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Effects of thermally-activated diffusion on 72 keV Ni ion implantation into Cu targets at elevated temperatures
Nuclear Instruments and Methods in Physics Research B 241 (2005) 573–577 www.elsevier.com/locate/nimb
Effects of thermally-activated diffusion on 72 keV Ni ion implantation into Cu targets at elevated temperatures W.F. Tsai a
a,b,*
, J.H. Liang a, J.J. Kai
a
Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan, ROC b Physics Division, Institute of Nuclear Energy Research, Taoyuan, Taiwan, ROC Available online 15 August 2005
Abstract This work experimentally and theoretically investigates the effects of thermally-activated diffusion on the depth profiles of nickel atoms in copper. Nickel ions of 72 keV and 5 · 1015 ions/cm2 were implanted into copper targets at elevated temperatures of 200, 400 and 500 C, respectively. The experimental nickel depth profiles were obtained by the secondary ion mass spectrometry (SIMS). The calculated profiles were obtained using a thermally-activated diffusion model in which both the radiation-enhanced diffusion (RED) and radiation-induced segregation (RIS) are considered. Furthermore, lattice dilation and preferential sputtering were taken into account by means of an appropriate coordinate transformation. The results indicated a strong temperature-dependence of nickel depth profiles. In addition, the nickel depth profiles tend to broaden and surface concentration increase with temperatures. 2005 Elsevier B.V. All rights reserved. PACS: 61.72.Ww; 61.80.Az; 61.72.Ji; 29.27.a Keywords: Ion implantation; Radiation effects; Point defects; Accelerator
1. Introduction High-temperature ion implantation has attained much interest in last decades, particularly * Corresponding author. Address: Physics Division, Institute of Nuclear Energy Research, Taoyuan, Taiwan, ROC. Tel.: +886 3 4711400x7401; fax: +886 3 4711408. E-mail address: [email protected] (W.F. Tsai).
for its applications involving modifications of thick depths [1–3]. Several studies have shown that thermally-activated diffusion resulted from the radiation-enhanced diffusion and radiation-induced segregation has a considerable effect on the depth profile of the implanted atoms [3–7]. Due to the additionally generated defects, radiation-enhanced diffusion may cause the implanted atoms to move from shallow implanted layers into a deep
0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.07.070
574
W.F. Tsai et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 573–577
region. Radiation-induced segregation may induce the surface enrichment or depletion of the implanted atoms because of the preferential coupling between the defect fluxes and the fluxes of certain target elements. In the previous work [7], we studied the effects of thermally-activated diffusion on the high-temperature implantation of copper ions into a nickel target. It was found that, accompanied with a greater depletion of the surface concentration of copper atoms, the depth profiles of implanted copper atoms broaden as target temperatures increase. However, as various experimental and theoretical investigations shown [8–10], the strong surface segregation of nickel atoms occurs during Ar+ or Ni+ irradiation of Ni–Cu systems at the temperatures of 420–610 C. Therefore, it is imperative to explore the effects of the radiation-enhanced diffusion and radiation-induced segregation on the depth profiles of nickel implanted into a copper target at elevated temperatures. In this study, we investigated experimentally and theoretically the diffusion of implanted nickel atoms in a copper target.
2. Experimental The copper specimens of high purity (99.98%) were implanted with 72 keV Ni1 ions using a NEC 9SDH tandem accelerator located at National Tsing Hua University. The ion fluence and implantation time were 5 · 1015 ions/cm2 and 1 h, respectively. The pressure was around 106 Torr. By heating externally with a halogen lamp, the implantation temperature of the specimen were in the range of 200–500 C. The temperature of the specimen holder was measured using a thermocouple. The specimen temperature was calibrated with an infrared pyrometer. The accuracy of the temperature measurements was estimated to be ±10 C. The depth profiles of nickel atoms were obtained by a Cameca IMS-4f secondary ion mass spectrometry (SIMS) with a 10 keV Cþ s primary beam. The Cþ ion beam was rastered over an area s of 0.025 cm · 0.025 cm to generate flat-bottomed craters. A Dektak-3030 profilometer was used to determine the depths of craters.
3. Theoretical model The present model evolves from the previous one developed for studying the thermally-activated diffusion during high-temperature ion implantation [7]. During ion implantation, the time evolution of the concentration of vacancy (Cv), interstitial (Ci) and constituent elements (Cj) can be described by sets of nonlinear diffusion equations as follow: oC v ¼ K v Lvd Lr r ðXJ v Þ; ot oC i ¼ K i Lid Lr r ðXJ i Þ; ot oC j ¼ r ðXJ j Þ; j ¼ 1; 2; . . . ; n þ 1; ot
ð1Þ ð2Þ ð3Þ
where Kx = eK0 (x = v, i) is the defect production rate. K0 is the theoretical displacement rate obtained from SRIM code [11] and e the point-defect production efficiency. Lvd and Lid are vacancy and interstitial loss rates, due to interactions with dislocations [6], respectively. Lr is the recombination rate of vacancies and interstitials [9]. The sign j denotes the jth component in the n-component target plus the implanted-ion species. X is the atomic volume. The net vacancy, interstitial and atomic fluxes are expressed as X X Jv ¼ J vj ; J i ¼ J ij ; ð4Þ j
j
J j ¼ J ij J vj ;
ð5Þ
where Jvj and Jij are the vacancy and interstitial fluxes via jth component which are XJ vj ¼ d vj ðC v rC j C j rC v Þ;
ð6Þ
XJ ij ¼ d ij ðC i rC j C j rC i Þ;
ð7Þ
where the partial diffusivities dvj and dij are given by k2j Em vj d vj ¼ Z j mvj exp ; ð8Þ 6 kT k2j Em ij d ij ¼ Z j mij exp . ð9Þ 6 kT where kj and Zj are the jump distance and coordination number of the jth component. mvj and mij are
W.F. Tsai et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 573–577
the vibration frequency of vacancy and interstitial, m respectively. Em vj and E ij are the migration energy of vacancy and interstitial for the jth component, respectively. The loss terms are expressed by X 2pqd Lvd ¼ ðC v C eq d vj C j ; ð10Þ v Þ lnðRd =R0 Þ j X 2pqd ðC i C eq Lid ¼ d ij C j ; ð11Þ i Þ lnðRd =R0 Þ j X ðd ij þ d vj Þ Cj ; Lr ¼ 4pC v C i riv ð12Þ X j where qd is the dislocation density [5], Rd = (pqd)1/2 the spacing between dislocations, R0 the dislocation core radius, riv the radius of the recomeq bination volume, C eq v and C i the thermal vacancy and interstitial concentrations, respectively. The ion collection, preferential sputtering and lattice dilation were also considered in the present model. At each time step, dt, the increment of the implanted ions du(x) = dt/f(x) was added to the existing profile which was zero initially, where the normalized depth profile of implanted ions, f(x), is obtained from the SRIM code and / is ion flux. The sputtering thickness is dxs = / dtYs/Nti, where the preferential sputtering Pnþ1 yield, Y s ¼ j¼1 Cð0; tÞY j , and the atomic denPnþ1 Pnþ1 sity, N ti ¼ j¼1 N j Cð0; tÞ= j¼1 N j Cð0; tÞ; whereas Table 1 Physical parameters of the Cu–Ni system used in this study Parameter
Magnitude
Ref.
mv-Cu, mv-Ni mi-Cu, mi-Ni Em v-Cu Em v-Ni Em i-Cu Em i-Ni Efv-Cu Efv-Ni Efi-Cu Efi-Ni S fv-Cu ; S fv-Ni
5 · 1013 s1 5 · 1012 s1 1.06 eV 1.28 eV 0.15 eV 0.12 eV 1.31 eV 1.8 eV 4.0 eV 4.0 eV 3K
[10] [10] [9] [14] [10] [9] [13] [13] [10] [10] [10]
S fi-Cu ; S fi-Ni YCu YNi e riv
0K 5.5 atoms/ion 7.5 atoms/ion 0.3 3.6a0 (a0: lattice constant)
[10] [12] [12] [5] [9]
575
C(0, t) is the surface concentration at time t. Nj and Yj are the atomic number density and sputtering yield of the jth component. The accumulative lattice-dilation PIthickness up to index I is calculated by dxc ðIÞ ¼ k¼0 dxðkÞ, where the lattice-dilation thickness of index k (with a spatial increment Dxk) is given by dx(k) = / dtf(xk)/Nti. Therefore, after a time increment, dt, the coordinate x is transformed to a new coordinate x 0 in the form of x 0 (I) = x(I) + dxc(I) dxs. Physical parameters used in this study are listed in Table 1.
4. Results and discussion Fig. 1 shows the initially normalized depth profiles of 72 keV implanted nickel atoms in copper target and the defect production. Both the curves were calculated from the SRIM code. The ion flux is 1.29 · 1012 ions/cm2 s and its corresponding defect peak is 3.32 · 103 dpa/s (i.e. displacements per atom per second). Fig. 2 shows the experimentally measured and theoretically predicted depth profiles of implanted nickel atoms in copper with and without diffusion at 200, 400 and 500 C, respectively. As shown in the figure, with diffusion the experimental and theoretical profiles are in good agreement. When compared to that of without diffusion, the thermally-activated diffusion of nickel atoms alters their depth profiles significantly. The corresponding alteration indicates that both the profile spreading and surface enrichment of nickel atoms increase with the temperatures. The concentration gradient of defects created during the ion bombardments results in the defects flow from its peak region toward the surface and the bulk. Since the implanted nickel atoms and point defects migrate in the same direction [9], the nickel atoms also have a net flux from the peak region of the point defects to the surface and the bulk. This leads to the surface segregation and profile spreading of nickel atoms. Since the irradiation damages are in the vicinity of the surface, and acts as a perfect sink for point defects, most defects escaped from interstitial–vacancy recombination will migrate toward the surface. Therefore, a larger amount of implanted nickel atoms transport into near target surface region at
Concentration (normalized)
576
W.F. Tsai et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 573–577
tion-induced segregation. If the flux of nickel atoms toward the surface is larger than the nickel loss rate due to the preferential sputtering, the accumulation and enrichment of nickel atoms at the surface region will occur. This is what we observed for the implantation at the temperature above 400 C. In addition, the increase of point defect mobility with temperature results in the extension of the implanted nickel atoms into much larger depths.
72 keV Ni in Cu
1.0
Ion
0.8
Defect 0.6 0.4 0.2
Rd
Ri
0.0 0
20
40 Depth (nm)
60
80
Fig. 1. The depth profiles of the irradiation-induced defects and implanted nickel atoms for 72 keV Ni1 ion implantation in copper targets. Rd and Ri represent the peak locations of defects and nickel atoms (calculated from the SRIM code).
2.5E-2 72 keV Ni in Cu T = 500 oC
2.0E-2 1.5E-2
Measured (arbitary unit) Calculated (w/ diffusion)
1.0E-2
Calculated (w/o diffusion)
Ni concentration (at. fraction)
5.0E-3 0.0E+0 2.5E-2
5. Conclusion The effects of thermally-activation diffusion on the depth profiles of nickel ions implanted into a copper target have been investigated theoretically and experimentally. It was found that the theoretically calculated depth distributions of nickel atoms agree well with the profiles obtained experimentally. As the implantation temperature increases, the concentration of nickel atoms decreases which enhances surface enrichment and broadens the profiles. This can be well described by the mechanism of radiation-enhanced diffusion and radiation-induced segregation as presented in our model.
72 keV Ni in Cu T = 400 oC
2.0E-2
Acknowledgements
Measured (arbitary unit)
1.5E-2
Calculated (w/ diffusion)
1.0E-2
The authors would like to acknowledge the financial support of the National Science Council of the Republic of China that makes this work possible. We also wish to thank Mr. C.H. Wang and M.S. Tseng of National Tsing Hua University for their assistance with these experiments.
Calculated (w/o diffusion)
5.0E-3 0.0E+0 2.5E-2 72 keV Ni in Cu T = 200 oC
2.0E-2
Measured (arbitary unit)
1.5E-2
Calculated (w/ diffusion)
1.0E-2
References
Calculated (w/o diffusion)
5.0E-3 0.0E+0 0 R R d i
40
80
120
160
Depth (nm)
Fig. 2. The depth profiles of nickel atoms for 72 keV Ni1 ion implantation in copper at 200, 400, and 500 C, respectively.
elevated temperatures as a result of the mechanisms of radiation-enhanced diffusion and radia-
[1] R.E.J. Watkins, Radiat. Eff. 84 (1985) 27. [2] R. Wei, P.J. Wilbur, O. Ozturk, D.L. Williamson, Surf. Coat. Technol. 65 (1994) 15. [3] S.H. Valiev, T.S. Pugacheva, F.G. Jurabekova, S.A. Lem, Y. Miyagawa, Nucl. Instr. and Meth. B 127–128 (1997) 265. [4] A.D. Marwick, R.C. Piller, Radiat. Eff. 47 (1980) 195. [5] N.Q. Lam, G.K. Leaf, J. Mater. Res. 1 (1986) 251. [6] S.H. Han, G.L. Kulcinski, J.R. Conrad, Nucl. Instr. and Meth. B 45 (1990) 701. [7] W.F. Tsai, J.H. Liang, J.J. Kai, G.L. Kulcinski, Nucl. Instr. and Meth. B 228 (2005) 151.
W.F. Tsai et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 573–577 [8] L.E. Rehn, W. Wagner, H. Wiedersich, Ser. Metall. 15 (1981) 683. [9] W. Wagner, L.E. Rehn, H. Wiedersich, N. Naundort, Phys. Rev. B 28 (1983) 6780. [10] N.Q. Lam, H.A. Hoff, H. Wiedersich, L.E. Rehn, Surf. Sci. 149 (1985) 517. [11] J.F. Ziegler, J.P. Biersack, SRIM: The Stopping and Range of Ions in Matter, Version 96.07, IBM-Research, Yorktown, 1996.
577
[12] N. Matsunami, Y. Yamamura, Y. Itikawa, N. Itoh, Y. Kazumata, S. Miyagawa, K. Morita, R. Shimizu, Nagoya University Report IPPJ-AM-14, 1980. [13] R.W. Siehel, in: J.J. Takamura, M. Doyama, M. Kiritani (Eds.), Point Defects and Defect Interactions in Metals, North-Holland Publishing Company, Amsterdam, 1982. [14] W. Wycisk, M. Feller-kniepmeier, Phys. Status Solidi (a) 37 (1976) 183.
Effects of thermally-activated diffusion on 72 keV Ni ion implantation into Cu targets at elevated temperatures W.F. Tsai a
a,b,*
, J.H. Liang a, J.J. Kai
a
Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan, ROC b Physics Division, Institute of Nuclear Energy Research, Taoyuan, Taiwan, ROC Available online 15 August 2005
Abstract This work experimentally and theoretically investigates the effects of thermally-activated diffusion on the depth profiles of nickel atoms in copper. Nickel ions of 72 keV and 5 · 1015 ions/cm2 were implanted into copper targets at elevated temperatures of 200, 400 and 500 C, respectively. The experimental nickel depth profiles were obtained by the secondary ion mass spectrometry (SIMS). The calculated profiles were obtained using a thermally-activated diffusion model in which both the radiation-enhanced diffusion (RED) and radiation-induced segregation (RIS) are considered. Furthermore, lattice dilation and preferential sputtering were taken into account by means of an appropriate coordinate transformation. The results indicated a strong temperature-dependence of nickel depth profiles. In addition, the nickel depth profiles tend to broaden and surface concentration increase with temperatures. 2005 Elsevier B.V. All rights reserved. PACS: 61.72.Ww; 61.80.Az; 61.72.Ji; 29.27.a Keywords: Ion implantation; Radiation effects; Point defects; Accelerator
1. Introduction High-temperature ion implantation has attained much interest in last decades, particularly * Corresponding author. Address: Physics Division, Institute of Nuclear Energy Research, Taoyuan, Taiwan, ROC. Tel.: +886 3 4711400x7401; fax: +886 3 4711408. E-mail address: [email protected] (W.F. Tsai).
for its applications involving modifications of thick depths [1–3]. Several studies have shown that thermally-activated diffusion resulted from the radiation-enhanced diffusion and radiation-induced segregation has a considerable effect on the depth profile of the implanted atoms [3–7]. Due to the additionally generated defects, radiation-enhanced diffusion may cause the implanted atoms to move from shallow implanted layers into a deep
0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.07.070
574
W.F. Tsai et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 573–577
region. Radiation-induced segregation may induce the surface enrichment or depletion of the implanted atoms because of the preferential coupling between the defect fluxes and the fluxes of certain target elements. In the previous work [7], we studied the effects of thermally-activated diffusion on the high-temperature implantation of copper ions into a nickel target. It was found that, accompanied with a greater depletion of the surface concentration of copper atoms, the depth profiles of implanted copper atoms broaden as target temperatures increase. However, as various experimental and theoretical investigations shown [8–10], the strong surface segregation of nickel atoms occurs during Ar+ or Ni+ irradiation of Ni–Cu systems at the temperatures of 420–610 C. Therefore, it is imperative to explore the effects of the radiation-enhanced diffusion and radiation-induced segregation on the depth profiles of nickel implanted into a copper target at elevated temperatures. In this study, we investigated experimentally and theoretically the diffusion of implanted nickel atoms in a copper target.
2. Experimental The copper specimens of high purity (99.98%) were implanted with 72 keV Ni1 ions using a NEC 9SDH tandem accelerator located at National Tsing Hua University. The ion fluence and implantation time were 5 · 1015 ions/cm2 and 1 h, respectively. The pressure was around 106 Torr. By heating externally with a halogen lamp, the implantation temperature of the specimen were in the range of 200–500 C. The temperature of the specimen holder was measured using a thermocouple. The specimen temperature was calibrated with an infrared pyrometer. The accuracy of the temperature measurements was estimated to be ±10 C. The depth profiles of nickel atoms were obtained by a Cameca IMS-4f secondary ion mass spectrometry (SIMS) with a 10 keV Cþ s primary beam. The Cþ ion beam was rastered over an area s of 0.025 cm · 0.025 cm to generate flat-bottomed craters. A Dektak-3030 profilometer was used to determine the depths of craters.
3. Theoretical model The present model evolves from the previous one developed for studying the thermally-activated diffusion during high-temperature ion implantation [7]. During ion implantation, the time evolution of the concentration of vacancy (Cv), interstitial (Ci) and constituent elements (Cj) can be described by sets of nonlinear diffusion equations as follow: oC v ¼ K v Lvd Lr r ðXJ v Þ; ot oC i ¼ K i Lid Lr r ðXJ i Þ; ot oC j ¼ r ðXJ j Þ; j ¼ 1; 2; . . . ; n þ 1; ot
ð1Þ ð2Þ ð3Þ
where Kx = eK0 (x = v, i) is the defect production rate. K0 is the theoretical displacement rate obtained from SRIM code [11] and e the point-defect production efficiency. Lvd and Lid are vacancy and interstitial loss rates, due to interactions with dislocations [6], respectively. Lr is the recombination rate of vacancies and interstitials [9]. The sign j denotes the jth component in the n-component target plus the implanted-ion species. X is the atomic volume. The net vacancy, interstitial and atomic fluxes are expressed as X X Jv ¼ J vj ; J i ¼ J ij ; ð4Þ j
j
J j ¼ J ij J vj ;
ð5Þ
where Jvj and Jij are the vacancy and interstitial fluxes via jth component which are XJ vj ¼ d vj ðC v rC j C j rC v Þ;
ð6Þ
XJ ij ¼ d ij ðC i rC j C j rC i Þ;
ð7Þ
where the partial diffusivities dvj and dij are given by k2j Em vj d vj ¼ Z j mvj exp ; ð8Þ 6 kT k2j Em ij d ij ¼ Z j mij exp . ð9Þ 6 kT where kj and Zj are the jump distance and coordination number of the jth component. mvj and mij are
W.F. Tsai et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 573–577
the vibration frequency of vacancy and interstitial, m respectively. Em vj and E ij are the migration energy of vacancy and interstitial for the jth component, respectively. The loss terms are expressed by X 2pqd Lvd ¼ ðC v C eq d vj C j ; ð10Þ v Þ lnðRd =R0 Þ j X 2pqd ðC i C eq Lid ¼ d ij C j ; ð11Þ i Þ lnðRd =R0 Þ j X ðd ij þ d vj Þ Cj ; Lr ¼ 4pC v C i riv ð12Þ X j where qd is the dislocation density [5], Rd = (pqd)1/2 the spacing between dislocations, R0 the dislocation core radius, riv the radius of the recomeq bination volume, C eq v and C i the thermal vacancy and interstitial concentrations, respectively. The ion collection, preferential sputtering and lattice dilation were also considered in the present model. At each time step, dt, the increment of the implanted ions du(x) = dt/f(x) was added to the existing profile which was zero initially, where the normalized depth profile of implanted ions, f(x), is obtained from the SRIM code and / is ion flux. The sputtering thickness is dxs = / dtYs/Nti, where the preferential sputtering Pnþ1 yield, Y s ¼ j¼1 Cð0; tÞY j , and the atomic denPnþ1 Pnþ1 sity, N ti ¼ j¼1 N j Cð0; tÞ= j¼1 N j Cð0; tÞ; whereas Table 1 Physical parameters of the Cu–Ni system used in this study Parameter
Magnitude
Ref.
mv-Cu, mv-Ni mi-Cu, mi-Ni Em v-Cu Em v-Ni Em i-Cu Em i-Ni Efv-Cu Efv-Ni Efi-Cu Efi-Ni S fv-Cu ; S fv-Ni
5 · 1013 s1 5 · 1012 s1 1.06 eV 1.28 eV 0.15 eV 0.12 eV 1.31 eV 1.8 eV 4.0 eV 4.0 eV 3K
[10] [10] [9] [14] [10] [9] [13] [13] [10] [10] [10]
S fi-Cu ; S fi-Ni YCu YNi e riv
0K 5.5 atoms/ion 7.5 atoms/ion 0.3 3.6a0 (a0: lattice constant)
[10] [12] [12] [5] [9]
575
C(0, t) is the surface concentration at time t. Nj and Yj are the atomic number density and sputtering yield of the jth component. The accumulative lattice-dilation PIthickness up to index I is calculated by dxc ðIÞ ¼ k¼0 dxðkÞ, where the lattice-dilation thickness of index k (with a spatial increment Dxk) is given by dx(k) = / dtf(xk)/Nti. Therefore, after a time increment, dt, the coordinate x is transformed to a new coordinate x 0 in the form of x 0 (I) = x(I) + dxc(I) dxs. Physical parameters used in this study are listed in Table 1.
4. Results and discussion Fig. 1 shows the initially normalized depth profiles of 72 keV implanted nickel atoms in copper target and the defect production. Both the curves were calculated from the SRIM code. The ion flux is 1.29 · 1012 ions/cm2 s and its corresponding defect peak is 3.32 · 103 dpa/s (i.e. displacements per atom per second). Fig. 2 shows the experimentally measured and theoretically predicted depth profiles of implanted nickel atoms in copper with and without diffusion at 200, 400 and 500 C, respectively. As shown in the figure, with diffusion the experimental and theoretical profiles are in good agreement. When compared to that of without diffusion, the thermally-activated diffusion of nickel atoms alters their depth profiles significantly. The corresponding alteration indicates that both the profile spreading and surface enrichment of nickel atoms increase with the temperatures. The concentration gradient of defects created during the ion bombardments results in the defects flow from its peak region toward the surface and the bulk. Since the implanted nickel atoms and point defects migrate in the same direction [9], the nickel atoms also have a net flux from the peak region of the point defects to the surface and the bulk. This leads to the surface segregation and profile spreading of nickel atoms. Since the irradiation damages are in the vicinity of the surface, and acts as a perfect sink for point defects, most defects escaped from interstitial–vacancy recombination will migrate toward the surface. Therefore, a larger amount of implanted nickel atoms transport into near target surface region at
Concentration (normalized)
576
W.F. Tsai et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 573–577
tion-induced segregation. If the flux of nickel atoms toward the surface is larger than the nickel loss rate due to the preferential sputtering, the accumulation and enrichment of nickel atoms at the surface region will occur. This is what we observed for the implantation at the temperature above 400 C. In addition, the increase of point defect mobility with temperature results in the extension of the implanted nickel atoms into much larger depths.
72 keV Ni in Cu
1.0
Ion
0.8
Defect 0.6 0.4 0.2
Rd
Ri
0.0 0
20
40 Depth (nm)
60
80
Fig. 1. The depth profiles of the irradiation-induced defects and implanted nickel atoms for 72 keV Ni1 ion implantation in copper targets. Rd and Ri represent the peak locations of defects and nickel atoms (calculated from the SRIM code).
2.5E-2 72 keV Ni in Cu T = 500 oC
2.0E-2 1.5E-2
Measured (arbitary unit) Calculated (w/ diffusion)
1.0E-2
Calculated (w/o diffusion)
Ni concentration (at. fraction)
5.0E-3 0.0E+0 2.5E-2
5. Conclusion The effects of thermally-activation diffusion on the depth profiles of nickel ions implanted into a copper target have been investigated theoretically and experimentally. It was found that the theoretically calculated depth distributions of nickel atoms agree well with the profiles obtained experimentally. As the implantation temperature increases, the concentration of nickel atoms decreases which enhances surface enrichment and broadens the profiles. This can be well described by the mechanism of radiation-enhanced diffusion and radiation-induced segregation as presented in our model.
72 keV Ni in Cu T = 400 oC
2.0E-2
Acknowledgements
Measured (arbitary unit)
1.5E-2
Calculated (w/ diffusion)
1.0E-2
The authors would like to acknowledge the financial support of the National Science Council of the Republic of China that makes this work possible. We also wish to thank Mr. C.H. Wang and M.S. Tseng of National Tsing Hua University for their assistance with these experiments.
Calculated (w/o diffusion)
5.0E-3 0.0E+0 2.5E-2 72 keV Ni in Cu T = 200 oC
2.0E-2
Measured (arbitary unit)
1.5E-2
Calculated (w/ diffusion)
1.0E-2
References
Calculated (w/o diffusion)
5.0E-3 0.0E+0 0 R R d i
40
80
120
160
Depth (nm)
Fig. 2. The depth profiles of nickel atoms for 72 keV Ni1 ion implantation in copper at 200, 400, and 500 C, respectively.
elevated temperatures as a result of the mechanisms of radiation-enhanced diffusion and radia-
[1] R.E.J. Watkins, Radiat. Eff. 84 (1985) 27. [2] R. Wei, P.J. Wilbur, O. Ozturk, D.L. Williamson, Surf. Coat. Technol. 65 (1994) 15. [3] S.H. Valiev, T.S. Pugacheva, F.G. Jurabekova, S.A. Lem, Y. Miyagawa, Nucl. Instr. and Meth. B 127–128 (1997) 265. [4] A.D. Marwick, R.C. Piller, Radiat. Eff. 47 (1980) 195. [5] N.Q. Lam, G.K. Leaf, J. Mater. Res. 1 (1986) 251. [6] S.H. Han, G.L. Kulcinski, J.R. Conrad, Nucl. Instr. and Meth. B 45 (1990) 701. [7] W.F. Tsai, J.H. Liang, J.J. Kai, G.L. Kulcinski, Nucl. Instr. and Meth. B 228 (2005) 151.
W.F. Tsai et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 573–577 [8] L.E. Rehn, W. Wagner, H. Wiedersich, Ser. Metall. 15 (1981) 683. [9] W. Wagner, L.E. Rehn, H. Wiedersich, N. Naundort, Phys. Rev. B 28 (1983) 6780. [10] N.Q. Lam, H.A. Hoff, H. Wiedersich, L.E. Rehn, Surf. Sci. 149 (1985) 517. [11] J.F. Ziegler, J.P. Biersack, SRIM: The Stopping and Range of Ions in Matter, Version 96.07, IBM-Research, Yorktown, 1996.
577
[12] N. Matsunami, Y. Yamamura, Y. Itikawa, N. Itoh, Y. Kazumata, S. Miyagawa, K. Morita, R. Shimizu, Nagoya University Report IPPJ-AM-14, 1980. [13] R.W. Siehel, in: J.J. Takamura, M. Doyama, M. Kiritani (Eds.), Point Defects and Defect Interactions in Metals, North-Holland Publishing Company, Amsterdam, 1982. [14] W. Wycisk, M. Feller-kniepmeier, Phys. Status Solidi (a) 37 (1976) 183.