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Blistering and trapping characteristics of aluminum during Ar ion implantation and post-irradiation annealing
Journal
76
of Nuclear
Materials 168 (1989) 76-82 North-Holland. Amsterdam
BLISTERING AND TRAPPING CHARACTERISTICS OF ALUMINUM DURING Ar ION IMPLANTATION AND POST-IRRADIATION ANNEALING N.T. MY, F. PASZTI,
A. MANUABA,
G. MEZEY
and E. K6TAI
Central Research Institute for Physics, P. 0. Box 49, H-1525 Budapest,
Hungary
I.A. GOHAR Physics Department, Received
22 February
Faculty of Science, Mansoura 1989; accepted
20 March
University, Egypt 1989
High dose Ar implantation of pure aluminum samples with different energies resulted in blisters on the implanted area with mean diameters of d, = 9.5R,. At RT implantation the critical doses for the onset of blistering correspond to 23 at’% Ar peak concentration, independent of the applied bombarding energies (300-700 keV). During vacuum isochronic annealing of pre-implanted samples, it is found that the critical peak concentration of He decreases with increasing sample temperature, according to the weakening of the host material yield strength. The Rutherford back scattering (RBS) analyses performed during annealing show that the Ar release initiates at the blister formation and increases drastically (50% of implanted Ar) at the blister ruptures around 570 K, where channel network of interbubble cracks has interconnected laterally the cavities under all blisters including the unopened ones. The Ar escapes completely at temperatures higher than 750 K.
1. Introduction The ions of gaseous elements (especially H and He) that will be implanted into the first wall of future thermonuclear reactors will cause serious problems. This area has been widely investigated in model experiments at different laboratories in the past 15 years, and it was proved that if the gas is unable to escape, it will coalesce and precipitate to form gas filled bubbles in the host material. These bubbles may grow by capturing additional gas atoms and vacancies or by punching out interstitial dislocation-loops, and if the temperature is low and the radiation damage is not too serious they are overpressurized [l]. The pressure inside these bubbles may lead to interbubble cracking [2], or the bubbles of equilibrium pressure will coalesce to form a crack parallel to the sample surface. The layer separated from the substrate by this crack may contain a huge compressive lateral stress. This stress and/or the pressure of the gas accumulated in the cavity formed by the crack lifts the covering layer up, deforms it plastically and may even tear it off from the bulk [3-51. If this process takes place on well defined usually circular spots, it is called blistering, otherwise exfoliation. If the detached layer falls off, the process is referred to as flaking [6].
0022-3115/89/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
The present work is to study the effect of another noble gas, i.e. Ar, in high dose implantations of different energy into aluminum. We hope that implantation of heavier noble gas ions can simulate the fusion reactor environment in a more complex way: the lattice damage by fast neutrons, the sputtering caused by the deuterium fuel and other impurities, as well as the bubble formation and surface deformations caused by high energy He fusion products may be modelled simultaneously. By irradiations with different energies of Ar at RT, and post-irradiation annealing, one may expect useful information to be extracted from the variation of the critical dose for surface deformation with temperature and physical quantities characterizing the behaviour of Ar trapping/re-emission in Al.
2. Experimental Polycrystalline Al samples of high purity (99.999%) were first mechanically polished and rinsed in an ultrasonic bath of pure ethanol and then implanted with 300, 400 and 700 keV Ar ion beams to different doses (table 1). The implantations were performed at RT using a 5
B.V.
N. T. My et al. / Blistering and trapping characteristics Table 1 Experimental
conditions
of Ar irradiation
and the post-irradiation
annealing
treatment
17
of Al
together
with the critical
parameters
Critical temperature
Critical concentration
(R)
(at%)
425k40 390 * 40 300 52Ok40 470 f 40 _ 390 + 40 300 300
18 20 22+2 11 15 18 20 21+_2 24+4
for the
onset of blistering E (keV
Implanted dose (10” ions cmm2)
Critical dose (10” ions cmm2)
Surface modification
Post-irradiation treatment a)
(RT) 300
400
700 400 + 300
no no blistering no no no no blistering blistering blistering
1.75 2.0 2.25 1.25 1.75 2.25 2.50 2.15 14.0 2.5 + 2.25
‘) ann, post-irradiation
annealing;
opt, optical
ann + opt ann + opt _
1.9+0.2 _ _ _ _ 2.6 f 0.2
ann ann ann ann ann
4.8 f 0.7
_
microscope
investigation;
MeV Van de Graaff accelerator (VDG) and a 600 keV heavy ion cascade implanter (HIC). During implantation the vacuum in the target chamber connected to VDG and HIC were maintained at 7 X lop5 Pa and 2 x 10e4 Pa, while the Ar fluxes were kept at 3 X 1013 and 5 x lOi ions cm-* s-i respectively. In the VDG the beam spot of 1.2 x 1.5 mm* was cut out from the wide homogeneous beam. The 3 mm beam size of the HIC implanter was swept over a spot of 15 X 15 mm2. The double implantation was performed in HIC by irradiating the sample first with 400 keV and sequentially with 300 keV ions. After implantation the bombarded areas of all samples were examined in a JEOL-ISM-35 type scanning electron microscope. The 300 keV and 400 keV implanted samples (the blistered as well as the non-blistered ones) were afterwards annealed from 300 to 850 K in the VDG target chamber by heating the sample holder with a 100 W projector lamp. The temperature was measured by means of a Ni-CrNi thermocouple fixed to the sample holder, and for calibration the chamber temperature and the
+ + + + +
opt opt RBS opt
RBS
RBS, Rutherford
backscatteting
analysis.
melting point of pure Al were used. In two cases (see table 1) isochronic annealing was performed by raising the temperature in - 75 K steps of 600 s length and the implanted Ar profile at the end of each step was measured in situ by RBS analysis using a 3500 keV 4He+ beam. The backscattered helium was detected by a surface barrier detector (ORTEC) of 15 keV energy resolution positioned at 165 O. In five cases of non-blistered samples (see table l), the annealing was performed with the aim of determining the critical temperature at the appearance of blistering. To determine the critical dose for the onset of blistering two different methods were used: for samples implanted in the HIC (300, 400 and 300 + 400 keV implantation) the critical dose was considered as the mean value of the dose where blisters had been observed first and the dose immediately before. For the sample implanted in the VDG (700 keV implantation) it was determined by observing the implanted spot continuously through the chamber window using a telescope of 10 X magnification.
Table 2 The calculated values of the critical concentration for blistering (C,,) induced on Al by implantation with different Ar energies (E) at room temperature. For the calculation we use the broadened depth distribution (AX,,) estimated from the measured critical dose (@cc) and the sputtering yield (S). Also included are the values of depth profile parameters (Rr, AR,) as calculated by the Brice code as well as the values of AX and C extracted from RBS measurements (AX,,,, CexP) E
4 (pm)
AR,
(kev) 300
0.285
0.035
400 700
0.390 0.670
0.045 0.071
MO
s (atoms/ion)
A Xth (pm)
1.9
1.3
2.6 4.8
1.1 0.8
+c (10” ions cm
-2
)
A Xexp
c,h
C=v
(rm)
(at%)
(at%)
0.12
_
20
_
0.16 0.25
0.25 _
21 24
18 _
78
N. T. My et al. / Blisrering and trapping characteristics
3. Results and discussion The critical doses for the onset of blistering at RT for different implantation energies are shown in table 1. To verify the assumption that the critical dose is only the manifestation of the constant concentration at which the interbubble fracture takes place, preceding the elevation of detaching layers to blistering or exfoliation, it was transformed into the critical peak concentration of the distribution. For this purpose the implanted depth distributions as calculated by the Brice code [7] together with their broadening due to sputtering as estimated from the measured critical doses and the sputtering yields [S] were used (see table 2.). As can be seen in fig. 1, the calculated critical peak concentrations are constant within error bars (23 at% of Ar). It should be mentioned that the critical concentration as measured by RBS for 400 keV implantation is somewhat lower than the calculated value. The possible explanation may be found amongst uncertainties existing in the implanted depth distribution and sputtering yie!ds as well as in the reflection and escape of Ar atoms from the target. Fig. 2 shows SEM micrographs of the observed blisters for the 300, 400, 700 and 300 + 400 keV im-
2 b
5o---l
al 40-_c
l
Th.
n
Exp.
2 ‘;; C 30-‘;j -. .= b ”
1-
f
20--
i 10-v
0. 0
200
400
600
800
E [keVl Fig. 1. Critical peak concentration for the onset of blistering at RT as a function of Ar energy. The values (th) calculated using the theoretical depth profile of Ar and the values (exp) obtained from measurement are plotted together.
ofAI
planted spots, while their blister diameter distribution functions are plotted in fig. 3, showing that the implanted surface fraction covered by blistering and the mean blister size grow with the implanted energy. As inserted in fig. 3, the mean blister diameter d follows the relation d = ct as suggested by the gas pressure model [2] rather than d = ct3/* suggested by the stress model [9] (t is the blister cover thickness). The thicknesses of blister skins measured by SEM were found to be approximately 15% smaller than the calculated projected range presumably due to sputtering and stretching of the blister skin. The double implantation (400 + 300 keV) induced blisters showed a diameter distribution according to the superimposition of those obtained by the 300 and 400 keV single implantations. The following results were obtained from the postirradiation annealing of 300 and 400 keV implanted samples. During annealing the non-blistered implanted areas suffered blistering and the critical temperatures at which the blistering occurred depended on the quantity of pre-implanted doses (see table 1). These pre-implanted doses are then the critical doses for blistering at those temperatures and are transformed to the corresponding critical peak concentrations. Assuming that the basic interbubble fracture mechanism will still operate in this temperature range (as proposed by Evans [2]), the critical dose at different temperatures will have a strong correlation with the temperature dependence of the yield strength of the sample. For this purpose we include in fig. 4, where the critical data are plotted, the values of the yield strength [lo] as a function of temperature. As can clearly be seen, the prediction mentioned above is also true in the case of Ar implantation, i.e. the plotted critical data for different energy implantations follow the decrease of the yield strength with increasing temperature well. A similar relation was obtained for MeV energy He implantation of pure Al and Al-alloys [ll]. As predicted by Evans [2], this relation confirms the dependence of the interbubble fracture mechanism on temperature by the variation of the yield strength for both He and Ar implantations. During annealing, due to the increase of gas pressure inside the blister and the decrease of the yield strength, the size of blisters increases and some of them rupture. From RBS spectra performed during annealing (fig. 5) we obtained the peak concentration-depth distribution as well as the total amount of retained Ar as a function of temperature (figs. 6 and 7). As can be seen in fig. 7 in the case of a non-blistered sample the Ar did not escape below 425 K. This temperature is considered as the critical temperature for blistering at the given peak Ar concentration of 18 at% (fig. 4). After the
N. T. My et al. / Blistering and trapping C~~racteFist~cs of Al
Fig. 2. SEM micrographs of blistering induced on Al at RT by (a) 300, (b) 400, (c) 700 and (d) 400 + 300 keV Ar.
blistering event, as the annealing temperature increased, the implanted gas slowly escaped up to - 570 K when a drastic gas outflow could be observed originating from the depth of high Ar concentration (fig. 6). This event should be connected to the blister cover ruptures but this rupture process was restricted to some blisters only during annealing. As a consequence, one may speculate that this re-emitted gas originates from both the cavities under the blister covers and from the channel network which had interconnected these cavities. With the increase in the temperature the gas release became weaker and the RBS analysis shows (fig. 6) that the retained gas profile in the central part of the distribution comes slowly to a low level. This means that the gas from the cavities and the channel network in the Ar rich region escaped completely but that the temperature was not high enough to mobilize the gas trapped in the separate bubbles or in the surrounding bulk material. This part of the gas escaped only at temperatures higher than 750 K. The situation in the blistered sample was
the same except that 7% of the implanted gas had escaped during blistering at RT. In fig. 7 can be seen that the gas slowly escaped until a drastic release occurred at 570 K. Quantitatively the following results were observed: - 15% of the implanted gas escaped during the blistering event and the subsequent annealing before blister rupture, 50% was contained in both the channel network and the cavities under blisters and - 35% in the surrounding material.
4. Conclusions As in the case of high dose He implantation, the peak Ar concentration corresponding to a critical dose for the onset of blistering is in strong correlation with the yield strength of the Al target. At RT a constant value of 23 at% Ar (much lower than in the case of He) is found, not depending on the bombarding energy,
N. T. My et al. / Blistering and trapping characteristics
of Al
. 6-
3OOkeVC 10%)
T[Kl 0123456?8
ii blister
diameter [pm]
to
Fig. 4. The critical peak concentration of Ar at different energies and temperatures are plotted on a (temperature-gas concen~ation) state diagram together with the yield strength of Al as a function of temperature (solid curve).
11
Fig. 3. The dist~bution of blister diameters induced by 300, 400, 700 and (400 + 300) keV Ar implantation at RT. Values in brackets denote fractions of the implanted area covered by blisters. The relation between mean blister diameter and the implanted range as suggested by the gas pressure model (solid line) and stress model (dashed line) is inserted together with
gests that the interbubble fracture mechanism proposed by Evans [2] is still applicable and depends on temperature mainly through the variation of the yield strength of the host material, even though the radiation damage induced by Ar is much more serious than in the case of He. During post-irradiation annealing the Ar release initiates at the blister formation and increases drastically
the measured values.
while at elevated temperatures it decreases in accordance with the temperature dependence of the yield strength of the bombarded material. This relation sug-
Analysis
4000-
5 E 30002
Al
”
1 . yic .@?% .
Gi E 2 zooo2 9 al s
Ar
KJOO-
. ..-‘-..
?.
;._.f I
100
Fig. 5. Typical
RBS spectrum
of Ar implanted
150
Al performed
Channel
200 number
during
annealing
‘-.*I
250
300
(500 K) using a 3500 keV He+ anatysing
beam.
N. T. My et al. / Blistering and trapping characteristics of AI
Implanted
dose:
2.7 x 10” Arlcmz
81
. + . *
300K 375K 450K 500K l 575K ’ 650K 0 750K 6. 825K
0.5
0.4
0.3
0.2
0.1
0
Depth Cum1 lmalanted
0.9
0.8
0.7
0.6
0.5
0.4
dose:
0.3
2.25x1@’
0.2
Arlcmz
0.1
* 300K + 350K l 425K n 500K * 550K l 600K 0 650K A 825K t,
Depth l~ml Fig. 6. Concentration-depth
profile of retained
Ar in Al as a function samples
I
3,
I
implanted
I
-x- 2.7~10’~ Arlcm2
of annealing
temperature
for (a) blistered
and (b) non-blistered
by 400 keV Ar.
(- 50% of implanted Ar) at around 570 K where some blisters become ruptured. At this temperature a channel network of interbubble cracks has been laterally interconnecting the cavities under all blisters, including unopened blisters. At temperatures higher than 750 K the Ar escapes completely.
References
I
400
500
600
temperature
IKI
I
I
700
800
Fig. 7. Total amount of retained Ar as a function of annealing temperature for the blistered (dashed line) and non-blistered (solid line) samples implanted with 400 keV Ar.
(11 H. Trinkaus, Radiat. Eff. 78 (1983) 189. [2] J.H. Evans, J. Nucl. Mater. 68 (1977) 129. [3] M. Risch, J. Roth and B.M.U. Schetzer, in: Proc. Int. Symp. on Plasma-Wall Interaction (Pergamon Press, Oxford, 1977) p. 351. Radiat. Eff. 18 (1973) 141 G.K. Erents and G.M. McCracken, 245. of Materials, Vol. 1: Ion 151 0. Auciello, Beam Modification Bombardment Modification of Surfaces, Eds. 0. Auciello and R. Kelly (Elsevier, Amsterdam, 1984) p. 1. M. Fried, A. Manuaba, Gy. 161 G. Mezey, F. P&n, Vizkelethy, Cs. Hajdu and E. K&i, Twenty Years of Plasma Physics, Ed. B. McNamara (World Scientific, Philadelphia, 1984) p. 95.
82 [7] D.K. Brice, Ion Implantation
N. T. My et al. / Blistering and trapping characteristics of Al
Range and Energy Deposition Codes, Core& RASE4, and DAMG2, Sandia Reports 75-0622 (1977). [8] N. Matsunami, Y. Yamamura, Y. Itikawa, N. Itoh, 3’. Kazumata, S. Miyagawa, K. Morita and R. Shimizu, Energy Dependence of Sputtering Yield of Monoatomic Solids, Institute of Plasma Physics, Nagoya University, Report IPPJ AM-14.
[9] E.P. Eemisse and S.T. Picraux, J. Appl. Phys. 48 (1) (1977). [lo] Charles T. Lynch, Ed., Handbook of Materials Science, Vol. 2 (CRC Press, Cleveland, 1974). [ll] N.T. My, F. Paszti, G. Mezey, A. Manuaba, E. Kotai and J. Gyulai, to be published.
76
of Nuclear
Materials 168 (1989) 76-82 North-Holland. Amsterdam
BLISTERING AND TRAPPING CHARACTERISTICS OF ALUMINUM DURING Ar ION IMPLANTATION AND POST-IRRADIATION ANNEALING N.T. MY, F. PASZTI,
A. MANUABA,
G. MEZEY
and E. K6TAI
Central Research Institute for Physics, P. 0. Box 49, H-1525 Budapest,
Hungary
I.A. GOHAR Physics Department, Received
22 February
Faculty of Science, Mansoura 1989; accepted
20 March
University, Egypt 1989
High dose Ar implantation of pure aluminum samples with different energies resulted in blisters on the implanted area with mean diameters of d, = 9.5R,. At RT implantation the critical doses for the onset of blistering correspond to 23 at’% Ar peak concentration, independent of the applied bombarding energies (300-700 keV). During vacuum isochronic annealing of pre-implanted samples, it is found that the critical peak concentration of He decreases with increasing sample temperature, according to the weakening of the host material yield strength. The Rutherford back scattering (RBS) analyses performed during annealing show that the Ar release initiates at the blister formation and increases drastically (50% of implanted Ar) at the blister ruptures around 570 K, where channel network of interbubble cracks has interconnected laterally the cavities under all blisters including the unopened ones. The Ar escapes completely at temperatures higher than 750 K.
1. Introduction The ions of gaseous elements (especially H and He) that will be implanted into the first wall of future thermonuclear reactors will cause serious problems. This area has been widely investigated in model experiments at different laboratories in the past 15 years, and it was proved that if the gas is unable to escape, it will coalesce and precipitate to form gas filled bubbles in the host material. These bubbles may grow by capturing additional gas atoms and vacancies or by punching out interstitial dislocation-loops, and if the temperature is low and the radiation damage is not too serious they are overpressurized [l]. The pressure inside these bubbles may lead to interbubble cracking [2], or the bubbles of equilibrium pressure will coalesce to form a crack parallel to the sample surface. The layer separated from the substrate by this crack may contain a huge compressive lateral stress. This stress and/or the pressure of the gas accumulated in the cavity formed by the crack lifts the covering layer up, deforms it plastically and may even tear it off from the bulk [3-51. If this process takes place on well defined usually circular spots, it is called blistering, otherwise exfoliation. If the detached layer falls off, the process is referred to as flaking [6].
0022-3115/89/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
The present work is to study the effect of another noble gas, i.e. Ar, in high dose implantations of different energy into aluminum. We hope that implantation of heavier noble gas ions can simulate the fusion reactor environment in a more complex way: the lattice damage by fast neutrons, the sputtering caused by the deuterium fuel and other impurities, as well as the bubble formation and surface deformations caused by high energy He fusion products may be modelled simultaneously. By irradiations with different energies of Ar at RT, and post-irradiation annealing, one may expect useful information to be extracted from the variation of the critical dose for surface deformation with temperature and physical quantities characterizing the behaviour of Ar trapping/re-emission in Al.
2. Experimental Polycrystalline Al samples of high purity (99.999%) were first mechanically polished and rinsed in an ultrasonic bath of pure ethanol and then implanted with 300, 400 and 700 keV Ar ion beams to different doses (table 1). The implantations were performed at RT using a 5
B.V.
N. T. My et al. / Blistering and trapping characteristics Table 1 Experimental
conditions
of Ar irradiation
and the post-irradiation
annealing
treatment
17
of Al
together
with the critical
parameters
Critical temperature
Critical concentration
(R)
(at%)
425k40 390 * 40 300 52Ok40 470 f 40 _ 390 + 40 300 300
18 20 22+2 11 15 18 20 21+_2 24+4
for the
onset of blistering E (keV
Implanted dose (10” ions cmm2)
Critical dose (10” ions cmm2)
Surface modification
Post-irradiation treatment a)
(RT) 300
400
700 400 + 300
no no blistering no no no no blistering blistering blistering
1.75 2.0 2.25 1.25 1.75 2.25 2.50 2.15 14.0 2.5 + 2.25
‘) ann, post-irradiation
annealing;
opt, optical
ann + opt ann + opt _
1.9+0.2 _ _ _ _ 2.6 f 0.2
ann ann ann ann ann
4.8 f 0.7
_
microscope
investigation;
MeV Van de Graaff accelerator (VDG) and a 600 keV heavy ion cascade implanter (HIC). During implantation the vacuum in the target chamber connected to VDG and HIC were maintained at 7 X lop5 Pa and 2 x 10e4 Pa, while the Ar fluxes were kept at 3 X 1013 and 5 x lOi ions cm-* s-i respectively. In the VDG the beam spot of 1.2 x 1.5 mm* was cut out from the wide homogeneous beam. The 3 mm beam size of the HIC implanter was swept over a spot of 15 X 15 mm2. The double implantation was performed in HIC by irradiating the sample first with 400 keV and sequentially with 300 keV ions. After implantation the bombarded areas of all samples were examined in a JEOL-ISM-35 type scanning electron microscope. The 300 keV and 400 keV implanted samples (the blistered as well as the non-blistered ones) were afterwards annealed from 300 to 850 K in the VDG target chamber by heating the sample holder with a 100 W projector lamp. The temperature was measured by means of a Ni-CrNi thermocouple fixed to the sample holder, and for calibration the chamber temperature and the
+ + + + +
opt opt RBS opt
RBS
RBS, Rutherford
backscatteting
analysis.
melting point of pure Al were used. In two cases (see table 1) isochronic annealing was performed by raising the temperature in - 75 K steps of 600 s length and the implanted Ar profile at the end of each step was measured in situ by RBS analysis using a 3500 keV 4He+ beam. The backscattered helium was detected by a surface barrier detector (ORTEC) of 15 keV energy resolution positioned at 165 O. In five cases of non-blistered samples (see table l), the annealing was performed with the aim of determining the critical temperature at the appearance of blistering. To determine the critical dose for the onset of blistering two different methods were used: for samples implanted in the HIC (300, 400 and 300 + 400 keV implantation) the critical dose was considered as the mean value of the dose where blisters had been observed first and the dose immediately before. For the sample implanted in the VDG (700 keV implantation) it was determined by observing the implanted spot continuously through the chamber window using a telescope of 10 X magnification.
Table 2 The calculated values of the critical concentration for blistering (C,,) induced on Al by implantation with different Ar energies (E) at room temperature. For the calculation we use the broadened depth distribution (AX,,) estimated from the measured critical dose (@cc) and the sputtering yield (S). Also included are the values of depth profile parameters (Rr, AR,) as calculated by the Brice code as well as the values of AX and C extracted from RBS measurements (AX,,,, CexP) E
4 (pm)
AR,
(kev) 300
0.285
0.035
400 700
0.390 0.670
0.045 0.071
MO
s (atoms/ion)
A Xth (pm)
1.9
1.3
2.6 4.8
1.1 0.8
+c (10” ions cm
-2
)
A Xexp
c,h
C=v
(rm)
(at%)
(at%)
0.12
_
20
_
0.16 0.25
0.25 _
21 24
18 _
78
N. T. My et al. / Blisrering and trapping characteristics
3. Results and discussion The critical doses for the onset of blistering at RT for different implantation energies are shown in table 1. To verify the assumption that the critical dose is only the manifestation of the constant concentration at which the interbubble fracture takes place, preceding the elevation of detaching layers to blistering or exfoliation, it was transformed into the critical peak concentration of the distribution. For this purpose the implanted depth distributions as calculated by the Brice code [7] together with their broadening due to sputtering as estimated from the measured critical doses and the sputtering yields [S] were used (see table 2.). As can be seen in fig. 1, the calculated critical peak concentrations are constant within error bars (23 at% of Ar). It should be mentioned that the critical concentration as measured by RBS for 400 keV implantation is somewhat lower than the calculated value. The possible explanation may be found amongst uncertainties existing in the implanted depth distribution and sputtering yie!ds as well as in the reflection and escape of Ar atoms from the target. Fig. 2 shows SEM micrographs of the observed blisters for the 300, 400, 700 and 300 + 400 keV im-
2 b
5o---l
al 40-_c
l
Th.
n
Exp.
2 ‘;; C 30-‘;j -. .= b ”
1-
f
20--
i 10-v
0. 0
200
400
600
800
E [keVl Fig. 1. Critical peak concentration for the onset of blistering at RT as a function of Ar energy. The values (th) calculated using the theoretical depth profile of Ar and the values (exp) obtained from measurement are plotted together.
ofAI
planted spots, while their blister diameter distribution functions are plotted in fig. 3, showing that the implanted surface fraction covered by blistering and the mean blister size grow with the implanted energy. As inserted in fig. 3, the mean blister diameter d follows the relation d = ct as suggested by the gas pressure model [2] rather than d = ct3/* suggested by the stress model [9] (t is the blister cover thickness). The thicknesses of blister skins measured by SEM were found to be approximately 15% smaller than the calculated projected range presumably due to sputtering and stretching of the blister skin. The double implantation (400 + 300 keV) induced blisters showed a diameter distribution according to the superimposition of those obtained by the 300 and 400 keV single implantations. The following results were obtained from the postirradiation annealing of 300 and 400 keV implanted samples. During annealing the non-blistered implanted areas suffered blistering and the critical temperatures at which the blistering occurred depended on the quantity of pre-implanted doses (see table 1). These pre-implanted doses are then the critical doses for blistering at those temperatures and are transformed to the corresponding critical peak concentrations. Assuming that the basic interbubble fracture mechanism will still operate in this temperature range (as proposed by Evans [2]), the critical dose at different temperatures will have a strong correlation with the temperature dependence of the yield strength of the sample. For this purpose we include in fig. 4, where the critical data are plotted, the values of the yield strength [lo] as a function of temperature. As can clearly be seen, the prediction mentioned above is also true in the case of Ar implantation, i.e. the plotted critical data for different energy implantations follow the decrease of the yield strength with increasing temperature well. A similar relation was obtained for MeV energy He implantation of pure Al and Al-alloys [ll]. As predicted by Evans [2], this relation confirms the dependence of the interbubble fracture mechanism on temperature by the variation of the yield strength for both He and Ar implantations. During annealing, due to the increase of gas pressure inside the blister and the decrease of the yield strength, the size of blisters increases and some of them rupture. From RBS spectra performed during annealing (fig. 5) we obtained the peak concentration-depth distribution as well as the total amount of retained Ar as a function of temperature (figs. 6 and 7). As can be seen in fig. 7 in the case of a non-blistered sample the Ar did not escape below 425 K. This temperature is considered as the critical temperature for blistering at the given peak Ar concentration of 18 at% (fig. 4). After the
N. T. My et al. / Blistering and trapping C~~racteFist~cs of Al
Fig. 2. SEM micrographs of blistering induced on Al at RT by (a) 300, (b) 400, (c) 700 and (d) 400 + 300 keV Ar.
blistering event, as the annealing temperature increased, the implanted gas slowly escaped up to - 570 K when a drastic gas outflow could be observed originating from the depth of high Ar concentration (fig. 6). This event should be connected to the blister cover ruptures but this rupture process was restricted to some blisters only during annealing. As a consequence, one may speculate that this re-emitted gas originates from both the cavities under the blister covers and from the channel network which had interconnected these cavities. With the increase in the temperature the gas release became weaker and the RBS analysis shows (fig. 6) that the retained gas profile in the central part of the distribution comes slowly to a low level. This means that the gas from the cavities and the channel network in the Ar rich region escaped completely but that the temperature was not high enough to mobilize the gas trapped in the separate bubbles or in the surrounding bulk material. This part of the gas escaped only at temperatures higher than 750 K. The situation in the blistered sample was
the same except that 7% of the implanted gas had escaped during blistering at RT. In fig. 7 can be seen that the gas slowly escaped until a drastic release occurred at 570 K. Quantitatively the following results were observed: - 15% of the implanted gas escaped during the blistering event and the subsequent annealing before blister rupture, 50% was contained in both the channel network and the cavities under blisters and - 35% in the surrounding material.
4. Conclusions As in the case of high dose He implantation, the peak Ar concentration corresponding to a critical dose for the onset of blistering is in strong correlation with the yield strength of the Al target. At RT a constant value of 23 at% Ar (much lower than in the case of He) is found, not depending on the bombarding energy,
N. T. My et al. / Blistering and trapping characteristics
of Al
. 6-
3OOkeVC 10%)
T[Kl 0123456?8
ii blister
diameter [pm]
to
Fig. 4. The critical peak concentration of Ar at different energies and temperatures are plotted on a (temperature-gas concen~ation) state diagram together with the yield strength of Al as a function of temperature (solid curve).
11
Fig. 3. The dist~bution of blister diameters induced by 300, 400, 700 and (400 + 300) keV Ar implantation at RT. Values in brackets denote fractions of the implanted area covered by blisters. The relation between mean blister diameter and the implanted range as suggested by the gas pressure model (solid line) and stress model (dashed line) is inserted together with
gests that the interbubble fracture mechanism proposed by Evans [2] is still applicable and depends on temperature mainly through the variation of the yield strength of the host material, even though the radiation damage induced by Ar is much more serious than in the case of He. During post-irradiation annealing the Ar release initiates at the blister formation and increases drastically
the measured values.
while at elevated temperatures it decreases in accordance with the temperature dependence of the yield strength of the bombarded material. This relation sug-
Analysis
4000-
5 E 30002
Al
”
1 . yic .@?% .
Gi E 2 zooo2 9 al s
Ar
KJOO-
. ..-‘-..
?.
;._.f I
100
Fig. 5. Typical
RBS spectrum
of Ar implanted
150
Al performed
Channel
200 number
during
annealing
‘-.*I
250
300
(500 K) using a 3500 keV He+ anatysing
beam.
N. T. My et al. / Blistering and trapping characteristics of AI
Implanted
dose:
2.7 x 10” Arlcmz
81
. + . *
300K 375K 450K 500K l 575K ’ 650K 0 750K 6. 825K
0.5
0.4
0.3
0.2
0.1
0
Depth Cum1 lmalanted
0.9
0.8
0.7
0.6
0.5
0.4
dose:
0.3
2.25x1@’
0.2
Arlcmz
0.1
* 300K + 350K l 425K n 500K * 550K l 600K 0 650K A 825K t,
Depth l~ml Fig. 6. Concentration-depth
profile of retained
Ar in Al as a function samples
I
3,
I
implanted
I
-x- 2.7~10’~ Arlcm2
of annealing
temperature
for (a) blistered
and (b) non-blistered
by 400 keV Ar.
(- 50% of implanted Ar) at around 570 K where some blisters become ruptured. At this temperature a channel network of interbubble cracks has been laterally interconnecting the cavities under all blisters, including unopened blisters. At temperatures higher than 750 K the Ar escapes completely.
References
I
400
500
600
temperature
IKI
I
I
700
800
Fig. 7. Total amount of retained Ar as a function of annealing temperature for the blistered (dashed line) and non-blistered (solid line) samples implanted with 400 keV Ar.
(11 H. Trinkaus, Radiat. Eff. 78 (1983) 189. [2] J.H. Evans, J. Nucl. Mater. 68 (1977) 129. [3] M. Risch, J. Roth and B.M.U. Schetzer, in: Proc. Int. Symp. on Plasma-Wall Interaction (Pergamon Press, Oxford, 1977) p. 351. Radiat. Eff. 18 (1973) 141 G.K. Erents and G.M. McCracken, 245. of Materials, Vol. 1: Ion 151 0. Auciello, Beam Modification Bombardment Modification of Surfaces, Eds. 0. Auciello and R. Kelly (Elsevier, Amsterdam, 1984) p. 1. M. Fried, A. Manuaba, Gy. 161 G. Mezey, F. P&n, Vizkelethy, Cs. Hajdu and E. K&i, Twenty Years of Plasma Physics, Ed. B. McNamara (World Scientific, Philadelphia, 1984) p. 95.
82 [7] D.K. Brice, Ion Implantation
N. T. My et al. / Blistering and trapping characteristics of Al
Range and Energy Deposition Codes, Core& RASE4, and DAMG2, Sandia Reports 75-0622 (1977). [8] N. Matsunami, Y. Yamamura, Y. Itikawa, N. Itoh, 3’. Kazumata, S. Miyagawa, K. Morita and R. Shimizu, Energy Dependence of Sputtering Yield of Monoatomic Solids, Institute of Plasma Physics, Nagoya University, Report IPPJ AM-14.
[9] E.P. Eemisse and S.T. Picraux, J. Appl. Phys. 48 (1) (1977). [lo] Charles T. Lynch, Ed., Handbook of Materials Science, Vol. 2 (CRC Press, Cleveland, 1974). [ll] N.T. My, F. Paszti, G. Mezey, A. Manuaba, E. Kotai and J. Gyulai, to be published.