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Raman characterization of singlewalled carbon nanotubes and PMMA-nanotubes composites
ELSEVIER
SyntheticMetals 103(1999) 251&2512
Raman characterization of singlewalled carbon nanotubes and PMMA-nanohtbes
composites
M. Lamy de la Chap&e i5b C Stkphan’, T. P. Nguyena, S. Lefiant’, C. Journet’, P. Bernie?, E. Mnnozd, A. Benitod, W. K. h4aserd, M. <. &xtinezd, G. F. de la Fuente’, T. Guillard’, G. Flaman~, L. Alvarezc, D. LaplazeC a Laboratoire
de Physique Cristalline, MN, Universitk de Naties, France b Trinity College, Dublin, Ireland ’ Groupe de Dynamique des Phases condenskes, Universite’ Montpeliier 2, Montpeliier, d Institute de Carboquimica CSIC, Zivagoza, Spain e institute de Cienca de Mareriales de Aragon, Zuragoza, Spain f IMP-CNRS, Odeillo, France
France
Abstract The Ramanspectroscopyhave allowed us to performstudieson singlewalled nanotubes(SWNT’s) produced by following methods: electric arc, laserablationand solarenergy.As this characterizationmethodprovidesa great dealof informations,we will presenta comparisonbetweenthe nanotubesproducedby all theseprocesses andthe influenceof somesynthesisparameters. By using spin casting, we have produced thin ftis of PMMA-SWNT’s for different concentrations. Then, we have characterizedthesenew materialsby Ramanspectroscopy.The aimof theseinvestigations is to get information on the possible interactionsbetweenthesetwo materials.In particular,we have studiedthe evolution of the compositesfilms spectraas a function of the nauotubesconcentrationin the polymer. Keywords:
nanotubes,PMMA, composites,spincasting,Ramanspectroscopy.
Co (0,6 / 0,6 at, %) mixture and xmdera pressureof 500 Ton:
1. Introduction The discovery of carbon nanotubes [l] has encouraged m=v studies about their properties and potential applications. The main ciiffkulty which limited such a developmentwas their production in rather smallquantities. But new methodsof synthesis, laserablation [2] and electric arc technique [3], have been presentedrecently which in addition lead to the formation of singlewalled nanotubes (SWNT’s), moreattractive in termsof electronic properties.In this paper, we mainly describeRamanresults performedon SWNT’s which provide a great deal of information on the nature of the SWNT’s studied and put clearly in evidencea diametersize distribution which dependson the location of the extractedsamplefrom the synthesischamber.We focus our studies on carbon nanotubes preparedby the electric arc method,and comparisonis madewith samplesobtained by different preparationtechniques. In addition, it has also beenconsideredcorn&sites such that nanotubeswere dispersedin a polymer mati [4]. Thus, we have madea composite using singlewalled nanotubes (SWNT’s) and poly(methy1 methacrylate)(PMMA). We have investigated vibrational properties of the PMMA-SWNT’s composites. 2. Experiments SWNT’s were producedby the arc dischargemethod(see ref. [3]), by laserablation and using solar energy. The second one have beenproduced in sublimating graphite with a Ni J 0379~67791996 - see front matter PII: s0379-6779(98)01080-7
0 1999 Elsevier
Science %A.
The third one waspreparedat the Odeillo solar furnace,The flm concentratedin the chamberis near 950 W/m*. In there conditions, during the evaporation process of the target (graphite / Ni / Co : 96 I 2 I 2 at. %) under an argon atmosphere(400 mbar, flow : 0,2 m3ih), the temperature increasesup to 3000K, whereasthe collected soot should be synthesisbetween2000 and 800 K. For the composite formation, the nanotubes powder (electric arc sample)and PMMA were mixed together in toluene in severalnanotubesconcentrationsspecifiedas the weight % in the polymer.Then the solution was mixedin an ultrasonicbath. Thin films werepreparedby spin casting onto KBr substrates.We have also made a nanotubes film by deposinga toluene-SWNT’ssolution on a KBr substrate.To obtainRamanspectra,a excitation wavelengthof 1064 nmhas beenused.All the dataare normalizedto the main peak of the nanotubesspectrumat 1593cm-‘. 3. SWNT’s studies With all the informations given by the Raman spectroscopy[5-71, it is possibleto makesystematicstudies on samplescontainingSWNT’s. For all spectrashown below, the laserexcitationwavelengthis the argon line at 514.5mu. In a fist step, we have performedexperimentson one co&ret, which is deposited on the cathode during the production processand where the higher concentration of SWNT’s is found. After having splitted it in several parts,we have studiedseveralspotson eachas shownin the exampleof figure 1.
All rights reserved.
M.L. de la Chapelle
et al. I Synthetic
Metals
IO3 (1999)
2510-2512
2511
similar to those obtained with the electric arc samples, We can always observe the Ezg2splitted mode, the same peaks at the same position at low frequencies or in the intermediate (2501200 cd) range. The tubes produced by the electric arc or laser ablation seems identical. Or the other hand, some other parts of the solar energy sample lead to the lower spectrum of tig. 3. This spectrum presents a broad peak at 1520 cm-’ and more than 10 peaks Corn 130 to 255 ti’. This corresponds to a very large diameter distribution shown by the low frequency bands and confiied by the broader splitting of the EQZ graphite mode. In this case, the diameter is expected to go liom a very low value near 8 A to 20 A. In this latter case, it seems that the synthesis conditions are not completely comparable to the two previous one, even if a large scale of SWNTs are also produced. From these observations, it can be suggested that the experimental parameters used for the sublimation of graphite do not play a major role in the production of nanotubes. On the contrary, the plasma conditions after sublimation turn out to be of real importance.
Fig 1 : Part the collaret with studied
the position of the 6 points
We have been able to see a gradual evolution of the diameter distribution on this part with the low frequency group of bands. Then it is clearly observed that along the sample from point 1 to point 6, the diameter distribution changes continuously from low diameter to higher ones. This is an indication that the conditions in the synthesis chamber are not homogeneous and that the tube production changes f?om one point to the other and then some specific diameters are favoured compared to others. As a consequence, we can conclude that the location of the extracted sample in the synthesis chamber is of real importance on the production of tubes with a specific diameter.
*
202
400
Mx)
800
loo0
1200
1403
1600
1800
Raman shift (cm’) Fig 3 : Raman spectra of laser ablation sample
(6) (5) (4) (3) (2)
(1) 1W
150
ml
250
Ramanshift (cm-‘) Fig 2 : Evolution of the Raman spectra from the point 1 to the point 6
In a second step, we have studied samples produced by other methods, namely laser ablation and solar energy. As shown in figures 3 and 4, the two Raman spectra obtained for laser ablation and the upper one of the solar energy look
200
400
600
SW
loo0
SC0
14M,
1600
l&W
Raman shift (cm-‘) Fig 4 : Raman spectra of solar energy sample 4. Composites
studies
The Raman bands of SWNT’s are clearly observed in PMMA-SWNT’s spectra (Fig. 5) but PMMA ones do not appear because of it low resonance behavior. In addition, a hump appears between 2250 and 3750 cm-‘. This hump which
seems to be asymmetric, increases with the nanotubes concentration. In the pristine PMMA fti and the SWNT’s powder spectra using the same excitation wavelength and laser power, no hump emerges. The spectrum of the SWNT’s
2512
ML.
de la Chapelle
et al. I Synthetic
film obtained in the same conditions shows the presence of the hump. Its appearance is due to the forming of a complex between the solvent and the nanotubes or amorphous carbon. The increase of the peak at 1270 Cm’ assigned to the disorder and the corresponding second order one at 2540 m’ [7l means that there is a high dispersion of the amorphous carbon for the low nanotubes concentrations. The bands in the range 1500-1650 cm?, attributed to a splitting of the E2s2 vibrational mode of graphite [S], show significant changes. First, the intensities of the bands at 1528, 1555, 1570 and 1603 cni’ in the composites spectra are lower than the SW’s film spectnun ones. Second, the main peak width of the composites increases as a function of the SWNT’s concentration but is lower than the nanotubes film one.
Metals
IO3 (1999)
2510-2512
In the low frequency range, two bands appear clearly (Fig. 6). They are shifted toward higher frequencies in the presence of PMMA and when the SWNT’s concentration increases. This means that the nanotubes are under the influence of their environment. Moreover, their widths have the same behavior than the peak at 1593 cm-‘: the bundles seem to be undone in low nanotubes concentration samples. 5.
Conclusion
We have presented Raman studies on SWNTs. This nondestructive method is efficient to characterize these materials since we can get a diameter distribution and con&n the existence of “armcha? tubes and induce selective study by resonance effects. Therefore, it is possible to perform systematic studies. As an example, we are able to show that on the collaret, the diameter distribution changes significantly loom one spot to another in a gradual way and then, that the location in the synthesis chamber is of a great importance in the tubes production. On the contrary, the sublimation process of graphite seems to have a limited influence, since similar spectra are observed on SWXT’s produced by different methods. This studies have also shown that the introduction of nanotubes in a polymer mati modifies their structure and their organization. At low SWNT’s concentrations, the amorphous carbon is dispersed in PMMA, bundles seem to be undone. We notice also modifications of the bands assigned to the splitting of the EZ~Zmode of graphite. 6.
Acknowledgement
This work has been fully supported by the European Community through its Training and Mobility of Researcher program under network contract : NAMITECH, ERBFMRXCT96-0067 @GlZ-MIHT) and by the tiench CNRS program : ULTIMATECH.
h
7. 2800 3600 1200 2000 Raman shift (cm ‘I) Fig. 5 : PMMA-SWNT’s spectra for several concentiations. 400
t~~~I,~~l,,,l,,,l,,,i 160 180 200 220 120 140 Raman shift (cm “) Fig 6 : Low frequency range PMMA-SWNT’s (% in weight) films and SWNT’s film (top)
References
[l] S. Iijima, Nature 354 (1991) 56. [2] A. Thess, R. Lee, P. Nikolaev, H. Dai, P. Petif J. Robe& C. Xu, Y. H. Lee, S. G. Kim,A. G. Rinzler,D. T. Colbert, G. E. Scusaia, D. Tomanek, J. E. Fisher and R E. Smalley, Science, 273, 483 (1996). [3] C. Journet, W. K. Maser, P. Bernier, A. Loiseau, M Lamy de la Chapelle, S. Letiant, P. Deniard, R Lee and J. E. Fischer, Nature 388 (1997) 756. [4] S. Curran, P. Ajayan, W. Blau, D. Carroll, 3. Coleman, A. Dalton, A. P Davey, 3. McCarthy and A. Stevens, Advanced materials (in press). [S] M. Lamy de la Chapelle, S. Lefi-ant, Ph. Molinib, C. Godon, W. K. Maser, P. Bernier, P. Ajayan, in Proceedings of the SPIE conference, 2854,246-253, (1996). [6] A. M Rao, E. Richter, S. Bandow, B. Chase, P. C. Eklund, K. A. Williams, S. Fang, K. R. Subbaswamy, M Menon, A. Thess, R E. Smalley, G. Dresselhaus, M S. Dresselhaus, Science, 275, 187-191 (1997). [7] M. Lamy de la Chapelle, S. Lefianf C. Joumef W. Maser, P. Bernier and A. Loiseau, Carbon (1998) in press. [S] C. Eklund, J. M Holden and R. A. Jishi, Carbon 33 (1995) 959.
SyntheticMetals 103(1999) 251&2512
Raman characterization of singlewalled carbon nanotubes and PMMA-nanohtbes
composites
M. Lamy de la Chap&e i5b C Stkphan’, T. P. Nguyena, S. Lefiant’, C. Journet’, P. Bernie?, E. Mnnozd, A. Benitod, W. K. h4aserd, M. <. &xtinezd, G. F. de la Fuente’, T. Guillard’, G. Flaman~, L. Alvarezc, D. LaplazeC a Laboratoire
de Physique Cristalline, MN, Universitk de Naties, France b Trinity College, Dublin, Ireland ’ Groupe de Dynamique des Phases condenskes, Universite’ Montpeliier 2, Montpeliier, d Institute de Carboquimica CSIC, Zivagoza, Spain e institute de Cienca de Mareriales de Aragon, Zuragoza, Spain f IMP-CNRS, Odeillo, France
France
Abstract The Ramanspectroscopyhave allowed us to performstudieson singlewalled nanotubes(SWNT’s) produced by following methods: electric arc, laserablationand solarenergy.As this characterizationmethodprovidesa great dealof informations,we will presenta comparisonbetweenthe nanotubesproducedby all theseprocesses andthe influenceof somesynthesisparameters. By using spin casting, we have produced thin ftis of PMMA-SWNT’s for different concentrations. Then, we have characterizedthesenew materialsby Ramanspectroscopy.The aimof theseinvestigations is to get information on the possible interactionsbetweenthesetwo materials.In particular,we have studiedthe evolution of the compositesfilms spectraas a function of the nauotubesconcentrationin the polymer. Keywords:
nanotubes,PMMA, composites,spincasting,Ramanspectroscopy.
Co (0,6 / 0,6 at, %) mixture and xmdera pressureof 500 Ton:
1. Introduction The discovery of carbon nanotubes [l] has encouraged m=v studies about their properties and potential applications. The main ciiffkulty which limited such a developmentwas their production in rather smallquantities. But new methodsof synthesis, laserablation [2] and electric arc technique [3], have been presentedrecently which in addition lead to the formation of singlewalled nanotubes (SWNT’s), moreattractive in termsof electronic properties.In this paper, we mainly describeRamanresults performedon SWNT’s which provide a great deal of information on the nature of the SWNT’s studied and put clearly in evidencea diametersize distribution which dependson the location of the extractedsamplefrom the synthesischamber.We focus our studies on carbon nanotubes preparedby the electric arc method,and comparisonis madewith samplesobtained by different preparationtechniques. In addition, it has also beenconsideredcorn&sites such that nanotubeswere dispersedin a polymer mati [4]. Thus, we have madea composite using singlewalled nanotubes (SWNT’s) and poly(methy1 methacrylate)(PMMA). We have investigated vibrational properties of the PMMA-SWNT’s composites. 2. Experiments SWNT’s were producedby the arc dischargemethod(see ref. [3]), by laserablation and using solar energy. The second one have beenproduced in sublimating graphite with a Ni J 0379~67791996 - see front matter PII: s0379-6779(98)01080-7
0 1999 Elsevier
Science %A.
The third one waspreparedat the Odeillo solar furnace,The flm concentratedin the chamberis near 950 W/m*. In there conditions, during the evaporation process of the target (graphite / Ni / Co : 96 I 2 I 2 at. %) under an argon atmosphere(400 mbar, flow : 0,2 m3ih), the temperature increasesup to 3000K, whereasthe collected soot should be synthesisbetween2000 and 800 K. For the composite formation, the nanotubes powder (electric arc sample)and PMMA were mixed together in toluene in severalnanotubesconcentrationsspecifiedas the weight % in the polymer.Then the solution was mixedin an ultrasonicbath. Thin films werepreparedby spin casting onto KBr substrates.We have also made a nanotubes film by deposinga toluene-SWNT’ssolution on a KBr substrate.To obtainRamanspectra,a excitation wavelengthof 1064 nmhas beenused.All the dataare normalizedto the main peak of the nanotubesspectrumat 1593cm-‘. 3. SWNT’s studies With all the informations given by the Raman spectroscopy[5-71, it is possibleto makesystematicstudies on samplescontainingSWNT’s. For all spectrashown below, the laserexcitationwavelengthis the argon line at 514.5mu. In a fist step, we have performedexperimentson one co&ret, which is deposited on the cathode during the production processand where the higher concentration of SWNT’s is found. After having splitted it in several parts,we have studiedseveralspotson eachas shownin the exampleof figure 1.
All rights reserved.
M.L. de la Chapelle
et al. I Synthetic
Metals
IO3 (1999)
2510-2512
2511
similar to those obtained with the electric arc samples, We can always observe the Ezg2splitted mode, the same peaks at the same position at low frequencies or in the intermediate (2501200 cd) range. The tubes produced by the electric arc or laser ablation seems identical. Or the other hand, some other parts of the solar energy sample lead to the lower spectrum of tig. 3. This spectrum presents a broad peak at 1520 cm-’ and more than 10 peaks Corn 130 to 255 ti’. This corresponds to a very large diameter distribution shown by the low frequency bands and confiied by the broader splitting of the EQZ graphite mode. In this case, the diameter is expected to go liom a very low value near 8 A to 20 A. In this latter case, it seems that the synthesis conditions are not completely comparable to the two previous one, even if a large scale of SWNTs are also produced. From these observations, it can be suggested that the experimental parameters used for the sublimation of graphite do not play a major role in the production of nanotubes. On the contrary, the plasma conditions after sublimation turn out to be of real importance.
Fig 1 : Part the collaret with studied
the position of the 6 points
We have been able to see a gradual evolution of the diameter distribution on this part with the low frequency group of bands. Then it is clearly observed that along the sample from point 1 to point 6, the diameter distribution changes continuously from low diameter to higher ones. This is an indication that the conditions in the synthesis chamber are not homogeneous and that the tube production changes f?om one point to the other and then some specific diameters are favoured compared to others. As a consequence, we can conclude that the location of the extracted sample in the synthesis chamber is of real importance on the production of tubes with a specific diameter.
*
202
400
Mx)
800
loo0
1200
1403
1600
1800
Raman shift (cm’) Fig 3 : Raman spectra of laser ablation sample
(6) (5) (4) (3) (2)
(1) 1W
150
ml
250
Ramanshift (cm-‘) Fig 2 : Evolution of the Raman spectra from the point 1 to the point 6
In a second step, we have studied samples produced by other methods, namely laser ablation and solar energy. As shown in figures 3 and 4, the two Raman spectra obtained for laser ablation and the upper one of the solar energy look
200
400
600
SW
loo0
SC0
14M,
1600
l&W
Raman shift (cm-‘) Fig 4 : Raman spectra of solar energy sample 4. Composites
studies
The Raman bands of SWNT’s are clearly observed in PMMA-SWNT’s spectra (Fig. 5) but PMMA ones do not appear because of it low resonance behavior. In addition, a hump appears between 2250 and 3750 cm-‘. This hump which
seems to be asymmetric, increases with the nanotubes concentration. In the pristine PMMA fti and the SWNT’s powder spectra using the same excitation wavelength and laser power, no hump emerges. The spectrum of the SWNT’s
2512
ML.
de la Chapelle
et al. I Synthetic
film obtained in the same conditions shows the presence of the hump. Its appearance is due to the forming of a complex between the solvent and the nanotubes or amorphous carbon. The increase of the peak at 1270 Cm’ assigned to the disorder and the corresponding second order one at 2540 m’ [7l means that there is a high dispersion of the amorphous carbon for the low nanotubes concentrations. The bands in the range 1500-1650 cm?, attributed to a splitting of the E2s2 vibrational mode of graphite [S], show significant changes. First, the intensities of the bands at 1528, 1555, 1570 and 1603 cni’ in the composites spectra are lower than the SW’s film spectnun ones. Second, the main peak width of the composites increases as a function of the SWNT’s concentration but is lower than the nanotubes film one.
Metals
IO3 (1999)
2510-2512
In the low frequency range, two bands appear clearly (Fig. 6). They are shifted toward higher frequencies in the presence of PMMA and when the SWNT’s concentration increases. This means that the nanotubes are under the influence of their environment. Moreover, their widths have the same behavior than the peak at 1593 cm-‘: the bundles seem to be undone in low nanotubes concentration samples. 5.
Conclusion
We have presented Raman studies on SWNTs. This nondestructive method is efficient to characterize these materials since we can get a diameter distribution and con&n the existence of “armcha? tubes and induce selective study by resonance effects. Therefore, it is possible to perform systematic studies. As an example, we are able to show that on the collaret, the diameter distribution changes significantly loom one spot to another in a gradual way and then, that the location in the synthesis chamber is of a great importance in the tubes production. On the contrary, the sublimation process of graphite seems to have a limited influence, since similar spectra are observed on SWXT’s produced by different methods. This studies have also shown that the introduction of nanotubes in a polymer mati modifies their structure and their organization. At low SWNT’s concentrations, the amorphous carbon is dispersed in PMMA, bundles seem to be undone. We notice also modifications of the bands assigned to the splitting of the EZ~Zmode of graphite. 6.
Acknowledgement
This work has been fully supported by the European Community through its Training and Mobility of Researcher program under network contract : NAMITECH, ERBFMRXCT96-0067 @GlZ-MIHT) and by the tiench CNRS program : ULTIMATECH.
h
7. 2800 3600 1200 2000 Raman shift (cm ‘I) Fig. 5 : PMMA-SWNT’s spectra for several concentiations. 400
t~~~I,~~l,,,l,,,l,,,i 160 180 200 220 120 140 Raman shift (cm “) Fig 6 : Low frequency range PMMA-SWNT’s (% in weight) films and SWNT’s film (top)
References
[l] S. Iijima, Nature 354 (1991) 56. [2] A. Thess, R. Lee, P. Nikolaev, H. Dai, P. Petif J. Robe& C. Xu, Y. H. Lee, S. G. Kim,A. G. Rinzler,D. T. Colbert, G. E. Scusaia, D. Tomanek, J. E. Fisher and R E. Smalley, Science, 273, 483 (1996). [3] C. Journet, W. K. Maser, P. Bernier, A. Loiseau, M Lamy de la Chapelle, S. Letiant, P. Deniard, R Lee and J. E. Fischer, Nature 388 (1997) 756. [4] S. Curran, P. Ajayan, W. Blau, D. Carroll, 3. Coleman, A. Dalton, A. P Davey, 3. McCarthy and A. Stevens, Advanced materials (in press). [S] M. Lamy de la Chapelle, S. Lefi-ant, Ph. Molinib, C. Godon, W. K. Maser, P. Bernier, P. Ajayan, in Proceedings of the SPIE conference, 2854,246-253, (1996). [6] A. M Rao, E. Richter, S. Bandow, B. Chase, P. C. Eklund, K. A. Williams, S. Fang, K. R. Subbaswamy, M Menon, A. Thess, R E. Smalley, G. Dresselhaus, M S. Dresselhaus, Science, 275, 187-191 (1997). [7] M. Lamy de la Chapelle, S. Lefianf C. Joumef W. Maser, P. Bernier and A. Loiseau, Carbon (1998) in press. [S] C. Eklund, J. M Holden and R. A. Jishi, Carbon 33 (1995) 959.