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Solubilized multi-walled carbon nanotubes with broadband optical limiting effect
20 June 2002
Chemical Physics Letters 359 (2002) 191–195 www.elsevier.com/locate/cplett
Solubilized multi-walled carbon nanotubes with broadband optical limiting effect Luqi Liu a, Shuang Zhang a, Tengjiao Hu a, Zhi-Xin Guo Liming Dai a,b, Daoben Zhu a a
a,*
, Cheng Ye a,
Institute of Chemistry, Center for Molecular Sciences, Chinese Academy of Sciences, Beijing 100080, China b CSIRO Molecular Science, Bag 10, Clayton South, Vic. 3169, Australia Received 15 March 2002
Abstract Multi-walled carbon nanotubes (MWNTs) were solubilized in organic solvents by the reaction of a secondary amine with the carboxylic acid groups bound to nanotubes. The solubilized MWNTs exhibited good optical limiting performances in both 532 and 1064 nm nanosecond laser pulses, which indicating that the solubilized carbon nanotubes are candidates for potential broadband optical limiting materials. A possible mechanism for the observed effects is suggested. Ó 2002 Elsevier Science B.V. All rights reserved.
1. Introduction Since their discovery by Iijima in 1991 [1], carbon nanotubes have emerged as a novel class of materials with unique physical properties and many potential applications [2–4]. The chemical modification of carbon nanotubes have also received much recent attention. For example, Haddon first synthesized solubilized carbon nanotubes by the amidation reaction of long chain amines with carboxylic acid groups bound to nanotubes [5,6]. Sun and co-workers reported the functionalization of carbon nanotubes with aminopolymers by the similar reaction [7,8]. The aminopolymer modified nanotubes also show
*
Corresponding author. Fax: +86-10-6255-9373. E-mail address: [email protected] (Z.-X. Guo).
strong photoinduced luminescence [7]. Very recently, the sidewall functionalization of carbon nanotubes through nucleophilic reaction, cycloaddition reaction, and radical addition have also been reported [9–11]. Carbon nanotubes have been proved to be good optical limiters [12–15]. The most attractive feature is the broadband optical limiting effect. Because of its poor solubility, the optical limiting response of carbon nanotubes were measured in suspension which were unstable at high concentration. Hence it is highly desirable to obtain stable solutions containing carbon nanotubes and study the optical limiting properties [16]. In this Letter, we report the solubilization of multi-walled carbon nanotubes (MWNTs) by secondary amine through carboxylic acid groups bound to nanotubes. The solubilized MWNTs were characterized by UV–Vis-NIR absorption, transmission electron
0009-2614/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4 ( 0 2 ) 0 0 7 1 0 - 8
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L. Liu et al. / Chemical Physics Letters 359 (2002) 191–195
microscopy (TEM), and laser light scattering (LLS). The optical limiting behavior of the solubilized MWNTs was investigated at both 532 and 1064 nm using a nanosecond laser.
2. Experimental 2.1. Materials MWNTs were purchased from Sun Nanotech (Nanchang, China). The nanotubes were produced via the chemical vapor deposition (CVD) method and well characterized [17]. The MWNTs were purified by the following method: 1 g of the pristine MWNTs was refluxed 36 h in 30 ml of concentrated nitric acid. The excess concentrated nitric acid was removed by centrifuging. The resulting black solid was washed thoroughly with deionized water until the pH value of the water is about 5–6. The purified MWNTs were dried at 50 °C in the vacuum overnight before use. The solubilized MWNTs were obtained by the following route: 100 mg of purified MWNTs were stirred in 20 ml of SOCl2 at 76 °C for 24 h to convert the surface-bound carboxylic acid groups of MWNTs into acylchloride groups. After centrifugation, the remaining solid was washed with anhydrous tetrahydrofuran. 10 mg of this nanotubes were then mixed well with 100 mg of didecylamine (DDA) and the mixture was heated at 90–100 °C for 96 h. After cooling to room temperature, the excess DDA was removed by repeated washing with ethanol. The remaining solid was dissolved in chloroform and was centrifuged to remove any residual insoluble materials. The final sample was obtained by filtering the solution through 0:2 lm PTFE membrane, resulting a homogeneous black solution (MDDA). The octadecylamine modified carbon nanotubes (MODA) were also obtained through the above procedure as well as the procedure reported by the literature [5].
linear transmittance parts in the NIR region were measured using a computer controlled Nicolet Magna IR-750 spectrometer. TEM analyses were conducted on Hitachi H-800 transmission electron microscopy system. The operation voltage is 100 kV. The size distribution of the solubilized nanotubes was measured by dynamic laser light scattering (LLS) spectrometer (ALV/SP-125 with the incident light wavelength at 632.8 nm) at the angle of 15°. The optical limiting measurements were performed with linearly polarized 10 ns pulses generated from a Q-switched Nd:YAG laser at 1064 or 532 nm. The spatial profiles of the pulses were nearly of Gaussian form. The pulses were split into two parts: the reflected was used as reference. The sample was placed in a 1 mm quartz cuvette and measured by Z-scan method [18]. In our experiments, the maximum incident fluence at the sample was set at 10 J=cm2 . The incident and transmitted pulse energies were detected simultaneously by using two power meters (LPE-1A) individually. The laser pulses were produced at single shots or 10 Hz repetition rate. All of the sample concentrations were adjusted to have same linear transmittance of 50% at 532 nm.
3. Results and discussion The black homogeneous solution is a simple visual indication of nanotubes. Fig. 1 shows the
2.2. Measurements Linear transmittance spectra in the UV–Vis region were obtained using a computer controlled Shimadzu UV-2501PC spectrophotometer. The
Fig. 1. Transmission spectra of MDDA (solid dash), MODA (dashed line) in chloroform.
L. Liu et al. / Chemical Physics Letters 359 (2002) 191–195
193
(a)
Fig. 3. Size distribution of MDDA in toluene obtained by dynamic light scattering.
(b) Fig. 2. TEM images of purified MWNTs (a) and MDDA (b).
linear transmittance spectra of MDDA, and MODA in chloroform solution, respectively. These spectra are very similar and essentially featureless in the measured region, similar to the spectra of other solubilized carbon nanotubes [10]. The TEM images provide the most direct evidence for the presence of nanotubes in the colored solutions. Fig. 2b is a typical TEM image of the samples prepared from the MDDA solution. The nanotubes are well dispersed with an average diameter of 30 nm and length of several hundred nanometers. Compared with the TEM image of the precursor purified nanotubes (Fig. 2a), the solubilized nanotubes have the same morphology as that of the purified tubes, indicating that the solubilization does not affect the morphology of the nanotubes. The TEM images also imply a relatively high concentration of nanotubes in the homogeneous solution. Fig. 3 shows the size distribution of the solubilized MDDA in toluene measured by the method of dynamic LLS. The size distribution is relatively narrow, the hydrodynamic radius of the nanotubes centers at 58.9 nm with a range from 24.9 to
161.5 nm. The combination of the mean square radius of gyration, hydrodynamic radius and the diameter of the nanotube reveals that the scattering substrates are not rigid rods. This is in agreement with the TEM images of MDDA. The optical limiting performance of MDDA and MODA in chloroform were measured in both 532 and 1064 nm of nanosecond laser pulses. C60 was employed as a standard in the 532 nm pulses. For comparison, the concentrations of all samples were adjusted to be 50% linear transmittance at 532 nm. For the 532 nm pulses, the nonlinear transmission of both MDDA and MODA occur at 0:1 J=cm2 , almost the same as that of C60 . Also, the optical performance of both MDDA and MODA in homogeneous solutions are comparable with that of C60 in toluene up to 6 J=cm2 of 532 nm nanosecond pulses (Fig. 4a). At 1064 nm, both of MDDA and MODA begin to show nonlinear transmission at 0:2 J=cm2 and exhibit the good optical limiting performance in the range of measurements (Fig. 4b), while C60 does not limit any light at all. These results imply the solubilized MWNTs are good optical limiters at both 532 and 1064 nm. It was reported that carbon nanotube suspensions were not only found to be competitive optical limiters at 532 nm but also appeared to be very efficient at 1064 nm [12,13,19,20]. Mechanistically, it has been proposed that optical response of the carbon nanotubes suspension is dominated by
194
L. Liu et al. / Chemical Physics Letters 359 (2002) 191–195
(a)
(b) Fig. 4. (a) Optical limiting responses to 10 ns, 532 nm optical pulses, of MDDA ( ), MODA (M), and C60 () in chloroform solutions; (b) Optical limiting responses to 10 ns, 1064 nm optical pulses, of MDDA ( ) and MODA (M) in chloroform solutions.
nonlinear scattering, essentially sharing the same mechanism with that of carbon black suspension. Other mechanisms such as self-defocusing and thermal lensing have also been suggested [14,19]. In the nonlinear scattering process, heating due to the presence of the laser pulses can lead to vaporization and ionization of carbon nanotubes, and then form rapidly expanding microplasmas. In return, these microplasma strongly scatter light from the transmitted beam direction, leading to the decrease in the measured transmitted light energy. At the same time, the heat conduction from the nanotubes to the surrounding liquid lead to solvent microbubbles growth, which could decrease in the measured transmitted light. Recently, Sun and co-workers [16] synthesized aminopolymer modified solubilized carbon nanotubes and
measured their optical limiting properties for 532 nm pulsed laser irradiation. The optical limiting performance was weaker than that of C60 solution. They proposed a nonlinear absorption mechanism for the optical limiting of the solubilized carbon nanotubes based on that the polymer-bound carbon nanotubes are solely responsible for the observed light absorption at 532 nm. The present results in this study show that the optical limiting performances of both MDDA and MODA in homogeneous solutions are comparable with that of C60 at 532 nm. Moreover, both of the solubilized carbon nanotubes show good optical limiting performances at 1064 nm. In addition, the nanotube moieties in the homogeneous solution of both of MDDA and MODA absorb light of 532 nm, but also absorb light of 1064 nm (Fig. 1), strongly support the nonlinear absorption mechanism. This deduction is supported by recent nanosecond flash photolysis measurements of MDDA in homogeneous solution of chloroform or toluene [21]. The transient absorption spectrum shows a featureless broadband absorption in the range of 350–850 nm, very similar to the ground state absorption. The lifetime of the dominant excited state absorption is less than a few nanoseconds, which is typically the singlet–singlet excited states absorption. This implies that the nonlinear absorption mechanism for the solubilized carbon nanotubes should be different from that of C60 , which dominates triplet–triplet excited states absorption. In summary, good optical limiting responses of a new solubilized carbon nanotube have been observed at both 532 and 1064 nm with nanosecond laser pulses. A nonlinear absorption mechanism is proposed and discussed. The solubilized carbon nanotubes are flexible and have potential application in the protection of optical sensors from high-intensity laser beams, particularly in the infrared spectral region.
Acknowledgements This work was supported by the Chinese Academy of Sciences and the Major State Basic Research Development Program (Grant No. G2000077500).
L. Liu et al. / Chemical Physics Letters 359 (2002) 191–195
References [1] S. Iijima, Nature (London) 354 (1991) 56. [2] M.S. Dresselhaus, G. Dresselhaus, P.C. Eklund, Science of Fullerenes and Carbon Nanotubes, Academic, New York, 1996. [3] K. Tanaka, T. Yamabe, K. Fukui, The Science and Technology of Carbon Nanotubes, Elsevier, Amsterdam, 1999. [4] P.J.F. Harris, Carbon Nanotubes and Related Structures: New Materials for The Twenty-first Century, Cambridge University, Cambridge, 1999. [5] J. Chen, M.A. Hamon, H. Hu, Y. Chen, A.M. Rao, P.C. Eklund, R.C. Haddon, Science 282 (1998) 95. [6] M.A. Hamon, J. Chen, H. Hu, Y. Chen, M.E. Itkis, A.M. Rao, P.C. Eklund, R.C. Haddon, Adv. Mater. 11 (1999) 834. [7] J.E. Riggs, Z. Guo, D.L. Carroll, Y.P. Sun, J. Am. Chem. Soc. 122 (2000) 5879. [8] R. Czerw, Z. Guo, P.M. Ajayan, Y.P. Sun, D.L. Carroll, Nano Lett. 1 (2001) 423. [9] Y. Sun, S.R. Wilson, D.L. Schuster, J. Am. Chem. Soc. 123 (2001) 5348. [10] J.L. Bahr, J. Yang, D.V. Kosynkin, M.J. Bronikowski, R.E. Smalley, J.M. Tour, J. Am. Chem. Soc. 123 (2001) 6536.
195
[11] M. Holzinger, O. Vostrowsky, A. Hirsch, F. Hennrich, M. Kappes, R. Weiss, F. Jellen, Angew. Chem. Int. Ed. 40 (2001) 4002. [12] X. Sun, R.Q. Yu, G.Q. Xu, T.S.A. Hor, W. Ji, Appl. Phys. Lett. 73 (1998) 3632. [13] P. Chen, X. Wu, X. Sun, J. Lin, W. Ji, K.L. Tan, Phys. Rev. Lett. 82 (1999) 2548. [14] L. Vivien, E. Anglaret, D. Riehl, F. Bacou, C. Journet, C. Goze, M. Andrieux, M. Brunet, F. Lafonta, P. Bernier, F. Hache, Chem. Phys. Lett. 307 (1999) 317. [15] S.R. Mishra, H.S. Rawat, S.C. Mehendale, K.C. Rustagi, A.K. Sood, R. Bandyopadhyay, A. Govindaraj, C.N.R. Rao, Chem. Phys. Lett. 317 (2000) 510. [16] J.E. Riggs, D.B. Walker, D.L. Carroll, Y.P. Sun, J. Phys. Chem. B 104 (2000) 7071. [17] http:// www.sunnano.com. [18] P. Wang, S. Zhang, P. Wu, C. Ye, H. Liu, F. Xi, Chem. Phys. Lett. 340 (2001) 261. [19] L. Vivien, D. Riehl, P. Lancon, F. Hache, E. Anglaret, Opt. Lett. 26 (2001) 223. [20] L. Vivien, D. Riehl, F. Hache, E. Anglaret, J. Nonlinear Opt. Phys. Mater. 9 (2000) 297. [21] J. Feng, L. Liu, J. Zhang, Z. Guo, (in preparation).
Chemical Physics Letters 359 (2002) 191–195 www.elsevier.com/locate/cplett
Solubilized multi-walled carbon nanotubes with broadband optical limiting effect Luqi Liu a, Shuang Zhang a, Tengjiao Hu a, Zhi-Xin Guo Liming Dai a,b, Daoben Zhu a a
a,*
, Cheng Ye a,
Institute of Chemistry, Center for Molecular Sciences, Chinese Academy of Sciences, Beijing 100080, China b CSIRO Molecular Science, Bag 10, Clayton South, Vic. 3169, Australia Received 15 March 2002
Abstract Multi-walled carbon nanotubes (MWNTs) were solubilized in organic solvents by the reaction of a secondary amine with the carboxylic acid groups bound to nanotubes. The solubilized MWNTs exhibited good optical limiting performances in both 532 and 1064 nm nanosecond laser pulses, which indicating that the solubilized carbon nanotubes are candidates for potential broadband optical limiting materials. A possible mechanism for the observed effects is suggested. Ó 2002 Elsevier Science B.V. All rights reserved.
1. Introduction Since their discovery by Iijima in 1991 [1], carbon nanotubes have emerged as a novel class of materials with unique physical properties and many potential applications [2–4]. The chemical modification of carbon nanotubes have also received much recent attention. For example, Haddon first synthesized solubilized carbon nanotubes by the amidation reaction of long chain amines with carboxylic acid groups bound to nanotubes [5,6]. Sun and co-workers reported the functionalization of carbon nanotubes with aminopolymers by the similar reaction [7,8]. The aminopolymer modified nanotubes also show
*
Corresponding author. Fax: +86-10-6255-9373. E-mail address: [email protected] (Z.-X. Guo).
strong photoinduced luminescence [7]. Very recently, the sidewall functionalization of carbon nanotubes through nucleophilic reaction, cycloaddition reaction, and radical addition have also been reported [9–11]. Carbon nanotubes have been proved to be good optical limiters [12–15]. The most attractive feature is the broadband optical limiting effect. Because of its poor solubility, the optical limiting response of carbon nanotubes were measured in suspension which were unstable at high concentration. Hence it is highly desirable to obtain stable solutions containing carbon nanotubes and study the optical limiting properties [16]. In this Letter, we report the solubilization of multi-walled carbon nanotubes (MWNTs) by secondary amine through carboxylic acid groups bound to nanotubes. The solubilized MWNTs were characterized by UV–Vis-NIR absorption, transmission electron
0009-2614/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4 ( 0 2 ) 0 0 7 1 0 - 8
192
L. Liu et al. / Chemical Physics Letters 359 (2002) 191–195
microscopy (TEM), and laser light scattering (LLS). The optical limiting behavior of the solubilized MWNTs was investigated at both 532 and 1064 nm using a nanosecond laser.
2. Experimental 2.1. Materials MWNTs were purchased from Sun Nanotech (Nanchang, China). The nanotubes were produced via the chemical vapor deposition (CVD) method and well characterized [17]. The MWNTs were purified by the following method: 1 g of the pristine MWNTs was refluxed 36 h in 30 ml of concentrated nitric acid. The excess concentrated nitric acid was removed by centrifuging. The resulting black solid was washed thoroughly with deionized water until the pH value of the water is about 5–6. The purified MWNTs were dried at 50 °C in the vacuum overnight before use. The solubilized MWNTs were obtained by the following route: 100 mg of purified MWNTs were stirred in 20 ml of SOCl2 at 76 °C for 24 h to convert the surface-bound carboxylic acid groups of MWNTs into acylchloride groups. After centrifugation, the remaining solid was washed with anhydrous tetrahydrofuran. 10 mg of this nanotubes were then mixed well with 100 mg of didecylamine (DDA) and the mixture was heated at 90–100 °C for 96 h. After cooling to room temperature, the excess DDA was removed by repeated washing with ethanol. The remaining solid was dissolved in chloroform and was centrifuged to remove any residual insoluble materials. The final sample was obtained by filtering the solution through 0:2 lm PTFE membrane, resulting a homogeneous black solution (MDDA). The octadecylamine modified carbon nanotubes (MODA) were also obtained through the above procedure as well as the procedure reported by the literature [5].
linear transmittance parts in the NIR region were measured using a computer controlled Nicolet Magna IR-750 spectrometer. TEM analyses were conducted on Hitachi H-800 transmission electron microscopy system. The operation voltage is 100 kV. The size distribution of the solubilized nanotubes was measured by dynamic laser light scattering (LLS) spectrometer (ALV/SP-125 with the incident light wavelength at 632.8 nm) at the angle of 15°. The optical limiting measurements were performed with linearly polarized 10 ns pulses generated from a Q-switched Nd:YAG laser at 1064 or 532 nm. The spatial profiles of the pulses were nearly of Gaussian form. The pulses were split into two parts: the reflected was used as reference. The sample was placed in a 1 mm quartz cuvette and measured by Z-scan method [18]. In our experiments, the maximum incident fluence at the sample was set at 10 J=cm2 . The incident and transmitted pulse energies were detected simultaneously by using two power meters (LPE-1A) individually. The laser pulses were produced at single shots or 10 Hz repetition rate. All of the sample concentrations were adjusted to have same linear transmittance of 50% at 532 nm.
3. Results and discussion The black homogeneous solution is a simple visual indication of nanotubes. Fig. 1 shows the
2.2. Measurements Linear transmittance spectra in the UV–Vis region were obtained using a computer controlled Shimadzu UV-2501PC spectrophotometer. The
Fig. 1. Transmission spectra of MDDA (solid dash), MODA (dashed line) in chloroform.
L. Liu et al. / Chemical Physics Letters 359 (2002) 191–195
193
(a)
Fig. 3. Size distribution of MDDA in toluene obtained by dynamic light scattering.
(b) Fig. 2. TEM images of purified MWNTs (a) and MDDA (b).
linear transmittance spectra of MDDA, and MODA in chloroform solution, respectively. These spectra are very similar and essentially featureless in the measured region, similar to the spectra of other solubilized carbon nanotubes [10]. The TEM images provide the most direct evidence for the presence of nanotubes in the colored solutions. Fig. 2b is a typical TEM image of the samples prepared from the MDDA solution. The nanotubes are well dispersed with an average diameter of 30 nm and length of several hundred nanometers. Compared with the TEM image of the precursor purified nanotubes (Fig. 2a), the solubilized nanotubes have the same morphology as that of the purified tubes, indicating that the solubilization does not affect the morphology of the nanotubes. The TEM images also imply a relatively high concentration of nanotubes in the homogeneous solution. Fig. 3 shows the size distribution of the solubilized MDDA in toluene measured by the method of dynamic LLS. The size distribution is relatively narrow, the hydrodynamic radius of the nanotubes centers at 58.9 nm with a range from 24.9 to
161.5 nm. The combination of the mean square radius of gyration, hydrodynamic radius and the diameter of the nanotube reveals that the scattering substrates are not rigid rods. This is in agreement with the TEM images of MDDA. The optical limiting performance of MDDA and MODA in chloroform were measured in both 532 and 1064 nm of nanosecond laser pulses. C60 was employed as a standard in the 532 nm pulses. For comparison, the concentrations of all samples were adjusted to be 50% linear transmittance at 532 nm. For the 532 nm pulses, the nonlinear transmission of both MDDA and MODA occur at 0:1 J=cm2 , almost the same as that of C60 . Also, the optical performance of both MDDA and MODA in homogeneous solutions are comparable with that of C60 in toluene up to 6 J=cm2 of 532 nm nanosecond pulses (Fig. 4a). At 1064 nm, both of MDDA and MODA begin to show nonlinear transmission at 0:2 J=cm2 and exhibit the good optical limiting performance in the range of measurements (Fig. 4b), while C60 does not limit any light at all. These results imply the solubilized MWNTs are good optical limiters at both 532 and 1064 nm. It was reported that carbon nanotube suspensions were not only found to be competitive optical limiters at 532 nm but also appeared to be very efficient at 1064 nm [12,13,19,20]. Mechanistically, it has been proposed that optical response of the carbon nanotubes suspension is dominated by
194
L. Liu et al. / Chemical Physics Letters 359 (2002) 191–195
(a)
(b) Fig. 4. (a) Optical limiting responses to 10 ns, 532 nm optical pulses, of MDDA ( ), MODA (M), and C60 () in chloroform solutions; (b) Optical limiting responses to 10 ns, 1064 nm optical pulses, of MDDA ( ) and MODA (M) in chloroform solutions.
nonlinear scattering, essentially sharing the same mechanism with that of carbon black suspension. Other mechanisms such as self-defocusing and thermal lensing have also been suggested [14,19]. In the nonlinear scattering process, heating due to the presence of the laser pulses can lead to vaporization and ionization of carbon nanotubes, and then form rapidly expanding microplasmas. In return, these microplasma strongly scatter light from the transmitted beam direction, leading to the decrease in the measured transmitted light energy. At the same time, the heat conduction from the nanotubes to the surrounding liquid lead to solvent microbubbles growth, which could decrease in the measured transmitted light. Recently, Sun and co-workers [16] synthesized aminopolymer modified solubilized carbon nanotubes and
measured their optical limiting properties for 532 nm pulsed laser irradiation. The optical limiting performance was weaker than that of C60 solution. They proposed a nonlinear absorption mechanism for the optical limiting of the solubilized carbon nanotubes based on that the polymer-bound carbon nanotubes are solely responsible for the observed light absorption at 532 nm. The present results in this study show that the optical limiting performances of both MDDA and MODA in homogeneous solutions are comparable with that of C60 at 532 nm. Moreover, both of the solubilized carbon nanotubes show good optical limiting performances at 1064 nm. In addition, the nanotube moieties in the homogeneous solution of both of MDDA and MODA absorb light of 532 nm, but also absorb light of 1064 nm (Fig. 1), strongly support the nonlinear absorption mechanism. This deduction is supported by recent nanosecond flash photolysis measurements of MDDA in homogeneous solution of chloroform or toluene [21]. The transient absorption spectrum shows a featureless broadband absorption in the range of 350–850 nm, very similar to the ground state absorption. The lifetime of the dominant excited state absorption is less than a few nanoseconds, which is typically the singlet–singlet excited states absorption. This implies that the nonlinear absorption mechanism for the solubilized carbon nanotubes should be different from that of C60 , which dominates triplet–triplet excited states absorption. In summary, good optical limiting responses of a new solubilized carbon nanotube have been observed at both 532 and 1064 nm with nanosecond laser pulses. A nonlinear absorption mechanism is proposed and discussed. The solubilized carbon nanotubes are flexible and have potential application in the protection of optical sensors from high-intensity laser beams, particularly in the infrared spectral region.
Acknowledgements This work was supported by the Chinese Academy of Sciences and the Major State Basic Research Development Program (Grant No. G2000077500).
L. Liu et al. / Chemical Physics Letters 359 (2002) 191–195
References [1] S. Iijima, Nature (London) 354 (1991) 56. [2] M.S. Dresselhaus, G. Dresselhaus, P.C. Eklund, Science of Fullerenes and Carbon Nanotubes, Academic, New York, 1996. [3] K. Tanaka, T. Yamabe, K. Fukui, The Science and Technology of Carbon Nanotubes, Elsevier, Amsterdam, 1999. [4] P.J.F. Harris, Carbon Nanotubes and Related Structures: New Materials for The Twenty-first Century, Cambridge University, Cambridge, 1999. [5] J. Chen, M.A. Hamon, H. Hu, Y. Chen, A.M. Rao, P.C. Eklund, R.C. Haddon, Science 282 (1998) 95. [6] M.A. Hamon, J. Chen, H. Hu, Y. Chen, M.E. Itkis, A.M. Rao, P.C. Eklund, R.C. Haddon, Adv. Mater. 11 (1999) 834. [7] J.E. Riggs, Z. Guo, D.L. Carroll, Y.P. Sun, J. Am. Chem. Soc. 122 (2000) 5879. [8] R. Czerw, Z. Guo, P.M. Ajayan, Y.P. Sun, D.L. Carroll, Nano Lett. 1 (2001) 423. [9] Y. Sun, S.R. Wilson, D.L. Schuster, J. Am. Chem. Soc. 123 (2001) 5348. [10] J.L. Bahr, J. Yang, D.V. Kosynkin, M.J. Bronikowski, R.E. Smalley, J.M. Tour, J. Am. Chem. Soc. 123 (2001) 6536.
195
[11] M. Holzinger, O. Vostrowsky, A. Hirsch, F. Hennrich, M. Kappes, R. Weiss, F. Jellen, Angew. Chem. Int. Ed. 40 (2001) 4002. [12] X. Sun, R.Q. Yu, G.Q. Xu, T.S.A. Hor, W. Ji, Appl. Phys. Lett. 73 (1998) 3632. [13] P. Chen, X. Wu, X. Sun, J. Lin, W. Ji, K.L. Tan, Phys. Rev. Lett. 82 (1999) 2548. [14] L. Vivien, E. Anglaret, D. Riehl, F. Bacou, C. Journet, C. Goze, M. Andrieux, M. Brunet, F. Lafonta, P. Bernier, F. Hache, Chem. Phys. Lett. 307 (1999) 317. [15] S.R. Mishra, H.S. Rawat, S.C. Mehendale, K.C. Rustagi, A.K. Sood, R. Bandyopadhyay, A. Govindaraj, C.N.R. Rao, Chem. Phys. Lett. 317 (2000) 510. [16] J.E. Riggs, D.B. Walker, D.L. Carroll, Y.P. Sun, J. Phys. Chem. B 104 (2000) 7071. [17] http:// www.sunnano.com. [18] P. Wang, S. Zhang, P. Wu, C. Ye, H. Liu, F. Xi, Chem. Phys. Lett. 340 (2001) 261. [19] L. Vivien, D. Riehl, P. Lancon, F. Hache, E. Anglaret, Opt. Lett. 26 (2001) 223. [20] L. Vivien, D. Riehl, F. Hache, E. Anglaret, J. Nonlinear Opt. Phys. Mater. 9 (2000) 297. [21] J. Feng, L. Liu, J. Zhang, Z. Guo, (in preparation).