Ion induced Auger electron emission is used to study the surfaces of Al, Mg, Cu - 10 at. % Al, Cu - 19.6 at. % Al, and Cu - 7.4 at. % Mg. A neon (Ne) ion beam whose energy is varied from 0.5 to 3 keV is directed at the surface. Excitation of the lighter Ne occurs by the promotion mechanism of Barat and Lichten in asymmetric collisions with Al or Mg atoms. Two principal Auger peaks are observed in the Ne spectrum: one at 22 eV and one at 25 eV. Strong matrix effects are observed in the alloys as a function of energy in which the population of the second peak is greatly enhanced relative to the first over the pure materials. For the pure material over this energy range this ratio is  1.0. For the alloys it can rise to the electronic structure of alloys and to other surface tools such as secondary ion mass spectroscopy

Ferrante, J.

Pepper, S. V.

English

NASA Technical Reports Server

NASA Technical Memorandum 83061 
NASA-TM-83061 19840002855 
Matrix Effects in Ion-Induced Auger 
Emission as Observed in Ne Collisions With 
Cu-Mg and Cu-AI Alloys 
John Ferrante and Stephen V. Pepper 
Lewis Research Center 
Cleveland, Ohio 
September 1983 
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ERRATA 
NASA Techn1cal Memorandum 83061 
MATRIX EFFECTS IN ION-INDUCED AUGER EMISSION AS OBSERVED 
IN Ne COLLISIONS WITH Cu-Mg AND Cu-Al ALLOYS 
John Ferrante and Stephen V. Pepper 
September 1983 
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MATRIX EFFECTS IN ION-INDUCED AUGER EMISSION AS OBSERVED 
IN Ne COLLISIONS WITH Cu-Mg AND Cu-Al ALLOYS 
John Ferrante and Stephen V. Pepper 
National Aeronautics and Space Administration 
Lewis Research Center 
Cleveland, Ohio 
SUMMARY 
_ Ion-induced Auger electron emission is used to study the surfaces of Al, 
Mg, Cu - 10 at. % Al, Cu - 19.6 at. % Al, and Cu - 7.4 at. % Mg. A neon (Ne) 
ion beam whose energy is varied from 0.5 to 3 keV is directed at the surface. 
Excitation of the lighter Ne occurs by the promotion mechanism of Barat and 
Lichten in asymmetric collisons with Al or Mg atoms. Two principal Auger peaks 
are observed in the Ne spectrum: one at 22 eV and one at 25 eVe Strong matrix 
effects are observed in the alloys as a function of energy in which the popu-
lation of the second peak is greatly enhanced relative to the first over the 
pure materials. For the pure material over this energy range this ratio is 
<1.0. For the alloys it can rise to 4.0. Thus, an interesting effect is ob-
served which may be of relevance to the electronic structure of alloys and to 
other surface tools such as secondary ion mass spectroscopy. 
INTRODUCTION 
The topic of Auger emission from solids resulting from ion bombardment 
(refs. 1 to 3) has received little interest among surface scientists. Its 
primary use has been in ion beam alignment and quantitative SIMS. Although it 
has been suggested that it may be useful in detecting rare gas implantation 
(ref. 2) or surface composition in certain alloys (refs. 4 to 6), there is a 
good reason for this lack of interest. The Auger spectrum from the surface is 
very atomic like. That is, the deexcitation process appears -in sputtered par-
ticles and is thus decoupled from the substrate. 
In recent papers (refs. 7 and 8) the authors reported a study of the bom-
bardment of solid Mg, Al, and Si surfaces by Ne ions with incident energies 
from 0.5 to 3 keV. In this study Auger electrons from the projectile as well 
as from the substrate were observed. This occurs since the promotion mechan-
ism of Barat and Lichten (ref. 9) favors excitation of the lighter atom. Thus 
an asymmetrical collision between Ne and the substrate atom produced the exci-
tation. The substrate excitations were produced by the symmetrical knock on 
collisions between substrate atoms. 
The authors observed two principal peaks in the Auger spectrum of the 
deexciting Ne at 21.9 and 25.1 eVe In pure materials the peak at 25 eV was 
substantially larger than that at 22 eVe The authors report in reference 8 
that in alloys of these materials the relative magnitude of these two peaks 
inverts and thus there is a matrix effect indicating that the substrate is 
affecting the ion-induced Auger emission process. Hiraki, et al. (ref. 5) and 
Iwani, et al. (ref. 6), also report an alloy effect in Si alloys. In their 
case there were also two Auger peaks of interest - one described as atomic 
like and the other as bulk like. They found an enhancement of the atomic like 
peak in the alloys presumably as a result of a change of species as nearest 
neighbors. 
In this paper we report the relative population of the 25 and 22 eV Ne 
peaks as a function of bombardment energy and angle of incidence for pure Mg 
and Al and Cu-Al and CU-Mg alloys. 
EXPERIMENTAL 
The experiments were performed in a standard ultrahigh vacuum system with 
a base pressure of 1x10-10 torr. The ion gun used was equipment commercially 
available for sputter cleaning surfaces and depth profiling with a nominal spot 
size of 2 mm. Both retarding field analyzers and cylindrical mirror analyzers 
were used for Auger analysis. 
The experiment was performed by turning off the ion pumps and backfilling 
the system to 5x1o-5 torr Ne. The surfaces were sputter cleaned until no 
oxygen or carbon were seen in the electron induced Auger spectrum. The elec-
tron gun was then turned off leaving the ion-induced AES spectrum. The angle 
of incidence (angle between the ion beam and the surface normal) was varied 
between 5° and 85°. At each angle the beam energy was varied from 0.5 to 3 
keV. The ion-induced Auger spectrum was taken at each setting. Auger spectra 
were taken with a 2-V p-p modulation voltage. The samples used were pure Mg, 
pure Al, Cu - 7.4 at. % Mg, Cu - 10 at.% Al and Cu - 10.6 at.% Al. Some 
typical spectrum results for pure Mg and Cu-Mg and Cu-Al alloys are shown in 
figure 1. As can readily be seen, the population of the second Ne state is 
greatly enhanced over the first in the alloys. It is interesting to examine 
the energy dependence at a fixed energy. The ratio is used since it is diffi-
cult to determine geometrical effects such as acceptance angles at the CMA as 
the angle is varied; also, the ion beam current is a function of energy. Hope-
fully these effects are cancelled by using the ratio. We will use the nomen-
clature R for the ratio where 
R _ Peak to peak height of 25 eV feature 
- Peak to peak height of 22 eV feature 
Actually, an indication of a material effect was previously reported by 
the authors in reference 8. We can see that there is a substantial variation 
in this ratio depending on material with RMg, RA1, and RSi (fig. 2). 
In figure 3 we show the energy dependence of R for the pure materials 
and the Cu-Mg and Cu-Al alloys. We see that R increases with energy for 
both pure materials and the alloys. However. with the alloys we have a very 
strong energy dependence; in fact. there is inversion of population of the Ne 
excited states which produces the final state. We also see that unlike the 
pure materials the energy dependence in the Cu-Mg alloy is very strong since 
there is only 7 at. % Mg in this alloy whereas we have 20 at. % Al in the 
other. The Cu-Mg alloys are above the solubility limit (ref. 10) and are 
probably a mixture of intermetallics and solid solutions. The Cu - 19.6 at.% 
Al is at the solubility limit and is also probably a mixture. The Cu - 10 
at. % Al is a single crystal solid solution. 
2 
Figure 4 shows the angular dependence for pure Al and Cu - 19.6 at. % Al 
for two incident energies (1000 and 2500 eV). These represent the trends ob-
served in all cases. There seems to be a strange dependence in that there 
seems to be an increase in R for both more normal and grazing incidence. 
The trends in the pure materials and the alloys are the' same. 
DISCUSSION 
The authors reported in references 7 and 8 on ion-induced Auger electron 
emission from Ne interactions with Mg, Al, and Si surfaces. In those papers a 
material dependence was reported for the population of the two principal Ne 
Auger peaks at 22 and 25 eV. In this paper those results are expanded, and the 
material dependence in alloys is investigated in more detail. The most impor-
tant result of this study is the strong energy dependence (fig. 3) and the 
population inversion of the two peaks as compared with collisions with the pure 
materials. This result indicates that work must be done in determining physi-
cal models for the collision and excitation process. Zampieri and Baragiola 
(ref. 11) have proposed an explanation for the excited states that produce the 
observed peaks based on the work of Anderson, Olsen, and Bisgaard (refs. 12 to 
14) which differs from that of the authors. They speculate that the transi-
tions ar!se ~rom excited states that involve two holes in the 2p level of Ne -
e.g., 2p 3s states rather than a 2s hole. This identification is probably 
correct because the bombardment energies are sufficiently low that the distance 
of closest approach needed to obtain a 2s hole is not achieved and adiabatic (ref. 9) effects dominate. This excitation scheme leads to 18 possible transi-
tions out of which only three are observed - two principle peaks and one much 
weaker at 27 eV. Zampieri and Baragiola argue that if the binding energy of 
the excited states is less than the work function that resonance ionization of 
the Ne occurs by tunneling into empty states in the conduction band. This 
would eliminate all but six of the states. They further argue that three of 
the remaining six that have binding energies greater than but close to the 
work function have their binding energies shifted to lower values by inter-
action of the Ne with the metal. Finally, they argue not unreasonably that the 
pop~lation of the tW8 states which they identify as giving the two Ne peaks 
[2p (3 p) 3s2 3p, 2p (10) 3s2 10] should be in the ratio of their multiplici-
ties, 9:5. Unfortunately, these results do not fit the previous and present 
observations of the authors. 
First, the arguments concerning eliminating certain transition based on 
the work function of Al must be reconsidered since the same peaks are observed 
for three materials (Mg, Al, and Si); e.g., the work function of Al is 4.2 eV 
whereas that of Mg is 3.7 eV (ref. 15). If we examine figure 2 we see that 
RMq « 1 whereas RSi • 1. Also, in the present work we show that there is an 
en~rgy dependence for R even with pure materials (fig. 3) R (3000 eV) > R 
(500 eV). Finally, we see that there is a strong energy dependence in the 
alloys leading to a inversion of population of the states producing the Auger 
peaks. The angular dependence of R (fig. 4) unfortunately provides no addi-
tional information since the trends are the same for both pure materials and 
alloys. 
Thus, we have a very interesting matrix effect in ion-induced Auger emis-
sion which requires detailed knowledge of the. collision. kinematics as well as 
3 
the electronic processes involved in creating the excited states. It is pos-
sible that understanding these processes could lead to a new diagnostic tool 
for certain alloys. 
Finally, we would like to comment on a controversy over the interpretation 
of the principal Ne peaks that has appeared in the literature (refs. 8, 10, 
and 16). The present authors assert that the origin of the Ne peaks is due to 
asymmetric collisions between the Ne and substrate atoms. The primary reasons 
for this assertion are no dose dependence with implanted Ne, the lack of ion-
induced peaks in other materials highly dosed with Ne, and the correct sensi-
tivity dependence according to the promotion mechanism for Mg, Al, and Si. 
Benezeth, et al. (ref. 16), state that the peaks are due to symmetric colli-
sions with implanted Ne. They argue that the low energy for the maximum in 
the collision cross section and a lack of a Doppler shift in the spectrum of 
the recoiling Ne as detected by them are evidence for symmetric collisions. 
Zampieri and Baragiola (ref. 11) have detected the Doppler shift in the recoil-
ing Ne spectra. There remains the low energy for the maximum in the production 
cross section. A low energy maximum in the cross section might be expected in 
asymmetric collisions which are probably a surface process, since at higher 
energies there will be greater penetration of the Ne and thus the escape of 
the emitted low energy electrons would be more difficult. However, if this is 
not a strong factor we have the population increase of the second feature 
(25 eV) indicating that as the incident energy is increased the population of 
the first peak may decrease whereas the second may continue to increase. It 
is evident that further studies are needed. 
CONCLUSION 
Strong matrix effects are observed in the spectrum of ion-induced Auger 
peaks for Ne in collision with certain materials. These matrix effects are 
manifested by population inversion with energy of the two Ne Auger peaks at 22 
and 25 eV in Cu-Mg and Cu-Al alloys. It is possible that this effect may 
provide information concerning the electronic structure of alloys. Further 
study is needed to investigate the implication of these observations. 
4 
REFERENCES 
1. J. F. Hennequin, J. Phys. (Paris) 29 (1968) 1053. 
2. J. F. Hennequin and P. Viaris de Lesengo, Surface Science, 42 (1974) 50. 
3. J. T. Grant et al J. Vac. Sci. Tech. 12 (1975) 481. 
4. P. Viaris de Lesegno and J. F. Hennequin, Surface Science, 80 (1979) 656. 
5. A. Hiraki, S. C. Kim, T. Imura, and I. Iwami, Jap. J. Appl. Phys. 18 (1979) 1767 --
6. M. Iwami, S. C. Kim, Y. Kataoka, T. Imura, A. Hiraki, and F. Fujimoto, 
Jap J. Appl. Phys. 19 (1980) 1627. 
7. J. Ferrante and S. V. Pepper, Surface Science 57 (1976) 420. 
8. S. V. Pepper and J. Ferrante, Surface Science 88 (1979) Ll. 
9. M. Barat and W. Lichten, Phys. Rev. A6 (1972) 2fl. 
10. M. Hansen, Constitution of Binary A1TOys, McGraw-Hill Book Co. Inc., New 
York, 1958. 
11. G. E. Zampieri and R. A. Baragiola, Surface Science 114 (1982) L15. 
12. J. O. Olsen and N. Andersen, J. Phys. 810 (1977) 101--.--
13. N. Andersen and J. O. Olsen, J. Phys. 810 (1977) L719. 
14. P. Bisgaard, J. O. Olsen, and N. Andersen, J. Phys. B13 (1980) 1403. 
15. N. D. Lang and A. R. Williams, Phys. Rev. Lett. 34, ~5) 531. 
16. C. Benezeth, N. Benezeth, L. Viel and M. Negre, Surface Science, 97 (1980) 171. --
5 
22eV 
l 
(a) (b) (c) 
(a) Pure Mg. 
(b) Cu - 7. 4 at. % Mg alloy. 
(c) Cu -19.6 at % AI alloy. 
Figure 1. - Typical ion-induced Ne Auger peak 
taken atVs • 3000 V and an angle of 60U 
with surface normal. 
w Qlw Z-c 
o 
Al~X1 
IYv ~ 
x10 
21. 9 eV 
Figure 2. - Auger spectra from Si, 
AI, and Mg bombarded by 3 keY 
Ne+. Emod = 0.75 eV p-p, angle 
of incidence = 600 from surface 
normal. (Spectrum from Si am-
plified by 10 relative to the spec-
tra from AI and Mg. ) 
4 
<> Mg t;,. 
o AI 
o Cu-19.6at.%AI 
t;,. Cu -7.4at.o/.Mg 
• Cu - 10 at. % AI 
t;,. . 
3 0 Cu -19.6at.%AI at lOOOeV :; incident energy (RFA) 
'" !:::J t;,. 0 Cu - 19.6 at. %AI at 2500 eV ;: incident energy (RFA) 
'" t:::,. Pure AI at 1000 eV Kl 
0 
A 
incident energy (RFAl 
~ CMA 
.... 
• <> Pure AI at 2500 eV :c 2 t;,. incident energy (RFAl c:n 2 '0; 
• CMA 
.c 
:; 
""" '" (1) 
'" !:::J Co 0 0 .s ;: 
""" i (1) 0 
'" 
'" 0 
(1) 
t:::,. 0 ~ o 0 0-
t;,. 0 g 00 • E 0 t:::,. 0 0 :c 
• 
.~ 
(1) 0 .c 0 
""" '" 
o 0 t $ • 0 0 0 2l.. 0 
<> <> .s ; ~ <> <> """ ~ ~ ~ ~ I I '" (1) 0- f 0 2 3 Ion beam energy. keY 0 20 40 60 80 
Figure 3. - Ratio of 25 to 22 eV Ne peak to peak heights Figure 4. - Neon peak height ratio 
as function of incident ion energy for ion beam at (25 eV 122 eV) as function of 300 with the surface normal. angle at incidence (angle between 
ion beam and surface normal). 
12. Government Accession No. 1. Report No. 
NASA n1-~" cg-~O<O I 
4. Title and Subtitle 
Matrix Effects in Ion-Induced Auger Emission as 
Observed in Ne Collisions With Cu-Mg and Cu-Al Alloys 
7. Author(s) 
John Ferrante and Stephen V. Pepper 
9. Performing Organization Name and Address 
National Aeronautics and Space Administration 
Lewis Research Center 
Cleveland, Ohio 44135 
12. Sponsoring Agency Name and Address 
National Aeronautics and Space Administration 
Washington, D.C. 20546 
15. Supplementary Notes 
16. Abstract 
3. Recipient's Catalog No. 
5. Report Date 
September· 1983 
B."Performlng Organization Code 
505-53-1B 
8. Performing Organization Report No. 
E-1532 
10. Work Unit No. 
11. Contract or Grant No. 
13. Type of Report and Period Covered 
Technical Memorandum 
14. Sponsoring Agency Code 
Ion-induced Auger electron emission is used to study the surfaces of Al, Mg, 
Cu - 10 at. % Al, Cu - 19.6 at. % Al, and Cu - 7.4 at. % Mg. A neon (Ne) ion 
beam whose energy is varied from 0.5 to 3 keV is directed at the surface. 
Excitation of the lighter Ne occurs by the promotion mechanism of Barat and 
Lichten in asymmetric collisions with Al or Mg atoms. Two principal Auger peaks 
are observed in the Ne spectrum: one at 22 eV and one at 25 eV. Strong matrix 
effects are observed in the alloys as a function of energy in which the population 
of the second peak is greatly enhanced relative to the first over the pure 
materials. For the pure material over this energy range this ratio is <1.0. 
For the alloys it can rise to 4.0. Thus, an interesting effect is observed which 
may be of relevance to the electro-ic structure of alloys and to other surface 
tools such as secondary ion mass spectroscopy. 
17. Key Words (Suggested by Author(s» 
Auger 
Autoionization 
Ion-bombardment 
19. Security Classlf. (of this report) 
Uncl assi fi ed 
18. Distribution Statement 
Unclassified - unlimited 
STAR Category 72 
20. Security Classl!. (of this page) 
Uncl assi fi ed 
" 21. No. of pages 
*For sale by the National Technical Information Service, Springfield, Virginia 22161 
22. Price· 
End of Document 


Matrix effects in ion-induced emission as observed in Ne collisions with Cu-Mg and Cu-Al alloys

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