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Shock synthesis of concentric shell fullerene dimers and trimers
Carbon 42 (2004) 3003–3042 www.elsevier.com/locate/carbon
Letters to the Editor
Shock synthesis of concentric shell fullerene dimers and trimers Kenjiro Yamada Department of Chemistry, National Defense Academy, Hashirimizu, Yokosuka 239-8686, Japan Received 10 April 2004; accepted 1 June 2004 Available online
Keywords: A. Fullerene; B. Pyrolysis, gasification; C. Electron microscopy; D. Microstructure
In recent years there has been much interest in preparing fullerene oligomers and many workers have attempted to polymerize fullerene C60 by various methods such as photoirradiation [1–3], high-pressure compression at high temperature [4,5], and alkali-metal doping [6]. According to theoretical calculations, the C60 dimer has a dumbbell-shaped structure, with the two C60 cages connected with a square cyclobutane ring, like sp3 hybridization. Therefore, the C60 polymer has been considered to be formed via a [2 + 2] cycloadditional fourmembered ring structure. On the other hand, although concentric shell fullerenes have been prepared by means of the dc arc-discharge evaporation of carbon [7] and the electron beam irradiation of amorphous carbon particles [8], they were monomers. The aim of the present work is to discuss a formation process of the concentric shell fullerene dimers and trimers from carbon vapor generated by thermal decomposition of a carboneous compound using shock compression. Tetracyanoethylene powder (Wako GP grade) was used as the starting carboneous compound. Pyrolysis of the tetracyanoethylene powder occurs at 199 C. Fig. 1(a) shows a diagram of the apparatus used in this work. The tapered mild steel cylinder has a sample chamber 10 mm in diameter and 60 mm in height. When samples weighting more than about 0.60 g were shockcompressed, the container was ruptured due to large thermal pressure induced by the reflection of the shock wave at the bottom of the sample chamber and the high pressure of carbon and nitrogen gas generated by thermal decomposition and gasification of the sample. In order to avoid this a sample weighing 0.55 g was
E-mail address: [email protected] 0008-6223/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2004.06.021
used. The sample was tamped into the container to form a cylinder 10 mm in diameter and about 10 mm in height. Then a mild steel rod (diameter 9.9 mm; length 10 mm) was fixed at a position 40 mm from the bottom of sample chamber. The inlet of sample chamber was covered with a brass disc (diameter 12 mm; length 10 mm). The shock compression was carried out using trimethylene trinitramine explosive weighing 80 g. Fig. 1(b) shows a vertical-section view of the container after the shock compression. The samples were mechanically taken out of the container and were treated with dilute HCl to remove the Fe contaminant from the container. The residues were then washed with distilled water to remove hydrogen chloride. Both the purified residue and the initial sample were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM) at 200 kV. The TEM was equipped with an energy dispersive X-ray (EDX) analyzer. The XRD analysis was performed using Cu Ka1 radiation operating (40 kV and 60 mA). The specimens were dispersed in ethanol and samples prepared for the TEM studies by dipping molybdenum grids covered with holey amorphous carbon into this suspension. SEM image of the post-shocked sample is shown in Fig. 2(a). This indicates that the specimen was composed of irregular shaped sheets and thick plate-like particles, and very small spherical particles indicated by arrows. XRD patterns of the powder of these particles showed, besides graphite diffraction peaks, two unknown weak peaks at 2h = 43.16 and 73.88 (Fig. 2(b)). These two peaks were assigned to a new simple cubic modification of carbon with a unit cell parameter of 0.514 nm [9]. In order to determine the composition and crystal structure of the spherical particles, the post-shocked
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Letters to the Editor / Carbon 42 (2004) 3003–3042
Fig. 1. (a) Schematic cross-sectional view of the apparatus and (b) vertical cross-section of the shocked sample container for: (a) (1) steel sample container; (2) tetracyanoethylene powder; (3) cavity; (4) free space; (5) steel plug; (6) thick brass disk; (7) explosive charge; (8) wooden plug; (9) polyvinyl chloride plastic tube; (10) electric detonator.
Fig. 3. (a) TEM image of concentric shell particles having a particle size of the order of several tens of nanometer in diameter, and (b) the corresponding EDX spectrum.
powder was examined by HREM and EDX analysis and examples are shown in Fig. 3. It was determined from these data that the spherical particles are carbon with
a multiple-shell structure (concentric shell fullerenes). The interplanar distance (d value) is 0.338 nm, slightly larger than the (0 0 2) lattice spacing of bulk graphite
Fig. 2. (a) SEM image of the shock-compressed samples. The arrows show fine spherical particles. (b) X-ray diffraction patterns of (i) the tetracyanoethylene powder and (ii) the shock-compressed sample. (d) Graphite; (m) Cubic modification of carbon.
Letters to the Editor / Carbon 42 (2004) 3003–3042
Fig. 4. TEM image of a trimer consisting of fullerenes shown in Fig. 4. The carbon layers in the particle junction region and the non-junction region are well stacked.
(d0 0 2 = 0.336 nm). In this work, not only were concentric shell fullerene monomers obtained but also dimers
3005
and trimers. The size of monomers was in the range several tens to several hundreds of nanometer in diameter. To investigate a possible agglomeration process of the concentric shell fullerenes, the microstructure of the particle junction region of dimers and trimers was examined using HREM. Fig. 4 shows a HREM image of a trimer consisting of concentric shell fullerenes. This image indicates that the particles A and B are bound to each other by a sharing of two or three aromatic planes and the carbon layers in the particle junction as well as the nonjunction region are well stacked (arrow I). On the other hand, particles A and C are bound to each other via sharing slightly more aromatic planes than in the case of A and B; in this case the carbon layers in the junction are slightly disordered (arrow II). The TEM image in Fig. 5(a) shows a rather-wide particle-size distribution of the concentric shell fullerenes, in which we can see several dimers (arrow A) and trimers (arrow B) comprised of large concentric shell fullerenes. Higher magnification micrographs
Fig. 5. (a) TEM image of concentric shell fullerenes, having a particle size of the order of several hundred nanometers in diameter. Arrows A and B show a dimer and a trimer, respectively. (b) and (c) HREM images of the dimer particle junction and non-junction regions respectively, and the corresponding nanodiffraction patterns. The diffraction pattern in (b) consists of halos.
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Letters to the Editor / Carbon 42 (2004) 3003–3042
and nanodiffraction patterns of the dimer indicated by arrow A in the figure show that the particle junction of the dimer or trimer was almost amorphous (Fig. 5(b)), while the non-junction region had a concentric layered structure, though it contained many imperfections such as dislocations, bends, or non-parallel planes (Fig. 5(c)). From these results, i.e. necking of concentric shell fullerenes, merging to form larger spheres (arrow B in Fig. 5(a)), and the difference in the fine structures between the junction and non-junction regions, the formation processes of the dimer and trimer having a concentric graphitic shell structure can be assumed to occur in the following manner. First, the starting substance is thermally decomposed by the very high shock temperature and vaporized as a result of heating due to high residual energy. The resulting carbon vapor condenses by rapid post-shock cooling and the precursors of concentric shell fullerene, which are in the liquid state, are formed. Since the carbon droplets move violently, some of them collide and coalesce to form the structure of particle aggregates. Subsequently, solidification is initiated from the surface of the droplet toward the center, because the surface temperature is lower than the inner one [10]. In the case of the dimer or trimer precursors consisting of carbon droplets of the order of several tens of nanometer in diameter, since the junction region which is not in contact with the atmosphere is negligibly small, the whole of the precursor would be in an isotropic liquid state. In addition, the size of particles seems to be so small that in spite of rapid post-shock cooling, the constituent particles of the precursor have sufficient time for molecular orientation to establish the regularly concentric structure of carbon layers. The concentric arrangement of carbon layers starts from the particle surface of the precursor and propagates toward the center. On the other hand, in the case of dimer or trimer precursors consisting of carbon droplets of the order of several hundreds of nanometer in
diameter, the junction region which is not in contact with the atmosphere is broad, and hence its cooling rate is slower than that of the non-junction region. Moreover, it is thought that the particle size of the constituent carbon droplets is so large that a regular concentric arrangement of carbon layers could not be completed by migration of molecules under the rapid post-shock cooling conditions. Therefore, not only is the junction region frozen in an amorphous state, but also the non-junction region has less well-ordered stacking structure.
References [1] Rao AM, Zhou P, Wang K-A, Hager GT, Holden JM, Wang Y, et al. Photoinduced polymerization of solid C60 films. Science 1993;259:955–75. [2] Sun Y-P, Ma B, Bunker CE, Liu BJ. All-carbon (polyfullerenes) from photochemical reactions of fullerene clusters in roomtemperature solvent mixtures. Am Chem Soc 1995;117: 12705–12711. [3] Onoe J, Nakao A, Takeuchi K. XPS study of a photopolymerized C60. Phys Rev B 1997;55:10051–6. [4] Iwasa Y, Arima T, Fleming RM, Siegrist T, Zhou O, Haddon RC, et al. New phases of C60 synthesized at high pressure. Science 1994;264:1570–2. [5] Goze C, Rachdi F, Hajji L, Regueiro MN, Marques L, Hodeau JL, et al. High-resolution 13C NMR studies of high-pressurepolymerized C60: evidence for the [2 + 2] cycloaddition structure in the rhombohedral two-dimensional C60 polymer. Phys Rev B 1996;54:R3676–8. [6] Komatsu K, Fujiwara K, Tanaka T, Murata Y. The Fullerene dimer C120 and related carbon allotropes. Carbon 2000;38: 1529–4. [7] Iijima SJ. The 60-carbon cluster has been revealed. Phys Chem 1987;91:3466–7. [8] Ugarte D. Curling and closure of graphitic networks under electron-beam irradiation. Nature 1992;359:707–9. [9] Yamada K. Shock synthesis of a new cubic form. Carbon 2003;41:1309–13. [10] Marsh M. Are carbon blacks formed from liquid-crystal system. Carbon 1993;11:245–1313.
Letters to the Editor
Shock synthesis of concentric shell fullerene dimers and trimers Kenjiro Yamada Department of Chemistry, National Defense Academy, Hashirimizu, Yokosuka 239-8686, Japan Received 10 April 2004; accepted 1 June 2004 Available online
Keywords: A. Fullerene; B. Pyrolysis, gasification; C. Electron microscopy; D. Microstructure
In recent years there has been much interest in preparing fullerene oligomers and many workers have attempted to polymerize fullerene C60 by various methods such as photoirradiation [1–3], high-pressure compression at high temperature [4,5], and alkali-metal doping [6]. According to theoretical calculations, the C60 dimer has a dumbbell-shaped structure, with the two C60 cages connected with a square cyclobutane ring, like sp3 hybridization. Therefore, the C60 polymer has been considered to be formed via a [2 + 2] cycloadditional fourmembered ring structure. On the other hand, although concentric shell fullerenes have been prepared by means of the dc arc-discharge evaporation of carbon [7] and the electron beam irradiation of amorphous carbon particles [8], they were monomers. The aim of the present work is to discuss a formation process of the concentric shell fullerene dimers and trimers from carbon vapor generated by thermal decomposition of a carboneous compound using shock compression. Tetracyanoethylene powder (Wako GP grade) was used as the starting carboneous compound. Pyrolysis of the tetracyanoethylene powder occurs at 199 C. Fig. 1(a) shows a diagram of the apparatus used in this work. The tapered mild steel cylinder has a sample chamber 10 mm in diameter and 60 mm in height. When samples weighting more than about 0.60 g were shockcompressed, the container was ruptured due to large thermal pressure induced by the reflection of the shock wave at the bottom of the sample chamber and the high pressure of carbon and nitrogen gas generated by thermal decomposition and gasification of the sample. In order to avoid this a sample weighing 0.55 g was
E-mail address: [email protected] 0008-6223/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2004.06.021
used. The sample was tamped into the container to form a cylinder 10 mm in diameter and about 10 mm in height. Then a mild steel rod (diameter 9.9 mm; length 10 mm) was fixed at a position 40 mm from the bottom of sample chamber. The inlet of sample chamber was covered with a brass disc (diameter 12 mm; length 10 mm). The shock compression was carried out using trimethylene trinitramine explosive weighing 80 g. Fig. 1(b) shows a vertical-section view of the container after the shock compression. The samples were mechanically taken out of the container and were treated with dilute HCl to remove the Fe contaminant from the container. The residues were then washed with distilled water to remove hydrogen chloride. Both the purified residue and the initial sample were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM) at 200 kV. The TEM was equipped with an energy dispersive X-ray (EDX) analyzer. The XRD analysis was performed using Cu Ka1 radiation operating (40 kV and 60 mA). The specimens were dispersed in ethanol and samples prepared for the TEM studies by dipping molybdenum grids covered with holey amorphous carbon into this suspension. SEM image of the post-shocked sample is shown in Fig. 2(a). This indicates that the specimen was composed of irregular shaped sheets and thick plate-like particles, and very small spherical particles indicated by arrows. XRD patterns of the powder of these particles showed, besides graphite diffraction peaks, two unknown weak peaks at 2h = 43.16 and 73.88 (Fig. 2(b)). These two peaks were assigned to a new simple cubic modification of carbon with a unit cell parameter of 0.514 nm [9]. In order to determine the composition and crystal structure of the spherical particles, the post-shocked
3004
Letters to the Editor / Carbon 42 (2004) 3003–3042
Fig. 1. (a) Schematic cross-sectional view of the apparatus and (b) vertical cross-section of the shocked sample container for: (a) (1) steel sample container; (2) tetracyanoethylene powder; (3) cavity; (4) free space; (5) steel plug; (6) thick brass disk; (7) explosive charge; (8) wooden plug; (9) polyvinyl chloride plastic tube; (10) electric detonator.
Fig. 3. (a) TEM image of concentric shell particles having a particle size of the order of several tens of nanometer in diameter, and (b) the corresponding EDX spectrum.
powder was examined by HREM and EDX analysis and examples are shown in Fig. 3. It was determined from these data that the spherical particles are carbon with
a multiple-shell structure (concentric shell fullerenes). The interplanar distance (d value) is 0.338 nm, slightly larger than the (0 0 2) lattice spacing of bulk graphite
Fig. 2. (a) SEM image of the shock-compressed samples. The arrows show fine spherical particles. (b) X-ray diffraction patterns of (i) the tetracyanoethylene powder and (ii) the shock-compressed sample. (d) Graphite; (m) Cubic modification of carbon.
Letters to the Editor / Carbon 42 (2004) 3003–3042
Fig. 4. TEM image of a trimer consisting of fullerenes shown in Fig. 4. The carbon layers in the particle junction region and the non-junction region are well stacked.
(d0 0 2 = 0.336 nm). In this work, not only were concentric shell fullerene monomers obtained but also dimers
3005
and trimers. The size of monomers was in the range several tens to several hundreds of nanometer in diameter. To investigate a possible agglomeration process of the concentric shell fullerenes, the microstructure of the particle junction region of dimers and trimers was examined using HREM. Fig. 4 shows a HREM image of a trimer consisting of concentric shell fullerenes. This image indicates that the particles A and B are bound to each other by a sharing of two or three aromatic planes and the carbon layers in the particle junction as well as the nonjunction region are well stacked (arrow I). On the other hand, particles A and C are bound to each other via sharing slightly more aromatic planes than in the case of A and B; in this case the carbon layers in the junction are slightly disordered (arrow II). The TEM image in Fig. 5(a) shows a rather-wide particle-size distribution of the concentric shell fullerenes, in which we can see several dimers (arrow A) and trimers (arrow B) comprised of large concentric shell fullerenes. Higher magnification micrographs
Fig. 5. (a) TEM image of concentric shell fullerenes, having a particle size of the order of several hundred nanometers in diameter. Arrows A and B show a dimer and a trimer, respectively. (b) and (c) HREM images of the dimer particle junction and non-junction regions respectively, and the corresponding nanodiffraction patterns. The diffraction pattern in (b) consists of halos.
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Letters to the Editor / Carbon 42 (2004) 3003–3042
and nanodiffraction patterns of the dimer indicated by arrow A in the figure show that the particle junction of the dimer or trimer was almost amorphous (Fig. 5(b)), while the non-junction region had a concentric layered structure, though it contained many imperfections such as dislocations, bends, or non-parallel planes (Fig. 5(c)). From these results, i.e. necking of concentric shell fullerenes, merging to form larger spheres (arrow B in Fig. 5(a)), and the difference in the fine structures between the junction and non-junction regions, the formation processes of the dimer and trimer having a concentric graphitic shell structure can be assumed to occur in the following manner. First, the starting substance is thermally decomposed by the very high shock temperature and vaporized as a result of heating due to high residual energy. The resulting carbon vapor condenses by rapid post-shock cooling and the precursors of concentric shell fullerene, which are in the liquid state, are formed. Since the carbon droplets move violently, some of them collide and coalesce to form the structure of particle aggregates. Subsequently, solidification is initiated from the surface of the droplet toward the center, because the surface temperature is lower than the inner one [10]. In the case of the dimer or trimer precursors consisting of carbon droplets of the order of several tens of nanometer in diameter, since the junction region which is not in contact with the atmosphere is negligibly small, the whole of the precursor would be in an isotropic liquid state. In addition, the size of particles seems to be so small that in spite of rapid post-shock cooling, the constituent particles of the precursor have sufficient time for molecular orientation to establish the regularly concentric structure of carbon layers. The concentric arrangement of carbon layers starts from the particle surface of the precursor and propagates toward the center. On the other hand, in the case of dimer or trimer precursors consisting of carbon droplets of the order of several hundreds of nanometer in
diameter, the junction region which is not in contact with the atmosphere is broad, and hence its cooling rate is slower than that of the non-junction region. Moreover, it is thought that the particle size of the constituent carbon droplets is so large that a regular concentric arrangement of carbon layers could not be completed by migration of molecules under the rapid post-shock cooling conditions. Therefore, not only is the junction region frozen in an amorphous state, but also the non-junction region has less well-ordered stacking structure.
References [1] Rao AM, Zhou P, Wang K-A, Hager GT, Holden JM, Wang Y, et al. Photoinduced polymerization of solid C60 films. Science 1993;259:955–75. [2] Sun Y-P, Ma B, Bunker CE, Liu BJ. All-carbon (polyfullerenes) from photochemical reactions of fullerene clusters in roomtemperature solvent mixtures. Am Chem Soc 1995;117: 12705–12711. [3] Onoe J, Nakao A, Takeuchi K. XPS study of a photopolymerized C60. Phys Rev B 1997;55:10051–6. [4] Iwasa Y, Arima T, Fleming RM, Siegrist T, Zhou O, Haddon RC, et al. New phases of C60 synthesized at high pressure. Science 1994;264:1570–2. [5] Goze C, Rachdi F, Hajji L, Regueiro MN, Marques L, Hodeau JL, et al. High-resolution 13C NMR studies of high-pressurepolymerized C60: evidence for the [2 + 2] cycloaddition structure in the rhombohedral two-dimensional C60 polymer. Phys Rev B 1996;54:R3676–8. [6] Komatsu K, Fujiwara K, Tanaka T, Murata Y. The Fullerene dimer C120 and related carbon allotropes. Carbon 2000;38: 1529–4. [7] Iijima SJ. The 60-carbon cluster has been revealed. Phys Chem 1987;91:3466–7. [8] Ugarte D. Curling and closure of graphitic networks under electron-beam irradiation. Nature 1992;359:707–9. [9] Yamada K. Shock synthesis of a new cubic form. Carbon 2003;41:1309–13. [10] Marsh M. Are carbon blacks formed from liquid-crystal system. Carbon 1993;11:245–1313.