- Email: [email protected]
Ion-beam induced plastic deformation in amorphous materials investigated by marker implantation and RBS
Nuclear Instruments North-Holland
and Methods
in Physics Research
Nuclear Instruments & Methods in Physics Research
B64 (1992) 6X4-686
SKtlonB
Ion-beam induced plastic deformation in amorphous materials investigated by marker implantation and RBS A. Benyagoub
and S. Klaumiinzer
Huh - Meitner-Institut. POB 390128, D-1000 Berlin 39, Germany
L. Thorn&, J.C. Dran and F. Garrido Centre de Spectronuhie
Nucl6aire et de Spectromhrie
de Masse - IN2P3-CNRS, Ba^t. IOX, F-91405 Orsay-Campus, France
A. Dunlop CEA / DTA / CEREM/
DTM, Luhorutoire des Solides Irrudi&, Ecole Polytechnique, F-91128 Paluiseuu. Frunce
Ion electronic energy loss induces atomic transport (plastic deformation) in amorphous alloys irradiated with high-energy heavy ions. Such a phenomenon can be investigated by measuring, with the RBS technique, the modification of a marker profile implanted in the near-surface region of the irradiated target. Ion beams are thus used at three stages of the experiment: implantation, irradiation and analysis. Irradiation of amorphous Ni,B with hundreds-MeV Xe or I ions leads to a shift of the maximum of the Bi marker profile towards the surface of the sample together with a decrease of the peak width and of the peak integral. The results are in qualitative and quantitative agreement with the large plastic deformation observed in amorphous materials.
1. Introduction A remarkable and very surprising effect was discovered in the middle of the eighties: the ability of amorphous alloys to experience a huge plastic deformation when irradiated with high-energy (in the GeV range) heavy ions [l-5]. This phenomenon consists of an increase of the dimensions of the target perpendicular to the ion beam direction together with a shrinkage of the dimension parallel to it, in such a way that the volume of the sample remains constant. This effect was exclusively studied by macroscopic (length and electrical resistance) measurements and was demonstrated to be essentially due to ion electronic energy loss (dE/dx),. In this paper, we propose to investigate the plastic deformation at a more microscopic scale. The study, by Rutherford backscattering (RBS), of the ion beam-induced deformation of the profile of a heavy marker (Bi) implanted in the near-surface region of the irradiated alloy (Ni,B) serves such a purpose.
Bi (600
keV)
+El
:
ap_l
Step2
Implantation
:
of a heavy
High--energy
He (2.4
heavy
marker
Ion Irradiation
MeV)
%lIl
2. Experiment performed
apJ
As indicated in fig. 1, the present experiment quires the USC of an ion beam at three stages: 0168-583X/92/$05.00
0 1992 - Elsevier
Science
Publishers
re(1)
Fig.
:
RBS analysis
I. Schematic
B.V. All rights reserved
of the marker
representation formed.
of
the
ProfIle
experiment
per-
A. Benyagouh
et al. / Plastic deformation
implantation of the Bi marker which acts as a probe of the atomic transport investigated; (2) irradiation of the implanted target with high-energy heavy ions inducing the plastic deformation; (3) RBS analysis of the marker profile before and after irradiation. The samples are 4 p,rn thick amorphous and crystalline Ni,B foils (7 x 3 mm2 in size) prepared by sputtering (and subsequent annealing at 500 o C in the case of crystalline Ni,B). The Bi implantation was made at room temperature in the CSNSM-Orsay ion implanter at an energy of 600 keV (giving rise to a Bi profile centered at 65 nm beneath the foil surface) and at fluences of 2 x 10” at.cmm2. The high-energy irradiation was performed at liquid nitrogen temperature in the VICKSI-Berlin accelerator with various fluences (up to 6 x 10’” at. cme2) of 340 MeV ‘*‘Xe or 500 MeV “‘1 ions (flux: 10” at. cme2 s-l>, which provide an average electronic energy loss inside the target of - 40 keV nrn-- ‘. To prevent important target heating during irradiation, the samples were clamped between two copper plates in such a way that only a small portion (2 x 3 mm’) of each specimen was available for exposure to the high-energy ion beam. In spite of that, an unavoidable temperature gradient which can be estimated to - 70 K between the extreme points of the irradiated area was attained during irradiation. The RBS analysis of the implanted Bi profile before and after Xe or I irradiation was made at the ARAMISOrsay accelerator with 1.8 or 2.4 McV We ions (energy resolution - 15 keV corresponding to a depth resolution of - 10 nm). Measurements of the length and of the width of the samples were also performed before and after irradiation with an optical microscope in order to compare the macroscopic change of the target dimensions perpendicular to the ion beam direction to the modification of the Bi distribution profile (i.e. along the direction parallel to the ion beam).
Energy
405
3. Results and discussion Fig. 2 presents the high-energy part (i.e. the backscattering of the analyzing He ions on the Bi atoms) of RBS spectra recorded on crystalline and amorphous Ni,B foils implanted with the Bi marker before and after irradiation with 340 MeV Xe ions at a fluence of 4 x 10” at. cm-‘. It is quite clear that Xe irradiation has not induced any Bi profile modification in the case of crystalline Ni,B (fig. 2a), while it was responsible for a shift of the peak maximum towards the sample surface together with a decrease of the peak width and of the peak integral in the case of amorphous Ni,B (fig. 2b). The depth profiles of the implanted Bi marker were fitted by a Gaussian distribution centered at a position R, and of full width at half maximum (FWHM) AR,. Of course, this fitting procedure does not take into account the asymmet~ of the Bi profiles (consisting in a tail towards the great depths) which is more pronounced after irradiation due to the appearance of wrinkles created by the plastic deformation. Nevertheless, the uncertainty in the determination of R, and AR, caused by this asymmetry never exceeds 5%. Fig. 3 shows the relative variations of R,, AR,, and of the peak integral A,, deduced from the RBS spectra, as well as the relative changes of the length and width I, of the samples measured with the optical microscope, as a function of the irradiating ion fluence, in the case of amorphous Ni,B irradiated with 500 MeV 1 ions. It is worth noting that the parameters which characterize the variation of the target dimension along the ion beam direction (R,, AR, and Aa;) linearly decrease as the ion fluence increases, whereas the target dimensions perpendicular to the ion beam direction (I,) increase. The whole set of data indicates the presence of an effective fluence threshold for the irradiation-induced atomic movements.
2.10
2.20
(MeV)
2.15
2.20
I
I
’
6X5
materials
Energy
(MeV)
2.15
2.10
in amorphous
x
410
415
420
Channel
425
430
405
410
415
420
425
430
Channel
Fig. 2. Bi region of RBS spectra recorded on a Ni,B foil implanted with 600 keV Bi ions before (circles) and after (crosses) irradiation with 360 MeV Xe ions: (a) crystalline Ni,B; tb) amorphous Ni,B. Analyzing particles: 2.4 MeV 4He”i ions. XII. RANGE. STOPPING POWER
686
A. Benyagouh et al. / Plastic &formation in amorphous materials
FLUENCE ( 101’
I/cm”)
Fig. 3. Relative variation AX/X,, of the maximum of the Bi distribution R, (open circles), of its FWHM AR, (open triangles), of the integral of the Bi peak ABi (full triangles) and of the dimensions of the samples perpendicular to the ion beam direction (length and width) I, (full circles), as a function of the I irradiation fluence.
Low energy (hundreds-keV range) ion irradiation of alloys containing implanted or evaporated markers as probes of the ion-beam-induced atomic transport generally leads to a broadening of the marker distribution due to ballistic and diffusional mixing processes [h]. Such processes, essentially driven by nuclear elastic collisions, have been demonstrated to be mostly independent of the structure (crystalline or amorphous) of the irradiated target. The absence of any measurable broadening of the Bi profile obtained in the case of crystalline Ni,B (fig. 2a) indicates that ion-beam mixing effects are insignificant in the present experiments. This result can be explained by the high energy of the irradiating Xe or I ions, for which the nuclear energy loss is very small compared to the electronic energy loss (by a factor of the order of lo”), and by the low ion fluences used. The tremendous variations of the Bi profile observed in amorphous Ni,B (fig. 2b) can then be essentially accounted for by the plastic deformation phenomenon induced by electronic excitation. Thus, the decrease of R, is related to the shrinkage of the amorphous Ni,B layer located between the sample surface and the maximum of the marker profile. The decrease of AR, is caused by the dragging effect of the amorphous Ni,B lattice on the Bi atoms along the ion beam direction. The decrease of A,, (apparent loss of matter) is due to the dragging effect of amorphous
Ni,B on the Bi atoms along the directions pcrpendicular to the ion beam. The relative variation of R,, AR, and Aai with the heavy-ion fluence exhibited in fig. 3 gives a value of the growth-rate (one half the negative slope of the curve [7]) for the marker-sensed plastic deformation: g = 5.5 x lO_” cm’. The macroscopic length measurements also reported in fig. 3 indicate a growth-rate (slope of the curve Al/l,,) g = 6.3 x lo-‘” cm’. Both sets of data provide the same estimation of the incubation fluence (effective threshold [l]) for the growth phenomenon: d, _ 3 X IO” ionscm-“. The good agreement between the results deduced from these two independent measurements (i.e. RBS and length) demonstrates that the plastic deformation sensed by implanted Bi atoms is identical to that occurring in the bulk material. It can be concluded that the presence of the marker has not influenced the macroscopic growth phenomenon. It would then be particularly interesting to perform similar experiments where the marker would consist of a layer of larger thickness (introduced by evaporation) in order to study the influence of the marker layer thickncss on the plastic deformation process induced by swift heavy ion irradiation.
Acknowledgements We want to thank A. Chamberod for providing the Ni,B samples and B. Vassent for her help during the target preparation. We are also grateful to the VICKSI staff of the HMI-Berlin for their support during heavy ion irradiation experiments and the SEMIRAMIS group of the CSNSM-Orsay for their assistance during implantation and RBS experiments.
References [II S. Klaumiinzer,
Ming-dong Hou and G. Schumacher, Phys. Rev. Lett. 57 (1986) 850. E. Balanzat, G. Fuchs, J.C. Jousset, D. PI A. Audouard, Lesueur and L. Thorn& Europhys. Lett. 3 (1987) 327; 5 (1988) 241. [31 S. Klaumiinzer, Radiat. Eff. 110 (1989) 79. E. Balanzat, G. Fuchs, J.C. Jousset, D. [?I A. Audouard, Lesueur and L. Thorn&, Radiat. Eff. 110 (1989) 109. 151 Ming-dong Hou, S. Klaumiinzer and G. Schumacher, Phys. Rev. B41 (1990) 1144. of [61 See: Proc. 5th Int. Conf. on Ion Beam Modification Materials, Nucl. Instr. and Meth. B19/20 (1987). 171 S. Klaumiinzer and A. Benyagoub, Phys. Rev. B43 (1991) 7502.
and Methods
in Physics Research
Nuclear Instruments & Methods in Physics Research
B64 (1992) 6X4-686
SKtlonB
Ion-beam induced plastic deformation in amorphous materials investigated by marker implantation and RBS A. Benyagoub
and S. Klaumiinzer
Huh - Meitner-Institut. POB 390128, D-1000 Berlin 39, Germany
L. Thorn&, J.C. Dran and F. Garrido Centre de Spectronuhie
Nucl6aire et de Spectromhrie
de Masse - IN2P3-CNRS, Ba^t. IOX, F-91405 Orsay-Campus, France
A. Dunlop CEA / DTA / CEREM/
DTM, Luhorutoire des Solides Irrudi&, Ecole Polytechnique, F-91128 Paluiseuu. Frunce
Ion electronic energy loss induces atomic transport (plastic deformation) in amorphous alloys irradiated with high-energy heavy ions. Such a phenomenon can be investigated by measuring, with the RBS technique, the modification of a marker profile implanted in the near-surface region of the irradiated target. Ion beams are thus used at three stages of the experiment: implantation, irradiation and analysis. Irradiation of amorphous Ni,B with hundreds-MeV Xe or I ions leads to a shift of the maximum of the Bi marker profile towards the surface of the sample together with a decrease of the peak width and of the peak integral. The results are in qualitative and quantitative agreement with the large plastic deformation observed in amorphous materials.
1. Introduction A remarkable and very surprising effect was discovered in the middle of the eighties: the ability of amorphous alloys to experience a huge plastic deformation when irradiated with high-energy (in the GeV range) heavy ions [l-5]. This phenomenon consists of an increase of the dimensions of the target perpendicular to the ion beam direction together with a shrinkage of the dimension parallel to it, in such a way that the volume of the sample remains constant. This effect was exclusively studied by macroscopic (length and electrical resistance) measurements and was demonstrated to be essentially due to ion electronic energy loss (dE/dx),. In this paper, we propose to investigate the plastic deformation at a more microscopic scale. The study, by Rutherford backscattering (RBS), of the ion beam-induced deformation of the profile of a heavy marker (Bi) implanted in the near-surface region of the irradiated alloy (Ni,B) serves such a purpose.
Bi (600
keV)
+El
:
ap_l
Step2
Implantation
:
of a heavy
High--energy
He (2.4
heavy
marker
Ion Irradiation
MeV)
%lIl
2. Experiment performed
apJ
As indicated in fig. 1, the present experiment quires the USC of an ion beam at three stages: 0168-583X/92/$05.00
0 1992 - Elsevier
Science
Publishers
re(1)
Fig.
:
RBS analysis
I. Schematic
B.V. All rights reserved
of the marker
representation formed.
of
the
ProfIle
experiment
per-
A. Benyagouh
et al. / Plastic deformation
implantation of the Bi marker which acts as a probe of the atomic transport investigated; (2) irradiation of the implanted target with high-energy heavy ions inducing the plastic deformation; (3) RBS analysis of the marker profile before and after irradiation. The samples are 4 p,rn thick amorphous and crystalline Ni,B foils (7 x 3 mm2 in size) prepared by sputtering (and subsequent annealing at 500 o C in the case of crystalline Ni,B). The Bi implantation was made at room temperature in the CSNSM-Orsay ion implanter at an energy of 600 keV (giving rise to a Bi profile centered at 65 nm beneath the foil surface) and at fluences of 2 x 10” at.cmm2. The high-energy irradiation was performed at liquid nitrogen temperature in the VICKSI-Berlin accelerator with various fluences (up to 6 x 10’” at. cme2) of 340 MeV ‘*‘Xe or 500 MeV “‘1 ions (flux: 10” at. cme2 s-l>, which provide an average electronic energy loss inside the target of - 40 keV nrn-- ‘. To prevent important target heating during irradiation, the samples were clamped between two copper plates in such a way that only a small portion (2 x 3 mm’) of each specimen was available for exposure to the high-energy ion beam. In spite of that, an unavoidable temperature gradient which can be estimated to - 70 K between the extreme points of the irradiated area was attained during irradiation. The RBS analysis of the implanted Bi profile before and after Xe or I irradiation was made at the ARAMISOrsay accelerator with 1.8 or 2.4 McV We ions (energy resolution - 15 keV corresponding to a depth resolution of - 10 nm). Measurements of the length and of the width of the samples were also performed before and after irradiation with an optical microscope in order to compare the macroscopic change of the target dimensions perpendicular to the ion beam direction to the modification of the Bi distribution profile (i.e. along the direction parallel to the ion beam).
Energy
405
3. Results and discussion Fig. 2 presents the high-energy part (i.e. the backscattering of the analyzing He ions on the Bi atoms) of RBS spectra recorded on crystalline and amorphous Ni,B foils implanted with the Bi marker before and after irradiation with 340 MeV Xe ions at a fluence of 4 x 10” at. cm-‘. It is quite clear that Xe irradiation has not induced any Bi profile modification in the case of crystalline Ni,B (fig. 2a), while it was responsible for a shift of the peak maximum towards the sample surface together with a decrease of the peak width and of the peak integral in the case of amorphous Ni,B (fig. 2b). The depth profiles of the implanted Bi marker were fitted by a Gaussian distribution centered at a position R, and of full width at half maximum (FWHM) AR,. Of course, this fitting procedure does not take into account the asymmet~ of the Bi profiles (consisting in a tail towards the great depths) which is more pronounced after irradiation due to the appearance of wrinkles created by the plastic deformation. Nevertheless, the uncertainty in the determination of R, and AR, caused by this asymmetry never exceeds 5%. Fig. 3 shows the relative variations of R,, AR,, and of the peak integral A,, deduced from the RBS spectra, as well as the relative changes of the length and width I, of the samples measured with the optical microscope, as a function of the irradiating ion fluence, in the case of amorphous Ni,B irradiated with 500 MeV 1 ions. It is worth noting that the parameters which characterize the variation of the target dimension along the ion beam direction (R,, AR, and Aa;) linearly decrease as the ion fluence increases, whereas the target dimensions perpendicular to the ion beam direction (I,) increase. The whole set of data indicates the presence of an effective fluence threshold for the irradiation-induced atomic movements.
2.10
2.20
(MeV)
2.15
2.20
I
I
’
6X5
materials
Energy
(MeV)
2.15
2.10
in amorphous
x
410
415
420
Channel
425
430
405
410
415
420
425
430
Channel
Fig. 2. Bi region of RBS spectra recorded on a Ni,B foil implanted with 600 keV Bi ions before (circles) and after (crosses) irradiation with 360 MeV Xe ions: (a) crystalline Ni,B; tb) amorphous Ni,B. Analyzing particles: 2.4 MeV 4He”i ions. XII. RANGE. STOPPING POWER
686
A. Benyagouh et al. / Plastic &formation in amorphous materials
FLUENCE ( 101’
I/cm”)
Fig. 3. Relative variation AX/X,, of the maximum of the Bi distribution R, (open circles), of its FWHM AR, (open triangles), of the integral of the Bi peak ABi (full triangles) and of the dimensions of the samples perpendicular to the ion beam direction (length and width) I, (full circles), as a function of the I irradiation fluence.
Low energy (hundreds-keV range) ion irradiation of alloys containing implanted or evaporated markers as probes of the ion-beam-induced atomic transport generally leads to a broadening of the marker distribution due to ballistic and diffusional mixing processes [h]. Such processes, essentially driven by nuclear elastic collisions, have been demonstrated to be mostly independent of the structure (crystalline or amorphous) of the irradiated target. The absence of any measurable broadening of the Bi profile obtained in the case of crystalline Ni,B (fig. 2a) indicates that ion-beam mixing effects are insignificant in the present experiments. This result can be explained by the high energy of the irradiating Xe or I ions, for which the nuclear energy loss is very small compared to the electronic energy loss (by a factor of the order of lo”), and by the low ion fluences used. The tremendous variations of the Bi profile observed in amorphous Ni,B (fig. 2b) can then be essentially accounted for by the plastic deformation phenomenon induced by electronic excitation. Thus, the decrease of R, is related to the shrinkage of the amorphous Ni,B layer located between the sample surface and the maximum of the marker profile. The decrease of AR, is caused by the dragging effect of the amorphous Ni,B lattice on the Bi atoms along the ion beam direction. The decrease of A,, (apparent loss of matter) is due to the dragging effect of amorphous
Ni,B on the Bi atoms along the directions pcrpendicular to the ion beam. The relative variation of R,, AR, and Aai with the heavy-ion fluence exhibited in fig. 3 gives a value of the growth-rate (one half the negative slope of the curve [7]) for the marker-sensed plastic deformation: g = 5.5 x lO_” cm’. The macroscopic length measurements also reported in fig. 3 indicate a growth-rate (slope of the curve Al/l,,) g = 6.3 x lo-‘” cm’. Both sets of data provide the same estimation of the incubation fluence (effective threshold [l]) for the growth phenomenon: d, _ 3 X IO” ionscm-“. The good agreement between the results deduced from these two independent measurements (i.e. RBS and length) demonstrates that the plastic deformation sensed by implanted Bi atoms is identical to that occurring in the bulk material. It can be concluded that the presence of the marker has not influenced the macroscopic growth phenomenon. It would then be particularly interesting to perform similar experiments where the marker would consist of a layer of larger thickness (introduced by evaporation) in order to study the influence of the marker layer thickncss on the plastic deformation process induced by swift heavy ion irradiation.
Acknowledgements We want to thank A. Chamberod for providing the Ni,B samples and B. Vassent for her help during the target preparation. We are also grateful to the VICKSI staff of the HMI-Berlin for their support during heavy ion irradiation experiments and the SEMIRAMIS group of the CSNSM-Orsay for their assistance during implantation and RBS experiments.
References [II S. Klaumiinzer,
Ming-dong Hou and G. Schumacher, Phys. Rev. Lett. 57 (1986) 850. E. Balanzat, G. Fuchs, J.C. Jousset, D. PI A. Audouard, Lesueur and L. Thorn& Europhys. Lett. 3 (1987) 327; 5 (1988) 241. [31 S. Klaumiinzer, Radiat. Eff. 110 (1989) 79. E. Balanzat, G. Fuchs, J.C. Jousset, D. [?I A. Audouard, Lesueur and L. Thorn&, Radiat. Eff. 110 (1989) 109. 151 Ming-dong Hou, S. Klaumiinzer and G. Schumacher, Phys. Rev. B41 (1990) 1144. of [61 See: Proc. 5th Int. Conf. on Ion Beam Modification Materials, Nucl. Instr. and Meth. B19/20 (1987). 171 S. Klaumiinzer and A. Benyagoub, Phys. Rev. B43 (1991) 7502.