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The first observation of carbon nanotubes
Letters to the Editor
581
The first observation of carbon nanotubes H.P.BoEHM Institut ftir Anorganische Chemie der Universitlt Miinchen, MeiserstraDe 1, 80333 Mtinchen, Germany. Key Words - A. Nanoparticles. nanotubes
Carbon nanotubes, prepared in a dc arc dischange between graphite electrodes [ 1.21, have become of great interest because of their unique properties. They are built of nested, concentric cylinders made up of carbon honeycomb structures. The first observation of their formation in substantial quantities was described in 1991 [l]. Gibson, in a letter to Nature [3], indicated that similar structures had been prepared as early as 1953 by disproportionation of carbon monoxide at 450°C, catalyzed by iron oxides (or, rather, iron after reduction) contatned in firebrick [4]. However, these catalytically
Fig.1.
C. transmission electron microscopy
grown carbon filaments are quite different in their structure from carbon nanotubes [S, 61. They are usually bent or coiled while carbon nanotubes exhibit a straight, hollow needle-like appearance. However, carbon nanotubes have indeed been observed before Iijima’s report [I]. Carbons prepared from silicon carbide or metal carbides, e.g. tantalum carbide, by reaction with chlorine have been studied in the writer’s laboratory. If the reaction temperature is chosen not too high, only the metal is volatilized as the chloride, i.e. SiCl, or TaCl,, respectively, while highly
Electron microphotograph of the edge of a carbon particle produced from Sic Carbon nanotubes are marked A, and carbon nanoparticles are marked B.
582
Letters to the Editor
Fig. I. showing a conical carbon nanotube with of the layers in the end caps.
Fig.2. Enlargement of a section of scparatm
carbon remains dll ,ordcl red, mlcroporous form a pseudomorphosis -IlOll particles
(7.81. The after the ori ginal carbide crystals [9]. Such pseudomorphic Cal-bans can bc prepared even from large, plate-like SIC Cl)ISl91Sof l-2 cm diameter. At I 100 1200°C, silicon volatilized as SiCl, and Ccl, Calrhidc is completely I I( ).I 1I In a transmission electron microscope sludy of ,on obtained by chlorination of silicon carbide LhL of small particlc SIX at 800 - MO”C, the images PC’ n Figs. l-4 were obtained. Clearly, one can sec. she
Cal
among many other interesting features, the ca pped ends of multilayer carbon nanotubes, very simila r to those observed by Iijima [ I]. The spacing between the layers is about 340 pm. Figure 2 presents a magnific :ation of a detail of Fig. 1, showing the conical end of a nanotube with the Individual end caps separated by large distances. Such structures have been described in the literature 113.131. Since such features could bc observed only with a few particles, I considered this a singular olxervation not typical for this carbon material. Howe! ier, I was
F1g.i. Elccrron microphotograph showing nanoluhes (marked A) and nanoparlicles (marked 6) as well as ribhon-like structures of stacked graphene layers.
583
Letters to the Editor
Fig.4. Electron microphotograph showing a ribbon-like graphitic structure near the edge of a carbon particle produced from SIC. intrigued by the imaging of single, separated carbon layers, and I thought this to be of interest in the context of lattice imaging. A few years later, I made this photograph (Fig. 2) available to Millward and Jefferson who were working on an article on the lattice resolution of carbons by electron microscopy. The image of this carbon nanotube was published in their article [ 141. The original elctron microphotographs had been taken in April 1972. Thus, this was apparently the first observation of carbon nanotubes although it was not recognized at that time how such material is formed. In 1974, D. Crawford* showed me a TEM image of a carbon film produced as a carbon support for electron microscopy by an arc between pointed graphite electrodes. The film was contaminated with material looking like carbon nanotubes and nanoparticles although the resolution was not as high as in electron microphotographs in the present Letter. In additon to carbon nanotubes, the electron microphotographs in Figs. l-3 also show hollow graphitic polyhedral particles. Such nanoparticles have been often observed in the cathodic deposits formed in carbon nanotubc production (1%171. Also, the noncrystalline, porous carbon formed by the selective removal of silicon can be seen. Another interesting feature is the ribbon-like graphite structures. They appear also with particles that have no attached nanotubes or polyhedral nanoparticles, and they seem to occur predominantly near the surface of the particles of disordered carbon (Fig.4). Possibly they arise from beginning thermal decomposition when the silicon carbide is overheated during production. X-ray diffraction of the carbon prepared from sihcon carbide shows extremely weak and diffuse x-ray lines [X, 181. In our case, the broad 002 band of the non-crystalline carbon was superimposed on a relatively sharp graphite 002 reflection. Obviously, our silicon carbide was contaminated with graphite. In one electron microphotograph of the fine particle size silicon carbide, a vermicular, exfoliated graphite particle could be seen [7 ]. Tbe material had been treated with hydrofluoric acid *Northern Coke Research Laboratory, Univ. of Newcastleupon-Tyne
in the course of purification, and apparently a graphite particle had been intercalated by HF. A residue of 2.6s wt.% remained after oxidation in oxygen (200 mm. at 360°C) of the carbon obtained by chlorination that was identified as well-crystallized graphite. Certainly, the carbon nanotubes and the hollow polyhedral particles were not a result of the chlorination reaction. Very likely, they were already present in the silicon carbide precursor. Silicon carbide is produced by reduction of silica (quartz) with carbon (petrol coke) at 2000 - 2500°C. In the Acheson process as well as in the ESK (Elektroschmelawerke Kemptem) process, the high temperature is obtained by resistive heating of a graphite bar surrounded by the reaction mixture. The temperature of the graphite heater is said to reach 2500°C. Evidently the nanotubes and nanoparticles had formed under these conditions, although it is not clear how the necessary temperatures for carbon vaporization have been reached. It is conceivable that small, local electron arcs occurred when sufficient electrically conducting silicon carbide had formed to produce shunts in the electircal heating. It is very likely that substantial quantities of carbon nanotubes have been produced for a long time as a contaminant of industrial silicon carbide. The silicon carbide powder of 5 m2/g surface area was obtained from Elektroschmelzwerke Kcmpten. It was purified by consecutive treatment with hydrochloric acid, hydrofluoric acid and sodium hydroxide. Material of fine particle size was separated by sedimentation of a suspension in 0.02M ammonia. The transmission electron microphotographs were taken with a Philips EM 300 instrument. Acknowledgements: The electron micrographs were taken in the Electron Optics. Applications Laboratory of N.V. Philips Gloeilampenfabrieken, Eindhoven, Netherlands. I am indebted to Philips and Dr. Gross for this support. Financial support by Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie is gratefully acknowledged. Dedicated to Professor of his 65th birthday.
Wolfgang Beck on the occasion
Letters to rhe Editor
584 REFERENCES
IO. Moissan.
1. Iijina. S.. Nature 1991, 354, 56. 2. Ebbesen, T.W. and Ajayan, P.M .. Nature 1992, 358, 220.
3. Gibson, J.A.E., Nature 1992. 359, 369. 4. Davis, W.R., Slawson, R.J. and Rigby, G.R., Nuture 1953, 171, 756. 5. Baker, R.T.K. and Harris, P.S., in Chemistry and Physrcs of Carbon, Vol. 14, ed. P.L. Walker, Jr. and P.A. Thrower. Dekker, New York, 1978, pp. 83-165. Boehm, H.P., Curbon 1973, 11, 583. 76: FGrster, H.J., Die Chemie der Oberfliiche des Siliciumcarbids Eigenschaflen eines aus Siliciumcarbid hergestellten Kohlenstoffs. Dr.rer.nat. thesis, University of Heidelberg, Germany, 1967. 8. Boehm. H.P. and Warnecke, H.H., in Exlended Abstracts, 12th Bienn. ConJ on Carbon, Pittsburgh, PA, 1995, p. 149. 9 Euler, F. and Czerlinski, E.R., in Proc. Conf. on Silicon Carbide, Boston, MA ,1959, p, 155.
11. 12. 13. 14. 15. 16. 17. 18.
H., Compt. Rend. Acad. Sci.. Paris 1893, 117, 425. Lea, A.C., Truns.Brit.Ceram.Soc. 1941, 40, 93. Iijima, S., Ichihashi, T. and Ando, Y., Nature 1992, 356, 776. Ajayan, P.M. and Iijima, S., Nature 1992, 358,23. Millward, G.R. and Jefferson, D.A., in Chemistry und Physics of Carbon, Vol. 14, ed. P.L. Walker, Jr. and P.A. Thrower. Dekker, New York, 1978, pp. l-82. Dravid, V.P., Lin, X., Wang, Y., Wang, X.K., Yee, A., Ketterson, J.B. and Chang, R.P.H., Science 1993, 259, 1601. Ellacott. M.V., Pang, L.S.K., Prochazka, L., Wilson, M.A., Fitzgerald, J.D. and Taylor, G.H., Carbon 1994,32, 542. Kiang, C.H., Dresselhaus, M.S., Beyers, R. and Bethune. O.D.. Chem. Phvs. L.&t. 1996,259,41. Mohun, W.A.,‘in Proc. 4ih Biennial Con/: on Carbon, Oxford, 1960, Buffalo, N.Y., 1959. Pergamon, pp. 443-453.
581
The first observation of carbon nanotubes H.P.BoEHM Institut ftir Anorganische Chemie der Universitlt Miinchen, MeiserstraDe 1, 80333 Mtinchen, Germany. Key Words - A. Nanoparticles. nanotubes
Carbon nanotubes, prepared in a dc arc dischange between graphite electrodes [ 1.21, have become of great interest because of their unique properties. They are built of nested, concentric cylinders made up of carbon honeycomb structures. The first observation of their formation in substantial quantities was described in 1991 [l]. Gibson, in a letter to Nature [3], indicated that similar structures had been prepared as early as 1953 by disproportionation of carbon monoxide at 450°C, catalyzed by iron oxides (or, rather, iron after reduction) contatned in firebrick [4]. However, these catalytically
Fig.1.
C. transmission electron microscopy
grown carbon filaments are quite different in their structure from carbon nanotubes [S, 61. They are usually bent or coiled while carbon nanotubes exhibit a straight, hollow needle-like appearance. However, carbon nanotubes have indeed been observed before Iijima’s report [I]. Carbons prepared from silicon carbide or metal carbides, e.g. tantalum carbide, by reaction with chlorine have been studied in the writer’s laboratory. If the reaction temperature is chosen not too high, only the metal is volatilized as the chloride, i.e. SiCl, or TaCl,, respectively, while highly
Electron microphotograph of the edge of a carbon particle produced from Sic Carbon nanotubes are marked A, and carbon nanoparticles are marked B.
582
Letters to the Editor
Fig. I. showing a conical carbon nanotube with of the layers in the end caps.
Fig.2. Enlargement of a section of scparatm
carbon remains dll ,ordcl red, mlcroporous form a pseudomorphosis -IlOll particles
(7.81. The after the ori ginal carbide crystals [9]. Such pseudomorphic Cal-bans can bc prepared even from large, plate-like SIC Cl)ISl91Sof l-2 cm diameter. At I 100 1200°C, silicon volatilized as SiCl, and Ccl, Calrhidc is completely I I( ).I 1I In a transmission electron microscope sludy of ,on obtained by chlorination of silicon carbide LhL of small particlc SIX at 800 - MO”C, the images PC’ n Figs. l-4 were obtained. Clearly, one can sec. she
Cal
among many other interesting features, the ca pped ends of multilayer carbon nanotubes, very simila r to those observed by Iijima [ I]. The spacing between the layers is about 340 pm. Figure 2 presents a magnific :ation of a detail of Fig. 1, showing the conical end of a nanotube with the Individual end caps separated by large distances. Such structures have been described in the literature 113.131. Since such features could bc observed only with a few particles, I considered this a singular olxervation not typical for this carbon material. Howe! ier, I was
F1g.i. Elccrron microphotograph showing nanoluhes (marked A) and nanoparlicles (marked 6) as well as ribhon-like structures of stacked graphene layers.
583
Letters to the Editor
Fig.4. Electron microphotograph showing a ribbon-like graphitic structure near the edge of a carbon particle produced from SIC. intrigued by the imaging of single, separated carbon layers, and I thought this to be of interest in the context of lattice imaging. A few years later, I made this photograph (Fig. 2) available to Millward and Jefferson who were working on an article on the lattice resolution of carbons by electron microscopy. The image of this carbon nanotube was published in their article [ 141. The original elctron microphotographs had been taken in April 1972. Thus, this was apparently the first observation of carbon nanotubes although it was not recognized at that time how such material is formed. In 1974, D. Crawford* showed me a TEM image of a carbon film produced as a carbon support for electron microscopy by an arc between pointed graphite electrodes. The film was contaminated with material looking like carbon nanotubes and nanoparticles although the resolution was not as high as in electron microphotographs in the present Letter. In additon to carbon nanotubes, the electron microphotographs in Figs. l-3 also show hollow graphitic polyhedral particles. Such nanoparticles have been often observed in the cathodic deposits formed in carbon nanotubc production (1%171. Also, the noncrystalline, porous carbon formed by the selective removal of silicon can be seen. Another interesting feature is the ribbon-like graphite structures. They appear also with particles that have no attached nanotubes or polyhedral nanoparticles, and they seem to occur predominantly near the surface of the particles of disordered carbon (Fig.4). Possibly they arise from beginning thermal decomposition when the silicon carbide is overheated during production. X-ray diffraction of the carbon prepared from sihcon carbide shows extremely weak and diffuse x-ray lines [X, 181. In our case, the broad 002 band of the non-crystalline carbon was superimposed on a relatively sharp graphite 002 reflection. Obviously, our silicon carbide was contaminated with graphite. In one electron microphotograph of the fine particle size silicon carbide, a vermicular, exfoliated graphite particle could be seen [7 ]. Tbe material had been treated with hydrofluoric acid *Northern Coke Research Laboratory, Univ. of Newcastleupon-Tyne
in the course of purification, and apparently a graphite particle had been intercalated by HF. A residue of 2.6s wt.% remained after oxidation in oxygen (200 mm. at 360°C) of the carbon obtained by chlorination that was identified as well-crystallized graphite. Certainly, the carbon nanotubes and the hollow polyhedral particles were not a result of the chlorination reaction. Very likely, they were already present in the silicon carbide precursor. Silicon carbide is produced by reduction of silica (quartz) with carbon (petrol coke) at 2000 - 2500°C. In the Acheson process as well as in the ESK (Elektroschmelawerke Kemptem) process, the high temperature is obtained by resistive heating of a graphite bar surrounded by the reaction mixture. The temperature of the graphite heater is said to reach 2500°C. Evidently the nanotubes and nanoparticles had formed under these conditions, although it is not clear how the necessary temperatures for carbon vaporization have been reached. It is conceivable that small, local electron arcs occurred when sufficient electrically conducting silicon carbide had formed to produce shunts in the electircal heating. It is very likely that substantial quantities of carbon nanotubes have been produced for a long time as a contaminant of industrial silicon carbide. The silicon carbide powder of 5 m2/g surface area was obtained from Elektroschmelzwerke Kcmpten. It was purified by consecutive treatment with hydrochloric acid, hydrofluoric acid and sodium hydroxide. Material of fine particle size was separated by sedimentation of a suspension in 0.02M ammonia. The transmission electron microphotographs were taken with a Philips EM 300 instrument. Acknowledgements: The electron micrographs were taken in the Electron Optics. Applications Laboratory of N.V. Philips Gloeilampenfabrieken, Eindhoven, Netherlands. I am indebted to Philips and Dr. Gross for this support. Financial support by Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie is gratefully acknowledged. Dedicated to Professor of his 65th birthday.
Wolfgang Beck on the occasion
Letters to rhe Editor
584 REFERENCES
IO. Moissan.
1. Iijina. S.. Nature 1991, 354, 56. 2. Ebbesen, T.W. and Ajayan, P.M .. Nature 1992, 358, 220.
3. Gibson, J.A.E., Nature 1992. 359, 369. 4. Davis, W.R., Slawson, R.J. and Rigby, G.R., Nuture 1953, 171, 756. 5. Baker, R.T.K. and Harris, P.S., in Chemistry and Physrcs of Carbon, Vol. 14, ed. P.L. Walker, Jr. and P.A. Thrower. Dekker, New York, 1978, pp. 83-165. Boehm, H.P., Curbon 1973, 11, 583. 76: FGrster, H.J., Die Chemie der Oberfliiche des Siliciumcarbids Eigenschaflen eines aus Siliciumcarbid hergestellten Kohlenstoffs. Dr.rer.nat. thesis, University of Heidelberg, Germany, 1967. 8. Boehm. H.P. and Warnecke, H.H., in Exlended Abstracts, 12th Bienn. ConJ on Carbon, Pittsburgh, PA, 1995, p. 149. 9 Euler, F. and Czerlinski, E.R., in Proc. Conf. on Silicon Carbide, Boston, MA ,1959, p, 155.
11. 12. 13. 14. 15. 16. 17. 18.
H., Compt. Rend. Acad. Sci.. Paris 1893, 117, 425. Lea, A.C., Truns.Brit.Ceram.Soc. 1941, 40, 93. Iijima, S., Ichihashi, T. and Ando, Y., Nature 1992, 356, 776. Ajayan, P.M. and Iijima, S., Nature 1992, 358,23. Millward, G.R. and Jefferson, D.A., in Chemistry und Physics of Carbon, Vol. 14, ed. P.L. Walker, Jr. and P.A. Thrower. Dekker, New York, 1978, pp. l-82. Dravid, V.P., Lin, X., Wang, Y., Wang, X.K., Yee, A., Ketterson, J.B. and Chang, R.P.H., Science 1993, 259, 1601. Ellacott. M.V., Pang, L.S.K., Prochazka, L., Wilson, M.A., Fitzgerald, J.D. and Taylor, G.H., Carbon 1994,32, 542. Kiang, C.H., Dresselhaus, M.S., Beyers, R. and Bethune. O.D.. Chem. Phvs. L.&t. 1996,259,41. Mohun, W.A.,‘in Proc. 4ih Biennial Con/: on Carbon, Oxford, 1960, Buffalo, N.Y., 1959. Pergamon, pp. 443-453.