- Email: [email protected]
Nuclear and electronic energy loss synergy in the process of damage growth in ion implanted LiNbO3
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 249 (2006) 122–125 www.elsevier.com/locate/nimb
Nuclear and electronic energy loss synergy in the process of damage growth in ion implanted LiNbO3 M. Bianconi a,*, N. Argiolas b, M. Bazzan b, G.G. Bentini a, M. Chiarini c, A. Cerutti a, P. Mazzoldi b, G. Pennestrı` c, C. Sada b b
a CNR-IMM-Sezione di Bologna, Via P.Gobetti 101, I-40139 Bologna, Italy INFM and Universita` di Padova, Dipartimento di Fisica, Via Marzolo 8, 35131 Padova, Italy c Carlo Gavazzi Space Spa, Via Gallarate 150, 20151 Milano, Italy
Available online 6 May 2006
Abstract The damage formation by implantation of energetic (5 MeV) low Z ions (C, N, O, F) in LiNbO3 has been investigated. The surface damage growth as a function of the fluence is consistent with a mechanism of nucleation and 3D growth of fully disordered clusters. It is possible to describe this behaviour by considering two processes: the first one is the direct generation of nuclear damage whereas the second one is the partial conversion of the electronic excitation into atomic displacements, mediated by the local concentration of defects. Within this simple scenario the damage evolution has been described by an analytical formula. This formula suggested that the existence of pre-damage in the surface region can boost the damage growth. This was demonstrated by introducing nuclear damage in the first 0.6 lm surface layer by 500 keV O implantation followed by a subsequent 5 MeV O implantation. The final surface damage is not the mere sum of the two implantation steps, but it is strongly enhanced by the interaction of the two damage mechanisms (nuclear and electronic) and it is in very good quantitative agreement with the proposed analytical formula. A strong non-linear dependence of the electronic damage formation cross-section on the stopping power was evidenced by repeating the same experiment with carbon ions. 2006 Elsevier B.V. All rights reserved. PACS: 82.80.Yc; 61.85.+p; 61.72.y Keywords: Ion implantation; Lithium niobate; RBS channeling
1. Introduction In the last years the implantation of energetic (a few MeV) low-medium mass ions in lithium niobate (LN) has been employed to produce optical waveguides [1–5]. These studies have shown that, in some specific cases, a defective region is formed at the sample surface and that this damage is somehow related to the electronic energy loss process [6]. ˚) The energy loss range under examination (Se < 500 eV/A is below the threshold for amorphous tracks formation
*
Corresponding author. Tel.: +39 51 6399140; fax: +39 51 6399216. E-mail address: [email protected] (M. Bianconi).
0168-583X/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.03.095
observed for swift heavy ion irradiation [7]. In fact, the work of Ramos et al. [8] has given a clear indication that, on decreasing the electronic stopping power, the dynamics of the damage growth as a function of the fluence deviates from the linearity expected for the accumulation of single tracks. Moreover, it has been recently showed that, in the case of N, O and F ion implantation at energies around ˚ < Se < 300 eV/A ˚ ) the surface damage 5 MeV (240 eV/A evolution is consistent with a mechanism of nucleation and 3D growth of fully disordered clusters [6], whereas mainly nuclear damage is formed by 3.9 MeV carbon irra˚ ). In this paper the most important diation (Se < 200 eV/A features of the electronic damage formation and growth have been investigated.
M. Bianconi et al. / Nucl. Instr. and Meth. in Phys. Res. B 249 (2006) 122–125
X-cut congruent LN wafers from Crystal Technology Inc., were implanted with carbon and oxygen ions at medium and/or high energy. The sample holder was cooled in order to keep the temperature below 300 K, as it has been shown that the damage formation is reduced when implanting at higher temperature [6]. Provided that the temperature is controlled as mentioned above, we did not find any difference in samples processed in the flux range 3 · 1014 m2 s1 to 1.5 · 1015 m2 s1. The samples were analyzed by the RBS-channeling technique using a 2.2 MeV proton beam in the IBM geometry, with the detector placed at 170 scattering angle. The damage depth profiles were extracted from the Nb signal; the procedure has been described elsewhere [3]. 3. Modeling The observed mechanism of nucleation and 3D growth of fully disordered clusters under ion implantation of LN [6] suggests that the defective regions play an important role in the conversion of the energy released to the electronic subsystem into atomic displacement. In the framework of the thermal spike model [9,10] it has been recently proposed that the defects introduced by previous irradiation reduce the latent track threshold of LN [11], whereas Itoh [12] suggested that localisation of excited charge carriers is essential for damage formation in insulators and this localization may occur either by excitons selftrapping or by trapping at defects. As the identification of the mechanisms leading to electronic damage is beyond the scope of the present work, we simply assume that the damage induced by ion implantation in LN originates from two classes of process: the first one, characterized by the crosssection rn, is the direct generation of defective regions (nuclear damage or ion tracks regime) whereas the second one, characterized by the cross-section re, is the partial conversion of the electronic excitation into atomic displacements, mediated by the local concentration of defects. The damage accumulation at the depth z, as a function of the fluence U is then given by the following differential equation [13]: onðzÞ ¼ ½1 nðzÞrn ðzÞ þ ½1 nðzÞre ðzÞnðzÞ; oU
ð1Þ
where n is the relative concentration of scattering centres as determined by RBS channeling and the factor [1 n] accounts for the fraction of undamaged crystal. The form of Eq. (1) is analogous to the model of [14] used to describe the amorphization of silicon. The solution of Eq. (1) is analytical and, for a given z, is ðrn þ n0 re Þ exp½ðrn þ re ÞU ð1 n0 Þrn n¼ ; ðrn þ n0 re Þ exp½ðrn þ re ÞU þ ð1 n0 Þre
cesses and it is not a free parameter; its shape is derived from SRIM code [15] and its integral is adjusted to fit the EOR region of the damage profile. If re rn Eq. (2) actually describes the nucleation and 3D growth of fully disordered clusters and fits satisfactorily the data of [6]. It is worth noting that the dependence of n on the pre-existing damage n0 is relevant and this could explain some reproducibility problems encountered when using LN wafer from different manufacturers [6]. Moreover, this property has been used, as described in the next paragraph, both to test Eq. (2) and to verify the existence of a stopping power threshold for re. 4. Results and discussion The defect depth profile produced by 5 MeV, 2 · 1018 m2 (O_HE step) oxygen implantation in LN is shown in Fig. 1. An identical result was obtained for both X-axis and Y-axis alignments indicating that the damage is formed by randomly displaced atoms. The shape of the deeper part of the profile (z > 2 lm) is coincident with the SRIM profile, whereas in the surface region (z < 1 lm) the damage is enhanced by the additional contribution of the electronic energy loss processes. To understand the contribution of the defect produced by nuclear processes to the whole damage pile-up, one sample was pre-implanted with oxygen at 500 keV, 3 · 1018 m2 (O_LE step). The corresponding defect depth profile, shown in Fig. 1 as dashed line, extends down to 0.6 lm. This is an average of the profiles obtained for X-axis and Y-axis alignments; in fact it is known that, for low-medium energy ion implantation in LN, nuclear damage is not isotropic [16]. Finally, this last sample was subsequently implanted with the O_HE step. The resulting profile (O_LE + O_HE) is also shown in Fig. 1 (bold continuous line) and it is not the mere sum of the two steps. An
1.0
Nb displaced fraction (n)
2. Experimental
O_LE (500 keV 3 x 1018 m-2) O_HE (5000 keV 2 x 1018 m-2 ) O_LE + O_HE
0.8
0.6
0.4
0.2
0.0 0.0
ð2Þ
where n0 = n(U = 0) is the pre-existing damage. In the present experimental conditions rn only includes nuclear pro-
123
0.5
1.0
1.5
2.0
2.5
3.0
Depth (μm) Fig. 1. Nb defect depth profile for the oxygen low energy (O_LE), high energy (O_HE) and low energy + high energy (O_LE + O_HE) implantation.
M. Bianconi et al. / Nucl. Instr. and Meth. in Phys. Res. B 249 (2006) 122–125
impressive boost is obtained by the introduction of a relatively low level of damage (n0), leading to the almost full amorphization of the surface layer. This effect is limited to the O_LE implanted region whereas at larger depth the profile is unaffected (here the small differences are due to the uncertainty in the dechanneling calculation). It is noticeable that Eq. (2) with rn = 8.7 · 1021 m2 and re = 1.9 · 1018 m2, the cross sections obtained by fitting the oxygen data of [6] at z = 0.6 lm (where there is a reasonable statistics in the n0 profile), is not only in qualitative but also in excellent quantitative agreement with the data of Fig. 1 and this represents a strong support to this formulation [13]. In order to verify the existence of a stopping power threshold for this process the same experiment was repeated with the carbon ion. The defect depth profile produced by 3.9 MeV, 6 · 1018 m2 (C_HE step) carbon implantation is shown in Fig. 2. Again, the result was independent of the alignment. Then one sample was preimplanted with carbon at 440 keV, 3 · 1018 m2 (C_LE step), its defect depth profile is shown in Fig. 2 as dashed line and again this is an average of the profiles obtained for X-axis and Y-axis alignments. The two steps implantation defect depth profile (C_LE + C_HE) is also shown in Fig. 2 (bold continuous line) and, this time, this is the mean profile obtained for X-axis and Y-axis alignments (they differ at the surface) and, moreover, the C_LE + C_HE profile is roughly the sum of the two separate steps. This means that negligible ‘‘electronic’’ damage has been stimulated by pre-damaging the sample. Considering that 5.0 MeV oxygen and 3.9 MeV carbon ions have, more or less, the same velocity the only relevant parameter that changes is the stopping power and, therefore, the present results suggest the existence of a strong non-linear dependence of re on the stopping power or even a threshold for the formation of ‘‘electronic’’ damage. This is shown in Fig. 3 where the re cross-sections, obtained by fitting
Nb displaced fraction (n)
1.0 C_LE (440 keV 5 x 1018 m-2 )
0.8
C_HE (3900 keV 6 x 1018 m-2 ) C_LE + C_HE
6
0.3 MeV / amu 5
F σ e (10 -18 m 2 )
124
4 3
O 2 1 0
N C 200
220
240
260
280
300
320
Se (eV/Å) Fig. 3. Cross-section for the formation of the electronic damage (re) by implantation of 0.3 MeV/amu C, N, O and F ions as a function of the electronic stopping power.
our data of [6], are plotted as a function of the stopping power. The main contribution to the error bars comes from reproducibility problems [6], probably arising from the strong dependence on the base material. The uncertainty on the stopping power values, deduced from SRIM, is of difficult evaluation for these ion–target combinations. The Se region here considered is too limited to determine the functional dependence of re, however a practical Se threshold (at 0.3 MeV/amu) can be set in the 200–230 ˚ range. eV/A In conclusion, we have shown that 0.3 MeV/amu medium-light ion implantation of LN generates a surface defective region, provided that the stopping power is sufficiently large. A fraction of the energy released to the electronic sub-system is converted into atomic displacement (the cross-section is proportional to the electronic stopping power). Anyway the non-linear damage growth as a function of the fluence suggests that the direct formation of amorphous tracks is not the key process in the present experimental conditions. We have demonstrated that the defects formed by the nuclear energy deposition provide the necessary sites for the localization of the electronic excitation and subsequent damage formation.
0.6
Acknowledgement
0.4
This work was partially supported by the FIRB RBNE01KZ94_002 project.
0.2
References
0.0 0.0
0.5
1.0
1.5
2.0
2.5
3.0
Depth (μm) Fig. 2. Nb defect depth profile for the carbon low energy (C_LE), high energy (C_HE) and low energy + high energy (C_LE + C_HE) implantation.
[1] H. Hu, F. Lu, F. Chen, B.R. Shi, K.M. Wang, D.Y. Shen, J. Appl. Phys. 89 (2001) 5224. [2] F. Chen, H. Hu, J.H. Zhang, F. Lu, B.R. Shi, K.M. Wang, D.Y. Shen, C.Q. Wang, Phys. Stat. Sol. (a) 187 (2001) 543. [3] G.G. Bentini, M. Bianconi, M. Chiarini, L. Correra, C. Sada, P. Mazzoldi, N. Argiolas, M. Bazzan, R. Guzzi, J. Appl. Phys. 92 (2002) 6477.
M. Bianconi et al. / Nucl. Instr. and Meth. in Phys. Res. B 249 (2006) 122–125 [4] S.L. Li, K.M. Wang, F. Chen, X.L. Wang, G. Fu, D.Y. Shen, H.J. Ma, R. Nie, Opt. Express 12 (2004) 747. [5] J. Olivares, G. Garcı´a, A. Garcı´a-Navarro, F. Agullo´-Lo´pez, O. Caballero, A. Garcı´a-Caban˜es, Appl. Phys. Lett. 86 (2005) 183501. [6] G.G. Bentini, M. Bianconi, L. Correra, M. Chiarini, P. Mazzoldi, C. Sada, N. Argiolas, M. Bazzan, R. Guzzi, J. Appl. Phys. 96 (2004) 242. [7] B. Canut, S.M.M. Ramos, R. Brenier, P. Thevenard, J.L. Loubet, M. Toulemonde, Nucl. Instr. and Meth. B 107 (1996) 194. [8] S.M.M. Ramos, B. Canut, M. Ambri, N. Bonardi, M. Pitaval, H. Bernas, J. Chaumont, Rad. Eff. Defects Sol. 143 (1998) 299. [9] G. Szenes, Nucl. Instr. and Meth. B 141 (1996) 116. [10] M. Toulemonde, Ch. Dufour, A. Meftah, E. Paumier, Nucl. Instr. and Meth. B 166–167 (2000) 903.
125
[11] F. Agullo´-Lo´pez, G. Garcı´a, J. Olivares, J. Appl. Phys. 97 (2004) 093514. [12] N. Itoh, Nucl. Instr. and Meth. B 135 (1998) 175. [13] M. Bianconi, N. Argiolas, M. Bazzan, G.G. Bentini, M. Chiarini, A. Cerutti, P. Mazzoldi, G. Pennestrı`, C. Sada, Appl. Phys. Lett. 87 (2005) 072901. [14] N. Hecking, K.F. Heidemann, E. TeKatt, Nucl. Instr. and Meth. B 15 (1986) 760. [15] J.F. Ziegler, J.P. Biersack, U. Littmark (Eds.), The Stopping and Ranges of Ions in Solids, Pergamon, New York, 1985. Available from:. [16] G. Go¨zt, H. Karge, Nucl. Instr. and Meth. B 209–210 (1983) 1079.
Nuclear Instruments and Methods in Physics Research B 249 (2006) 122–125 www.elsevier.com/locate/nimb
Nuclear and electronic energy loss synergy in the process of damage growth in ion implanted LiNbO3 M. Bianconi a,*, N. Argiolas b, M. Bazzan b, G.G. Bentini a, M. Chiarini c, A. Cerutti a, P. Mazzoldi b, G. Pennestrı` c, C. Sada b b
a CNR-IMM-Sezione di Bologna, Via P.Gobetti 101, I-40139 Bologna, Italy INFM and Universita` di Padova, Dipartimento di Fisica, Via Marzolo 8, 35131 Padova, Italy c Carlo Gavazzi Space Spa, Via Gallarate 150, 20151 Milano, Italy
Available online 6 May 2006
Abstract The damage formation by implantation of energetic (5 MeV) low Z ions (C, N, O, F) in LiNbO3 has been investigated. The surface damage growth as a function of the fluence is consistent with a mechanism of nucleation and 3D growth of fully disordered clusters. It is possible to describe this behaviour by considering two processes: the first one is the direct generation of nuclear damage whereas the second one is the partial conversion of the electronic excitation into atomic displacements, mediated by the local concentration of defects. Within this simple scenario the damage evolution has been described by an analytical formula. This formula suggested that the existence of pre-damage in the surface region can boost the damage growth. This was demonstrated by introducing nuclear damage in the first 0.6 lm surface layer by 500 keV O implantation followed by a subsequent 5 MeV O implantation. The final surface damage is not the mere sum of the two implantation steps, but it is strongly enhanced by the interaction of the two damage mechanisms (nuclear and electronic) and it is in very good quantitative agreement with the proposed analytical formula. A strong non-linear dependence of the electronic damage formation cross-section on the stopping power was evidenced by repeating the same experiment with carbon ions. 2006 Elsevier B.V. All rights reserved. PACS: 82.80.Yc; 61.85.+p; 61.72.y Keywords: Ion implantation; Lithium niobate; RBS channeling
1. Introduction In the last years the implantation of energetic (a few MeV) low-medium mass ions in lithium niobate (LN) has been employed to produce optical waveguides [1–5]. These studies have shown that, in some specific cases, a defective region is formed at the sample surface and that this damage is somehow related to the electronic energy loss process [6]. ˚) The energy loss range under examination (Se < 500 eV/A is below the threshold for amorphous tracks formation
*
Corresponding author. Tel.: +39 51 6399140; fax: +39 51 6399216. E-mail address: [email protected] (M. Bianconi).
0168-583X/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.03.095
observed for swift heavy ion irradiation [7]. In fact, the work of Ramos et al. [8] has given a clear indication that, on decreasing the electronic stopping power, the dynamics of the damage growth as a function of the fluence deviates from the linearity expected for the accumulation of single tracks. Moreover, it has been recently showed that, in the case of N, O and F ion implantation at energies around ˚ < Se < 300 eV/A ˚ ) the surface damage 5 MeV (240 eV/A evolution is consistent with a mechanism of nucleation and 3D growth of fully disordered clusters [6], whereas mainly nuclear damage is formed by 3.9 MeV carbon irra˚ ). In this paper the most important diation (Se < 200 eV/A features of the electronic damage formation and growth have been investigated.
M. Bianconi et al. / Nucl. Instr. and Meth. in Phys. Res. B 249 (2006) 122–125
X-cut congruent LN wafers from Crystal Technology Inc., were implanted with carbon and oxygen ions at medium and/or high energy. The sample holder was cooled in order to keep the temperature below 300 K, as it has been shown that the damage formation is reduced when implanting at higher temperature [6]. Provided that the temperature is controlled as mentioned above, we did not find any difference in samples processed in the flux range 3 · 1014 m2 s1 to 1.5 · 1015 m2 s1. The samples were analyzed by the RBS-channeling technique using a 2.2 MeV proton beam in the IBM geometry, with the detector placed at 170 scattering angle. The damage depth profiles were extracted from the Nb signal; the procedure has been described elsewhere [3]. 3. Modeling The observed mechanism of nucleation and 3D growth of fully disordered clusters under ion implantation of LN [6] suggests that the defective regions play an important role in the conversion of the energy released to the electronic subsystem into atomic displacement. In the framework of the thermal spike model [9,10] it has been recently proposed that the defects introduced by previous irradiation reduce the latent track threshold of LN [11], whereas Itoh [12] suggested that localisation of excited charge carriers is essential for damage formation in insulators and this localization may occur either by excitons selftrapping or by trapping at defects. As the identification of the mechanisms leading to electronic damage is beyond the scope of the present work, we simply assume that the damage induced by ion implantation in LN originates from two classes of process: the first one, characterized by the crosssection rn, is the direct generation of defective regions (nuclear damage or ion tracks regime) whereas the second one, characterized by the cross-section re, is the partial conversion of the electronic excitation into atomic displacements, mediated by the local concentration of defects. The damage accumulation at the depth z, as a function of the fluence U is then given by the following differential equation [13]: onðzÞ ¼ ½1 nðzÞrn ðzÞ þ ½1 nðzÞre ðzÞnðzÞ; oU
ð1Þ
where n is the relative concentration of scattering centres as determined by RBS channeling and the factor [1 n] accounts for the fraction of undamaged crystal. The form of Eq. (1) is analogous to the model of [14] used to describe the amorphization of silicon. The solution of Eq. (1) is analytical and, for a given z, is ðrn þ n0 re Þ exp½ðrn þ re ÞU ð1 n0 Þrn n¼ ; ðrn þ n0 re Þ exp½ðrn þ re ÞU þ ð1 n0 Þre
cesses and it is not a free parameter; its shape is derived from SRIM code [15] and its integral is adjusted to fit the EOR region of the damage profile. If re rn Eq. (2) actually describes the nucleation and 3D growth of fully disordered clusters and fits satisfactorily the data of [6]. It is worth noting that the dependence of n on the pre-existing damage n0 is relevant and this could explain some reproducibility problems encountered when using LN wafer from different manufacturers [6]. Moreover, this property has been used, as described in the next paragraph, both to test Eq. (2) and to verify the existence of a stopping power threshold for re. 4. Results and discussion The defect depth profile produced by 5 MeV, 2 · 1018 m2 (O_HE step) oxygen implantation in LN is shown in Fig. 1. An identical result was obtained for both X-axis and Y-axis alignments indicating that the damage is formed by randomly displaced atoms. The shape of the deeper part of the profile (z > 2 lm) is coincident with the SRIM profile, whereas in the surface region (z < 1 lm) the damage is enhanced by the additional contribution of the electronic energy loss processes. To understand the contribution of the defect produced by nuclear processes to the whole damage pile-up, one sample was pre-implanted with oxygen at 500 keV, 3 · 1018 m2 (O_LE step). The corresponding defect depth profile, shown in Fig. 1 as dashed line, extends down to 0.6 lm. This is an average of the profiles obtained for X-axis and Y-axis alignments; in fact it is known that, for low-medium energy ion implantation in LN, nuclear damage is not isotropic [16]. Finally, this last sample was subsequently implanted with the O_HE step. The resulting profile (O_LE + O_HE) is also shown in Fig. 1 (bold continuous line) and it is not the mere sum of the two steps. An
1.0
Nb displaced fraction (n)
2. Experimental
O_LE (500 keV 3 x 1018 m-2) O_HE (5000 keV 2 x 1018 m-2 ) O_LE + O_HE
0.8
0.6
0.4
0.2
0.0 0.0
ð2Þ
where n0 = n(U = 0) is the pre-existing damage. In the present experimental conditions rn only includes nuclear pro-
123
0.5
1.0
1.5
2.0
2.5
3.0
Depth (μm) Fig. 1. Nb defect depth profile for the oxygen low energy (O_LE), high energy (O_HE) and low energy + high energy (O_LE + O_HE) implantation.
M. Bianconi et al. / Nucl. Instr. and Meth. in Phys. Res. B 249 (2006) 122–125
impressive boost is obtained by the introduction of a relatively low level of damage (n0), leading to the almost full amorphization of the surface layer. This effect is limited to the O_LE implanted region whereas at larger depth the profile is unaffected (here the small differences are due to the uncertainty in the dechanneling calculation). It is noticeable that Eq. (2) with rn = 8.7 · 1021 m2 and re = 1.9 · 1018 m2, the cross sections obtained by fitting the oxygen data of [6] at z = 0.6 lm (where there is a reasonable statistics in the n0 profile), is not only in qualitative but also in excellent quantitative agreement with the data of Fig. 1 and this represents a strong support to this formulation [13]. In order to verify the existence of a stopping power threshold for this process the same experiment was repeated with the carbon ion. The defect depth profile produced by 3.9 MeV, 6 · 1018 m2 (C_HE step) carbon implantation is shown in Fig. 2. Again, the result was independent of the alignment. Then one sample was preimplanted with carbon at 440 keV, 3 · 1018 m2 (C_LE step), its defect depth profile is shown in Fig. 2 as dashed line and again this is an average of the profiles obtained for X-axis and Y-axis alignments. The two steps implantation defect depth profile (C_LE + C_HE) is also shown in Fig. 2 (bold continuous line) and, this time, this is the mean profile obtained for X-axis and Y-axis alignments (they differ at the surface) and, moreover, the C_LE + C_HE profile is roughly the sum of the two separate steps. This means that negligible ‘‘electronic’’ damage has been stimulated by pre-damaging the sample. Considering that 5.0 MeV oxygen and 3.9 MeV carbon ions have, more or less, the same velocity the only relevant parameter that changes is the stopping power and, therefore, the present results suggest the existence of a strong non-linear dependence of re on the stopping power or even a threshold for the formation of ‘‘electronic’’ damage. This is shown in Fig. 3 where the re cross-sections, obtained by fitting
Nb displaced fraction (n)
1.0 C_LE (440 keV 5 x 1018 m-2 )
0.8
C_HE (3900 keV 6 x 1018 m-2 ) C_LE + C_HE
6
0.3 MeV / amu 5
F σ e (10 -18 m 2 )
124
4 3
O 2 1 0
N C 200
220
240
260
280
300
320
Se (eV/Å) Fig. 3. Cross-section for the formation of the electronic damage (re) by implantation of 0.3 MeV/amu C, N, O and F ions as a function of the electronic stopping power.
our data of [6], are plotted as a function of the stopping power. The main contribution to the error bars comes from reproducibility problems [6], probably arising from the strong dependence on the base material. The uncertainty on the stopping power values, deduced from SRIM, is of difficult evaluation for these ion–target combinations. The Se region here considered is too limited to determine the functional dependence of re, however a practical Se threshold (at 0.3 MeV/amu) can be set in the 200–230 ˚ range. eV/A In conclusion, we have shown that 0.3 MeV/amu medium-light ion implantation of LN generates a surface defective region, provided that the stopping power is sufficiently large. A fraction of the energy released to the electronic sub-system is converted into atomic displacement (the cross-section is proportional to the electronic stopping power). Anyway the non-linear damage growth as a function of the fluence suggests that the direct formation of amorphous tracks is not the key process in the present experimental conditions. We have demonstrated that the defects formed by the nuclear energy deposition provide the necessary sites for the localization of the electronic excitation and subsequent damage formation.
0.6
Acknowledgement
0.4
This work was partially supported by the FIRB RBNE01KZ94_002 project.
0.2
References
0.0 0.0
0.5
1.0
1.5
2.0
2.5
3.0
Depth (μm) Fig. 2. Nb defect depth profile for the carbon low energy (C_LE), high energy (C_HE) and low energy + high energy (C_LE + C_HE) implantation.
[1] H. Hu, F. Lu, F. Chen, B.R. Shi, K.M. Wang, D.Y. Shen, J. Appl. Phys. 89 (2001) 5224. [2] F. Chen, H. Hu, J.H. Zhang, F. Lu, B.R. Shi, K.M. Wang, D.Y. Shen, C.Q. Wang, Phys. Stat. Sol. (a) 187 (2001) 543. [3] G.G. Bentini, M. Bianconi, M. Chiarini, L. Correra, C. Sada, P. Mazzoldi, N. Argiolas, M. Bazzan, R. Guzzi, J. Appl. Phys. 92 (2002) 6477.
M. Bianconi et al. / Nucl. Instr. and Meth. in Phys. Res. B 249 (2006) 122–125 [4] S.L. Li, K.M. Wang, F. Chen, X.L. Wang, G. Fu, D.Y. Shen, H.J. Ma, R. Nie, Opt. Express 12 (2004) 747. [5] J. Olivares, G. Garcı´a, A. Garcı´a-Navarro, F. Agullo´-Lo´pez, O. Caballero, A. Garcı´a-Caban˜es, Appl. Phys. Lett. 86 (2005) 183501. [6] G.G. Bentini, M. Bianconi, L. Correra, M. Chiarini, P. Mazzoldi, C. Sada, N. Argiolas, M. Bazzan, R. Guzzi, J. Appl. Phys. 96 (2004) 242. [7] B. Canut, S.M.M. Ramos, R. Brenier, P. Thevenard, J.L. Loubet, M. Toulemonde, Nucl. Instr. and Meth. B 107 (1996) 194. [8] S.M.M. Ramos, B. Canut, M. Ambri, N. Bonardi, M. Pitaval, H. Bernas, J. Chaumont, Rad. Eff. Defects Sol. 143 (1998) 299. [9] G. Szenes, Nucl. Instr. and Meth. B 141 (1996) 116. [10] M. Toulemonde, Ch. Dufour, A. Meftah, E. Paumier, Nucl. Instr. and Meth. B 166–167 (2000) 903.
125
[11] F. Agullo´-Lo´pez, G. Garcı´a, J. Olivares, J. Appl. Phys. 97 (2004) 093514. [12] N. Itoh, Nucl. Instr. and Meth. B 135 (1998) 175. [13] M. Bianconi, N. Argiolas, M. Bazzan, G.G. Bentini, M. Chiarini, A. Cerutti, P. Mazzoldi, G. Pennestrı`, C. Sada, Appl. Phys. Lett. 87 (2005) 072901. [14] N. Hecking, K.F. Heidemann, E. TeKatt, Nucl. Instr. and Meth. B 15 (1986) 760. [15] J.F. Ziegler, J.P. Biersack, U. Littmark (Eds.), The Stopping and Ranges of Ions in Solids, Pergamon, New York, 1985. Available from: