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Auger electron spectroscopy as a tool in an industrial laboratory
A u g e r Electron S p e c t r o s c o p y as a tool in an industrial laboratory
Per-Eric Nilsson-Jatko, ASEA Metallurgy; Stefan Sehistedt and Lars Unneberg, Research & Innovation, ASEA S-72183 Vasteras, Sweden Abstract
A number of different surface analytical techniques have been developed during the 1970s and it has provedpossible to adapt some of these to meet the needs of industry. One such method, Auger Electron Spectroscopy (AES), is briefly presented. Some examples of the areas within ASEA, where this technique has been successfully applied, are described. The analytical technique makes itpossible to determine the chemical composition of extremely thin surface layers. The analysis depth is of the order of two to three atomic layers, that is about 10 Angstroms. Introduction Auger Electron Spectroscopy ( A E S ) is a technique used to determine the chemical composition of surfaces. Development work on the technique and the instrumentation commenced at the end of the 1960s. The technique was then used only for research purposes in physical laboratories. During the 1970s A E S was refined and it has now become a practical and accepted technique in materials laboratories throughout the world. In 1980 A S E A installed an A E S instrument of the Physical Electronics model 590 series. The A E S technique has proved to be of great value to activities at A S E A . This article describes some of the problems that have been solved with the aid of A E S . Principles of AES Auger electrons are created in the specimen by aiming a focussed electron beam at its surface. This beam penetrates about i/am down into the specimen and ionises the atoms in the material bombarded by the beam. Ionisation means that the atoms lose one electron from a certain energy level, for example, A in Fig. 2. W h e n these atoms relax to their equilibrium energy states, one electron falls from a higher energy level to a lower one ( B - ' A ) . The surplus energy may either be emitted in the form of a photon (this is utilised in electron microprobes) or be passed to a third electron (C), which then leaves the atom. The latter phenomenon was discovered by the F r e n c h physicist Pierre Auger. The emitted electron is therefore called " A u g e r electron".
Fig. 1 Since the process involves three electrons, it is not possible to analyse hydrogen and helium, the reason being that these have only one and two electrons, respectively. On the other hand, all other chemical elements can be detected. Auger electrons possess characteristic energies for each kind of atom. If we can collect such an electron and measure its energy, the kind of atom from which it is derived can consequently be determined. Since the characteristic energy depends on the valence state of the atom, it is also sometimes possible to determine this.
MATERIALS & DESIGN Vol. 7 No. 1 J A N U A R Y / F E B R U A R Y 1 9 8 6
_
./ w
C
A
'w~
B
w w
A
w
l
O
A
~,824
Fig. 2
The Auger Electron Spectroscopy technique.
17
Fig. 3
Schematic diagram of the AES instrument.
dNIdE
600 AT 5826
700
800
900
1000
Wk,eV
Fig. 4 Differentiated Auger spectrum for copper. The eurve shows the derived Auger intensity (dN/dE)versus the kinetic energy (WJ.
The low energies of Auger electrons mean that they are capable of penetrating only short distances into the material without being captured or retarded. This means that only those Auger electrons generated on, or immediately below, the surface of a solid body are able to leave the material. In reality, these electrons can only penetrate two to three atomic layers or about 10 A. Because of this we can analyse only the atoms that are present in an extremely thin surface layer. Another consequence of the small depth of analysis is that we have to work with an extremely good vacuum in the test chamber of the instrument to prevent undesired contamination of the surface. A vacuum of the order of 10.7 to 10 -s Pa ( l O l° to 10-l° torr) is normally necessary. In the instrument the specimen is bombarded with electrons. These can be focussed on a spot less than 1 x 1/an. This makes it possible to analyse very small areas. The emitted Auger electrons are analysed with of an electrostatic analyser and their number versus the energy is recorded. Fig. 3 shows a schematic diagram of the AES instrument and Fig. 4 how the result of the analysis is recorded. A special accessory makes it possible to etch the surface in situ by means of an ion sputter technique. The surface is bombarded with argon ions so that the specimen material is eroded. With successive Auger analyses we can obtain in this way a depth profile, which shows how impurities and alloy elements vary from the surface down into the specimen. Normal profiles usually comprise layers with thicknesses of a few/am. The combination of a high lateral resolution, small depth of analysis, the possibility to record concentration profiles with a high spatial resolution and the possibility to detect all chemical elements (with the exception of hydrogen and helium) means that AES differs radically from other analytical techniques. Further information about the Auger technique can be found in the literature. References 1-3 are examples of good overview articles. Fig. 1 shows ASEA's AES instrument.
Some applications
Fig. 5
The primary crack in the end bell of the Barseb/ick generator (x0.5).
18
Corrosion Grain boundaries in metals often constitute weak zones. A feature of several forms of corrosion is that the attack takes place just in the grain boundaries. As an example we can mention intergran-
MATERIALS & DESIGN VoL 7 No. 1 J A N U A R Y / F E B R U A R Y 1 9 8 6
ular stress corrosion in many materials, including copper, aluminium and nickel alloys, and grain boundary corrosion in the heat-affected zone of welded, austenitic stainless steel. These corrosion phenomenon are frequently caused by the fact that contaminants or alloy elements have segregated to the grain boundaries. The application of the Auger technique to an opened corrosion crack may therefore be of particular interest. A couple of practical cases will be illustrated here. Both these refer to material intended for generator end bells.
Fig. 6
Composition at different depths below the fracture surface ofthe end bell, dark band. Oxide layer approx. 6 pro.
AT 5828
Fig. 7
Fig. 8
i
Composition at different depths below the fracture surface opf the end bell, light band. Oxide layer approx. 0.6 pm.
Composition at different depths below the grain surface of 18Mn 18Cr steel, annealed at 600°C for 2 h.
MATERIALS & DESIGN Vol. 7 No. 1 JANUARY/FEBRUARY 1986
In the spring of 1979 a generator failure occurred at Barseb/ick Nuclear Power Station in southern Sweden. The reason for this could be quickly established as stress corrosion in one of the two end bells of the generator. Fig. 5 shows the primary fracture. From this it can be clearly seen that the fracture surface is striped and divided into dark and light bands of different thicknesses. The end bell was fabricated from a nonmagnetic, high-alloy manganese steel, which is the standard material for this application. By using Auger analysis on the fracture surface and after ion sputter-etching, it could be established that the dark and light bands had different compositions. As can be seen from Figs. 6 and 7, the oxidation state of the iron different in the two cases, which indicates that the oxygen content in the surroundings may have varied. It could be surmised that the end bell had been exposed to water over a longer period of time and that the bands could be correlated with the operating history of the generator. A new material, which has been developed for generator end bells, has such a high chromium content that it can be considered to be a stainless steel. To raise its strength, this steel has also been given a nitrogen content of approximately 0.5 percent. This material has proved to be very resistant to the type of stress corrosion that affected the Barseb/ick generator. If this steel is annealed over a longer period of time at about 600°C, however, it will become sensitive to corrosion. In laboratory experiments intergranular corrosion cracks produced were investigated by means of AES. It was then found that corrosion-sensitive material relatively speaking had very high nitrogen contents in the grain boundaries, see Fig. 8. The annealing consequently had the effect that nitrogen migrated to the grain boundaries and this in turn made the material sensitive to corrosion.
19
phide orzinc chloride may then be formed on the contact surface and this will increase the transition resistance. Fig. 9 shows a depth profile through a contact surface with such zinc enrichment.
Fig. 9
Composition at different depths below the contact surface with high transition resistance.
Fig. 10 AES spectrum for surface below the peeled-off copper coating. The reason for the poor adhesion is incomplete cleaning after an activator bath, containing among other things Pd and Sn. Contacts The transition resistance in electric contacts is generally determined by the chemical composition of the surface of the contact, i.e., by the composition in the outermost atomic layers. The presence of thin contaminant films is of decisive importance to the functioning of a contact, particularly in those cases where the contact transmits such low currents that its surface is not continuously regenerated and where gold, platinum or silver is used as contact material. A series of investigations were made on silver-coated contacts used in ASEA's type EG l0 contactors to clarify the factors influencing the transition resistance. These investigations showed that two different factors are of decisive
20
importance. One of these is environmental influence, by which is meant the way in which the contact material reacts with the surrounding atmosphere. The ability to withstand this influence is determined by the cleanness of the contacts on delivery and when they are taken into use. In simple terms a thin film of oil provides protection against atmospheric contamination. However, the amount of oil must not be so large that it influences the contact characteristics. The other factor affecting the transition resistance is the content of contaminants in the contact material itself. A small amount of, for example, zinc when brass is used as contact carrier material, may be enriched on the contact surface during manufacturing of the contact. Zinc oxide, zinc sul-
Adhesion In connection with the surface coating of different materials, poor adhesion of the applied layers sometimes occurs. With surface coating it is important that the surfaces are free from contaminants and that they are not oxidised. By means of AES it is possible to analyse, for example, flakes of the surface coating and the zone where the peeling off occurred. With this technique it is possible to determine exactly between which layers the peeling off occurred. In many cases, the surface coating comprises several layers, sometimes of the same material. Traces of chemicals from the surface coating process may then frequently be found on the flake and give information about which step in the process that has not functioned as intended, see Fig. 10. The direct cause of the flaking may sometimes even be identified. Ceramic materials The varistors manufactured by A S E A for use in surge arresters are made from ZnO with a grain size of approximately 5 pro, which has been sintered together with a few percent of Bi203 and other additives. The electrical characteristics of the material are determined by the composition of the thin grain boundary film formed between the ZnO grains. Different doping substances are added for the purpose of influencing both the current-voltage characteristics and the ageing characteristics of the varistors. By studying with AES fracture surfaces of varistor material, we can analyse the distribution of the doping elements and impurities. Such an analysis shows, for example, that the Bi203enriched grain boundary phase has a thickness of approximately 40 A and that in this case among other things Fe can be detected in the grain boundary phase and to a depth of about 300 A in the ZnO grains, see Figs. 11 and 12. With the AES instrument it is therefore possible to identify a grain surface and to analyse a small part of this surface, with a sensitivity for Fe in this case of less than 0.1%. The AES technique thus makes it possible to study the distribution of different additives in the grain boundary phase, which contributes to increased knowledge and consequently to the development of better varistors. Another ceramic material which has
MATERIALS & DESIGN Vol. 7 No. 1 JANUARY/FEBRUARY 1986
been successfully analysed is Si3N 4. Here, too, it is a question of a sintered material having a small grain size, where the properties are largely determined by the thin grain boundary phase, which is needed to facilitate the sintering. Discoloration
Discoloration is one of the more easily observed surface problems. This can be divided into two groups: discoloration of aesthetic importance and discoloration that entails changed critical characteristics. Such problems occur relatively frequently and can generally be successfully solved with the AES technique. Micro-electronics
Fig. 11 Composition at different depths below a grain surface in a ZnO varistor.
The AES technique has also proved to be successful when it comes to the treatment of surface problems in connection with micro-electronics. Manufacturing of integrated circuits involves a large number of different process steps, where the active surfaces are either protected or coated in a defined way and where the layers are formed by means of diffusion annealing. Figs. 13 and 14 show how an AES analysis of a p- and n-doped area in an elegant way can prove that Pt silicide has not been formed on an n ÷ area, because an insulating SiO2 layer prevented Pt and Si from reacting with one another. The total thickness of the layers is less than approx. 2000 A. Tool wear
Fig. 12 Analysis of contaminants and doping element in the grain surface in the ZnO varistor shown in Fig. 11.
Fig. 13 Composition at different depths below the surface of an n-t- area. The presence of an SIO 2 layer has prevented the formation of Pt silicide. MATERIALS & DESIGN Vol. 7 No. 1 J A N U A R Y / F E B R U A R Y 1 9 8 6
Thin strips of copper-beryllium alloys are used for manufacturing the spring elements and sockets for the COMBIFLEX ® system. The initial manufacturing step involves stamping. It has been found that the wear of the stamping tool varies with the surface condition of the strip. By using the AES technique, it has proved possible to establish that the presence of a thin surface layer, enriched with BeO, is the cause of the extra wear. Figs. 15 and 16 show examples of strips of good and poor quality in this respect. The BeO layer can then be attributed to different process parameters during the manufacturing of the strip (rolling and intermediate annealing operations). Conclusion The aim of this brief presentation of Auger Electron Spectroscopy has been to illustrate the extremely good capability of this technique to determine chemical compositions in thin surface layers. With the aid of ion sputteretching equipment it is also possible to obtain depth profiles. These normally comprise a layer only about 1-2 /am
21
thick of the surface of the specimen. The strength of this technique is to be found in the analysis of thin surface layers and not in the determination of bulk properties. The application areas for the A E S technique are those where surfaces play a decisive role. A number of such areas have been mentioned in this article, where A S E A has been applying AE S to solve different problems. Now that A S E A ' s Central Laboratories have procured an A E S instrument, their resources for handling surface problems have been greatly strengthened. The A E S instrument will continue to play a vital role also in the future in development work within many areas of technology.
Acknowledgement Fig. 14 Composition at different depths below the surface of a p area. Normally formed Pt silieide.
This article was originally published in the A S E A Journal 1-1983
Fig. 15 Composition at different depths below the surface of a berylliumcopper strip with normal tool wear.
References 1. Hillmer, T.: Auger Electron Spectrometry
i
Fig. 16 Composition at different depths below the surface of a berylliumcopper strip with high tool wear.
22
Part 1: Basic Principles and Equipment. Pract. Met. 19 (1982), p.431. 2. Hillmer, T.: Auger Electron Spectrometry Part 2: Practical Applications and Experience. Pract. Met. 19 (1982), p.509. 3. van Oostrom, A.: Some Aspects of Auger Microanalysis. Surface Science 89 (1979), p.615.
MATERIALS & DESIGN Vol. 7 No. 1 JANUARY/FEBRUARY 1986
Per-Eric Nilsson-Jatko, ASEA Metallurgy; Stefan Sehistedt and Lars Unneberg, Research & Innovation, ASEA S-72183 Vasteras, Sweden Abstract
A number of different surface analytical techniques have been developed during the 1970s and it has provedpossible to adapt some of these to meet the needs of industry. One such method, Auger Electron Spectroscopy (AES), is briefly presented. Some examples of the areas within ASEA, where this technique has been successfully applied, are described. The analytical technique makes itpossible to determine the chemical composition of extremely thin surface layers. The analysis depth is of the order of two to three atomic layers, that is about 10 Angstroms. Introduction Auger Electron Spectroscopy ( A E S ) is a technique used to determine the chemical composition of surfaces. Development work on the technique and the instrumentation commenced at the end of the 1960s. The technique was then used only for research purposes in physical laboratories. During the 1970s A E S was refined and it has now become a practical and accepted technique in materials laboratories throughout the world. In 1980 A S E A installed an A E S instrument of the Physical Electronics model 590 series. The A E S technique has proved to be of great value to activities at A S E A . This article describes some of the problems that have been solved with the aid of A E S . Principles of AES Auger electrons are created in the specimen by aiming a focussed electron beam at its surface. This beam penetrates about i/am down into the specimen and ionises the atoms in the material bombarded by the beam. Ionisation means that the atoms lose one electron from a certain energy level, for example, A in Fig. 2. W h e n these atoms relax to their equilibrium energy states, one electron falls from a higher energy level to a lower one ( B - ' A ) . The surplus energy may either be emitted in the form of a photon (this is utilised in electron microprobes) or be passed to a third electron (C), which then leaves the atom. The latter phenomenon was discovered by the F r e n c h physicist Pierre Auger. The emitted electron is therefore called " A u g e r electron".
Fig. 1 Since the process involves three electrons, it is not possible to analyse hydrogen and helium, the reason being that these have only one and two electrons, respectively. On the other hand, all other chemical elements can be detected. Auger electrons possess characteristic energies for each kind of atom. If we can collect such an electron and measure its energy, the kind of atom from which it is derived can consequently be determined. Since the characteristic energy depends on the valence state of the atom, it is also sometimes possible to determine this.
MATERIALS & DESIGN Vol. 7 No. 1 J A N U A R Y / F E B R U A R Y 1 9 8 6
_
./ w
C
A
'w~
B
w w
A
w
l
O
A
~,824
Fig. 2
The Auger Electron Spectroscopy technique.
17
Fig. 3
Schematic diagram of the AES instrument.
dNIdE
600 AT 5826
700
800
900
1000
Wk,eV
Fig. 4 Differentiated Auger spectrum for copper. The eurve shows the derived Auger intensity (dN/dE)versus the kinetic energy (WJ.
The low energies of Auger electrons mean that they are capable of penetrating only short distances into the material without being captured or retarded. This means that only those Auger electrons generated on, or immediately below, the surface of a solid body are able to leave the material. In reality, these electrons can only penetrate two to three atomic layers or about 10 A. Because of this we can analyse only the atoms that are present in an extremely thin surface layer. Another consequence of the small depth of analysis is that we have to work with an extremely good vacuum in the test chamber of the instrument to prevent undesired contamination of the surface. A vacuum of the order of 10.7 to 10 -s Pa ( l O l° to 10-l° torr) is normally necessary. In the instrument the specimen is bombarded with electrons. These can be focussed on a spot less than 1 x 1/an. This makes it possible to analyse very small areas. The emitted Auger electrons are analysed with of an electrostatic analyser and their number versus the energy is recorded. Fig. 3 shows a schematic diagram of the AES instrument and Fig. 4 how the result of the analysis is recorded. A special accessory makes it possible to etch the surface in situ by means of an ion sputter technique. The surface is bombarded with argon ions so that the specimen material is eroded. With successive Auger analyses we can obtain in this way a depth profile, which shows how impurities and alloy elements vary from the surface down into the specimen. Normal profiles usually comprise layers with thicknesses of a few/am. The combination of a high lateral resolution, small depth of analysis, the possibility to record concentration profiles with a high spatial resolution and the possibility to detect all chemical elements (with the exception of hydrogen and helium) means that AES differs radically from other analytical techniques. Further information about the Auger technique can be found in the literature. References 1-3 are examples of good overview articles. Fig. 1 shows ASEA's AES instrument.
Some applications
Fig. 5
The primary crack in the end bell of the Barseb/ick generator (x0.5).
18
Corrosion Grain boundaries in metals often constitute weak zones. A feature of several forms of corrosion is that the attack takes place just in the grain boundaries. As an example we can mention intergran-
MATERIALS & DESIGN VoL 7 No. 1 J A N U A R Y / F E B R U A R Y 1 9 8 6
ular stress corrosion in many materials, including copper, aluminium and nickel alloys, and grain boundary corrosion in the heat-affected zone of welded, austenitic stainless steel. These corrosion phenomenon are frequently caused by the fact that contaminants or alloy elements have segregated to the grain boundaries. The application of the Auger technique to an opened corrosion crack may therefore be of particular interest. A couple of practical cases will be illustrated here. Both these refer to material intended for generator end bells.
Fig. 6
Composition at different depths below the fracture surface ofthe end bell, dark band. Oxide layer approx. 6 pro.
AT 5828
Fig. 7
Fig. 8
i
Composition at different depths below the fracture surface opf the end bell, light band. Oxide layer approx. 0.6 pm.
Composition at different depths below the grain surface of 18Mn 18Cr steel, annealed at 600°C for 2 h.
MATERIALS & DESIGN Vol. 7 No. 1 JANUARY/FEBRUARY 1986
In the spring of 1979 a generator failure occurred at Barseb/ick Nuclear Power Station in southern Sweden. The reason for this could be quickly established as stress corrosion in one of the two end bells of the generator. Fig. 5 shows the primary fracture. From this it can be clearly seen that the fracture surface is striped and divided into dark and light bands of different thicknesses. The end bell was fabricated from a nonmagnetic, high-alloy manganese steel, which is the standard material for this application. By using Auger analysis on the fracture surface and after ion sputter-etching, it could be established that the dark and light bands had different compositions. As can be seen from Figs. 6 and 7, the oxidation state of the iron different in the two cases, which indicates that the oxygen content in the surroundings may have varied. It could be surmised that the end bell had been exposed to water over a longer period of time and that the bands could be correlated with the operating history of the generator. A new material, which has been developed for generator end bells, has such a high chromium content that it can be considered to be a stainless steel. To raise its strength, this steel has also been given a nitrogen content of approximately 0.5 percent. This material has proved to be very resistant to the type of stress corrosion that affected the Barseb/ick generator. If this steel is annealed over a longer period of time at about 600°C, however, it will become sensitive to corrosion. In laboratory experiments intergranular corrosion cracks produced were investigated by means of AES. It was then found that corrosion-sensitive material relatively speaking had very high nitrogen contents in the grain boundaries, see Fig. 8. The annealing consequently had the effect that nitrogen migrated to the grain boundaries and this in turn made the material sensitive to corrosion.
19
phide orzinc chloride may then be formed on the contact surface and this will increase the transition resistance. Fig. 9 shows a depth profile through a contact surface with such zinc enrichment.
Fig. 9
Composition at different depths below the contact surface with high transition resistance.
Fig. 10 AES spectrum for surface below the peeled-off copper coating. The reason for the poor adhesion is incomplete cleaning after an activator bath, containing among other things Pd and Sn. Contacts The transition resistance in electric contacts is generally determined by the chemical composition of the surface of the contact, i.e., by the composition in the outermost atomic layers. The presence of thin contaminant films is of decisive importance to the functioning of a contact, particularly in those cases where the contact transmits such low currents that its surface is not continuously regenerated and where gold, platinum or silver is used as contact material. A series of investigations were made on silver-coated contacts used in ASEA's type EG l0 contactors to clarify the factors influencing the transition resistance. These investigations showed that two different factors are of decisive
20
importance. One of these is environmental influence, by which is meant the way in which the contact material reacts with the surrounding atmosphere. The ability to withstand this influence is determined by the cleanness of the contacts on delivery and when they are taken into use. In simple terms a thin film of oil provides protection against atmospheric contamination. However, the amount of oil must not be so large that it influences the contact characteristics. The other factor affecting the transition resistance is the content of contaminants in the contact material itself. A small amount of, for example, zinc when brass is used as contact carrier material, may be enriched on the contact surface during manufacturing of the contact. Zinc oxide, zinc sul-
Adhesion In connection with the surface coating of different materials, poor adhesion of the applied layers sometimes occurs. With surface coating it is important that the surfaces are free from contaminants and that they are not oxidised. By means of AES it is possible to analyse, for example, flakes of the surface coating and the zone where the peeling off occurred. With this technique it is possible to determine exactly between which layers the peeling off occurred. In many cases, the surface coating comprises several layers, sometimes of the same material. Traces of chemicals from the surface coating process may then frequently be found on the flake and give information about which step in the process that has not functioned as intended, see Fig. 10. The direct cause of the flaking may sometimes even be identified. Ceramic materials The varistors manufactured by A S E A for use in surge arresters are made from ZnO with a grain size of approximately 5 pro, which has been sintered together with a few percent of Bi203 and other additives. The electrical characteristics of the material are determined by the composition of the thin grain boundary film formed between the ZnO grains. Different doping substances are added for the purpose of influencing both the current-voltage characteristics and the ageing characteristics of the varistors. By studying with AES fracture surfaces of varistor material, we can analyse the distribution of the doping elements and impurities. Such an analysis shows, for example, that the Bi203enriched grain boundary phase has a thickness of approximately 40 A and that in this case among other things Fe can be detected in the grain boundary phase and to a depth of about 300 A in the ZnO grains, see Figs. 11 and 12. With the AES instrument it is therefore possible to identify a grain surface and to analyse a small part of this surface, with a sensitivity for Fe in this case of less than 0.1%. The AES technique thus makes it possible to study the distribution of different additives in the grain boundary phase, which contributes to increased knowledge and consequently to the development of better varistors. Another ceramic material which has
MATERIALS & DESIGN Vol. 7 No. 1 JANUARY/FEBRUARY 1986
been successfully analysed is Si3N 4. Here, too, it is a question of a sintered material having a small grain size, where the properties are largely determined by the thin grain boundary phase, which is needed to facilitate the sintering. Discoloration
Discoloration is one of the more easily observed surface problems. This can be divided into two groups: discoloration of aesthetic importance and discoloration that entails changed critical characteristics. Such problems occur relatively frequently and can generally be successfully solved with the AES technique. Micro-electronics
Fig. 11 Composition at different depths below a grain surface in a ZnO varistor.
The AES technique has also proved to be successful when it comes to the treatment of surface problems in connection with micro-electronics. Manufacturing of integrated circuits involves a large number of different process steps, where the active surfaces are either protected or coated in a defined way and where the layers are formed by means of diffusion annealing. Figs. 13 and 14 show how an AES analysis of a p- and n-doped area in an elegant way can prove that Pt silicide has not been formed on an n ÷ area, because an insulating SiO2 layer prevented Pt and Si from reacting with one another. The total thickness of the layers is less than approx. 2000 A. Tool wear
Fig. 12 Analysis of contaminants and doping element in the grain surface in the ZnO varistor shown in Fig. 11.
Fig. 13 Composition at different depths below the surface of an n-t- area. The presence of an SIO 2 layer has prevented the formation of Pt silicide. MATERIALS & DESIGN Vol. 7 No. 1 J A N U A R Y / F E B R U A R Y 1 9 8 6
Thin strips of copper-beryllium alloys are used for manufacturing the spring elements and sockets for the COMBIFLEX ® system. The initial manufacturing step involves stamping. It has been found that the wear of the stamping tool varies with the surface condition of the strip. By using the AES technique, it has proved possible to establish that the presence of a thin surface layer, enriched with BeO, is the cause of the extra wear. Figs. 15 and 16 show examples of strips of good and poor quality in this respect. The BeO layer can then be attributed to different process parameters during the manufacturing of the strip (rolling and intermediate annealing operations). Conclusion The aim of this brief presentation of Auger Electron Spectroscopy has been to illustrate the extremely good capability of this technique to determine chemical compositions in thin surface layers. With the aid of ion sputteretching equipment it is also possible to obtain depth profiles. These normally comprise a layer only about 1-2 /am
21
thick of the surface of the specimen. The strength of this technique is to be found in the analysis of thin surface layers and not in the determination of bulk properties. The application areas for the A E S technique are those where surfaces play a decisive role. A number of such areas have been mentioned in this article, where A S E A has been applying AE S to solve different problems. Now that A S E A ' s Central Laboratories have procured an A E S instrument, their resources for handling surface problems have been greatly strengthened. The A E S instrument will continue to play a vital role also in the future in development work within many areas of technology.
Acknowledgement Fig. 14 Composition at different depths below the surface of a p area. Normally formed Pt silieide.
This article was originally published in the A S E A Journal 1-1983
Fig. 15 Composition at different depths below the surface of a berylliumcopper strip with normal tool wear.
References 1. Hillmer, T.: Auger Electron Spectrometry
i
Fig. 16 Composition at different depths below the surface of a berylliumcopper strip with high tool wear.
22
Part 1: Basic Principles and Equipment. Pract. Met. 19 (1982), p.431. 2. Hillmer, T.: Auger Electron Spectrometry Part 2: Practical Applications and Experience. Pract. Met. 19 (1982), p.509. 3. van Oostrom, A.: Some Aspects of Auger Microanalysis. Surface Science 89 (1979), p.615.
MATERIALS & DESIGN Vol. 7 No. 1 JANUARY/FEBRUARY 1986