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Dielectric response of heavy ion irradiated PADC track detector
Nuclear Instruments and Methods in Physics Research B 155 (1999) 116±119
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Dielectric response of heavy ion irradiated PADC q track detector T. Phukan a, D. Kanjilal b, T.D. Goswami a, H.L. Das a
a,*
Department of Physics, Gauhati University, Guwahati 781 014, Assam, India b Nuclear Science Centre, New Delhi 110 067, India Received 18 December 1998; received in revised form 9 March 1999
Abstract The frequency response of dielectric constant (0 ) has been studied both in the pristine and irradiated samples in the frequency range 80 Hz to 100 kHz. The frequency dependence of dielectric response for pristine and irradiated samples reveals the presence of a low frequency dispersion and a loss peak that can be related to interfacial polarisation between neighbouring carbon rich clusters. Formation of such clusters due to heavy ion irradiation has been ascertained by FTIR studies. The frequency dependence of 0 in both pristine and irradiated samples has been found to obey a relation of the type 0 / f nÿ1 , where n is a constant and f is the frequency. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 61.40.K; 61.80.J; 51.50 Keywords: Track detector; Ion irradiation; Dielectric constant
1. Introduction Due to the passage of a heavy ion in any track detector polymeric material, lattice deformations are produced. Depending upon the elastic strength of the lattice and the electric and dielectric properties of the pristine polymer material, the produced lattice deformations may remain as stored (latent) tracks or vanish by self-annealing in time [1]. The relevant electrical, dielectric and optical properties of the poly allyl diglucol carbonate
q
PADC (CR-39) ± Poly allyl diglucol carbonate. Corresponding author. Tel.: +0361-570533; fax: +0361570133. *
(PADC), commercially known as CR-39, exhibit modi®cations as a result of heavy ion irradiation. These modi®cations include rearrangement of bonding, formation of carbon-rich clusters in the polymer and changes in dielectric properties [2]. In this work, a study of the dielectric response of pristine and heavy ion irradiated PADC track detectors is presented.
2. Experimental details PADC samples of about 250 lm thickness were subjected to O5 (50 MeV) and Si8 (100 MeV) heavy ion irradiations of ¯uences (U) in the range 5 ´ 109 to 5 ´ 1012 cmÿ2 at the Nuclear Science
0168-583X/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 2 5 5 - 4
T. Phukan et al. / Nucl. Instr. and Meth. in Phys. Res. B 155 (1999) 116±119
Centre, New Delhi. Samples of dimension 0.9 cm ´ 0.9 cm were mounted on the liquid nitrogen cold ®nger arrangement of the scattering chamber. The irradiation temperatures were maintained at 85 2 K and vacuum was 3 ´ 10ÿ6 Torr. The dielectric constant of the samples was determined by measuring the capacitance of the samples. Simultaneously the loss factor was also measured. These parameters were measured with the help of a Marconi Universal bridge coupled with an external audio frequency generator. All the measurements were carried out in rotary pump vacuum. The accuracy of the bridge was 1% of the readings.
Fig. 1. Frequency response of dielectric constant of pristine and oxygen irradiated PADC samples. (a) Pristine, (b) U(O5 ) 5 ´ 1010 cmÿ2 , (c) U(O5 ) 5 ´ 1011 cmÿ2 and (d) U(O5 ) 5 ´ 1012 cmÿ2 .
117
3. Results and discussion Fig. 1 represents the dielectric response of the O5 irradiated samples compared to the pristine samples. It may be noted that for oxygen irradiated samples, the dielectric spectra consist of only one slope in the studied frequency region. For ¯uences in the range 5 ´ 1011 to 5 ´ 1012 cmÿ2 , the dielectric constant decreases to such a level that 0 lies lower than 0 of the pristine sample in the entire frequency range. Fig. 2 gives the characteristics of ln 00 vs ln f , where 00 is the dielectric loss. The value of 00 decreases with O5 ¯uence. The decrease of dielectric loss in oxygen irradiated samples is attributed to the fact that random (thermal) orientations of segments or groups of the polymeric material are faciliated due to bond dissociation [3]. The FTIR spectrum for O5 (5 ´ 1012 cmÿ2 ) irradiated samples reveals the formation of an increased number of conjugate (C¸C) bonds. The comparatively weaker C¸C bonds thus become a source of free carriers under the application of external bias. As a result, there will be
Fig. 2. Frequency response of dielectric loss of oxygen irradiated PADC samples. (a) U(O5 ) 5 ´ 1010 cmÿ2 , (b) U(O5 ) 5 ´ 1011 cmÿ2 and (c) U(O5 ) 5 ´ 1012 cmÿ2 .
118
T. Phukan et al. / Nucl. Instr. and Meth. in Phys. Res. B 155 (1999) 116±119
Fig. 4. Frequency response of dielectric loss of silicon irradiated PADC samples. (a) U(Si8 ) 1012 cmÿ2 and (b) U(Si8 ) 1010 cmÿ2 . Fig. 3. Frequency response of dielectric constant of silicon irradiated PADC samples. (a) U(Si8 ) 1012 cmÿ2 and (b) U(Si8 ) 1010 cmÿ2 .
increase in electrical conductivity and consequent decrease in the dielectric properties. Fig. 3 represents ln 0 vs ln f graphs of Si8 irradiated samples. It has been found that 0 increases with increasing ¯uence of Si8 . The dielectric spectra for Si8 irradiated samples are represented by two slopes as seen from the ®tted curves. The values of 0 in Si8 irradiated samples become higher compared to pristine values. From the FTIR spectrum for Si8 irradiated samples, it is seen that C¸C bonds break up to CAC bonds producing crosslinking eect [4]. Consequently, the free carrier density is substantially reduced. Fig. 4 gives the plot of ln 00 vs ln f for Si8 irradiated samples. From the ®tted curves, it is seen that the dielectric response in both pristine and irradiated samples obey the relation given by 0 / f nÿ1 and 0 00 / f n ÿ1 (in the post-peak region) where n and n0 are constants [5]. The values of n both for the
pristine and irradiated samples lie in the range 0.88 to 0.98 while the corresponding values of n0 lie in the range ÿ0.39 to 0.55. The nature of the frequency dependence of dielectric response for pristine and irradiated samples reveals the presence of a low frequency dispersion and a loss peak which can be related to interfacial polarisation [6]. Due to the presence of overlapping tracks of heavy ions, some of the polymer bonds are broken. As a result, some carbon rich clusters are formed in the polymer matrix [7,8]. This makes a favourable situation in the polymer matrix to develop built-in potential barriers in the depletion regions separating any two nearby clusters. The resulting dipoles in these capacitive regions thus give rise to interfacial polarisation. 4. Conclusion Due to heavy ion irradiation of the polymer, rearrangement of bonds occurs which results in modi®cations of the microstructures present in the
T. Phukan et al. / Nucl. Instr. and Meth. in Phys. Res. B 155 (1999) 116±119
polymer matrix. The modi®cations of these microstructures aect the dielectric properties of the material. The formation of C¸C bonds due to O5 heavy ion irradiation in the polymer matrix becomes the source of free carriers. The observed conversion of C¸C bonds to CAC bonds in the polymer due to Si8 irradiation causes a decrease of the free carriers by crosslinking and hence an increase in dielectric constant. Acknowledgements We highly acknowledge the Nuclear Science Center, New Delhi, for providing us ®nancial support and also some experimental facilities. References [1] R.L. Fleischer, P.B. Price, R.M. Walker, Nuclear Tracks in Solids: Principles and Applications, University of California Press, Berkley, 1975.
119
[2] A.L. Evelyn, D. Ila, R.L. Zimmerman, K. Bhat, D.B. Poker, D.K. Hensley, Nucl. Instr. and Meth. B 127/128 (1977) 694. [3] M. El-Shahawy, A. Hussein, A. Tawansi, J. Mater. Sci. 27 (1992) 6605. [4] L. Calcagno, G. Compagnini, G. Foti, Nucl. Instr. and Meth. B 65 (1992). [5] A.K. Jonscher, Nature 267 (1977). [6] M.L. Kaplan, S.R. Forrest, P.H. Schmidt, T. Venkatesan, J. Appl. Phys. 55 (3) (1984). [7] D. Fink, R. Klett, L.T. Chadderton, J. Cardoso, R. Montiel, M.H. Vazquez, A.A. Karanovich, Nucl. Instr. and Meth. B 111 (1996) 304. [8] D. Fink, W.H. Chung, R. Klett, A. Schmoldt, J. Cardoso, R. Montiel, M.H. Vazquez, L. Wang, F. Hosoi, H. Omichi, P. Goppelt-Langer, Radiation Eects and Defects in Solids (1995).
www.elsevier.nl/locate/nimb
Dielectric response of heavy ion irradiated PADC q track detector T. Phukan a, D. Kanjilal b, T.D. Goswami a, H.L. Das a
a,*
Department of Physics, Gauhati University, Guwahati 781 014, Assam, India b Nuclear Science Centre, New Delhi 110 067, India Received 18 December 1998; received in revised form 9 March 1999
Abstract The frequency response of dielectric constant (0 ) has been studied both in the pristine and irradiated samples in the frequency range 80 Hz to 100 kHz. The frequency dependence of dielectric response for pristine and irradiated samples reveals the presence of a low frequency dispersion and a loss peak that can be related to interfacial polarisation between neighbouring carbon rich clusters. Formation of such clusters due to heavy ion irradiation has been ascertained by FTIR studies. The frequency dependence of 0 in both pristine and irradiated samples has been found to obey a relation of the type 0 / f nÿ1 , where n is a constant and f is the frequency. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 61.40.K; 61.80.J; 51.50 Keywords: Track detector; Ion irradiation; Dielectric constant
1. Introduction Due to the passage of a heavy ion in any track detector polymeric material, lattice deformations are produced. Depending upon the elastic strength of the lattice and the electric and dielectric properties of the pristine polymer material, the produced lattice deformations may remain as stored (latent) tracks or vanish by self-annealing in time [1]. The relevant electrical, dielectric and optical properties of the poly allyl diglucol carbonate
q
PADC (CR-39) ± Poly allyl diglucol carbonate. Corresponding author. Tel.: +0361-570533; fax: +0361570133. *
(PADC), commercially known as CR-39, exhibit modi®cations as a result of heavy ion irradiation. These modi®cations include rearrangement of bonding, formation of carbon-rich clusters in the polymer and changes in dielectric properties [2]. In this work, a study of the dielectric response of pristine and heavy ion irradiated PADC track detectors is presented.
2. Experimental details PADC samples of about 250 lm thickness were subjected to O5 (50 MeV) and Si8 (100 MeV) heavy ion irradiations of ¯uences (U) in the range 5 ´ 109 to 5 ´ 1012 cmÿ2 at the Nuclear Science
0168-583X/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 2 5 5 - 4
T. Phukan et al. / Nucl. Instr. and Meth. in Phys. Res. B 155 (1999) 116±119
Centre, New Delhi. Samples of dimension 0.9 cm ´ 0.9 cm were mounted on the liquid nitrogen cold ®nger arrangement of the scattering chamber. The irradiation temperatures were maintained at 85 2 K and vacuum was 3 ´ 10ÿ6 Torr. The dielectric constant of the samples was determined by measuring the capacitance of the samples. Simultaneously the loss factor was also measured. These parameters were measured with the help of a Marconi Universal bridge coupled with an external audio frequency generator. All the measurements were carried out in rotary pump vacuum. The accuracy of the bridge was 1% of the readings.
Fig. 1. Frequency response of dielectric constant of pristine and oxygen irradiated PADC samples. (a) Pristine, (b) U(O5 ) 5 ´ 1010 cmÿ2 , (c) U(O5 ) 5 ´ 1011 cmÿ2 and (d) U(O5 ) 5 ´ 1012 cmÿ2 .
117
3. Results and discussion Fig. 1 represents the dielectric response of the O5 irradiated samples compared to the pristine samples. It may be noted that for oxygen irradiated samples, the dielectric spectra consist of only one slope in the studied frequency region. For ¯uences in the range 5 ´ 1011 to 5 ´ 1012 cmÿ2 , the dielectric constant decreases to such a level that 0 lies lower than 0 of the pristine sample in the entire frequency range. Fig. 2 gives the characteristics of ln 00 vs ln f , where 00 is the dielectric loss. The value of 00 decreases with O5 ¯uence. The decrease of dielectric loss in oxygen irradiated samples is attributed to the fact that random (thermal) orientations of segments or groups of the polymeric material are faciliated due to bond dissociation [3]. The FTIR spectrum for O5 (5 ´ 1012 cmÿ2 ) irradiated samples reveals the formation of an increased number of conjugate (C¸C) bonds. The comparatively weaker C¸C bonds thus become a source of free carriers under the application of external bias. As a result, there will be
Fig. 2. Frequency response of dielectric loss of oxygen irradiated PADC samples. (a) U(O5 ) 5 ´ 1010 cmÿ2 , (b) U(O5 ) 5 ´ 1011 cmÿ2 and (c) U(O5 ) 5 ´ 1012 cmÿ2 .
118
T. Phukan et al. / Nucl. Instr. and Meth. in Phys. Res. B 155 (1999) 116±119
Fig. 4. Frequency response of dielectric loss of silicon irradiated PADC samples. (a) U(Si8 ) 1012 cmÿ2 and (b) U(Si8 ) 1010 cmÿ2 . Fig. 3. Frequency response of dielectric constant of silicon irradiated PADC samples. (a) U(Si8 ) 1012 cmÿ2 and (b) U(Si8 ) 1010 cmÿ2 .
increase in electrical conductivity and consequent decrease in the dielectric properties. Fig. 3 represents ln 0 vs ln f graphs of Si8 irradiated samples. It has been found that 0 increases with increasing ¯uence of Si8 . The dielectric spectra for Si8 irradiated samples are represented by two slopes as seen from the ®tted curves. The values of 0 in Si8 irradiated samples become higher compared to pristine values. From the FTIR spectrum for Si8 irradiated samples, it is seen that C¸C bonds break up to CAC bonds producing crosslinking eect [4]. Consequently, the free carrier density is substantially reduced. Fig. 4 gives the plot of ln 00 vs ln f for Si8 irradiated samples. From the ®tted curves, it is seen that the dielectric response in both pristine and irradiated samples obey the relation given by 0 / f nÿ1 and 0 00 / f n ÿ1 (in the post-peak region) where n and n0 are constants [5]. The values of n both for the
pristine and irradiated samples lie in the range 0.88 to 0.98 while the corresponding values of n0 lie in the range ÿ0.39 to 0.55. The nature of the frequency dependence of dielectric response for pristine and irradiated samples reveals the presence of a low frequency dispersion and a loss peak which can be related to interfacial polarisation [6]. Due to the presence of overlapping tracks of heavy ions, some of the polymer bonds are broken. As a result, some carbon rich clusters are formed in the polymer matrix [7,8]. This makes a favourable situation in the polymer matrix to develop built-in potential barriers in the depletion regions separating any two nearby clusters. The resulting dipoles in these capacitive regions thus give rise to interfacial polarisation. 4. Conclusion Due to heavy ion irradiation of the polymer, rearrangement of bonds occurs which results in modi®cations of the microstructures present in the
T. Phukan et al. / Nucl. Instr. and Meth. in Phys. Res. B 155 (1999) 116±119
polymer matrix. The modi®cations of these microstructures aect the dielectric properties of the material. The formation of C¸C bonds due to O5 heavy ion irradiation in the polymer matrix becomes the source of free carriers. The observed conversion of C¸C bonds to CAC bonds in the polymer due to Si8 irradiation causes a decrease of the free carriers by crosslinking and hence an increase in dielectric constant. Acknowledgements We highly acknowledge the Nuclear Science Center, New Delhi, for providing us ®nancial support and also some experimental facilities. References [1] R.L. Fleischer, P.B. Price, R.M. Walker, Nuclear Tracks in Solids: Principles and Applications, University of California Press, Berkley, 1975.
119
[2] A.L. Evelyn, D. Ila, R.L. Zimmerman, K. Bhat, D.B. Poker, D.K. Hensley, Nucl. Instr. and Meth. B 127/128 (1977) 694. [3] M. El-Shahawy, A. Hussein, A. Tawansi, J. Mater. Sci. 27 (1992) 6605. [4] L. Calcagno, G. Compagnini, G. Foti, Nucl. Instr. and Meth. B 65 (1992). [5] A.K. Jonscher, Nature 267 (1977). [6] M.L. Kaplan, S.R. Forrest, P.H. Schmidt, T. Venkatesan, J. Appl. Phys. 55 (3) (1984). [7] D. Fink, R. Klett, L.T. Chadderton, J. Cardoso, R. Montiel, M.H. Vazquez, A.A. Karanovich, Nucl. Instr. and Meth. B 111 (1996) 304. [8] D. Fink, W.H. Chung, R. Klett, A. Schmoldt, J. Cardoso, R. Montiel, M.H. Vazquez, L. Wang, F. Hosoi, H. Omichi, P. Goppelt-Langer, Radiation Eects and Defects in Solids (1995).