatory limitations prior to use.
5.1.1.3 Auger signal strength instability.
2. Referenced Documents 5.1.2 Electronic excitation of surface, subsurface, and bulk
atoms and molecules leading to specimen changes (4, 5, 6)
2.1 ASTM Standards:
which include:
E 673 Terminology Relating to Surface Analysis
5.1.2.1 Dissociation.
E 996 Practice for Reporting Data in Auger Electron Spec-
2 5.1.2.2 Electron stimulated desorption (ESD) (7).
troscopy and X-Ray Photoelectron Spectroscopy
5.1.2.3 Electron stimulated adsorption (ESA) (8).
3. Terminology 5.1.2.4 Polymerization (9, 10).
5.1.2.5 Carburization (11, 12, 13).
3.1 SeeTerminology E 673 for terms used inAuger electron
5.1.2.6 Oxidation (14, 15).
spectroscopy.
5.1.2.7 Reduction (16).
NOTE 1—Electron beam effects and their consequences are widely
5.1.2.8 Decomposition (17, 18).
referred to in the literature using any one or more of the following terms:
5.1.2.9 Erosion.
electron beam damage, sample damage, specimen damage, beam effects,
5.1.2.10 Diffusion.
electron beam induced processes, and electron irradiation effects.
5.1.3 Charge accumulation in materials of poor electrical
4. Significance and Use
conductivity leading to specimen changes which include (19,
20):
4.1 When electron beam excitation is used in AES, the
5.1.3.1 Electric field enhanced diffusion.
incident electron beam can interact with the specimen material
5.1.3.2 Electromigration.
5.1.4 Heating which may cause:
5.1.4.1 Annealing.
This guide is under the jurisdiction of ASTM Committee E-42 on Surface
5.1.4.2 Segregation.
Analysisand is the direct responsibility of Subcommittee E42.03 onAuger Electron
Spectroscopy and XPS.
Current edition approved Sept. 15, 1994. Published November 1994. Originally
published as E 983 – 84. Last previous edition E 983 – 89. The boldface numbers in parentheses refer to the references listed at the end of
Annual Book of ASTM Standards, Vol 03.06. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E983
5.1.4.3 Volatilization. the values may be subject to future revision. The material
5.1.4.4 Chemical reaction. specific dose, D may be as low as 10A/m .
c
7.1.4 In practice, the electron dose is directly dependent
6. Practical Manifestations of Electron Beam Effects
upon the electron beam current density, J , (A/m ), the time of
B
6.1 Electron dose dependent changes in the intensity, en- electronirradiationinseconds,t(s);andtheangleofincidence,
2 2
ergy, peak shape of one or more Auger transitions; depending Q,ofthebeamonthesample.Thatis,D (C/m ) 5 J (A/m )·t
C B
upon the material, these changes may be complete within a (s)·cosQ. Putting the electron beam current density into com-
fraction of a second or they may progress for hours. monly used condition, 10 A/m would be equivalent to using
-8
6.2 Discoloration of the specimen at the electron beam 10 A incident beam current into a 33 µm electron beam
irradiated region. diameter at normal incidence.
6.3 Physical damage to the specimen such as erosion, 7.1.5 Theelectronbeam-inducedheatingofagivenmaterial
cracking, blistering, or densification. of poor thermal conductivity and the accumulation of charge
6.4 Pressure rises in the analytical vacuum chamber during on a material of poor electrical conductivity are dependent
electron irradiation. upon the electron beam current density.
6.5 Localized electric charge dependent changes in the 7.1.6 Current densities for a static electron beam should be
4 2
of the order 10 A/m or less for susceptible materials. In the
intensity, energy, or peak shape of all Auger transitions. These
changesmaybestablebutoftenareerraticresultinginunstable case of rastered or gated electron beams, the time-averaged
current density and the instantaneous current density must be
AES signals which may preclude AES data collection.
considered. Even though the time-averaged current density
7. Electron Beam Parameters
may be small, the instantaneous current density may be
7.1 Electron Dose and Current Density: sufficient to cause specimen damage or specimen charging.
7.1.7 Insmall-spotAESanalysis,orscanningAugermicros-
7.1.1 Electron dose and current density were previously
2 2
defined using units of C/cm and mA/cm , respectively. These copy, the use of electron probes with high current density is
inherent. Obviously a trade-off between signal-to-noise and the
units are not consistent with the SI system. To keep from
changing the magnitude of the numbers appearing in the perturbing effects of the electron beam is required (2).
7.2 Electron Energy:
literature(fromwhichTable1isadapted),themultipliersofthe
terms are being changed. A dose of C/cm is equivalent to 7.2.1 The electron beam effects which involve electronic
4 2 2 2
excitation are not strong functions of electron beam energies
10 C/m , while 1mA/cm is equivalent to 10A/m .
7.1.2 Specimenmaterialmodificationcanoftenberelatedto used for AES (1 to 25 keV). Changes in electron beam energy
the electron dose (D); that is, the number of electrons incident will affect the depth, and therefore the volume, in which such
on a unit area of the specimen, expressed in coulombs per changes occur.
square centimeter (C/cm ) (1). 7.2.2 Electronbeameffectsduetoheatingcanbeminimized
7.1.3 A number of materials, (for example, see Table 1), by reducing the electron beam power since this reduces the
exhibit dose-dependent effects when the electron dose exceeds power dissipation within the specimen.
7.2.3 Electron beam effects arising due to charging and
a material specific critical dose D . The magnitude of the
c
critical dose corresponds to the onset of detectable damage and electric fields in the surface can be minimized by appropriate
empirical choices of electron beam condition (accelerating
A voltage, current, and current density). It should be noted that
TABLE 1 Electron Beam Damage in AES
the electron beam angle of incidence (the angle between the
T 5 time at 1
4 2
Material Energy 10 C/m Refs
electron beam and the specimen normal, as defined in Termi-
10A/m
nology E 673) influences the electron emission coefficient of
Si N 2 keV stable . (21)
3 4
Al O 5 keV 10 3 h (2) the specimen surface.
2 3
Cu, Fe 1 keV 1 15 min (22)
Pthalocyanines
8. Susceptible Materials
SiO 2 keV 0.6 10 min (21)
8.1 Nonmetallic Materials, particularly oxides, fluorides,
Li WO 1 keV 0.05 8 min (23)
2 4
NaF, LiF 0.1 keV 0.06 60 s (18)
chlorides, alkali halides, carbonates, and organics are most
LiNO , LiSO 1 keV 0.05 50 s (23)
3 4
prone to decomposition under electron beam irradiation.
KCl 1.5 keV 0.03 30 s (18)
8.2 Adsorbed Species, particularly carbonaceous molecules,
TeO 2 keV 0.02 20 s (24)
H O(F) 1.5 keV 0.01 10 s (25)
2 water and halogens, are usually desorbed, but in some cases
−3
Native oxides 5 keV 2 3 10 2s (3)
may change their chemical form.
−4
C H (F) 0.1 keV 3 3 10 0.3 s (26)
6 12
−4 −3
8.3 Metal Surfaces (Clean), are most susceptible to ESA;
Na AlF 3 keV 10 −10 0.1 s (27
...
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