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Angular distributions of Au and Cu atoms sputtered from Au-Cu alloys by keV Ar+ ion bombardment
Surface Science 127 (1983) Ll79-Ll85 North-Holland Publishing Company
SURFACE
SCIENCE
L179
LETTERS
ANGULAR DISTRIBUTIONS OF Au AND Cu ATOMS SPUITERED FROM Au-Cu ALLOYS BY keV Ar + ION BOMBARDMENT Hee Jae RANG, Dep@tment Rec&ed
Y. MATSUDA
and R. SHIMIZU
of Applied Physics, Osaka University, 21 September
Suita - shi, Osaka 565, Japan
1982; accepted for publication
19 January 1983
Angular distributions of Au and Cu atoms sputtered from Au-Cu alloys under 3 keV AR+ ion bombardment were measured to understand the preferential sputtering. The surface composition of sdutter-deposited Au-Cu films on substrates mounted at different ejection angles was analyzed by Auger electron spectroscopy and electron probe. microanalysis. Although the result indicated that the proportion of sputtered Cu atoms to the Au atoms in the Au-Cu alloy depends on the ejection angle, marked enhancement of the lighter component in the direction normal to the surface has not been observed in spite of the larger mass ratio of the constituent atoms of the Au-Cu alloy.
Angular distribution of sputtered atoms from a solid surface under ion bombardment provides useful information on sputtering phenomena, particularly for understanding preferential sputtering. Wehner and his coworkers [ 1,2] have extensively investigated the angular distribution of component atoms in Fe-Ni alloys for Hg+ or Ar+ ion beams and pointed out that the Ni in the angular distribution becomes enriched normal to the target surface. They have also suggested an enhancement in the ejection of lighter component in the direction normal to the surface for isotope atoms in pure metals and they explained the results by binary collisions between constituent atoms. These works have drawn the attention to the angular distribution of the sputtered atoms being one of a clue for understanding the preferential sputtering. In the view point of the preferential sputtering study, Au-Cu alloy is andther interesting sample, as well as Cu-Ni alloy, because the Au-Cu alloy is the material with the longest history in the study of preferential sputtering since Gilliam’s [3] observation through electron diffraction in 1959 of altered layers in Au-Cu alloys caused by ion bombardment. He has pointed out that this is due to the difference between the sputtering yields of constituent Au and Cu atoms. On the other hand, several works [4-61 have recently reported that the preferential sputtering does not take place in Au-Cu alloys by Ar+ ion bombardment so far as AES is employed, whereas ISS measurements have 0039-6028/83/0000-0000/$03.00
0 1983 North-Holland
LIXO
H.J. Kang et al. / Angular distributions of Au and Cu atoms
revealed, as described in a previous paper [7], that ion bombardment caused drastic changes in the composition of the outermost atom layer of Au-Cu alloys resulting in a Au-rich outermost atom layer and a depletion layer of Au atoms beneath the outermost atom layer. Concerning Au and Cu monoatomic targets, Hucks et al. [8] measured the angular distribution of sputtered atoms from Cu and Au metals with 30 keV Ar+ ions, leading to the conclusion that the angular distribution deviated from the cosine law, especially in the incident direction of the projectile ions and perpendicular to it. Though the above experiments, including the present one, were done for amorphous or polycrystalline targets, the dynamic calculation for single crystalline Au-Cu alloy may be instructive. Applying the dynamic calculation, Garrison [9] recently investigated the preferential sputtering of binary compounds Cu-Au/Cu and Cu-Au/Au, showing that the atoms in the bottom three layers of the crystallite have the mass of copper or gold while the atomic mass in the first layer is composed of atoms with the masses of copper and gold. This work suggests that the light component tends to eject more in
A+ (a) sputtered
surface
AU-MNN
‘CU-LhlM (b)Sputter
’
I
600
900
-dcposikd
layer
1 ”I# I QOO I900 EneqyW
I
2000
I
1
2~3
2200
Fig. 1. Auger spectra of Au and Cu from a sputtered Au-Cu(43 at%) alloy sample and from a sputter-deposited layer at an ejection angle of 37.5” (from surface normal).
H.J. Kang et al. / Angular distributions
T
of Au and Cu atoms
Ll81
(EPMA)
b
a I
I
-90D
-60° +0
I
-30°
I
O” NORMAL
1
300
1
60’ e+
90”
Fig. 2. Angular distribution of the ratio of the intensity of the Au signal to that of the Cu signal. Data points are normalized with respect to the Au-to-Cu signal ratio for the Au-Cu alloy target. (a) Using the characteristic X-ray Cu-L and Au-M lines, and (b) using the Auger intensities of the Au-MNN and Cu-LMM signals.
the direction normal to the surface for 600 eV Ar+ ion. bombardment. Thus, the angular distribution of sputtered atoms from an alloy target provides useful information as well as the surface composition for understanding the preferential isputtering. Measurements of angular distributions of sputtered atoms for Au-Cu alloys, however, have yet to be done. In the present paper, therefore, we attempted to measure the angular distributions of Au and Cu atoms sputtered from Au-Cu alloys by a composition analysis of the sputter-deposited films on substrates mounted at different ejection angles. In the present investigation, we used Au-Cu (43 at%) alloys which were specially made at Shin-Nippon Steel Co. as a standard sample for electron probe microanalysis [lo]. The surface was polished with alumina very slowly pouring water until no scratches were visible. The surface compositions were examined by ion scattering spectroscopy and scanning Auger electron spectroscopy after Ar+ ion sputtering. Twelve substrates of either Ta or Al plates were set on a hemisphere of which the radius was 20 mm and the sample was placed at the center. These Ta substrates of 5 X 5 X 0.3 mm were attached to a hemispherical belt of stainless steel (5 mm wide and 30 pm thick) by spot-weldinjj ‘as described elsewhere [ 131. The ion beam impinged on the target surface at an angle of incidence of 0“ or. 45’ (measured from the surface normal), respectively. The sputter-deposition was done with a SIMS-SCANIIR apparatus described elsewhere [ 111,
Ll82
H.J. Kang et al. / Angular distributions
of Au and Cu atoms
00 3keV Ar*+Au-Cu(l3at%) Normal
s(8)
(orb.
incidence
unils)
Fig. 3. Angular distributions of Au and Cu atoms sputtered bombardment at normal incidence.
from Au-Cu
alloys
by 3 keV Ar+ ion
which was evacuated to - 10e9 Torr in vacuum. Sputtering was done with a 3 keV Ar+ ion beam of current intensity - 0.7 pA; the beam spot size is - 1.5 mm in diameter. This ion beam was collimated with the help of an electrostatic lens system. Sputter-deposited Au-Cu films on Ta substrates were investigated with a scanning Auger electron microprobe, JAMP-3. After the Auger analysis, the composition analysis of the same samples were done by both the electron probe microanalysis (EPMA) and fluorescence X-ray analysis for further confirmation. Fig. 1 shows AES spectra for Cu-LMM and Au-MNN Auger transitions, which were obtained from the sputtered Au-Cu alloy sample surface and sputter-deposited film at an ejection angle of 37.5’. We plotted the angular distribution by taking the ratio of the Auger signal intensity of the Au - MNN signal to that of the Cu-LMM signal normalized with respect to the Au-to-Cu signal ratio for the Au-Cu alloy target. Since sputtering of Au-Cu alloys does not cause any changes in surface composition so far as Auger analysis is employed, the ratio equal to unity suggests that the sputtered Au and Cu atoms are of the same composition as that of the bulk sample. The electron probe microanalysis was also done in the same manner by using the characteristic X-ray Cu-L and Au-M lines and the results are shown in fig. 2. The figure indicates that both the results show the same tendencies and agree with each other fairly well within experimental accuracy. The results show a slight Cu enrichment for larger 8, suggesting that the lighter atoms are not preferentially ejected normal to the target surface, against all expectations. Olson et al. [2] show that the Fe is enriched in the direction normal to the surface for an Fe-Ni alloy at 100 eV, whereas the Ni has become
H.J. Kang et al. / Angular distributions of Au and Cu atoms
Ll83
3KeV Ar~Au-C1.1(43oPl.)
S(8) (arb. units)
Fii. 4. Angular distributions of Au and Cu atoms sputtered from Au-Cu alloys by 3 keV Ar+ ion bombardment at an angle of in&dence of 45”.
enriched normal to the target surface at 1000 eV. They obtained a similar rest& for the Au-Ag alloy. Hence we may expect quite another angular distribution for low energy ion sputtering, but our apparatus did not allow experiments in such a low energy region to be made. The direct plottings of angular distributions of sputtered atoms for normal and tilting incidences are shown in figs. 3 and 4 which were obtained by EPMA. The solid line represents the angular distribution of the sputtered Cu atoms and the dotted the sputtered Au atoms, respectively. The results obtained by X-ray fluorescence analysis were in good agreement with those in fig. 3. Even though the mass ratio of the components is - 3, we do not find such a marked difference between the distribution of Cu and Au atoms. Pig. 4 shows the results obtained for an angle of incidence of 45”. The distribution in this case was normalized at the intensity for 8 = 0”. The angular distribution is not skewed toward positive B as often observed in pure metals [14]. Similar results were obtained by Hucks et al. [8] for pure Cu and Au targets with 30 keV Ar+ ions. They explained it by the surface topograph caused by ion bombardment. The observation of the surface of the Au-Cu alloy under scanning electron microscopy with JAMP-3, however, has revealed that only a very few cones were formed in a sputtered area under 3 keV Ar+ ion bombardment as seen in fig. 5a, while the sputtered surfaces of pure Au and Cu targets with 3.7 keV Ar+ ions clearly show formation of cones as reported by one of the authors [12]. In contrast to fig. 5a, the sputtering with higher energy Ar+ ions of 10 keV has, as seen in fig. 5b, caused such cones as those observed for pure Au and Cu targets under 3.7 [12] and 30 keV [S] Ar+ ion bombardments, although a slight difference is observed in the cone angles bet+een 3.7 and 30 keV Ar+ ions. consequently, the present results indicate that the proportion of sputtered
LlX4
H.J. Kang et al. / Angular distributions
of Au and Cu atoms
Fig. 5. SEM image of bombarded area of Au-Cu alloy under the conditi’ ons: (a) 3 keV Ar’ ion bombardment with beam current of 35 PA/cm’ at angle of incidence of 4 5’; (b) 10 keV Ar’ ion bombardment with beam current of 1.5 mA/cm’ at normal incidence.
Cu atoms to the Au atoms in Au-Cu alloy depends on the ejection angle. But we have not observed any marked increase of lighter elemen It atoms (Cu ate bms) sputtered in the direction normal to the surface even thougl h the mass ratic IS of
H.J. Kang et al. / Angular distributions ofAu and Cu atom
L185
the constituent atoms are large. Furthermore, the angular distributions of sputtered Au and Cu atoms are quite similar to those obtained for pure Au and Cu targets with 30 keV Ar+ ion by Hucks et al., even though very few cones are formed at the sputtered surface. The authors are very grateful to Mr. K. Obori of HORIBA, Ltd. for his technical assistance in performing electron probe microanalysis with HORIBA-EMAX and quantitative correction by ZAF method for co.mposition analysis.
Refkrences [l] [2] [3] [4] [5] [6] [7] [8] [9] [IO] [l l] [ 121 [ 131 [14]
R.R. Olson and G.K. Wehner, J. Vacuum Sci. Technol. 14 (1977) 319. R.R. Olson, M.E. Kingand and G.K. Wehner, J. Appl. Phys. 50 (1979) 3677. ‘M. Gilliam, J. Phys. Chem. Solids 11 (1959) 55. W. Fiber, G. Betz and P. Braun, Nucl. Instr. Methods 132 (1976) 351. H.G. Tompkins, J. Vacuum Sci. Technol. 16 (1976) 778. S. Ichimura and R. Shimizu, Surface Sci. 115 (1982) 259. H.J. Kang, R. Shimizu and T. Okutani, Surface Sci. 116 (1982) L173. P. Hucks, G. Stocklin, E. Vietzke and K. Vogelbrueh, J. Nucl. Mater 76/77 (1978) 136. B.J. Garrison, Surface Sci. 114 (1982) 23. L. Aoki and S. Sawatani, Technol. Rept. Steel Res. No. 254 (1966) 1, 6625. R. Shimizu and T. Okutani, Surface Sci. 69 (1977) 349. ‘R. Shimuzu, Japan. J. Appl. Phys. 13 (1974) 228. T. Okutani, M. Shikata, S. Ichimura and R. Shim&, J. Appl. Phys.‘ 51 (1980) 2884. 0. Betz, R. Dobrozemsky and F.P. Viehbock, Ned. Tijdschr. Vacuumtech. 8 (1970) 203.
SURFACE
SCIENCE
L179
LETTERS
ANGULAR DISTRIBUTIONS OF Au AND Cu ATOMS SPUITERED FROM Au-Cu ALLOYS BY keV Ar + ION BOMBARDMENT Hee Jae RANG, Dep@tment Rec&ed
Y. MATSUDA
and R. SHIMIZU
of Applied Physics, Osaka University, 21 September
Suita - shi, Osaka 565, Japan
1982; accepted for publication
19 January 1983
Angular distributions of Au and Cu atoms sputtered from Au-Cu alloys under 3 keV AR+ ion bombardment were measured to understand the preferential sputtering. The surface composition of sdutter-deposited Au-Cu films on substrates mounted at different ejection angles was analyzed by Auger electron spectroscopy and electron probe. microanalysis. Although the result indicated that the proportion of sputtered Cu atoms to the Au atoms in the Au-Cu alloy depends on the ejection angle, marked enhancement of the lighter component in the direction normal to the surface has not been observed in spite of the larger mass ratio of the constituent atoms of the Au-Cu alloy.
Angular distribution of sputtered atoms from a solid surface under ion bombardment provides useful information on sputtering phenomena, particularly for understanding preferential sputtering. Wehner and his coworkers [ 1,2] have extensively investigated the angular distribution of component atoms in Fe-Ni alloys for Hg+ or Ar+ ion beams and pointed out that the Ni in the angular distribution becomes enriched normal to the target surface. They have also suggested an enhancement in the ejection of lighter component in the direction normal to the surface for isotope atoms in pure metals and they explained the results by binary collisions between constituent atoms. These works have drawn the attention to the angular distribution of the sputtered atoms being one of a clue for understanding the preferential sputtering. In the view point of the preferential sputtering study, Au-Cu alloy is andther interesting sample, as well as Cu-Ni alloy, because the Au-Cu alloy is the material with the longest history in the study of preferential sputtering since Gilliam’s [3] observation through electron diffraction in 1959 of altered layers in Au-Cu alloys caused by ion bombardment. He has pointed out that this is due to the difference between the sputtering yields of constituent Au and Cu atoms. On the other hand, several works [4-61 have recently reported that the preferential sputtering does not take place in Au-Cu alloys by Ar+ ion bombardment so far as AES is employed, whereas ISS measurements have 0039-6028/83/0000-0000/$03.00
0 1983 North-Holland
LIXO
H.J. Kang et al. / Angular distributions of Au and Cu atoms
revealed, as described in a previous paper [7], that ion bombardment caused drastic changes in the composition of the outermost atom layer of Au-Cu alloys resulting in a Au-rich outermost atom layer and a depletion layer of Au atoms beneath the outermost atom layer. Concerning Au and Cu monoatomic targets, Hucks et al. [8] measured the angular distribution of sputtered atoms from Cu and Au metals with 30 keV Ar+ ions, leading to the conclusion that the angular distribution deviated from the cosine law, especially in the incident direction of the projectile ions and perpendicular to it. Though the above experiments, including the present one, were done for amorphous or polycrystalline targets, the dynamic calculation for single crystalline Au-Cu alloy may be instructive. Applying the dynamic calculation, Garrison [9] recently investigated the preferential sputtering of binary compounds Cu-Au/Cu and Cu-Au/Au, showing that the atoms in the bottom three layers of the crystallite have the mass of copper or gold while the atomic mass in the first layer is composed of atoms with the masses of copper and gold. This work suggests that the light component tends to eject more in
A+ (a) sputtered
surface
AU-MNN
‘CU-LhlM (b)Sputter
’
I
600
900
-dcposikd
layer
1 ”I# I QOO I900 EneqyW
I
2000
I
1
2~3
2200
Fig. 1. Auger spectra of Au and Cu from a sputtered Au-Cu(43 at%) alloy sample and from a sputter-deposited layer at an ejection angle of 37.5” (from surface normal).
H.J. Kang et al. / Angular distributions
T
of Au and Cu atoms
Ll81
(EPMA)
b
a I
I
-90D
-60° +0
I
-30°
I
O” NORMAL
1
300
1
60’ e+
90”
Fig. 2. Angular distribution of the ratio of the intensity of the Au signal to that of the Cu signal. Data points are normalized with respect to the Au-to-Cu signal ratio for the Au-Cu alloy target. (a) Using the characteristic X-ray Cu-L and Au-M lines, and (b) using the Auger intensities of the Au-MNN and Cu-LMM signals.
the direction normal to the surface for 600 eV Ar+ ion. bombardment. Thus, the angular distribution of sputtered atoms from an alloy target provides useful information as well as the surface composition for understanding the preferential isputtering. Measurements of angular distributions of sputtered atoms for Au-Cu alloys, however, have yet to be done. In the present paper, therefore, we attempted to measure the angular distributions of Au and Cu atoms sputtered from Au-Cu alloys by a composition analysis of the sputter-deposited films on substrates mounted at different ejection angles. In the present investigation, we used Au-Cu (43 at%) alloys which were specially made at Shin-Nippon Steel Co. as a standard sample for electron probe microanalysis [lo]. The surface was polished with alumina very slowly pouring water until no scratches were visible. The surface compositions were examined by ion scattering spectroscopy and scanning Auger electron spectroscopy after Ar+ ion sputtering. Twelve substrates of either Ta or Al plates were set on a hemisphere of which the radius was 20 mm and the sample was placed at the center. These Ta substrates of 5 X 5 X 0.3 mm were attached to a hemispherical belt of stainless steel (5 mm wide and 30 pm thick) by spot-weldinjj ‘as described elsewhere [ 131. The ion beam impinged on the target surface at an angle of incidence of 0“ or. 45’ (measured from the surface normal), respectively. The sputter-deposition was done with a SIMS-SCANIIR apparatus described elsewhere [ 111,
Ll82
H.J. Kang et al. / Angular distributions
of Au and Cu atoms
00 3keV Ar*+Au-Cu(l3at%) Normal
s(8)
(orb.
incidence
unils)
Fig. 3. Angular distributions of Au and Cu atoms sputtered bombardment at normal incidence.
from Au-Cu
alloys
by 3 keV Ar+ ion
which was evacuated to - 10e9 Torr in vacuum. Sputtering was done with a 3 keV Ar+ ion beam of current intensity - 0.7 pA; the beam spot size is - 1.5 mm in diameter. This ion beam was collimated with the help of an electrostatic lens system. Sputter-deposited Au-Cu films on Ta substrates were investigated with a scanning Auger electron microprobe, JAMP-3. After the Auger analysis, the composition analysis of the same samples were done by both the electron probe microanalysis (EPMA) and fluorescence X-ray analysis for further confirmation. Fig. 1 shows AES spectra for Cu-LMM and Au-MNN Auger transitions, which were obtained from the sputtered Au-Cu alloy sample surface and sputter-deposited film at an ejection angle of 37.5’. We plotted the angular distribution by taking the ratio of the Auger signal intensity of the Au - MNN signal to that of the Cu-LMM signal normalized with respect to the Au-to-Cu signal ratio for the Au-Cu alloy target. Since sputtering of Au-Cu alloys does not cause any changes in surface composition so far as Auger analysis is employed, the ratio equal to unity suggests that the sputtered Au and Cu atoms are of the same composition as that of the bulk sample. The electron probe microanalysis was also done in the same manner by using the characteristic X-ray Cu-L and Au-M lines and the results are shown in fig. 2. The figure indicates that both the results show the same tendencies and agree with each other fairly well within experimental accuracy. The results show a slight Cu enrichment for larger 8, suggesting that the lighter atoms are not preferentially ejected normal to the target surface, against all expectations. Olson et al. [2] show that the Fe is enriched in the direction normal to the surface for an Fe-Ni alloy at 100 eV, whereas the Ni has become
H.J. Kang et al. / Angular distributions of Au and Cu atoms
Ll83
3KeV Ar~Au-C1.1(43oPl.)
S(8) (arb. units)
Fii. 4. Angular distributions of Au and Cu atoms sputtered from Au-Cu alloys by 3 keV Ar+ ion bombardment at an angle of in&dence of 45”.
enriched normal to the target surface at 1000 eV. They obtained a similar rest& for the Au-Ag alloy. Hence we may expect quite another angular distribution for low energy ion sputtering, but our apparatus did not allow experiments in such a low energy region to be made. The direct plottings of angular distributions of sputtered atoms for normal and tilting incidences are shown in figs. 3 and 4 which were obtained by EPMA. The solid line represents the angular distribution of the sputtered Cu atoms and the dotted the sputtered Au atoms, respectively. The results obtained by X-ray fluorescence analysis were in good agreement with those in fig. 3. Even though the mass ratio of the components is - 3, we do not find such a marked difference between the distribution of Cu and Au atoms. Pig. 4 shows the results obtained for an angle of incidence of 45”. The distribution in this case was normalized at the intensity for 8 = 0”. The angular distribution is not skewed toward positive B as often observed in pure metals [14]. Similar results were obtained by Hucks et al. [8] for pure Cu and Au targets with 30 keV Ar+ ions. They explained it by the surface topograph caused by ion bombardment. The observation of the surface of the Au-Cu alloy under scanning electron microscopy with JAMP-3, however, has revealed that only a very few cones were formed in a sputtered area under 3 keV Ar+ ion bombardment as seen in fig. 5a, while the sputtered surfaces of pure Au and Cu targets with 3.7 keV Ar+ ions clearly show formation of cones as reported by one of the authors [12]. In contrast to fig. 5a, the sputtering with higher energy Ar+ ions of 10 keV has, as seen in fig. 5b, caused such cones as those observed for pure Au and Cu targets under 3.7 [12] and 30 keV [S] Ar+ ion bombardments, although a slight difference is observed in the cone angles bet+een 3.7 and 30 keV Ar+ ions. consequently, the present results indicate that the proportion of sputtered
LlX4
H.J. Kang et al. / Angular distributions
of Au and Cu atoms
Fig. 5. SEM image of bombarded area of Au-Cu alloy under the conditi’ ons: (a) 3 keV Ar’ ion bombardment with beam current of 35 PA/cm’ at angle of incidence of 4 5’; (b) 10 keV Ar’ ion bombardment with beam current of 1.5 mA/cm’ at normal incidence.
Cu atoms to the Au atoms in Au-Cu alloy depends on the ejection angle. But we have not observed any marked increase of lighter elemen It atoms (Cu ate bms) sputtered in the direction normal to the surface even thougl h the mass ratic IS of
H.J. Kang et al. / Angular distributions ofAu and Cu atom
L185
the constituent atoms are large. Furthermore, the angular distributions of sputtered Au and Cu atoms are quite similar to those obtained for pure Au and Cu targets with 30 keV Ar+ ion by Hucks et al., even though very few cones are formed at the sputtered surface. The authors are very grateful to Mr. K. Obori of HORIBA, Ltd. for his technical assistance in performing electron probe microanalysis with HORIBA-EMAX and quantitative correction by ZAF method for co.mposition analysis.
Refkrences [l] [2] [3] [4] [5] [6] [7] [8] [9] [IO] [l l] [ 121 [ 131 [14]
R.R. Olson and G.K. Wehner, J. Vacuum Sci. Technol. 14 (1977) 319. R.R. Olson, M.E. Kingand and G.K. Wehner, J. Appl. Phys. 50 (1979) 3677. ‘M. Gilliam, J. Phys. Chem. Solids 11 (1959) 55. W. Fiber, G. Betz and P. Braun, Nucl. Instr. Methods 132 (1976) 351. H.G. Tompkins, J. Vacuum Sci. Technol. 16 (1976) 778. S. Ichimura and R. Shimizu, Surface Sci. 115 (1982) 259. H.J. Kang, R. Shimizu and T. Okutani, Surface Sci. 116 (1982) L173. P. Hucks, G. Stocklin, E. Vietzke and K. Vogelbrueh, J. Nucl. Mater 76/77 (1978) 136. B.J. Garrison, Surface Sci. 114 (1982) 23. L. Aoki and S. Sawatani, Technol. Rept. Steel Res. No. 254 (1966) 1, 6625. R. Shimizu and T. Okutani, Surface Sci. 69 (1977) 349. ‘R. Shimuzu, Japan. J. Appl. Phys. 13 (1974) 228. T. Okutani, M. Shikata, S. Ichimura and R. Shim&, J. Appl. Phys.‘ 51 (1980) 2884. 0. Betz, R. Dobrozemsky and F.P. Viehbock, Ned. Tijdschr. Vacuumtech. 8 (1970) 203.