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Ion beam-induced formation of carbon nanofibers from decacyclene
Surface & Coatings Technology 201 (2007) 8506 – 8510 www.elsevier.com/locate/surfcoat
Ion beam-induced formation of carbon nanofibers from decacyclene Takahide Kimura, Hitoshi Koizumi, Tsuneki Ichikawa ⁎ Division of Materials Chemistry, Graduate School of Engineering, Hokkaido University, Sapporo, 060-8628 Japan Available online 14 March 2007
Abstract Vapor deposition of decacyclene, a polycyclic aromatic compound, under vacuum on a flat plate resulted in rapid formation of cylindrical decacyclene whiskers with a layered structure and with lengths and uniform diameters of 1–20 μm and 20–100 nm, respectively. The whiskers were converted to conducting amorphous carbon nanofibers by ion-beam irradiation at ambient temperature. Observation of the SEM images of the whiskers revealed that the growing whiskers were floated on the surfaces of supercooled decacyclene liquid droplets, and the diameter of each whiskers were kept constant during the growth by attractive and repulsive interactions between the liquid and surfaces of the whiskers parallel and perpendicular to the layer, respectively. Cyclic voltammetry of the carbon nanofibers in 1 mol/dm3 Na2SO4 showed the electrical capacitance of 41 F/g, which is comparable to the capacitance of various activated carbon fibers. © 2007 Elsevier B.V. All rights reserved. Keywords: Carbon nanofiber; Ion beam; Radiation effect; Whisker
1. Introduction Carbon nanofibers (CNFs) and nanotubes (CNTs) have recently attracted much attention because of their unique electrical, optical and chemical properties [1–3], and their potential utility as a hydrogen storage material for fuel cells [4], electron field emitters for optical displays [5–9], supports for catalysts [10], electrical double layer capacitors [11], and so on. CNFs and CNTs are usually produced by a Chemical Vapor Deposition (CVD) method in which they are grown from catalyst particles by thermal decomposition of hydrocarbon gas under high temperature [12,13]. However, the high temperature treatment makes it difficult to apply the CVD method to the implantation of CNFs and CNTs on chemical or electronic devices. Kaplan et al. showed that the ion-beam irradiation of the thin films of polycyclic aromatic compounds without catalyst at ambient temperature gave amorphous carbon with an electrical conductivity comparable to that of graphite [14,15], which suggested that the irradiation of the thick film of an aromatic compound with a low-fluence ion beam gave a conducting carbon nanofiber along the track of each ion. Although the attempt to generate conducting CNFs from an organic film by ⁎ Corresponding author. Tel.: +81 11 706 6747; fax: +81 11 706 7897. E-mail address: [email protected] (T. Ichikawa). 0257-8972/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.08.151
using the tracks of high-energy ions failed, we found that the irradiation of vapor-deposited decacyclene, a polycyclic aromatic compound known as a precursor of fullerene, gave amorphous CNFs [16,17]. Based on the SEM and TEM observation of the vapor-deposited plates before and after irradiation, we concluded that the CNFs were formed by carbonization of cylindrical decacyclene whiskers that were generated during the vapor-deposition. We suggested in a previous paper [17] that the whiskers were generated by a modified Vapor–Liquid–Solid (VLS) growth mechanism in which a whisker was grown by the solidification of a liquid droplet that was attached on the top of the whisker [18,19]. Although regular VLS necessitates the presence of some impurity in the droplet for keeping a uniform diameter, the modified VLS growth mechanism did not necessitate the impurity but rather a highly supercooled liquid droplet. The assumed mechanism of whisker formation was as follows; a seed crystal generated on a plate in the liquid stripped off the liquid from the plate to attach the liquid droplet on the top of the whisker. Minimization of the surface tension made the droplet spherical, so that the whisker with a uniform diameter was grown at the interface of the liquid. However, the detailed growth mechanism of the decacyclene whiskers has not been clarified yet. In addition, the internal structure of the CNFs was not yet examined. The present study is aimed at clarifying the growth mechanism of the decacyclene whiskers by detailed
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Fig. 1. SEM images of vapor-deposited decacyclene film at 45 s after turning-on the heater for the deposition.
Fig. 3. Enlarged SEM image of decacyclene film. The figure in the circle shows the growth of two whiskers from the same position.
observation with scanning electron microscope and examining the electrochemical characteristic of the resultant CNFs by cyclic voltammetry for obtaining structural information on the CNFs.
electrode for cyclic voltammetry was prepared by irradiating the decacyclene film (1 × 1 cm) on a Pt plate with the ion beam. The cyclic voltammetry was carried out by using a standard threeelectrode cell with 1 mol/dm3 Na2SO4 at 300 K (voltage range: −0.3–0.7 V, scanning rate: 5 mV/s). Two Pt plates and AgCl/Ag were used as the counter and the reference electrodes, respectively. The capacitance of the prepared CNFs was calculated from the sum of charge and discharge currents. After the cyclic voltammetry, the surface of the sample was observed with the scanning electron microscope to examine whether the CNFs were broken during the charge–discharge cycles.
2. Experimental Decacyclene, supplied by Aldrich, was used after purification by re-crystallization from hexane solution. Using a compact vacuum coater (ULVAC, VPC-260), about 4 mg of the purified decacyclene on a tungsten heater was vapor-deposited on a brass plate located at 6 cm above the heater. The thicknesses of the decacyclene films were monitored by using a quartz crystal oscillator-type deposition controller (ULVAC, CRTM-6000). The vapor-deposited plates were observed by using a scanning electron microscope (SEM: JEOL, JSM-6500F, operated at 5 keV). The plates with the whiskers were then irradiated at ambient temperature with a 200 keV N+ ion beam at a fluence of 4 × 1016 ions/cm2 and a flux of 9.6 × 1012 ions/cm2 s in vacuum. The temperature of the samples during the irradiation was estimated to be lower than 450 K. In order to examine the electrochemical characteristic of the resultant CNFs, a working
Fig. 2. Effect of vapor-deposition time on the number density of purified decacyclene whiskers. The heater for the vapor-deposition is turned-on at t = 0.
3. Results and discussion 3.1. Growth mechanism of the whiskers Fig. 1 shows the SEM image of decacyclene film that was prepared on a flat brass plate at 45 s after turning-on the heater
Fig. 4. TEM image of the top of a decacyclene whisker.
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Fig. 5. Schematic representation of the growth mechanism of a cylindrical whisker from a supercooled decacyclene droplet.
for the vapor-deposition of purified decacyclene. The vapordeposition was started at about 30 s after turning-on the heater. The plate was covered with cylindrical decacyclene whiskers with uniform diameters of 20–100 nm and lengths of 1–20 μm. As shown in Fig. 2, the number density of the whiskers increased by increasing duration of the vapor-deposition, and reached 2.2 × 108 fibers/cm2 at 45 s. Inspection of Fig. 2 reveals that the formation of each whisker is terminated within less than a few seconds. We have suggested in the previous paper [17] that a cylindrical whisker with a uniform diameter is generated from a supercooled liquid droplet of decacyclene that is attached on the top of whisker. However, a detailed SEM image indicates that the whisker is not grown with a droplet on the growing front of the whisker. Fig. 3 shows that two whiskers may possibly be grown from the same place, which is impossible in the previous mechanism since the previous mechanism necessitates a separation distance between the whiskers of more than the diameter of the droplets. Another discrepancy with the previous model is the shape of the whiskers at the top. The whisker must
Fig. 6. Cyclic voltamogram of the ion beam-irradiated decacyclene film.
show a conical boundary after consuming all the liquid on the top [20]. However, the TEM image in Fig. 4 shows that the top of the whisker is hemispherical. We therefore conclude that the whisker is grown not with a liquid droplet on the top, but on the surface of a supercooled liquid droplet that is attached on a plate. The cylindrical growth of the whisker arises from repulsive and attractive interfacial interactions between the liquid and the surfaces of the whiskers parallel and perpendicular to the axis of growth. Fig. 5 shows the schematic representation of the growth mechanism of the decacyclene whisker on a supercooled liquid. Ejection of a growing layer out of the liquid is prohibited as long as the radius of the growing layer is less than that of the cylinder, since the decrease of the attractive interaction by the ejection exceeds the decrease of the repulsive interaction between the wall of the layer and the liquid. The growing layer is ejected from the liquid
Fig. 7. Relation between electrical capacitance and the number of charge– discharge cycles.
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as soon as the radius of the layer becomes the same as that of the cylinder, since the ejection does not reduce the attractive interaction. The growth of the whisker continues until it has consumed all the liquid to the plate. The root of the whisker is finally fixed on a decacyclene film attached on the plate, which accords with the SEM observation. It is noted that the present model allows multiple formation of whiskers from the same liquid droplet. 3.2. Electrochemical characteristics of the carbon nanofibers We have shown in the previous paper that the ion beam irradiation of the whiskers up to 1016 ions/cm 2 causes graphitization of the whiskers without much change in appearance, to generate CNFs with high electrical conductivity [17]. Although the electrical conductivity of the CNFs is comparable to that of graphite, the specific gravity of the CNFs is much lower than that of graphite. Since the specific gravity of decacyclene is 1.4, the specific gravity of CNFs must be less than 1.4, which is about 58% of that of graphite. It is therefore expected that the resultant CNFs have a porous structure that might be advantageous for using the CNFs as a support for catalysts and so on. The degree of porosity can be estimated by measuring the electrochemical capacitance of the CNFs, since the penetration of ions in water into the CNFs causes an increase of the capacitance. Fig. 6 shows the cyclic voltamogram of an ion beam-irradiated decacyclene film with CNFs. Although the observed curve deviates from an ideal rectangular shape, the irradiated film showes a well-developed cyclic voltamogram curve without any redox peak. The electrical capacitance measured from the voltamogram is 445 μF. Assuming the capacitance of the carbon film per unit surface area to be the same as that of amorphous carbon, 10 μF/cm2, the surface area of the irradiated film is estimated to be 44.5 cm2, which is much larger than the surface area of the plate. The surface area of the film is given by the sum of those of CNFs and the carbon film with a rough surface. The total surface area of CNFs is estimated from the number density and average radius and length of the CNFs to be 0.46 cm2, which is much smaller than the surface area of the plate. Although the surface area of the carbon film is difficult to estimate, it may be comparable to the surface area of the plate. The electrochemical surface area of 44.5 cm2 therefore indicates that the resultant film has a porous structure which allows ions to penetrate. Fig. 7 shows the relation between the electrical capacitance of the CNFs and the number of charge–discharge cycles. Although the electrical capacitance initially decreased, it became stable after 4–5 cycles. Fig. 8 compares the SEM images of the CNFs before and after the cyclic voltammetry of 10 cycles. Although the capacitance decreased with increasing cycle number, the overall shapes of the CNFs were quite similar to each other. Penetration of ions in the CNFs did not result in the destruction of the structure. In conclusion, vapor-deposition of decacyclene on a plate results in the rapid formation of cylindrical whiskers that are floated and grown on the surfaces of supercooled liquid droplets of decacyclene. The resultant decacyclene film with whiskers is
Fig. 8. Comparison of the SEM images of decacyclene whiskers (a) before and (b) after the cyclic voltammetry of 10 cycles.
converted to a porous and conducting carbon film with carbon nanofibers. The resultant film might be suitable for use as a support for catalysts or as an electrode for a capacitor. References [1] J. Xu, J.P. Donohoe, C.U. Pittman Jr., Compos., Part A Appl. Sci. Manuf. 35 (6) (2004) 693. [2] S.-U. Kim, K.-H. Lee, Chem. Phys. Lett. 400 (1–3) (2004) 253. [3] G.S. Chai, S.B. Yoon, J.-S. Yu, Carbon 43 (2005) 3028. [4] A.C. Dillon, K.M. Jones, T.A. Bekkedahl, C.H. Kinang, D.S. Bethune, M.J. Heben, Nature 386 (1997) 377. [5] Q.H. Wang, T.D. Corrigan, J.Y. Dai, R.P.H. Chang, Appl. Phys. Lett. 70 (1997) 3308. [6] P.G. Collins, A. Zettl, Appl. Phys. Lett. 69 (1996) 1969. [7] W.A. de Heer, A. Chtelain, D. Ugarte, Science 270 (1999) 1179. [8] Y. Saito, S. Uemura, K. Hamaguchi, Jpn. J. Appl. Phys. 37 (1998) L346. [9] Y. Nakayama, S. Akita, Synth. Met. 117 (2001) 207. [10] P. Serp, M. Corriaas, P. Kalck, Appl. Catal. 337 (2003) A253. [11] K. Kinoshita, Carbon, Wiley, New York, 1988. [12] T. Koyama, M. Endo, Y. Onuma, J. Appl. Phys. 11 (1972) 445.
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[13] A. Oberlin, M. Endo, T. Koyama, J. Cryst. Growth 32 (1976) 335. [14] M.L. Kaplan, S.R. Forrest, P.H. Schmidt, T. Venkatesan, J. Appl. Phys. 55 (1984) 732. [15] A.J. Lovinger, S.R. Forrest, M.L. Kaplan, P.H. Schmidt, T. Venkatesan, J. Appl. Phys. 55 (1984) 476. [16] T. Kimura, H. Koizumi, H. Kinoshita, H. Takahashi, T. Ichikawa, Jpn. J. Appl. Phys. 43 (2004) L863.
[17] T. Kimura, H. Koizumi, H. Kinoshita, H. Takahashi, T. Ichikawa, Nucl. Instrum. Methods B 236 (2005) 474. [18] R.S. Wagner, W.C. Ellis, Trans. Metall. Soc. AIME 233 (1965) 1053. [19] F.R.N. Nabarro, P.J. Jackson, Growth of Crystal Whiskers; Growth and Perfection of Crystals, ed. John Wiley, 1958, p. 13. [20] V.A. Nebol'sin, A.A. Shchetinin, Inorg. Mater. 39 (2003) 899.
Ion beam-induced formation of carbon nanofibers from decacyclene Takahide Kimura, Hitoshi Koizumi, Tsuneki Ichikawa ⁎ Division of Materials Chemistry, Graduate School of Engineering, Hokkaido University, Sapporo, 060-8628 Japan Available online 14 March 2007
Abstract Vapor deposition of decacyclene, a polycyclic aromatic compound, under vacuum on a flat plate resulted in rapid formation of cylindrical decacyclene whiskers with a layered structure and with lengths and uniform diameters of 1–20 μm and 20–100 nm, respectively. The whiskers were converted to conducting amorphous carbon nanofibers by ion-beam irradiation at ambient temperature. Observation of the SEM images of the whiskers revealed that the growing whiskers were floated on the surfaces of supercooled decacyclene liquid droplets, and the diameter of each whiskers were kept constant during the growth by attractive and repulsive interactions between the liquid and surfaces of the whiskers parallel and perpendicular to the layer, respectively. Cyclic voltammetry of the carbon nanofibers in 1 mol/dm3 Na2SO4 showed the electrical capacitance of 41 F/g, which is comparable to the capacitance of various activated carbon fibers. © 2007 Elsevier B.V. All rights reserved. Keywords: Carbon nanofiber; Ion beam; Radiation effect; Whisker
1. Introduction Carbon nanofibers (CNFs) and nanotubes (CNTs) have recently attracted much attention because of their unique electrical, optical and chemical properties [1–3], and their potential utility as a hydrogen storage material for fuel cells [4], electron field emitters for optical displays [5–9], supports for catalysts [10], electrical double layer capacitors [11], and so on. CNFs and CNTs are usually produced by a Chemical Vapor Deposition (CVD) method in which they are grown from catalyst particles by thermal decomposition of hydrocarbon gas under high temperature [12,13]. However, the high temperature treatment makes it difficult to apply the CVD method to the implantation of CNFs and CNTs on chemical or electronic devices. Kaplan et al. showed that the ion-beam irradiation of the thin films of polycyclic aromatic compounds without catalyst at ambient temperature gave amorphous carbon with an electrical conductivity comparable to that of graphite [14,15], which suggested that the irradiation of the thick film of an aromatic compound with a low-fluence ion beam gave a conducting carbon nanofiber along the track of each ion. Although the attempt to generate conducting CNFs from an organic film by ⁎ Corresponding author. Tel.: +81 11 706 6747; fax: +81 11 706 7897. E-mail address: [email protected] (T. Ichikawa). 0257-8972/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.08.151
using the tracks of high-energy ions failed, we found that the irradiation of vapor-deposited decacyclene, a polycyclic aromatic compound known as a precursor of fullerene, gave amorphous CNFs [16,17]. Based on the SEM and TEM observation of the vapor-deposited plates before and after irradiation, we concluded that the CNFs were formed by carbonization of cylindrical decacyclene whiskers that were generated during the vapor-deposition. We suggested in a previous paper [17] that the whiskers were generated by a modified Vapor–Liquid–Solid (VLS) growth mechanism in which a whisker was grown by the solidification of a liquid droplet that was attached on the top of the whisker [18,19]. Although regular VLS necessitates the presence of some impurity in the droplet for keeping a uniform diameter, the modified VLS growth mechanism did not necessitate the impurity but rather a highly supercooled liquid droplet. The assumed mechanism of whisker formation was as follows; a seed crystal generated on a plate in the liquid stripped off the liquid from the plate to attach the liquid droplet on the top of the whisker. Minimization of the surface tension made the droplet spherical, so that the whisker with a uniform diameter was grown at the interface of the liquid. However, the detailed growth mechanism of the decacyclene whiskers has not been clarified yet. In addition, the internal structure of the CNFs was not yet examined. The present study is aimed at clarifying the growth mechanism of the decacyclene whiskers by detailed
T. Kimura et al. / Surface & Coatings Technology 201 (2007) 8506–8510
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Fig. 1. SEM images of vapor-deposited decacyclene film at 45 s after turning-on the heater for the deposition.
Fig. 3. Enlarged SEM image of decacyclene film. The figure in the circle shows the growth of two whiskers from the same position.
observation with scanning electron microscope and examining the electrochemical characteristic of the resultant CNFs by cyclic voltammetry for obtaining structural information on the CNFs.
electrode for cyclic voltammetry was prepared by irradiating the decacyclene film (1 × 1 cm) on a Pt plate with the ion beam. The cyclic voltammetry was carried out by using a standard threeelectrode cell with 1 mol/dm3 Na2SO4 at 300 K (voltage range: −0.3–0.7 V, scanning rate: 5 mV/s). Two Pt plates and AgCl/Ag were used as the counter and the reference electrodes, respectively. The capacitance of the prepared CNFs was calculated from the sum of charge and discharge currents. After the cyclic voltammetry, the surface of the sample was observed with the scanning electron microscope to examine whether the CNFs were broken during the charge–discharge cycles.
2. Experimental Decacyclene, supplied by Aldrich, was used after purification by re-crystallization from hexane solution. Using a compact vacuum coater (ULVAC, VPC-260), about 4 mg of the purified decacyclene on a tungsten heater was vapor-deposited on a brass plate located at 6 cm above the heater. The thicknesses of the decacyclene films were monitored by using a quartz crystal oscillator-type deposition controller (ULVAC, CRTM-6000). The vapor-deposited plates were observed by using a scanning electron microscope (SEM: JEOL, JSM-6500F, operated at 5 keV). The plates with the whiskers were then irradiated at ambient temperature with a 200 keV N+ ion beam at a fluence of 4 × 1016 ions/cm2 and a flux of 9.6 × 1012 ions/cm2 s in vacuum. The temperature of the samples during the irradiation was estimated to be lower than 450 K. In order to examine the electrochemical characteristic of the resultant CNFs, a working
Fig. 2. Effect of vapor-deposition time on the number density of purified decacyclene whiskers. The heater for the vapor-deposition is turned-on at t = 0.
3. Results and discussion 3.1. Growth mechanism of the whiskers Fig. 1 shows the SEM image of decacyclene film that was prepared on a flat brass plate at 45 s after turning-on the heater
Fig. 4. TEM image of the top of a decacyclene whisker.
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Fig. 5. Schematic representation of the growth mechanism of a cylindrical whisker from a supercooled decacyclene droplet.
for the vapor-deposition of purified decacyclene. The vapordeposition was started at about 30 s after turning-on the heater. The plate was covered with cylindrical decacyclene whiskers with uniform diameters of 20–100 nm and lengths of 1–20 μm. As shown in Fig. 2, the number density of the whiskers increased by increasing duration of the vapor-deposition, and reached 2.2 × 108 fibers/cm2 at 45 s. Inspection of Fig. 2 reveals that the formation of each whisker is terminated within less than a few seconds. We have suggested in the previous paper [17] that a cylindrical whisker with a uniform diameter is generated from a supercooled liquid droplet of decacyclene that is attached on the top of whisker. However, a detailed SEM image indicates that the whisker is not grown with a droplet on the growing front of the whisker. Fig. 3 shows that two whiskers may possibly be grown from the same place, which is impossible in the previous mechanism since the previous mechanism necessitates a separation distance between the whiskers of more than the diameter of the droplets. Another discrepancy with the previous model is the shape of the whiskers at the top. The whisker must
Fig. 6. Cyclic voltamogram of the ion beam-irradiated decacyclene film.
show a conical boundary after consuming all the liquid on the top [20]. However, the TEM image in Fig. 4 shows that the top of the whisker is hemispherical. We therefore conclude that the whisker is grown not with a liquid droplet on the top, but on the surface of a supercooled liquid droplet that is attached on a plate. The cylindrical growth of the whisker arises from repulsive and attractive interfacial interactions between the liquid and the surfaces of the whiskers parallel and perpendicular to the axis of growth. Fig. 5 shows the schematic representation of the growth mechanism of the decacyclene whisker on a supercooled liquid. Ejection of a growing layer out of the liquid is prohibited as long as the radius of the growing layer is less than that of the cylinder, since the decrease of the attractive interaction by the ejection exceeds the decrease of the repulsive interaction between the wall of the layer and the liquid. The growing layer is ejected from the liquid
Fig. 7. Relation between electrical capacitance and the number of charge– discharge cycles.
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as soon as the radius of the layer becomes the same as that of the cylinder, since the ejection does not reduce the attractive interaction. The growth of the whisker continues until it has consumed all the liquid to the plate. The root of the whisker is finally fixed on a decacyclene film attached on the plate, which accords with the SEM observation. It is noted that the present model allows multiple formation of whiskers from the same liquid droplet. 3.2. Electrochemical characteristics of the carbon nanofibers We have shown in the previous paper that the ion beam irradiation of the whiskers up to 1016 ions/cm 2 causes graphitization of the whiskers without much change in appearance, to generate CNFs with high electrical conductivity [17]. Although the electrical conductivity of the CNFs is comparable to that of graphite, the specific gravity of the CNFs is much lower than that of graphite. Since the specific gravity of decacyclene is 1.4, the specific gravity of CNFs must be less than 1.4, which is about 58% of that of graphite. It is therefore expected that the resultant CNFs have a porous structure that might be advantageous for using the CNFs as a support for catalysts and so on. The degree of porosity can be estimated by measuring the electrochemical capacitance of the CNFs, since the penetration of ions in water into the CNFs causes an increase of the capacitance. Fig. 6 shows the cyclic voltamogram of an ion beam-irradiated decacyclene film with CNFs. Although the observed curve deviates from an ideal rectangular shape, the irradiated film showes a well-developed cyclic voltamogram curve without any redox peak. The electrical capacitance measured from the voltamogram is 445 μF. Assuming the capacitance of the carbon film per unit surface area to be the same as that of amorphous carbon, 10 μF/cm2, the surface area of the irradiated film is estimated to be 44.5 cm2, which is much larger than the surface area of the plate. The surface area of the film is given by the sum of those of CNFs and the carbon film with a rough surface. The total surface area of CNFs is estimated from the number density and average radius and length of the CNFs to be 0.46 cm2, which is much smaller than the surface area of the plate. Although the surface area of the carbon film is difficult to estimate, it may be comparable to the surface area of the plate. The electrochemical surface area of 44.5 cm2 therefore indicates that the resultant film has a porous structure which allows ions to penetrate. Fig. 7 shows the relation between the electrical capacitance of the CNFs and the number of charge–discharge cycles. Although the electrical capacitance initially decreased, it became stable after 4–5 cycles. Fig. 8 compares the SEM images of the CNFs before and after the cyclic voltammetry of 10 cycles. Although the capacitance decreased with increasing cycle number, the overall shapes of the CNFs were quite similar to each other. Penetration of ions in the CNFs did not result in the destruction of the structure. In conclusion, vapor-deposition of decacyclene on a plate results in the rapid formation of cylindrical whiskers that are floated and grown on the surfaces of supercooled liquid droplets of decacyclene. The resultant decacyclene film with whiskers is
Fig. 8. Comparison of the SEM images of decacyclene whiskers (a) before and (b) after the cyclic voltammetry of 10 cycles.
converted to a porous and conducting carbon film with carbon nanofibers. The resultant film might be suitable for use as a support for catalysts or as an electrode for a capacitor. References [1] J. Xu, J.P. Donohoe, C.U. Pittman Jr., Compos., Part A Appl. Sci. Manuf. 35 (6) (2004) 693. [2] S.-U. Kim, K.-H. Lee, Chem. Phys. Lett. 400 (1–3) (2004) 253. [3] G.S. Chai, S.B. Yoon, J.-S. Yu, Carbon 43 (2005) 3028. [4] A.C. Dillon, K.M. Jones, T.A. Bekkedahl, C.H. Kinang, D.S. Bethune, M.J. Heben, Nature 386 (1997) 377. [5] Q.H. Wang, T.D. Corrigan, J.Y. Dai, R.P.H. Chang, Appl. Phys. Lett. 70 (1997) 3308. [6] P.G. Collins, A. Zettl, Appl. Phys. Lett. 69 (1996) 1969. [7] W.A. de Heer, A. Chtelain, D. Ugarte, Science 270 (1999) 1179. [8] Y. Saito, S. Uemura, K. Hamaguchi, Jpn. J. Appl. Phys. 37 (1998) L346. [9] Y. Nakayama, S. Akita, Synth. Met. 117 (2001) 207. [10] P. Serp, M. Corriaas, P. Kalck, Appl. Catal. 337 (2003) A253. [11] K. Kinoshita, Carbon, Wiley, New York, 1988. [12] T. Koyama, M. Endo, Y. Onuma, J. Appl. Phys. 11 (1972) 445.
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[13] A. Oberlin, M. Endo, T. Koyama, J. Cryst. Growth 32 (1976) 335. [14] M.L. Kaplan, S.R. Forrest, P.H. Schmidt, T. Venkatesan, J. Appl. Phys. 55 (1984) 732. [15] A.J. Lovinger, S.R. Forrest, M.L. Kaplan, P.H. Schmidt, T. Venkatesan, J. Appl. Phys. 55 (1984) 476. [16] T. Kimura, H. Koizumi, H. Kinoshita, H. Takahashi, T. Ichikawa, Jpn. J. Appl. Phys. 43 (2004) L863.
[17] T. Kimura, H. Koizumi, H. Kinoshita, H. Takahashi, T. Ichikawa, Nucl. Instrum. Methods B 236 (2005) 474. [18] R.S. Wagner, W.C. Ellis, Trans. Metall. Soc. AIME 233 (1965) 1053. [19] F.R.N. Nabarro, P.J. Jackson, Growth of Crystal Whiskers; Growth and Perfection of Crystals, ed. John Wiley, 1958, p. 13. [20] V.A. Nebol'sin, A.A. Shchetinin, Inorg. Mater. 39 (2003) 899.