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Single-walled carbon nanotubes produced by laser ablation under different inert atmospheres
ELSEVIER
SyntheticMetals 103(1999) 2490-2491
Single-walled carbon nanotubes produced by laser ablation under different inert atmospheres E. Mtioz %*,WK. Maser a,A.M. Benito a,G.F. de la Fuente b and M.T. Martinez ’ a Institute de Carboquimica (CSIC), chfaria de Luna 12, 50015 Zaragoza, Spain b Institute de Ciencia de Materiales de Aragdn (CSIC-Universidad de Zaragoza), c/Maria de Luna 3, 50015 Zaragoza, Spain
Abstract
In this work, single-walledcarbonnanotubes(SWNTs) have beenproducedunder atmospheres of argon, nitrogen, mixture of argon/nitrogen,and heliumusinga continuouswave modeCO2laser.High amountof SWNTmaterialwas achievedwhen argonand nitrogenand its mixture were employedas buffer gases,both under static and dynamicconditions,as it ~2s observedby electron microscopy.In contrastto the arc-discharge method,very low yields wereobtainedworkingunderheliumatmospheres. Keywords: A. Fullerenesandderivatives
1. introduction
Single-walledcarbon nanotubes(SWNTs) are quasi-1D systems whose structural perfection and chiral character determine their unique mechanical [I ] and electronic properties[ 21, which could lead to promisingapplicationsin fields of technologicalinterest.Up to now, the highestyields in the SWNT production were achieved by the arc discharge methodusinga statichelium atmosphere [ 31, and by a doublepulsedNd:YAG laser systemsweepingthe generatedmaterial with an argongasstream[ 4] In this work, SWNTs are producedby laser ablation of graphite/bimetalcompositetargets using a continuouswave modeCO1laser, Two kinds of experimentswere considered:a) productionof SWNTs underflowing argon,nitrogen,a mixture of argon/nitrogen,andhelium atmospheres, andb) productionof SWNTs under static conditionsusing the above mentioned gases,The high quality of the samplesgeneratedunder argon, nitrogenand a mixture argon/nitrogenis confirmedby scanning andtransmission electronmicroscopies (SEM, TEM).
Argon, nitrogen,anargon/nitrogenmixture, andheliumwere usedas buffer gases.All experimentswere carriedout undera pressureof 400 Ton. A gasflow of -1 l/min was established in the case of the experiments performed under dynamic conditions. The following metalconcentrations(in at%) of the metalgraphite compositetargets(cylindersof 5 mm in diameterand approximately 50 mm long) were used in the presentwork: Ni/Co (2/2; 0.6/0.6),Ni/Y (4.211;2/05)_andNi/Fe (2/0.5). During the vaporizationprocessabout200 mg of the target were consumedper hour. In the experimentscarried out under dynamic conditions,the generatedsoot was swept inside a quartz tube placedat the top of the evaporationchamberand partially collectedon an entangledcopperwire system.ln the caseof the experimentscatried out under static conditions,a similar copperwire systempiacedabove the target substituted the quartz tube. Additionally, in both cases,somesoot canbe found on the walls of the chamberaswell as on a filter at@hed~ to therotary pumpusedto evacuatethe experimentalsetup and alsoto establisha gasflow. The collectedsampleswere characterizedby SEM (JEOL JSM-6400)andTEM (PhillipsCM30,3OOkV).
2. Experimental
The production of SWNTs was achieved by laser vaporization of graphite/bimetal compositetargets using a simplemethodconsistingof a continuouswave mode250W CO2 laseroperatingat 1Opmand a vertical evaporationchamber,as describedin previousworks [5,6] . * Correspondmg author. edgar~ccarbon.icb.csic.es. PB94-0224). One of us Educaci6n y Cultura de la
Tel : +34 976 733977; Fax +34 976 733318; e-mail: This research was supported by the DGICYT (Progamm (E.M.) acknowledges funding from the Departamento de Comnidad Aut6noma de Arag6n.n.
3. Results and discussion
The carbonaceousmaterial produced under static and dynamic argon, nitrogen and the argon/nitrogen mixmrre atmospheres was collectedon the copperwire systemsin the form of dense aggregatesof web-like filaments of a few centimeterslong. SEM micrographs of the web materialproducedunderthese atmospheres showahigh densityof entangledfilamentsof about
0379~6779/99/$ - seefrontmatter0 1999ElsevierScience S.A. All rightsreserved. PII: s0379-6779(98)01082-0
W.K.
Maser
et al. / Synthetic
20 run in diameter and some microns long (Fig. 1). High resolution TEM micrographs (Fig. 2) show that these fibers are in fact bundles of SWNTs, and also that a high yield production has been achieved. These bundles are up to 20 nm in diameter (average diameters are in the range between 10 to 1.5run) and many microns long as seen by SEM. SEM and TEM studies of the rest of the produced soot show that it also contains a high density of bundles of SWNTs. However, Raman measurements [6] reveal a larger amorphous carbon content than in the web material.
Metals
103
(1999)
2490-2491
2491
from the results shown, so that further studies such as Raman measurements are necessary to determine possible differences in diameter distributions of the produced SWNTs, as well as to estimate the amorphous carbon content.
Fig. 1. Typical SEM micrograph of SWNT material produced by laser ablation of a Ni/Y (4.211 at%) target under a static 400 Torr nitrogen atmosphere. On the other hand, the generated material produced under helium atmospheres was collected as a powder having a rubbery texture, occasionally with some very few and tiny web-like filaments, SEM and TEM microscopies reveal that the use of helium provides very small SWNT yields. The laser-target-gas-plasma interactions that take place during the experiments described above may play an essential role in the SWNT formation and, consequently, in the appearence of the different textures which the generated soot exhibits. It is thus expected that the SWN’I production yield may be strongly affected by parameters such as the laser radiation wavelength, the buffer gas and its flow and pressure, and the composition of the targets. The 10.6 p laser radiation employed in this work work leads to plasma plumes about 1 cm long under argon and nitrogen atmospheres, as well as to a hot zone around the point where the incoming laser beam is focused, providing suitable conditions for supporting the SWNT growth. In contrast to the so-called laser-oven method [ 41, no additional temperature supply is needed to favour a high yield SWNT production, This fact reveals the differences of carrying out the vaporization processes using a CO2 laser operating under continuous wave conditions, or a double-pulsed Nd:YAG laser system. On the other hand, only small plasma plumes were induced when helium was used as buffer gas, due to its high ionization potential and high thermal conductivity [ 73 , leading to very low yields in the SWNT production. 4. Conclusions The laser ablation technique described in this paper is a versatile method that provides high yield productions of SWNTs under atmospheres of argon, nitrogen and argon/nitrogen mixtures. The influence of the gas flow is not clearly established
Fig.2. TEM micrograph of SWNT material produced by laser ablation of a Ni/Y (4.2/l at%) target under an atmosphere of 400 Torr of flowing nitrogen. 5. References [ 1] G. Ovemey, W. Zhong, D. Tomanek, Z. Phys. D. 27 (1993) 93. [ 21 J.W. Mintmire, B.I. Dunlop, C.T. Carter, Phys. Rev. Lett. 73 (1992) 2468. [ 3 ] C. Joumet, W.K. Maser, P. Bemier, A. Loiseau, M. Lamy de la Chapelle, S. Lefmnt, P. Deniard, R. Lee, J.E. Fischer, Nature 388 (1997) 756. [4] A. Thess, R. Lee, P. Nikolaev, H, Dai, P. Petit, J. Robert, C. Xu, Y.H. Lee, S.G. Kim, A.G. Rinzler, D.T. Colbert, G.E. Scuseria, D. Tomanek, J.E. Fischer, R.E. Smalley, Science 273 (1996) 483. [ 51 E. Mufioz, A.M. Benito, L.C. Estepa, J. Femandez, Y. Maniette, M.T. Martinez, G.F. de la Fuente, Carbon, 36 (1998) 525. [6] W.K. Maser, E. Mtioz,A.M. Benito, M.T. Martinez, G.F. de la Fuente, Y. Maniette, E. Anglaret, J.-L. Sauvajol, Chem. Phys. Lett.392 (1998) 587. [7] M. Kabasawa, M. Ono, K. Nakada and S. Kosuge in Laser Treatment of Materials, editor B.L. Mordike (DGM Informationsgesellschaft Verlag, Oberursel, 1992, ISBN 388355-185-6), p.667.
SyntheticMetals 103(1999) 2490-2491
Single-walled carbon nanotubes produced by laser ablation under different inert atmospheres E. Mtioz %*,WK. Maser a,A.M. Benito a,G.F. de la Fuente b and M.T. Martinez ’ a Institute de Carboquimica (CSIC), chfaria de Luna 12, 50015 Zaragoza, Spain b Institute de Ciencia de Materiales de Aragdn (CSIC-Universidad de Zaragoza), c/Maria de Luna 3, 50015 Zaragoza, Spain
Abstract
In this work, single-walledcarbonnanotubes(SWNTs) have beenproducedunder atmospheres of argon, nitrogen, mixture of argon/nitrogen,and heliumusinga continuouswave modeCO2laser.High amountof SWNTmaterialwas achievedwhen argonand nitrogenand its mixture were employedas buffer gases,both under static and dynamicconditions,as it ~2s observedby electron microscopy.In contrastto the arc-discharge method,very low yields wereobtainedworkingunderheliumatmospheres. Keywords: A. Fullerenesandderivatives
1. introduction
Single-walledcarbon nanotubes(SWNTs) are quasi-1D systems whose structural perfection and chiral character determine their unique mechanical [I ] and electronic properties[ 21, which could lead to promisingapplicationsin fields of technologicalinterest.Up to now, the highestyields in the SWNT production were achieved by the arc discharge methodusinga statichelium atmosphere [ 31, and by a doublepulsedNd:YAG laser systemsweepingthe generatedmaterial with an argongasstream[ 4] In this work, SWNTs are producedby laser ablation of graphite/bimetalcompositetargets using a continuouswave modeCO1laser, Two kinds of experimentswere considered:a) productionof SWNTs underflowing argon,nitrogen,a mixture of argon/nitrogen,andhelium atmospheres, andb) productionof SWNTs under static conditionsusing the above mentioned gases,The high quality of the samplesgeneratedunder argon, nitrogenand a mixture argon/nitrogenis confirmedby scanning andtransmission electronmicroscopies (SEM, TEM).
Argon, nitrogen,anargon/nitrogenmixture, andheliumwere usedas buffer gases.All experimentswere carriedout undera pressureof 400 Ton. A gasflow of -1 l/min was established in the case of the experiments performed under dynamic conditions. The following metalconcentrations(in at%) of the metalgraphite compositetargets(cylindersof 5 mm in diameterand approximately 50 mm long) were used in the presentwork: Ni/Co (2/2; 0.6/0.6),Ni/Y (4.211;2/05)_andNi/Fe (2/0.5). During the vaporizationprocessabout200 mg of the target were consumedper hour. In the experimentscarried out under dynamic conditions,the generatedsoot was swept inside a quartz tube placedat the top of the evaporationchamberand partially collectedon an entangledcopperwire system.ln the caseof the experimentscatried out under static conditions,a similar copperwire systempiacedabove the target substituted the quartz tube. Additionally, in both cases,somesoot canbe found on the walls of the chamberaswell as on a filter at@hed~ to therotary pumpusedto evacuatethe experimentalsetup and alsoto establisha gasflow. The collectedsampleswere characterizedby SEM (JEOL JSM-6400)andTEM (PhillipsCM30,3OOkV).
2. Experimental
The production of SWNTs was achieved by laser vaporization of graphite/bimetal compositetargets using a simplemethodconsistingof a continuouswave mode250W CO2 laseroperatingat 1Opmand a vertical evaporationchamber,as describedin previousworks [5,6] . * Correspondmg author. edgar~ccarbon.icb.csic.es. PB94-0224). One of us Educaci6n y Cultura de la
Tel : +34 976 733977; Fax +34 976 733318; e-mail: This research was supported by the DGICYT (Progamm (E.M.) acknowledges funding from the Departamento de Comnidad Aut6noma de Arag6n.n.
3. Results and discussion
The carbonaceousmaterial produced under static and dynamic argon, nitrogen and the argon/nitrogen mixmrre atmospheres was collectedon the copperwire systemsin the form of dense aggregatesof web-like filaments of a few centimeterslong. SEM micrographs of the web materialproducedunderthese atmospheres showahigh densityof entangledfilamentsof about
0379~6779/99/$ - seefrontmatter0 1999ElsevierScience S.A. All rightsreserved. PII: s0379-6779(98)01082-0
W.K.
Maser
et al. / Synthetic
20 run in diameter and some microns long (Fig. 1). High resolution TEM micrographs (Fig. 2) show that these fibers are in fact bundles of SWNTs, and also that a high yield production has been achieved. These bundles are up to 20 nm in diameter (average diameters are in the range between 10 to 1.5run) and many microns long as seen by SEM. SEM and TEM studies of the rest of the produced soot show that it also contains a high density of bundles of SWNTs. However, Raman measurements [6] reveal a larger amorphous carbon content than in the web material.
Metals
103
(1999)
2490-2491
2491
from the results shown, so that further studies such as Raman measurements are necessary to determine possible differences in diameter distributions of the produced SWNTs, as well as to estimate the amorphous carbon content.
Fig. 1. Typical SEM micrograph of SWNT material produced by laser ablation of a Ni/Y (4.211 at%) target under a static 400 Torr nitrogen atmosphere. On the other hand, the generated material produced under helium atmospheres was collected as a powder having a rubbery texture, occasionally with some very few and tiny web-like filaments, SEM and TEM microscopies reveal that the use of helium provides very small SWNT yields. The laser-target-gas-plasma interactions that take place during the experiments described above may play an essential role in the SWNT formation and, consequently, in the appearence of the different textures which the generated soot exhibits. It is thus expected that the SWN’I production yield may be strongly affected by parameters such as the laser radiation wavelength, the buffer gas and its flow and pressure, and the composition of the targets. The 10.6 p laser radiation employed in this work work leads to plasma plumes about 1 cm long under argon and nitrogen atmospheres, as well as to a hot zone around the point where the incoming laser beam is focused, providing suitable conditions for supporting the SWNT growth. In contrast to the so-called laser-oven method [ 41, no additional temperature supply is needed to favour a high yield SWNT production, This fact reveals the differences of carrying out the vaporization processes using a CO2 laser operating under continuous wave conditions, or a double-pulsed Nd:YAG laser system. On the other hand, only small plasma plumes were induced when helium was used as buffer gas, due to its high ionization potential and high thermal conductivity [ 73 , leading to very low yields in the SWNT production. 4. Conclusions The laser ablation technique described in this paper is a versatile method that provides high yield productions of SWNTs under atmospheres of argon, nitrogen and argon/nitrogen mixtures. The influence of the gas flow is not clearly established
Fig.2. TEM micrograph of SWNT material produced by laser ablation of a Ni/Y (4.2/l at%) target under an atmosphere of 400 Torr of flowing nitrogen. 5. References [ 1] G. Ovemey, W. Zhong, D. Tomanek, Z. Phys. D. 27 (1993) 93. [ 21 J.W. Mintmire, B.I. Dunlop, C.T. Carter, Phys. Rev. Lett. 73 (1992) 2468. [ 3 ] C. Joumet, W.K. Maser, P. Bemier, A. Loiseau, M. Lamy de la Chapelle, S. Lefmnt, P. Deniard, R. Lee, J.E. Fischer, Nature 388 (1997) 756. [4] A. Thess, R. Lee, P. Nikolaev, H, Dai, P. Petit, J. Robert, C. Xu, Y.H. Lee, S.G. Kim, A.G. Rinzler, D.T. Colbert, G.E. Scuseria, D. Tomanek, J.E. Fischer, R.E. Smalley, Science 273 (1996) 483. [ 51 E. Mufioz, A.M. Benito, L.C. Estepa, J. Femandez, Y. Maniette, M.T. Martinez, G.F. de la Fuente, Carbon, 36 (1998) 525. [6] W.K. Maser, E. Mtioz,A.M. Benito, M.T. Martinez, G.F. de la Fuente, Y. Maniette, E. Anglaret, J.-L. Sauvajol, Chem. Phys. Lett.392 (1998) 587. [7] M. Kabasawa, M. Ono, K. Nakada and S. Kosuge in Laser Treatment of Materials, editor B.L. Mordike (DGM Informationsgesellschaft Verlag, Oberursel, 1992, ISBN 388355-185-6), p.667.