- Email: [email protected]
Raman spectroscopy of the effect of reactor neutron irradiation on the structure of polycrystalline C60
870
Letters to the Editor / Carbon 43 (2005) 855–894
50% higher charge compared to the mesoporous carbon electrodes at the lower current density, but at current density higher than 70 mA/cm2 the latter perform better than activated carbon. It is interesting to note that the shift of pore size distribution towards slightly wider pores, i.e. from supermicropores (PX-21) to small mesopores (around 3 nm), proved highly effective for improvement of EDLCs-performance at high current intensity in aqueous media. The Ragone-type plot displayed in Fig. 4 confirms that the mesoporous carbons obtained in the present study compete favourably with activated carbon for high discharge rates. It also illustrates that the power density of the double layer capacitors is determined largely by the structural characteristics of the electrode material. The electrode corresponding to carbon C4, with a high equivalent surface area (1620 m2/g), a homogeneous pore size distribution around 3 nm and textural porosity from voids between nanometric particles appears to have the higher level of performance, since it can deliver the energy at higher rate. No improvement is detected for carbons with larger pore size (i.e. carbon C2, pore size 8 nm) or bimodal pore size distribution (i.e. carbon C5), which indicates that an average pore size around 3 nm is sufficiently wide for high rate capability in H2SO4 media. In summary, the templating technique is particularly important for the preparation of carbons to be used as electrodes in supercapacitors, where the design of pore
size distribution of the material is required to suit the size of electrolyte ions and enhance the performance at high rate. Carbon materials with a narrow pore size distribution around 3 nm and particles size in the nanometric range are specially adapted for EDLC-electrodes in aqueous media, as they combine large amounts of energy with high power density.
Acknowledgments The authors wish to thank Prof. F. Stoeckli (University of Neuchatel) for providing carbon PX-21. The financial support for this research provided by the Spanish MCyT (MAT2002-00059) is gratefully acknowledged. S. Alvarez also acknowledges to the Spanish MCyT for her FPI grant.
References [1] Conway BE. Electrochemical Supercapacitors. New York: Kluwer Academic; 1999. [2] Frackowiak E, Beguin F. Carbon 2001;39:937–50. [3] Qu D, Shi H. J Power Sources 1998;74:99–107. [4] Fuertes AB. J Mater Chem 2003;13:3085–8. [5] Fuertes AB, Pico´ F, Rojo JM. J Power Sources 2004;133: 329–36. [6] Fitzer E, Schaefer W, Yamada S. Carbon 1969;7:643–6.
Raman spectroscopy of the effect of reactor neutron irradiation on the structure of polycrystalline C60 Tibor Braun a, Henrik Rausch
b,* ,
Ja´nos Mink
c
a
b
Institute of Inorganic and Analytical Chemistry, L. Eo¨tvo¨s University, P.O. Box 123, 1443 Budapest, Hungary KFKI, Atomic Energy Research Institute of the Hungarian Academy of Sciences, P.O. Box 49, 1525 Budapest, Hungary c Analytical Chemistry Department, University of Veszpre´m, P.O. Box 158, 8201 Veszpre´m, Hungary Received 20 September 2004; accepted 25 October 2004 Available online 8 December 2004
Keywords: A. Fullerenes; C. Raman spectroscopy; D. Defects, Radiation damage
*
Corresponding author. Tel.: +36 1 392 2222; fax: +36 1 395 9293. E-mail addresses: [email protected] (T. Braun), rausch.henrik@ axelero.hu (H. Rausch). 0008-6223/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2004.10.046
During our investigations of trace element impurities in fullerenes [1] we have found that samples of C60 and C70 commercialized by different producers contain different concentration levels of approx. 40 impurities in
Letters to the Editor / Carbon 43 (2005) 855–894
a. The trace impurities are on the surface of the crystallites, b. they are in the crystal lattice in tetrahedral or octahedral holes of the fcc crystals, c. some of them could be in endohedral positions in the fullerene cages. As a serendipitous result we have found that e.g., the argon impurity originally adsorbed on the crystallites entered the C60 cage forming a carrier-free 41Ar containing endohedral 41Ar@C60 by nuclear recoil implosion after neutron irradiation [2]. This opens the way to an easy, cheap and efficient route to the preparation of radiolabelled fullerenes containing endohedrally carrier-free radionuclides. For synthesis purposes, as described in [2–4] the survival of the C60 crystals and of the C60 molecules in the intensive radioactive environment of a nuclear reactor, where the neutron irradiations were made, information on the radiation damage of the crystal lattice is of paramount importance. We have considered it essential to find out the neutron dose to which C60 remains unaffected by radiation damage. The results as given in [3] have shown that as measured by positron lifetime spectroscopy and DSC, the C60 resists a neutron dose up to 1016 n cm2. However, due to some changes in colour and cracking on the irradiated C60 crystals we have decided to investigate the radiation damage also by Raman spectroscopy. This note deals with our findings in this respect. The C60 molecule has attracted considerable attention of vibrational spectroscopists during the last 15 years. The IR and Raman spectra of C60 have been obtained by Bethune et al. [5] and by a number of other authors [6–10]. C60 belongs to the highest point group, Ih. It has two Ag and eight Hg Raman active vibrations. The strongest Ag bands at 1469 and 496 cm1 belong to the so-called pentagonal pinching (m1) and radial breathing (m2), respectively. The third strong low frequency band at 272 cm1 (m23) is the cage-squashing mode. The position of these bands indicates the purity of the sample, but their relative intensities depend very much on the excitation laser wavelength. Because of decomposition the formation of graphite or amorphous carbon can be expected. Various forms of amorphous carbon and ordered–disordered graphite have been intensively investigated during the last decade [11]. Raman spectroscopy is one of the richest sources of information concerning the properties of these type of samples [12,13]. The regular graphite peaks (G) were generally observed around 1590 cm1, whereas the disorder-related (D) peaks were
obtained around 1290 and 1350 cm1. The relative intensities of the two bands depend on the extent of regularity. Amorphous carbon shows Raman bands close to the graphite G and D bands but generally the disorder-related peak is the more intense one. The gold grade type C60 samples were acquired from A.G. Hoechst (Frankfurt/M) in polycrystalline form, and have been used without any pre-treatment. Five samples of about 0.4 g were irradiated in a vertical channel of the recently reconstructed WWR-H type 10MW nuclear research reactor of the Atomic Energy Research Institute, Budapest. The samples were exposed to increasing reactor neutron doses including thermal, epithermal, and fast neutrons from 1014 to 1018 n cm2. The cumulative neutron doses were measured by Zr and Ni foil flux monitors. The irradiated samples were cooled for 14 days before processing FT-Raman spectra of C60 and its irradiated samples. They were recorded by a Digilab (BioRad) dedicated FT-Raman spectrometer, equipped with a dynamically aligned high throughput interferometer and a 300 mW (at sample compartment) 1064 nm wavelength Nd:YAG laser. The samples were measured in a special copper disc holder with a 2 mm diameter small sample hole in the middle. 180 excitation and collection geometry was used. The spectral resolution was 2 cm1 and 128 scans were accumulated for C60 and 512 scans for weaker scatters (irradiated samples). Fig. 1 represents the Raman spectrum of the starting C60 sample. The spectrum agreed completely with the spectrum reported in [5], e.g., the band position agreed within a few wave numbers (Table 1). The results of our Raman measurements of the irradiated sample at the lowest neutron dose of 1.32 Æ 1015 n cm2 are shown in Fig. 2. Due to the slight colour changes and cracking of the irradiated C60 crystals, the FT-Raman spectrum becomes much weaker, e.g., the intensities of fundamental bands of C60 decreased by about one order of magnitude (Table 1). The other experimental effect was a strong heat emission from the sample resulting in a complicated fluctuation of the spectral background. All these observations support 1468
1.5 496
Raman Intensity
the ppb to ppm range. When trying to understand where these impurities are located in or on the crystalline network of C60 and/or C70 samples, three options have been envisaged:
871
1
272
.5 772 1099
432
1574
1250 1425
0 200
400
600
800
1000
1200
1400
Raman Shift (cm -1 )
Fig. 1. FT-Raman spectrum of powdered crystalline C60 sample before irradiation.
872
Letters to the Editor / Carbon 43 (2005) 855–894
Table 1 Observed Raman features of C60 effected by neutron irradiation C60 starting sample
C60 from Ref. [5]
272 (540)b 432 (60) 496 (470) 710 vvw 772 (100) – 1099 (93) – 1250 (88) 1425 (41) – – 1468 (1000) 1574 (14)
273 sc 437 w 496 vs 710 vw 774 w
a b c
1099 vw 1250 vw 1428 w, sh
1470 vvs 1575 w
Irradiateda
Assignments
A
B
268 (120) – 492 (115) – 774 (47) 963 vvw 1099 (32) 1174 vvw 1246 (54) – 1459 w, sh 1463 vw, sh 1468 (160) 1574 vvw
268 (117) 430 (14) 494 (95) – 772 (25) 951 vvw 1099 (23) 1169 vvw 1246 (48) – 1457 w, sh 1463 vw, sh 1465 (150) 1574 vw
C
D
1459 (7) 1462 (30)
Doses of neutron irradiation A: 1.32 Æ 1015 n cm2, B: 8.28 Æ 1015 n cm2, C: 7.56 Æ 1016 n cm2, D: 1.03 Æ 1018 n cm2. In brackets are the relative integrated band intensities normalised to m1, Ag band of C60 at 1468 cm1. Band intensities: s, strong; m, medium; w, weak; and v, very.
D
1468
1
492
772
Raman Intensity
0.8 0.6
1459
1.2
1
Raman Intensity
m23, Hg cage squashing m22, Hg m2, Ag radial breathing m21, Hg m20, Hg Polymerised C60 m19, Hg Polymerised C60 m18, Hg m17, Hg Polymerised C60 Polymerised C60 m1, Ag pentagonal pinching m17, Hg
268
0.4 0.2
1462
C
0.8 1465
0.6
268
B 772
430
0.4 0.2
494
268
951
1574
1099 1169 1246
1468
492 772
A 963
1574
1099 1174 1246
0
0
200
500
1000 1500 Raman Shift (cm-1)
2000
Fig. 2. FT-Raman spectrum of C60 powder sample irradiated at 1.32 Æ 1015 n cm2 neutron dose, as observed without baseline correction.
the fact that the C60 crystals had already sustained some decomposition at this stage. After a proper baseline correction the spectra of all irradiated samples (A, B, C and D) are shown in Fig. 3. All the observed Raman features together with their relative intensities are shown in Table 1. As seen, the strongest Raman feature at 1469 cm1 is shifted to slightly lower frequencies of 1468, 1465, 1462 and 1459 cm1 for the A, B, C and D samples, respectively. Beside these shifts the m1 band shapes become very asymmetric at the low frequency side indicating the presence of decomposition products, probably polymerised C60 species. Other extra features around 960 cm1 are characteristic of the sp3 intermolecular bonds of the polymerised C60. The very weak band at 1170 cm1 should also be assigned to some surface decomposition product. However, spectra of A and B in Fig. 3. still represent clearly the most characteristic bands of the starting C60 sample. As a result of irradiation the surface of the original shiny black C60 sample seems to be partially
400
600
800
1000
1200
1400
Raman Shift (cm -1 )
Fig. 3. FT-Raman spectra of irradiated polycrystalline C60 powders with different neutron doses. (A) 1.32 Æ 1015 n Æ cm2, (B) 8.28 Æ 1015 n cm2, (C) 7.56 Æ 1016 n cm2, (D) 1.03, after specific baseline corrections.
covered with a very thin layer of carbon deposit which lead to a colour change and to a drastic reduction of the Raman cross-section. With increased radiation dose (spectra C and D in Fig. 2) the only C60 like feature is the strongest band (originally representing the m1 symmetric stretching mode) at 1462 and 1459 cm1. The downshifted Ag mode is characteristic of well polymerised C60 species. The very weak intensities (Table 1) of these bands and the featureless Raman spectrum in the whole spectral range under investigation indicate considerable structural damage to the C60 fcc crystal. As a result of the damage it can be seen that during irradiation at a dose of 1.32 Æ 1015 n cm2 a surface decomposition starts, and at 7.56 Æ 1016 n Æ cm2 the C60 starts to behave like a blackbody or greybody due to its strong structural damage. As a consequence, the Raman scattering becomes drastically weakened or disappears almost completely.
Letters to the Editor / Carbon 43 (2005) 855–894 1300 0.08
Raman Intensity
1592 0.07 A 1588 0.06 1291 0.05 B
800
1000
1200
1400 1600 Raman Shift (cm-1 )
1800
2000
Fig. 4. FT-Raman spectra of amorphous carbon (A) and graphite (B).
The formation of amorphous carbon or graphite from C60 under neutron irradiation is a logical expectation. Therefore we have recorded the FT-Raman spectra of both the amorphous carbon and graphite as well (Fig. 4). The two sharper graphite D and G bands are observed at 1291 and 1588 cm1, respectively. Similar bands were observed for amorphous carbon at 1300 and 1592 cm1. The very strong band at 1300 cm1 indicates the strong disordered structure in amorphous carbon. It is clearly seen that there are no traces of these Raman features in the spectra of irradiated C60 in Fig. 3. Probably the extent of surface decomposition is very weak, not detectable by conventional FT-Raman spectroscopy but strong enough to destroy to efficiency of Raman scattering. FT-Raman spectroscopic studies of irradiated C60 crystals indicated a quite early decomposition of the samples already at the lowest neutron dose applied, close to 1015 n cm [2]. Our earlier positron lifetime
873
spectroscopic and DSC studies [3] indicated that C60 resists up to a neutron dose of approx 1016 n cm2. This difference can be explained by the fact that Raman spectroscopy is very sensitive to the slight surface decomposition which did not affect the general properties of the bulk material. It was not possible to detect the formation of amorphous carbon or graphite by FT-Raman spectroscopy but weak features of polymerised C60 were detected. It can be concluded that FT-Raman spectroscopy is a very sensitive tool for the detection of the minor surface decomposition of polycrystalline C60. References [1] Braun T, Rausch H. Anal Chem 1995;67:1512–5. [2] Braun T, Rausch H. Chem Phys Lett 1995;238:443–6. [3] Braun T, Konkoly-Thege I, Rausch H, Su¨vegh K, Ve´rtes A. Chem Phys Lett 1995;238:290–4. [4] Braun T, Rausch H. J Radioanal Nucl Chem 2000;243(1):27–30. [5] Bethune DS, Meijer G, Tang WC, Rosen HJ, Golden WG, Seki H, et al. Chem Phys Lett 1991;179(5):181–6. [6] Stanton RE, Newton MD. J Phys Chem 1988;92(8):2141–5. [7] Hare JP, Dennis TJ, Kroto HW, Taylor R, Allaf AW, Balm S, et al. J Chem Soc Chem Commun 1991:412–3. [8] From CI, Engelman Jr R, Hedderich HG, Bernath PF, Lamb LD, Huffman DR. Chem Phys Lett 1991;176(3):504–7. [9] Dennis TJ, Hare JP, Kroto HW, Taylor R, Walton DR, Hendra PJ. Spectrochim Acta 1991;47A(9–10):1289–92. [10] Dresselhaus MS, Dresselhaus G, Ecklund PC. Science of fullerenes and carbon nanotubes. San Diego: Academic Press; 1996. [11] Robertson J. Adv Phys 1986;35:317–74. [12] Po´csik I, Hundhausen M, Koo´s M. J Non-Cryst Solids 1998;227– 230:1083–5. [13] Po´csik I, Koo´s M, Moustafa S. Mikrochim Acta 1997;14(Suppl.): 755–6.
Double walled carbon nanotube/polymer composites via in-situ nitroxide mediated polymerisation of amphiphilic block copolymers Vitaliy Datsyuk a, Christelle Guerret-Pie´court a,*, Sylvie Dagre´ou a, Laurent Billon a, Jean-Charles Dupin b, Emmanuel Flahaut c, Alain Peigney c, Christophe Laurent c a
Laboratoire de Physico-Chimie des Polyme`res, UMR-CNRS 5067, Universite´ de Pau et des Pays de l’Adour, 64013 PAU, France Laboratoire de Physico-Chimie Mole´culaire, UMR-CNRS 5624, Universite´ de Pau et des Pays de l’Adour, 64013 PAU, France Centre Interuniversitaire de Recherche et d’Inge´nie´rie des Materiaux, UMR-CNRS 5085, Universite´ Paul Sabatier, 31062 Toulouse, France b
c
Received 27 August 2004; accepted 28 October 2004 Available online 21 December 2004
*
Corresponding author. Tel.: +33 559 407708; fax: +33 559 407744. E-mail address: [email protected] (C. Guerret-Pie´court).
0008-6223/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2004.10.052
Letters to the Editor / Carbon 43 (2005) 855–894
50% higher charge compared to the mesoporous carbon electrodes at the lower current density, but at current density higher than 70 mA/cm2 the latter perform better than activated carbon. It is interesting to note that the shift of pore size distribution towards slightly wider pores, i.e. from supermicropores (PX-21) to small mesopores (around 3 nm), proved highly effective for improvement of EDLCs-performance at high current intensity in aqueous media. The Ragone-type plot displayed in Fig. 4 confirms that the mesoporous carbons obtained in the present study compete favourably with activated carbon for high discharge rates. It also illustrates that the power density of the double layer capacitors is determined largely by the structural characteristics of the electrode material. The electrode corresponding to carbon C4, with a high equivalent surface area (1620 m2/g), a homogeneous pore size distribution around 3 nm and textural porosity from voids between nanometric particles appears to have the higher level of performance, since it can deliver the energy at higher rate. No improvement is detected for carbons with larger pore size (i.e. carbon C2, pore size 8 nm) or bimodal pore size distribution (i.e. carbon C5), which indicates that an average pore size around 3 nm is sufficiently wide for high rate capability in H2SO4 media. In summary, the templating technique is particularly important for the preparation of carbons to be used as electrodes in supercapacitors, where the design of pore
size distribution of the material is required to suit the size of electrolyte ions and enhance the performance at high rate. Carbon materials with a narrow pore size distribution around 3 nm and particles size in the nanometric range are specially adapted for EDLC-electrodes in aqueous media, as they combine large amounts of energy with high power density.
Acknowledgments The authors wish to thank Prof. F. Stoeckli (University of Neuchatel) for providing carbon PX-21. The financial support for this research provided by the Spanish MCyT (MAT2002-00059) is gratefully acknowledged. S. Alvarez also acknowledges to the Spanish MCyT for her FPI grant.
References [1] Conway BE. Electrochemical Supercapacitors. New York: Kluwer Academic; 1999. [2] Frackowiak E, Beguin F. Carbon 2001;39:937–50. [3] Qu D, Shi H. J Power Sources 1998;74:99–107. [4] Fuertes AB. J Mater Chem 2003;13:3085–8. [5] Fuertes AB, Pico´ F, Rojo JM. J Power Sources 2004;133: 329–36. [6] Fitzer E, Schaefer W, Yamada S. Carbon 1969;7:643–6.
Raman spectroscopy of the effect of reactor neutron irradiation on the structure of polycrystalline C60 Tibor Braun a, Henrik Rausch
b,* ,
Ja´nos Mink
c
a
b
Institute of Inorganic and Analytical Chemistry, L. Eo¨tvo¨s University, P.O. Box 123, 1443 Budapest, Hungary KFKI, Atomic Energy Research Institute of the Hungarian Academy of Sciences, P.O. Box 49, 1525 Budapest, Hungary c Analytical Chemistry Department, University of Veszpre´m, P.O. Box 158, 8201 Veszpre´m, Hungary Received 20 September 2004; accepted 25 October 2004 Available online 8 December 2004
Keywords: A. Fullerenes; C. Raman spectroscopy; D. Defects, Radiation damage
*
Corresponding author. Tel.: +36 1 392 2222; fax: +36 1 395 9293. E-mail addresses: [email protected] (T. Braun), rausch.henrik@ axelero.hu (H. Rausch). 0008-6223/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2004.10.046
During our investigations of trace element impurities in fullerenes [1] we have found that samples of C60 and C70 commercialized by different producers contain different concentration levels of approx. 40 impurities in
Letters to the Editor / Carbon 43 (2005) 855–894
a. The trace impurities are on the surface of the crystallites, b. they are in the crystal lattice in tetrahedral or octahedral holes of the fcc crystals, c. some of them could be in endohedral positions in the fullerene cages. As a serendipitous result we have found that e.g., the argon impurity originally adsorbed on the crystallites entered the C60 cage forming a carrier-free 41Ar containing endohedral 41Ar@C60 by nuclear recoil implosion after neutron irradiation [2]. This opens the way to an easy, cheap and efficient route to the preparation of radiolabelled fullerenes containing endohedrally carrier-free radionuclides. For synthesis purposes, as described in [2–4] the survival of the C60 crystals and of the C60 molecules in the intensive radioactive environment of a nuclear reactor, where the neutron irradiations were made, information on the radiation damage of the crystal lattice is of paramount importance. We have considered it essential to find out the neutron dose to which C60 remains unaffected by radiation damage. The results as given in [3] have shown that as measured by positron lifetime spectroscopy and DSC, the C60 resists a neutron dose up to 1016 n cm2. However, due to some changes in colour and cracking on the irradiated C60 crystals we have decided to investigate the radiation damage also by Raman spectroscopy. This note deals with our findings in this respect. The C60 molecule has attracted considerable attention of vibrational spectroscopists during the last 15 years. The IR and Raman spectra of C60 have been obtained by Bethune et al. [5] and by a number of other authors [6–10]. C60 belongs to the highest point group, Ih. It has two Ag and eight Hg Raman active vibrations. The strongest Ag bands at 1469 and 496 cm1 belong to the so-called pentagonal pinching (m1) and radial breathing (m2), respectively. The third strong low frequency band at 272 cm1 (m23) is the cage-squashing mode. The position of these bands indicates the purity of the sample, but their relative intensities depend very much on the excitation laser wavelength. Because of decomposition the formation of graphite or amorphous carbon can be expected. Various forms of amorphous carbon and ordered–disordered graphite have been intensively investigated during the last decade [11]. Raman spectroscopy is one of the richest sources of information concerning the properties of these type of samples [12,13]. The regular graphite peaks (G) were generally observed around 1590 cm1, whereas the disorder-related (D) peaks were
obtained around 1290 and 1350 cm1. The relative intensities of the two bands depend on the extent of regularity. Amorphous carbon shows Raman bands close to the graphite G and D bands but generally the disorder-related peak is the more intense one. The gold grade type C60 samples were acquired from A.G. Hoechst (Frankfurt/M) in polycrystalline form, and have been used without any pre-treatment. Five samples of about 0.4 g were irradiated in a vertical channel of the recently reconstructed WWR-H type 10MW nuclear research reactor of the Atomic Energy Research Institute, Budapest. The samples were exposed to increasing reactor neutron doses including thermal, epithermal, and fast neutrons from 1014 to 1018 n cm2. The cumulative neutron doses were measured by Zr and Ni foil flux monitors. The irradiated samples were cooled for 14 days before processing FT-Raman spectra of C60 and its irradiated samples. They were recorded by a Digilab (BioRad) dedicated FT-Raman spectrometer, equipped with a dynamically aligned high throughput interferometer and a 300 mW (at sample compartment) 1064 nm wavelength Nd:YAG laser. The samples were measured in a special copper disc holder with a 2 mm diameter small sample hole in the middle. 180 excitation and collection geometry was used. The spectral resolution was 2 cm1 and 128 scans were accumulated for C60 and 512 scans for weaker scatters (irradiated samples). Fig. 1 represents the Raman spectrum of the starting C60 sample. The spectrum agreed completely with the spectrum reported in [5], e.g., the band position agreed within a few wave numbers (Table 1). The results of our Raman measurements of the irradiated sample at the lowest neutron dose of 1.32 Æ 1015 n cm2 are shown in Fig. 2. Due to the slight colour changes and cracking of the irradiated C60 crystals, the FT-Raman spectrum becomes much weaker, e.g., the intensities of fundamental bands of C60 decreased by about one order of magnitude (Table 1). The other experimental effect was a strong heat emission from the sample resulting in a complicated fluctuation of the spectral background. All these observations support 1468
1.5 496
Raman Intensity
the ppb to ppm range. When trying to understand where these impurities are located in or on the crystalline network of C60 and/or C70 samples, three options have been envisaged:
871
1
272
.5 772 1099
432
1574
1250 1425
0 200
400
600
800
1000
1200
1400
Raman Shift (cm -1 )
Fig. 1. FT-Raman spectrum of powdered crystalline C60 sample before irradiation.
872
Letters to the Editor / Carbon 43 (2005) 855–894
Table 1 Observed Raman features of C60 effected by neutron irradiation C60 starting sample
C60 from Ref. [5]
272 (540)b 432 (60) 496 (470) 710 vvw 772 (100) – 1099 (93) – 1250 (88) 1425 (41) – – 1468 (1000) 1574 (14)
273 sc 437 w 496 vs 710 vw 774 w
a b c
1099 vw 1250 vw 1428 w, sh
1470 vvs 1575 w
Irradiateda
Assignments
A
B
268 (120) – 492 (115) – 774 (47) 963 vvw 1099 (32) 1174 vvw 1246 (54) – 1459 w, sh 1463 vw, sh 1468 (160) 1574 vvw
268 (117) 430 (14) 494 (95) – 772 (25) 951 vvw 1099 (23) 1169 vvw 1246 (48) – 1457 w, sh 1463 vw, sh 1465 (150) 1574 vw
C
D
1459 (7) 1462 (30)
Doses of neutron irradiation A: 1.32 Æ 1015 n cm2, B: 8.28 Æ 1015 n cm2, C: 7.56 Æ 1016 n cm2, D: 1.03 Æ 1018 n cm2. In brackets are the relative integrated band intensities normalised to m1, Ag band of C60 at 1468 cm1. Band intensities: s, strong; m, medium; w, weak; and v, very.
D
1468
1
492
772
Raman Intensity
0.8 0.6
1459
1.2
1
Raman Intensity
m23, Hg cage squashing m22, Hg m2, Ag radial breathing m21, Hg m20, Hg Polymerised C60 m19, Hg Polymerised C60 m18, Hg m17, Hg Polymerised C60 Polymerised C60 m1, Ag pentagonal pinching m17, Hg
268
0.4 0.2
1462
C
0.8 1465
0.6
268
B 772
430
0.4 0.2
494
268
951
1574
1099 1169 1246
1468
492 772
A 963
1574
1099 1174 1246
0
0
200
500
1000 1500 Raman Shift (cm-1)
2000
Fig. 2. FT-Raman spectrum of C60 powder sample irradiated at 1.32 Æ 1015 n cm2 neutron dose, as observed without baseline correction.
the fact that the C60 crystals had already sustained some decomposition at this stage. After a proper baseline correction the spectra of all irradiated samples (A, B, C and D) are shown in Fig. 3. All the observed Raman features together with their relative intensities are shown in Table 1. As seen, the strongest Raman feature at 1469 cm1 is shifted to slightly lower frequencies of 1468, 1465, 1462 and 1459 cm1 for the A, B, C and D samples, respectively. Beside these shifts the m1 band shapes become very asymmetric at the low frequency side indicating the presence of decomposition products, probably polymerised C60 species. Other extra features around 960 cm1 are characteristic of the sp3 intermolecular bonds of the polymerised C60. The very weak band at 1170 cm1 should also be assigned to some surface decomposition product. However, spectra of A and B in Fig. 3. still represent clearly the most characteristic bands of the starting C60 sample. As a result of irradiation the surface of the original shiny black C60 sample seems to be partially
400
600
800
1000
1200
1400
Raman Shift (cm -1 )
Fig. 3. FT-Raman spectra of irradiated polycrystalline C60 powders with different neutron doses. (A) 1.32 Æ 1015 n Æ cm2, (B) 8.28 Æ 1015 n cm2, (C) 7.56 Æ 1016 n cm2, (D) 1.03, after specific baseline corrections.
covered with a very thin layer of carbon deposit which lead to a colour change and to a drastic reduction of the Raman cross-section. With increased radiation dose (spectra C and D in Fig. 2) the only C60 like feature is the strongest band (originally representing the m1 symmetric stretching mode) at 1462 and 1459 cm1. The downshifted Ag mode is characteristic of well polymerised C60 species. The very weak intensities (Table 1) of these bands and the featureless Raman spectrum in the whole spectral range under investigation indicate considerable structural damage to the C60 fcc crystal. As a result of the damage it can be seen that during irradiation at a dose of 1.32 Æ 1015 n cm2 a surface decomposition starts, and at 7.56 Æ 1016 n Æ cm2 the C60 starts to behave like a blackbody or greybody due to its strong structural damage. As a consequence, the Raman scattering becomes drastically weakened or disappears almost completely.
Letters to the Editor / Carbon 43 (2005) 855–894 1300 0.08
Raman Intensity
1592 0.07 A 1588 0.06 1291 0.05 B
800
1000
1200
1400 1600 Raman Shift (cm-1 )
1800
2000
Fig. 4. FT-Raman spectra of amorphous carbon (A) and graphite (B).
The formation of amorphous carbon or graphite from C60 under neutron irradiation is a logical expectation. Therefore we have recorded the FT-Raman spectra of both the amorphous carbon and graphite as well (Fig. 4). The two sharper graphite D and G bands are observed at 1291 and 1588 cm1, respectively. Similar bands were observed for amorphous carbon at 1300 and 1592 cm1. The very strong band at 1300 cm1 indicates the strong disordered structure in amorphous carbon. It is clearly seen that there are no traces of these Raman features in the spectra of irradiated C60 in Fig. 3. Probably the extent of surface decomposition is very weak, not detectable by conventional FT-Raman spectroscopy but strong enough to destroy to efficiency of Raman scattering. FT-Raman spectroscopic studies of irradiated C60 crystals indicated a quite early decomposition of the samples already at the lowest neutron dose applied, close to 1015 n cm [2]. Our earlier positron lifetime
873
spectroscopic and DSC studies [3] indicated that C60 resists up to a neutron dose of approx 1016 n cm2. This difference can be explained by the fact that Raman spectroscopy is very sensitive to the slight surface decomposition which did not affect the general properties of the bulk material. It was not possible to detect the formation of amorphous carbon or graphite by FT-Raman spectroscopy but weak features of polymerised C60 were detected. It can be concluded that FT-Raman spectroscopy is a very sensitive tool for the detection of the minor surface decomposition of polycrystalline C60. References [1] Braun T, Rausch H. Anal Chem 1995;67:1512–5. [2] Braun T, Rausch H. Chem Phys Lett 1995;238:443–6. [3] Braun T, Konkoly-Thege I, Rausch H, Su¨vegh K, Ve´rtes A. Chem Phys Lett 1995;238:290–4. [4] Braun T, Rausch H. J Radioanal Nucl Chem 2000;243(1):27–30. [5] Bethune DS, Meijer G, Tang WC, Rosen HJ, Golden WG, Seki H, et al. Chem Phys Lett 1991;179(5):181–6. [6] Stanton RE, Newton MD. J Phys Chem 1988;92(8):2141–5. [7] Hare JP, Dennis TJ, Kroto HW, Taylor R, Allaf AW, Balm S, et al. J Chem Soc Chem Commun 1991:412–3. [8] From CI, Engelman Jr R, Hedderich HG, Bernath PF, Lamb LD, Huffman DR. Chem Phys Lett 1991;176(3):504–7. [9] Dennis TJ, Hare JP, Kroto HW, Taylor R, Walton DR, Hendra PJ. Spectrochim Acta 1991;47A(9–10):1289–92. [10] Dresselhaus MS, Dresselhaus G, Ecklund PC. Science of fullerenes and carbon nanotubes. San Diego: Academic Press; 1996. [11] Robertson J. Adv Phys 1986;35:317–74. [12] Po´csik I, Hundhausen M, Koo´s M. J Non-Cryst Solids 1998;227– 230:1083–5. [13] Po´csik I, Koo´s M, Moustafa S. Mikrochim Acta 1997;14(Suppl.): 755–6.
Double walled carbon nanotube/polymer composites via in-situ nitroxide mediated polymerisation of amphiphilic block copolymers Vitaliy Datsyuk a, Christelle Guerret-Pie´court a,*, Sylvie Dagre´ou a, Laurent Billon a, Jean-Charles Dupin b, Emmanuel Flahaut c, Alain Peigney c, Christophe Laurent c a
Laboratoire de Physico-Chimie des Polyme`res, UMR-CNRS 5067, Universite´ de Pau et des Pays de l’Adour, 64013 PAU, France Laboratoire de Physico-Chimie Mole´culaire, UMR-CNRS 5624, Universite´ de Pau et des Pays de l’Adour, 64013 PAU, France Centre Interuniversitaire de Recherche et d’Inge´nie´rie des Materiaux, UMR-CNRS 5085, Universite´ Paul Sabatier, 31062 Toulouse, France b
c
Received 27 August 2004; accepted 28 October 2004 Available online 21 December 2004
*
Corresponding author. Tel.: +33 559 407708; fax: +33 559 407744. E-mail address: [email protected] (C. Guerret-Pie´court).
0008-6223/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2004.10.052