- Email: [email protected]
Raman study of Kr ion irradiated sodium aluminoborosilicate glass
Nuclear Instruments and Methods in Physics Research B 307 (2013) 566–569
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Raman study of Kr ion irradiated sodium aluminoborosilicate glass L. Chen ⇑, T.S. Wang ⇑, K.J. Yang, H.B. Peng, G.F. Zhang, L.M. Zhang, H. Jiang, Q. Wang School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China
a r t i c l e
i n f o
a b s t r a c t
Article history: Received 30 September 2012 Received in revised form 28 January 2013 Accepted 30 January 2013 Available online 23 March 2013
Raman spectroscopy was used to investigate the microstructure evolution of sodium aluminoborosilicate glass after 4 MeV Kr17+ ions irradiation at various fluences from 3.1 1011 to 1.8 1015 ions/cm2. The Si–O–Si vibration band around 450 cm 1 was slightly shifted to higher Raman shift after irradiation, and stabilized after the nuclear deposited energy reached about 1024 eV/cm3. An increase in the population of 3-membered rings and decrease in the species of 4-membered rings were evidenced in the irradiated samples. These have been correlated to the densification process of glass. Depolymerization of glass network caused by Kr ion irradiation was also observed. These results indicate that the microstructural modifications caused by Kr ion irradiation are the consequence of ballistic effects. Ó 2013 Elsevier B.V. All rights reserved.
Keywords: Sodium aluminoborosilicate glass Radiation effects Raman spectroscopy Densification
1. Introduction Multicomponent aluminoborosilicate glasses are used for a wide variety of applications including flat panel display substrates, fiber glass, and photochromic glass. Understanding the structure evolution under irradiation is crucial for its basic and advanced technological applications, especially for evaluating its performance after long-term interactions with the irradiation environment. Ion irradiation is a powerful and versatile tool for this purpose, which is also already applied for the modification of silica and silicate glass surfaces [1–5]. The macroscopic and microscopic modifications induced by irradiation on silica have been extensively studied [1]. Radiation is observed to densify silica with a saturation of densification of around 3% for nuclear displacement doses 1 1024 eV/cm3, and energy deposited in the form of ionization is found to be nearly three orders of magnitude less efficient, 6 1026 eV/cm3. The densification process in silica can be attributed to stable point defect creation, reorganization through ‘‘rebonding’’ of the network. For complex oxide glass, Raman spectroscopy has been proved to be a particular effective tool and sensitive technique for studying the modifications on the network structure after irradiation [5– 7]. Changes in measured Raman spectra as a function of radiation dose can be explained in terms of localized bond length changes or changes in bonding angles and can provide unambiguous information about localized molecular species formed by radiation. Of special interest is borosilicate-based multi-component glass which ⇑ Corresponding authors. Tel.: +86 13619316564. E-mail addresses: (T.S. Wang).
[email protected]
(L.
Chen),
[email protected]
0168-583X/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nimb.2013.01.089
is used in nuclear industry, the modifications on the network structure induced by ion irradiation have been investigated by Raman spectroscopy [5]. The peak shift of Si–O–Si vibration band and depolymerization of glass network have been observed, which have been correlated to the densification process. However, the conclusion on the correlation of densification with polymerization was only based on that they have same trend with the increase of Na2O contents. This conclusion is inadequate in the case of electron irradiation, where densification was also observed while increase of polymerization was evidenced [6]. Thus, the micromechanism of these microscopic evolution under irradiation is still not well understood. In this study, Raman spectroscopy is used to investigate the microstructure evolution under ion irradiation in sodium aluminoborosilicate glass. The peak deconvolution method is employed to get accurate peak shift of Si–O–Si vibration band and information of the modifications on the ring structures. Based on our experimental results, the micromechanism of irradiation induced densification of glass network is discussed. 2. Experimental Commercial sodium aluminoborosilicate glass with composition 80.6 wt.% SiO2, 12.8 wt.% B2O3, 4.1 wt.% Na2O, 2.4 wt.% Al2O3 and minor others was used in this study. The sample size is 5 5 mm2, with a thickness of 0.5 mm. The irradiation was conducted by a 320 kV electron cyclotron resonance (ECR) ion source in the national laboratory of Heavy Ion Accelerator Research Facility, Lanzhou (HIRFL). All samples were irradiated with 4 MeV Kr17+ ions at room temperature. The beam current were about 50 nA and 2.0 lA, respectively, in order to reach a low and high fluence in
L. Chen et al. / Nuclear Instruments and Methods in Physics Research B 307 (2013) 566–569
reasonable time. Different fluences from 3.1 1011 to 1.8 1015 ions/cm2 were used in our irradiation experiment. The Raman spectra were obtained on a Labram HR 800 microspectrometer using the 532 nm line of an argon ion laser at 100 mW. In the present experimental conditions, the optical penetration depth of Raman excitation light was about 1 lm [5], which was less than the energy deposition range of 4 MeV Kr ion (about 3 lm [8]), so that the Raman spectra reflected the characteristics of near surface layer and could be considered as representative of the irradiated zones. The spectrometer resolution was approximately 1 cm 1. 3. Results and discussion The Raman spectra of pristine and irradiated glasses for Raman shifts between 200 1800 cm 1 are presented in Fig.1. All Raman spectra were normalized to the intensity of broad band observed around 450 cm 1 and shifted vertically for clarity. The intense band around 450 cm 1 dominates the Raman spectrum, which can be assigned to mixed stretching and bending modes of Si–O– Si units [9,10]. The weak shoulder at around 602 cm 1 corresponds to the symmetric oxygen breathing vibration of three-membered siloxane rings of SiO4 tetrahedra, which is so called D2 band [11,12]. The intense band at 800 cm 1 is assigned to the Si–O stretching vibration with dominant Si motion [12]. The band peaked at 930 cm 1 should arise from the B–O–Si bond stretching vibration [6]. The band around 1069 cm 1 is due to Si–O stretching in a structural unit with one nonbridging oxygen per silicon (Q3). The high-frequency band around 1170 cm 1 results from the presence of fully polymerized units (Q4) [9]. Finally, the broad band between 1250 and 1530 cm 1 can be assigned to B–O stretching in chain-type metaborate groups [6,10]. As shown in the inset of Fig.1, the intense band around 450 cm 1 is slightly shifted to higher Raman shift after irradiation. In addition, the intensity of D2 band (602 cm 1) increases with the ion fluence and then come with a saturation. However, as the overlaps of different peaks, it is very difficult to get quantitative results. Thus, based on the peak deconvolution method previous reported [10,13,14], the Raman spectrum in the range of 200 670 cm 1 was fitted with five Gaussian peaks, corresponding to mixed Si– O–Si bond stretching and bending vibration band, D1 and D2 band, respectively. A second-order polynominal for the background curve were used. In the processes of curve-fitting, the peak parameters, which are wave number, width and intensity, were adjusted
Fig. 1. Evolution of Raman spectra versus ion fluence (ions/cm2). Inset is an enlargement of band shift of 450 cm 1 band.
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to attain the least value of chi square by the Levenberg–Marquardst nonlinear least-squares optimization. The example of the fitting result of unirradiated sample is shown in Fig.2. The standard deviations of the fitted peak parameters were less than 2 cm 1 in position, and 10% in intensity, respectively. The evolutions of the peak position of Si–O–Si vibration band are shown in Fig.3. As we can see, the Raman shift of Si–O–Si vibration band is gradually increased with the increase of ion fluence. Since there is generally an inverse correlation between the frequency of this band and the Si–O–Si angle in condensed silicate [9], indicates that a decrease of the average Si–O–Si angle with increase of total fluence. A decrease of the Si–O–Si angle is generally interpreted as a decrease in the average size of SiO4 rings in glass network. A ring is a closed path consisting of Si–O bonds. The number of Si atoms in a ring is used to represent the size of this ring. The ring structure in amorphous silica is a well-accepted concept [15], which has a lognormal distribution extends from four- to ten-membered rings, with a maximum of about six-membered rings. For Na silicate glasses [16,17], as the increase of sodium concentration, the ring size distribution becomes essentially bimodal, the number of rings associated with the pure silica network structure (i.e., 4–10 membered rings) decreases with a corresponding increase of smaller and larger sized rings. The smaller rings are close to planar and present vibration frequencies that can be detected spectroscopically. As shown in Fig.2, the weak bands around 490 cm 1 (D1) and 610 cm 1 (D2) correspond to 4- and 3-membered rings can be resolved by curve-fitting of Raman spectrum. Radiation induced modifications on the ring structure of silica and silicate glass have been evidenced by both simulation and experiments [14,18], which have shown enhancement of the D1 and D2 bands associated with 4- and 3-membered rings, respectively. In our results, the intensities of the deconvoluted D1 and D2 peaks were normalized by that of the 450 cm 1 peak convoluted from the three Gaussians. As shown in Fig.4, the relative intensity of D1 is gradually decreased while the relative intensity of D2 band is increased with the ion fluence, corresponding to decrease in number of 4-membered rings and increase in population of 3-membered rings, respectively. This result is consistent with the increase the frequency of Si–O–Si vibration band (Fig.3), i.e., the decrease of average Si–O–Si angle. According to MD study of ring structures in vitreous silica by Rino et al. [19], the average Si–O– Si bond angle for three-membered rings was 130.5°. This value is
Fig. 2. Gaussian fits of Raman spectrum in the 200–670 cm 1 range of unirradiated glass. The dashed line is the convoluted curve with three Gaussian lines centered around 287 cm 1, 414 cm 1 and 463 cm 1, respectively, which is assigned to mixed Si–O–Si bond stretching and bending vibration band.
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L. Chen et al. / Nuclear Instruments and Methods in Physics Research B 307 (2013) 566–569
Fig. 3. Position changes of Si–O–Si vibration band versus ion fluence. (The dashed line is a guide for the eyes.).
Fig. 5. Gaussian fits of Raman spectrum in the 990–1290 cm ated glass.
1
range of unirradi-
Fig. 4. Evolution of D1, D2 intensities versus ion fluence. (The curves are the guides for the eyes.).
Fig. 6. Evolution of Q4/Q3 species concentration ratio versus ion fluence. (The dashed line is a guide for the eyes.).
smaller than the average of Si–O–Si bond angle in amorphous SiO2, at around 150°. Thus an increase in population of three-membered rings and decrease in species of 4-membered rings shift the angular distribution to lower angle, and also decrease in the average size of SiO4 rings. The decrease of the average Si–O–Si angle and average size of SiO4 rings are consistent with previous studies on silica and silicate glasses [6,14], which suggest that densification of glass network has been caused by Kr ion irradiation. The shifts of Si–O–Si band up to 30 cm 1 to higher Raman shift, obviously decrease of its band intensity and densified a-SiO2 by 3% have been observed, and saturated when the deposited energy in the form of nuclear displacement is 1 1024 eV/cm3 or 6 1026 eV/cm3 into ionization [1]. However, according to former result [20] (about 5.5 cm 1 per degree), the average Si–O–Si angle decreases less than 2° in our samples after 2 1014 ions/cm2 Kr ions irradiation and then stabilizes above this fluence, which correspond to a densification only about 1% even after nuclear deposited energy up to 1024 eV/cm3. Comparing with previous studies after neutron or electron irradiation [1,6], minor effects on densification can be caused by Kr ion irradiation, which may result from the recovery of most partial damage, caused by thermal quenching associated with thermal spike effect [21].
Moreover, the Qn bands also show slight changes in the band shape after irradiation with respect to the unirradiated samples. As the overlapping of each different Qn band, the Raman spectra were extracted out in order to clearly show the modifications on Qn species. After a linear subtraction for removing the background due to Rayleigh scattering, they were fitted with different Gaussian peaks as shown in Fig.5. Contributions from Q1, Q2 units were negligible for the glass networks, which are usually centered near 910 cm 1 and 960 cm 1, respectively. The Q4 component centered around 1150 cm 1 can be attributed to SiO4 units bonding SiO4 units, while the component at about 1225 cm 1 is assigned to SiO4 units bonding BO4 units. The ratios of Q4/Q3 obtained from the Gaussian fits and its relation with the fluence are shown in Fig.6, which slightly decreases as the fluence increase. It means that the intensity of the band corresponding to Q4 species decreases relatively to the bands of Q3 species, which indicates a decrease of the network polymerization after Kr-ions irradiation. This result is consistent with previous molecular dynamics simulation [22,23], which suggests that the decrease of polymerization are induced mainly by ballistic process. Ballistic collisions caused by incident Kr ions can permanently displace target atoms from their network sites and generate a larger numbers of intrinsic defects as a result of broken Si–O bonds,
L. Chen et al. / Nuclear Instruments and Methods in Physics Research B 307 (2013) 566–569
and thus cause significant depolymerization of glass network. The silicate network tries to maintain its structural continuity by the subsequent recombination of neighboring defects to reduce the potential energy of unpaired electron, and smaller-ring structures can be form through recombination of these intrinsic defects [14]. Therefore, the decrease of network polymerization is consistent with decrease in average size of SiO4 rings. 4. Conclusions The microstructure evolutions of sodium aluminoborosilicate glasses after Kr ion irradiation were studied by Raman spectroscopy. The polymerization of glass network is decreased after irradiation. More 3-membered rings are evidenced to be formed during the recombination of depolymerized glass network, which cause decrease in average size of SiO4 rings and average Si–O–Si angle. The average Si–O–Si angle is decreased by less than 2° after nuclear deposited energy up to 1024 eV/cm3 and then stabilized above this dose, indicating densification of only 1% have been caused by irradiation. Comparing with previous studies after neutron or electron irradiation, minor effects caused by Kr ion irradiation may result from the recovery of most partial damage, caused by thermal quenching associated with thermal spike effect. Acknowledgements The authors are grateful to the Public Center for Characterization and Test, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences. The ECR-group in Institute of Modern Physics, Lanzhou, is acknowledged for providing technical supports.
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References [1] R.A.B. Devine, Nucl. Instr. Meth. B 91 (1994) 378. [2] A. Abbas, Y. Serruys, D. Ghaleb, J.M. Delaye, B. Boizot, B. Reynard, G. Calas, Nucl. Instr. Meth. B 166 (2000) 445. [3] S. Peuget, P.-Y. Noel, J.-L. Loubet, S. Pavan, P. Nivet, A. Chenet, Nucl. Instr. Meth. B 246 (2006) 379. [4] S. Peuget, J.-N. Cachia, C. Jegou, X. Deschanels, D. Roudil, V. Broudic, J.M. Delaye, J.-M. Bart, J. Nucl. Mater. 354 (2006) 1. [5] J. Bonfils, S. Peuget, G. Panczer, D. ligny, S. Henry, P.Y. Noel, A. Chenet, B. Champagnon, J. Non-Cryst. Solids 356 (2010) 388. [6] B. Boizot, G. Petite, D. Ghaleb, B. Reynard, G. Calas, J. Non-Cryst. Solids 243 (1999) 268. [7] N. Ollier, B. Boizot, B. Reynard, D. Ghaleb, G. Petite, J. Nucl. Mater. 340 (2005) 209. [8] J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Pergamon, New York, 1985. [9] P.F. McMillan, Am. Mineral. 69 (1984) 622. [10] D. Manara, A. Grandjean, D.R. Neuville, Am. Mineral. 94 (2009) 777. [11] F.L. Galeener, R.A. Barrio, E. Martinez, R.J. Elliott, Phys. Rev. Lett. 53 (1984) 2429. [12] B. Boizot, S. Agnello, B. Reynard, R. Boscaino, G. Petite, J. Non-Cryst. Solids 325 (2003) 22. [13] D.D. Goller, R.T. Phillips, I.G. Sayce, J. Non-Cryst. Solids 355 (2009) 1747. [14] Tengfei Yang, Yuan Gao, Xuejun. Huang, Yanwen Zhang, Marcel Toulemonde, Jianming Xue, Sha Yan, Yugang Wang, J. Non-Cryst. Solids 357 (2011) 3245. [15] S. Kohara, K. Suzuya, J. Phys.: Condens. Matter 17 (2005) S77. [16] J. Du, A.N. Cormack, J. Non-Cryst. Solids 349 (2004) 66. [17] J. Du, A.N. Cormack, J. Non-Cryst. Solids 351 (2005) 2263. [18] F. Mota, M.-J. Caturla, J.M. Perlado, J. Mollá, A. Ibarra, J. Nucl. Mater. 386–388 (2009) 75. [19] J.P. Rino, I. Ebbsjo, R.K. Kalia, A. Nakano, P. Vashishta, Phys. Rev. B 47 (1993) 3053. [20] M. Okuno, B. Reynard, Y. Shimada, Y. Syono, C. Willaime, Phys. Chem. Miner. 26 (1999) 304. [21] W. Primak, Phys. Rev. 110 (1958) 1240. [22] J.-M. Delaye, D. Ghaleb, Phys. Rev. B 71 (2005) 224204. [23] J.-M. Delaye, D. Ghaleb, Nucl. Instr. Meth. B 250 (2006) 57.
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Raman study of Kr ion irradiated sodium aluminoborosilicate glass L. Chen ⇑, T.S. Wang ⇑, K.J. Yang, H.B. Peng, G.F. Zhang, L.M. Zhang, H. Jiang, Q. Wang School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China
a r t i c l e
i n f o
a b s t r a c t
Article history: Received 30 September 2012 Received in revised form 28 January 2013 Accepted 30 January 2013 Available online 23 March 2013
Raman spectroscopy was used to investigate the microstructure evolution of sodium aluminoborosilicate glass after 4 MeV Kr17+ ions irradiation at various fluences from 3.1 1011 to 1.8 1015 ions/cm2. The Si–O–Si vibration band around 450 cm 1 was slightly shifted to higher Raman shift after irradiation, and stabilized after the nuclear deposited energy reached about 1024 eV/cm3. An increase in the population of 3-membered rings and decrease in the species of 4-membered rings were evidenced in the irradiated samples. These have been correlated to the densification process of glass. Depolymerization of glass network caused by Kr ion irradiation was also observed. These results indicate that the microstructural modifications caused by Kr ion irradiation are the consequence of ballistic effects. Ó 2013 Elsevier B.V. All rights reserved.
Keywords: Sodium aluminoborosilicate glass Radiation effects Raman spectroscopy Densification
1. Introduction Multicomponent aluminoborosilicate glasses are used for a wide variety of applications including flat panel display substrates, fiber glass, and photochromic glass. Understanding the structure evolution under irradiation is crucial for its basic and advanced technological applications, especially for evaluating its performance after long-term interactions with the irradiation environment. Ion irradiation is a powerful and versatile tool for this purpose, which is also already applied for the modification of silica and silicate glass surfaces [1–5]. The macroscopic and microscopic modifications induced by irradiation on silica have been extensively studied [1]. Radiation is observed to densify silica with a saturation of densification of around 3% for nuclear displacement doses 1 1024 eV/cm3, and energy deposited in the form of ionization is found to be nearly three orders of magnitude less efficient, 6 1026 eV/cm3. The densification process in silica can be attributed to stable point defect creation, reorganization through ‘‘rebonding’’ of the network. For complex oxide glass, Raman spectroscopy has been proved to be a particular effective tool and sensitive technique for studying the modifications on the network structure after irradiation [5– 7]. Changes in measured Raman spectra as a function of radiation dose can be explained in terms of localized bond length changes or changes in bonding angles and can provide unambiguous information about localized molecular species formed by radiation. Of special interest is borosilicate-based multi-component glass which ⇑ Corresponding authors. Tel.: +86 13619316564. E-mail addresses: (T.S. Wang).
[email protected]
(L.
Chen),
[email protected]
0168-583X/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nimb.2013.01.089
is used in nuclear industry, the modifications on the network structure induced by ion irradiation have been investigated by Raman spectroscopy [5]. The peak shift of Si–O–Si vibration band and depolymerization of glass network have been observed, which have been correlated to the densification process. However, the conclusion on the correlation of densification with polymerization was only based on that they have same trend with the increase of Na2O contents. This conclusion is inadequate in the case of electron irradiation, where densification was also observed while increase of polymerization was evidenced [6]. Thus, the micromechanism of these microscopic evolution under irradiation is still not well understood. In this study, Raman spectroscopy is used to investigate the microstructure evolution under ion irradiation in sodium aluminoborosilicate glass. The peak deconvolution method is employed to get accurate peak shift of Si–O–Si vibration band and information of the modifications on the ring structures. Based on our experimental results, the micromechanism of irradiation induced densification of glass network is discussed. 2. Experimental Commercial sodium aluminoborosilicate glass with composition 80.6 wt.% SiO2, 12.8 wt.% B2O3, 4.1 wt.% Na2O, 2.4 wt.% Al2O3 and minor others was used in this study. The sample size is 5 5 mm2, with a thickness of 0.5 mm. The irradiation was conducted by a 320 kV electron cyclotron resonance (ECR) ion source in the national laboratory of Heavy Ion Accelerator Research Facility, Lanzhou (HIRFL). All samples were irradiated with 4 MeV Kr17+ ions at room temperature. The beam current were about 50 nA and 2.0 lA, respectively, in order to reach a low and high fluence in
L. Chen et al. / Nuclear Instruments and Methods in Physics Research B 307 (2013) 566–569
reasonable time. Different fluences from 3.1 1011 to 1.8 1015 ions/cm2 were used in our irradiation experiment. The Raman spectra were obtained on a Labram HR 800 microspectrometer using the 532 nm line of an argon ion laser at 100 mW. In the present experimental conditions, the optical penetration depth of Raman excitation light was about 1 lm [5], which was less than the energy deposition range of 4 MeV Kr ion (about 3 lm [8]), so that the Raman spectra reflected the characteristics of near surface layer and could be considered as representative of the irradiated zones. The spectrometer resolution was approximately 1 cm 1. 3. Results and discussion The Raman spectra of pristine and irradiated glasses for Raman shifts between 200 1800 cm 1 are presented in Fig.1. All Raman spectra were normalized to the intensity of broad band observed around 450 cm 1 and shifted vertically for clarity. The intense band around 450 cm 1 dominates the Raman spectrum, which can be assigned to mixed stretching and bending modes of Si–O– Si units [9,10]. The weak shoulder at around 602 cm 1 corresponds to the symmetric oxygen breathing vibration of three-membered siloxane rings of SiO4 tetrahedra, which is so called D2 band [11,12]. The intense band at 800 cm 1 is assigned to the Si–O stretching vibration with dominant Si motion [12]. The band peaked at 930 cm 1 should arise from the B–O–Si bond stretching vibration [6]. The band around 1069 cm 1 is due to Si–O stretching in a structural unit with one nonbridging oxygen per silicon (Q3). The high-frequency band around 1170 cm 1 results from the presence of fully polymerized units (Q4) [9]. Finally, the broad band between 1250 and 1530 cm 1 can be assigned to B–O stretching in chain-type metaborate groups [6,10]. As shown in the inset of Fig.1, the intense band around 450 cm 1 is slightly shifted to higher Raman shift after irradiation. In addition, the intensity of D2 band (602 cm 1) increases with the ion fluence and then come with a saturation. However, as the overlaps of different peaks, it is very difficult to get quantitative results. Thus, based on the peak deconvolution method previous reported [10,13,14], the Raman spectrum in the range of 200 670 cm 1 was fitted with five Gaussian peaks, corresponding to mixed Si– O–Si bond stretching and bending vibration band, D1 and D2 band, respectively. A second-order polynominal for the background curve were used. In the processes of curve-fitting, the peak parameters, which are wave number, width and intensity, were adjusted
Fig. 1. Evolution of Raman spectra versus ion fluence (ions/cm2). Inset is an enlargement of band shift of 450 cm 1 band.
567
to attain the least value of chi square by the Levenberg–Marquardst nonlinear least-squares optimization. The example of the fitting result of unirradiated sample is shown in Fig.2. The standard deviations of the fitted peak parameters were less than 2 cm 1 in position, and 10% in intensity, respectively. The evolutions of the peak position of Si–O–Si vibration band are shown in Fig.3. As we can see, the Raman shift of Si–O–Si vibration band is gradually increased with the increase of ion fluence. Since there is generally an inverse correlation between the frequency of this band and the Si–O–Si angle in condensed silicate [9], indicates that a decrease of the average Si–O–Si angle with increase of total fluence. A decrease of the Si–O–Si angle is generally interpreted as a decrease in the average size of SiO4 rings in glass network. A ring is a closed path consisting of Si–O bonds. The number of Si atoms in a ring is used to represent the size of this ring. The ring structure in amorphous silica is a well-accepted concept [15], which has a lognormal distribution extends from four- to ten-membered rings, with a maximum of about six-membered rings. For Na silicate glasses [16,17], as the increase of sodium concentration, the ring size distribution becomes essentially bimodal, the number of rings associated with the pure silica network structure (i.e., 4–10 membered rings) decreases with a corresponding increase of smaller and larger sized rings. The smaller rings are close to planar and present vibration frequencies that can be detected spectroscopically. As shown in Fig.2, the weak bands around 490 cm 1 (D1) and 610 cm 1 (D2) correspond to 4- and 3-membered rings can be resolved by curve-fitting of Raman spectrum. Radiation induced modifications on the ring structure of silica and silicate glass have been evidenced by both simulation and experiments [14,18], which have shown enhancement of the D1 and D2 bands associated with 4- and 3-membered rings, respectively. In our results, the intensities of the deconvoluted D1 and D2 peaks were normalized by that of the 450 cm 1 peak convoluted from the three Gaussians. As shown in Fig.4, the relative intensity of D1 is gradually decreased while the relative intensity of D2 band is increased with the ion fluence, corresponding to decrease in number of 4-membered rings and increase in population of 3-membered rings, respectively. This result is consistent with the increase the frequency of Si–O–Si vibration band (Fig.3), i.e., the decrease of average Si–O–Si angle. According to MD study of ring structures in vitreous silica by Rino et al. [19], the average Si–O– Si bond angle for three-membered rings was 130.5°. This value is
Fig. 2. Gaussian fits of Raman spectrum in the 200–670 cm 1 range of unirradiated glass. The dashed line is the convoluted curve with three Gaussian lines centered around 287 cm 1, 414 cm 1 and 463 cm 1, respectively, which is assigned to mixed Si–O–Si bond stretching and bending vibration band.
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L. Chen et al. / Nuclear Instruments and Methods in Physics Research B 307 (2013) 566–569
Fig. 3. Position changes of Si–O–Si vibration band versus ion fluence. (The dashed line is a guide for the eyes.).
Fig. 5. Gaussian fits of Raman spectrum in the 990–1290 cm ated glass.
1
range of unirradi-
Fig. 4. Evolution of D1, D2 intensities versus ion fluence. (The curves are the guides for the eyes.).
Fig. 6. Evolution of Q4/Q3 species concentration ratio versus ion fluence. (The dashed line is a guide for the eyes.).
smaller than the average of Si–O–Si bond angle in amorphous SiO2, at around 150°. Thus an increase in population of three-membered rings and decrease in species of 4-membered rings shift the angular distribution to lower angle, and also decrease in the average size of SiO4 rings. The decrease of the average Si–O–Si angle and average size of SiO4 rings are consistent with previous studies on silica and silicate glasses [6,14], which suggest that densification of glass network has been caused by Kr ion irradiation. The shifts of Si–O–Si band up to 30 cm 1 to higher Raman shift, obviously decrease of its band intensity and densified a-SiO2 by 3% have been observed, and saturated when the deposited energy in the form of nuclear displacement is 1 1024 eV/cm3 or 6 1026 eV/cm3 into ionization [1]. However, according to former result [20] (about 5.5 cm 1 per degree), the average Si–O–Si angle decreases less than 2° in our samples after 2 1014 ions/cm2 Kr ions irradiation and then stabilizes above this fluence, which correspond to a densification only about 1% even after nuclear deposited energy up to 1024 eV/cm3. Comparing with previous studies after neutron or electron irradiation [1,6], minor effects on densification can be caused by Kr ion irradiation, which may result from the recovery of most partial damage, caused by thermal quenching associated with thermal spike effect [21].
Moreover, the Qn bands also show slight changes in the band shape after irradiation with respect to the unirradiated samples. As the overlapping of each different Qn band, the Raman spectra were extracted out in order to clearly show the modifications on Qn species. After a linear subtraction for removing the background due to Rayleigh scattering, they were fitted with different Gaussian peaks as shown in Fig.5. Contributions from Q1, Q2 units were negligible for the glass networks, which are usually centered near 910 cm 1 and 960 cm 1, respectively. The Q4 component centered around 1150 cm 1 can be attributed to SiO4 units bonding SiO4 units, while the component at about 1225 cm 1 is assigned to SiO4 units bonding BO4 units. The ratios of Q4/Q3 obtained from the Gaussian fits and its relation with the fluence are shown in Fig.6, which slightly decreases as the fluence increase. It means that the intensity of the band corresponding to Q4 species decreases relatively to the bands of Q3 species, which indicates a decrease of the network polymerization after Kr-ions irradiation. This result is consistent with previous molecular dynamics simulation [22,23], which suggests that the decrease of polymerization are induced mainly by ballistic process. Ballistic collisions caused by incident Kr ions can permanently displace target atoms from their network sites and generate a larger numbers of intrinsic defects as a result of broken Si–O bonds,
L. Chen et al. / Nuclear Instruments and Methods in Physics Research B 307 (2013) 566–569
and thus cause significant depolymerization of glass network. The silicate network tries to maintain its structural continuity by the subsequent recombination of neighboring defects to reduce the potential energy of unpaired electron, and smaller-ring structures can be form through recombination of these intrinsic defects [14]. Therefore, the decrease of network polymerization is consistent with decrease in average size of SiO4 rings. 4. Conclusions The microstructure evolutions of sodium aluminoborosilicate glasses after Kr ion irradiation were studied by Raman spectroscopy. The polymerization of glass network is decreased after irradiation. More 3-membered rings are evidenced to be formed during the recombination of depolymerized glass network, which cause decrease in average size of SiO4 rings and average Si–O–Si angle. The average Si–O–Si angle is decreased by less than 2° after nuclear deposited energy up to 1024 eV/cm3 and then stabilized above this dose, indicating densification of only 1% have been caused by irradiation. Comparing with previous studies after neutron or electron irradiation, minor effects caused by Kr ion irradiation may result from the recovery of most partial damage, caused by thermal quenching associated with thermal spike effect. Acknowledgements The authors are grateful to the Public Center for Characterization and Test, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences. The ECR-group in Institute of Modern Physics, Lanzhou, is acknowledged for providing technical supports.
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References [1] R.A.B. Devine, Nucl. Instr. Meth. B 91 (1994) 378. [2] A. Abbas, Y. Serruys, D. Ghaleb, J.M. Delaye, B. Boizot, B. Reynard, G. Calas, Nucl. Instr. Meth. B 166 (2000) 445. [3] S. Peuget, P.-Y. Noel, J.-L. Loubet, S. Pavan, P. Nivet, A. Chenet, Nucl. Instr. Meth. B 246 (2006) 379. [4] S. Peuget, J.-N. Cachia, C. Jegou, X. Deschanels, D. Roudil, V. Broudic, J.M. Delaye, J.-M. Bart, J. Nucl. Mater. 354 (2006) 1. [5] J. Bonfils, S. Peuget, G. Panczer, D. ligny, S. Henry, P.Y. Noel, A. Chenet, B. Champagnon, J. Non-Cryst. Solids 356 (2010) 388. [6] B. Boizot, G. Petite, D. Ghaleb, B. Reynard, G. Calas, J. Non-Cryst. Solids 243 (1999) 268. [7] N. Ollier, B. Boizot, B. Reynard, D. Ghaleb, G. Petite, J. Nucl. Mater. 340 (2005) 209. [8] J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Pergamon, New York, 1985. [9] P.F. McMillan, Am. Mineral. 69 (1984) 622. [10] D. Manara, A. Grandjean, D.R. Neuville, Am. Mineral. 94 (2009) 777. [11] F.L. Galeener, R.A. Barrio, E. Martinez, R.J. Elliott, Phys. Rev. Lett. 53 (1984) 2429. [12] B. Boizot, S. Agnello, B. Reynard, R. Boscaino, G. Petite, J. Non-Cryst. Solids 325 (2003) 22. [13] D.D. Goller, R.T. Phillips, I.G. Sayce, J. Non-Cryst. Solids 355 (2009) 1747. [14] Tengfei Yang, Yuan Gao, Xuejun. Huang, Yanwen Zhang, Marcel Toulemonde, Jianming Xue, Sha Yan, Yugang Wang, J. Non-Cryst. Solids 357 (2011) 3245. [15] S. Kohara, K. Suzuya, J. Phys.: Condens. Matter 17 (2005) S77. [16] J. Du, A.N. Cormack, J. Non-Cryst. Solids 349 (2004) 66. [17] J. Du, A.N. Cormack, J. Non-Cryst. Solids 351 (2005) 2263. [18] F. Mota, M.-J. Caturla, J.M. Perlado, J. Mollá, A. Ibarra, J. Nucl. Mater. 386–388 (2009) 75. [19] J.P. Rino, I. Ebbsjo, R.K. Kalia, A. Nakano, P. Vashishta, Phys. Rev. B 47 (1993) 3053. [20] M. Okuno, B. Reynard, Y. Shimada, Y. Syono, C. Willaime, Phys. Chem. Miner. 26 (1999) 304. [21] W. Primak, Phys. Rev. 110 (1958) 1240. [22] J.-M. Delaye, D. Ghaleb, Phys. Rev. B 71 (2005) 224204. [23] J.-M. Delaye, D. Ghaleb, Nucl. Instr. Meth. B 250 (2006) 57.