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Thickening of chemical vapor deposited carbon fiber
PERGAMON
Carbon 39 (2001) 835–839
Thickening of chemical vapor deposited carbon fiber Jyh-Ming Ting*, N.Z. Huang Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan Received 21 February 2000; accepted 4 July 2000
Abstract Effects of temperature and hydrocarbon concentration on the thickening of CVD carbon fiber were examined. Various concentrations of hydrocarbon, ranging from 17 to 83%, balanced by hydrogen, were used. The hydrocarbon concentration ranged from 17 to 83%. The growth temperatures were 8008C, 9008C, 10008C, 11008C, 12008C, 13008C, and 13008C. It was found that the thickening rate peaks at temperatures near 1100 and 12008C when 40% methane and 33% propane were used as the hydrocarbon sources, respectively. At these peak thickening rates, CVD fibers exhibit rough pitted surfaces, which are not commonly seen. 2001 Elsevier Science Ltd. All rights reserved. Keywords: A. Carbon fibers; B. Chemical vapor deposition, Catalyst; C. Electron microscopy; D. Microstructure
1. Introduction Traditionally, carbon fibers are synthesized by a meltspun process, employing polymeric precursors such as polyacrylonitrile or pitch, and many processing steps [1,2]. An alternative carbon fiber, known as vapor grown carbon fiber (VGCF), is synthesized by a chemical vapor deposited (CVD) process. This latter method is a single-step process and requires the use of a metallic particle as a catalyst to nucleate fiber growth [3]. Due to the differences in preparing these two types of carbon fibers, the resulting fibers have very different microstructure and properties [4,5]. Tubular carbons with outer diameters ranging from 10 0 nm to 10 1 mm can be synthesized by employing appropriate CVD techniques [6]. Such CVD fibers are distinguished from melt-spun fibers by a hollow core and an annular structure of graphene planes. The small diameters, vapor derived carbon fibers are classified as carbon nanotubes (CNT) [7–9]. The tubular structure of such fibers, synthesized with a hollow center, is more obvious when the dosimeter of the fiber is small. A sub-micron tubular CVD fiber with an outer diameter of |0.2 mm and an inner diameter of |0.15 mm is shown in Fig. 1 [10].
*Corresponding author. Tel.: 1886-6-275-7575; fax: 1886-6238-5613. E-mail address: [email protected] (J.-M. Ting).
Larger vapor derived carbon fibers are synthesized by addition of a CVD layer. Such fiber has an outer diameter ranging from 0.2 to 7 mm or larger [11]. The differences among these fibers or tubes are obviously not only in the physical dimensions but also in the microstructure, and therefore the properties. It has been shown that a well-ordered, defect-free CNT exhibits a Young’s modulus in the range of tera-Pascal, approaching the theoretical limit [12]. On the other hand, the microstructure of CVD carbon fiber / tube varies radially. Depending on the processing conditions, disordered structure
Fig. 1. A sub-micron tubular CVD carbon with an outer diameter and an inner diameter of |0.2 and |0.15 mm, respectively.
0008-6223 / 01 / $ – see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S0008-6223( 00 )00194-9
836
J.-M. Ting, N.Z. Huang / Carbon 39 (2001) 835 – 839
Fig. 2. A broken end of CVD carbon fiber where the core remains intact.
[13] and polycrystalline [10] structure may be found near the hollow center. Also, either better-ordered or lessordered structure may be seen when moving radially outward toward the fiber surface. Occasionally, sp 3 structure can be obtained [14]. Therefore variation in the diameter often leads to fibers / tubes with different physical properties. Investigation of fractured cross sessions of CVD carbon fiber indicates that the core exhibits a much higher stiffness [15]. Fig. 2 shows a broken end of such CVD carbon fiber where the core remains intact after the fiber was broken. Although CVD carbon fiber has been investigated in the past decades and intensive studies on CNT are being carried out, less research effort on the thickening behavior of these tubular carbon has been made. As mentioned above, CVD carbon fiber can have different diameters, leading to the differences in the microstructure and therefore the properties. It is thus realized that the control of fiber diameter can be a part of microstructure engineering. Such control relies on an understanding of the growth kinetics and mechanisms. As a result, the objective of this study was to investigate the thickening behavior of CVD fiber. Effects of growth parameters including gaseous composition, temperature, and time were examined.
2. Experimental A 1-inch horizontal tubular furnace was used for the growth of CVD carbon fiber. Growth of the fiber was performed using a technique similar to those described elsewhere [16,17]. In short, the carbon fibers were grown through the pyrolysis of a hydrocarbon gas. In this study, the hydrocarbon gas used was either methane or propane. The catalyst used was nano-sized iron particles with an average diameter of 100620 nm. Various concentrations of the hydrocarbon, balanced by hydrogen, were used. The hydrocarbon concentration ranged from 17 to 83%. The
growth temperatures were 8008C, 9008C, 10008C, 11008C, 12008C, 13008C, and 13008C, which were determined by the furnace set point. In each experiment, the hydrocarbon / hydrogen gas mixture at atmospheric pressure was introduced to the growth tube when it reached the desired temperature. Prior to the admission of the gas mixture, the growth tube was purged with argon, vacuumed, and kept at a pressure less than 1310 23 Torr. The growth time was varied from less than 5 to 60 min. As the thickening of CVD carbon fiber follows a lengthening stage, a minimum growth time was selected for each growth condition such that the following characterization were all pertinent to the thickening of the fibers [3,13]. Kinetic study shows that thickening of CVD carbon fiber starts at a time very near the end of lengthening [18]. Carbon fibers produced were examined using scanning electron microscopy (SEM).
3. Results and discussion CVD fibers with various diameters were produced. In general, these CVD carbon fibers exhibit typical smooth surfaces. However, at temperatures of 1100 and 12008C, rough or pitted surface morphologies were observed, as shown in Figs. 3 and 4, respectively. Fig. 3 shows SEM micrographs of such CVD fibers obtained at a methane concentration of 40% and various growth times. Granular morphology is seen on the surfaces of both the 5-min (Fig. 3A) and 10-min (Fig. 3B) fibers. The grains are larger on the 10-min fiber, indicating the growth of them with time. As the growth time is further increased, coalescence occurs, leaving pits on the surface, as shown in Fig. 3C. When propane was used as the hydrocarbon source, a similar morphology was also observed. Fig. 4 shows a carbon fiber with pitted surface. The fiber was grown using a propane concentration of 33% and a temperature of 12008C for 30 min. Although the exact mechanism is not known, such morphologies are attributed to the high thickening rates as discussed below. Effects of temperature on the thickening rate of CVD fibers were then investigated for 40% methane and 33% propane. Fibers with different diameters were determined using SEM micrographs of fibers obtained at various growth times. When methane was used as the hydrocarbon source, fiber thickening was not observed at 800 and 9008C, and was not significant at 10008C. Fiber ‘thickening’ at 9008C is shown in Fig. 5A. It appears that at 800 and 9008C, fibers were at the so-called lengthening stage 3 and therefore the diameters are close to that of the catalyst particles. As the temperature was increased, thickening was observed, although the rate was insignificant at 10008C, as shown in Fig. 5A. Data analysis indicates that the thickening rate at 10008C is merely 0.4 nm / min, which is the slope of the straight line. As the temperature further increases, significant thickening was observed and the rates vary as shown in Fig. 5B. It appears that the rate increases
J.-M. Ting, N.Z. Huang / Carbon 39 (2001) 835 – 839
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Fig. 3. Surface morphologies of fibers obtained at a methane concentration of 40% and a temperature of 11008C. The growth times are, respectively, (A) 5 min, (B) 10 min, and (C) 30 min.
Fig. 4. A carbon fiber with pitted surface. The fiber was grown at 12008C using a propane concentration of 33% for 30 min.
and then decreases as the temperature varies from 1100 to 13008C. The highest thickening rate, 238 nm / min, was obtained at 11008C, as indicated in Fig. 5B. Such a variation of thickening rate as a function of temperature was also observed when propane was used as the carbon source. When propane was used as the hydrocarbon source, fiber thickening was not observed at 8008C. Thickening took place as the temperature was equal to or greater than 9008C, as shown in Fig. 6. The highest thickening rate, 266 nm / min, occurred at 12008C. For comparison, the thickening rates or the slopes obtained from Figs. 5 and 6 are shown in Figs. 7 and 8, respectively, as a function of temperature. Four-parameter log normal curve fitting was used to analyze that data shown in Figs. 7 and 8. It is clear that the thickening rate increases and then decreases as the temperature raises from 800 to 13008C. The rates peak at temperatures near 1100 and 12008C when methane and propane were used as the hydrocarbon sources, respectively. It was further found that hydrocarbon concentration
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J.-M. Ting, N.Z. Huang / Carbon 39 (2001) 835 – 839
Fig. 7. Thickening rate as a function of temperature (40% methane concentration). (Dashed line represents curve fitting).
Fig. 5. Thickening of CVD fibers at (A) 900 and 10008C, and (B) 1100–13008C. The methane concentration used was 40%. (Dashed lines are linear fits). Fig. 8. Thickening rate as a function of temperature (33% propane concentration). (Dashed line represents curve fitting).
Fig. 6. Thickening of CVD fibers at various temperatures and a propane concentration of 33%. (Dashed lines are linear fits).
exhibits similar effect on the thickening rate. Various methane and propane concentrations were respectively used for fiber growth at the peak temperatures of 1100 and 12008C (Figs. 7 and 8). The thickening rates were determined as before and are shown in Fig. 9 as a function of hydrocarbon concentration. It is obvious that the rates peaks at concentrations of 40% methane and 30% propane, respectively. As noted above, at a temperature of 11008C and a concentration of 49% methane; and at 12008C when 33% was used, rough or pitted surface morphologies were observed (Figs. 3 and 4). These growth conditions are those when the highest thickening rates were found (Figs. 7, 8 and 9). The morphologies shown in Figs. 3 and 4 are therefore attributed to the high CVD thickening rates [19].
J.-M. Ting, N.Z. Huang / Carbon 39 (2001) 835 – 839
Fig. 9. Thickening rate as a function of hydrocarbon concentration. (Dashed lines represent curve fitting).
4. Conclusion Thickening of CVD carbon fiber was studied. It was found that the thickening rate increases and then decreases as the CVD temperature raises from 800 to 13008C. The rates peak at temperatures near 1100 and 12008C when methane and propane were used as the hydrocarbon sources, respectively. It was also found that hydrocarbon concentration exhibits similar effect on the thickening rate. The thickening rates peak at concentrations of 40% methane and 30% propane, respectively. At these peak rates, CVD fibers exhibit rough are pitted surface, which are not commonly seen.
Acknowledgements This work was sponsored by the National Science Council in Taiwan under Contract [ NSC 88-2216-E-006018.
References [1] Chwastiak S, Barr JB, Didchenko R. Carbon 1979;17(1):49– 53.
839
[2] Hamada T, Nishida T, Sajiki Y, Matsumoto M, Endo M. J Mater Res 1987;2(6):850–7. [3] Tibbetts GG, Endo M, Beetz Jr. CP. SAMPE J 1986;5:22–8. [4] Lake ML, Ting JM. In: Burchell T, editor, Carbon materials for advanced technologies, New York: Elsevier, 1999, pp. 139–68. [5] Heremans J, Beetz Jr. CP. Phys Rev 1985;B32(4):1981–6. [6] Cheng HM, Li F, Su G, Pan HY, Sun LL, Dresselhaus MS. Appl Phys Lett 1998;73(22):3282–4. ˜ ´ [7] Benito A, Maniette Y, Munoz E, Martınez MT. Carbon 1999;36(5-6):681–3. [8] Chen P, Wu X, Lin J, Li H, Tan KL. Carbon 2000;38(1):139–43. [9] Ting JM, Lan BC, Chen YM, Huang NZ. Proceedings, 5th annual microelectromechanical system meeting. National Cheng Kung University (Tainan. Taiwan): National Cheng Kung University, 1999; 105–110. [10] Ting JM, Huang NZ, Lan BC. J Mater Sci 1999;34(21):5233–5. [11] Lake ML, Ting JM, Alig RL. Proceedings, 8th annual conf. on materials technology. Southern Illinois University (Illinois, USA): Southern Illinois University, 1992:55–61. [12] Ebbsen TW. Nature 1996;381(20):678–80. [13] Oberlin A, Endo M, Koyama T. Carbon 1976;14(2):133–5. [14] Anderson DP, Ting JM, Lake ML, Alig RL. Extended abstract, 22nd biennial conf. on carbon. UC San Diego (California, USA): American Carbon Society; 1995: 304– 305. [15] Ting JM, Guth JR. Extended abstract, 22nd biennial. conf. on carbon. UC San Diego (California, USA): American Carbon Society, 1995; 296–297. [16] Tibbetts GG. In: Figueiredo JL, Bernardo CA, Baker RTK, ¨ Huttinger KJ, editors, Carbon fibers, filaments, and composites, The Netherlands: Kluwer Academic Publishers, 1990, pp. 73–94. [17] Ting JM, Lake ML. In: Upadhya, editor, Processing, Fabrication, and Applications of Advanced Composites, Ohio: ASM International, 1993:117–127. [18] Endo M, Koyoma T. Kotai Butsuri 1977;12:1–32. [19] Smith DL. In: Thin-film deposition: principles & practice, New York: McGraw-Gill, 1995, pp. 119–219.
Carbon 39 (2001) 835–839
Thickening of chemical vapor deposited carbon fiber Jyh-Ming Ting*, N.Z. Huang Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan Received 21 February 2000; accepted 4 July 2000
Abstract Effects of temperature and hydrocarbon concentration on the thickening of CVD carbon fiber were examined. Various concentrations of hydrocarbon, ranging from 17 to 83%, balanced by hydrogen, were used. The hydrocarbon concentration ranged from 17 to 83%. The growth temperatures were 8008C, 9008C, 10008C, 11008C, 12008C, 13008C, and 13008C. It was found that the thickening rate peaks at temperatures near 1100 and 12008C when 40% methane and 33% propane were used as the hydrocarbon sources, respectively. At these peak thickening rates, CVD fibers exhibit rough pitted surfaces, which are not commonly seen. 2001 Elsevier Science Ltd. All rights reserved. Keywords: A. Carbon fibers; B. Chemical vapor deposition, Catalyst; C. Electron microscopy; D. Microstructure
1. Introduction Traditionally, carbon fibers are synthesized by a meltspun process, employing polymeric precursors such as polyacrylonitrile or pitch, and many processing steps [1,2]. An alternative carbon fiber, known as vapor grown carbon fiber (VGCF), is synthesized by a chemical vapor deposited (CVD) process. This latter method is a single-step process and requires the use of a metallic particle as a catalyst to nucleate fiber growth [3]. Due to the differences in preparing these two types of carbon fibers, the resulting fibers have very different microstructure and properties [4,5]. Tubular carbons with outer diameters ranging from 10 0 nm to 10 1 mm can be synthesized by employing appropriate CVD techniques [6]. Such CVD fibers are distinguished from melt-spun fibers by a hollow core and an annular structure of graphene planes. The small diameters, vapor derived carbon fibers are classified as carbon nanotubes (CNT) [7–9]. The tubular structure of such fibers, synthesized with a hollow center, is more obvious when the dosimeter of the fiber is small. A sub-micron tubular CVD fiber with an outer diameter of |0.2 mm and an inner diameter of |0.15 mm is shown in Fig. 1 [10].
*Corresponding author. Tel.: 1886-6-275-7575; fax: 1886-6238-5613. E-mail address: [email protected] (J.-M. Ting).
Larger vapor derived carbon fibers are synthesized by addition of a CVD layer. Such fiber has an outer diameter ranging from 0.2 to 7 mm or larger [11]. The differences among these fibers or tubes are obviously not only in the physical dimensions but also in the microstructure, and therefore the properties. It has been shown that a well-ordered, defect-free CNT exhibits a Young’s modulus in the range of tera-Pascal, approaching the theoretical limit [12]. On the other hand, the microstructure of CVD carbon fiber / tube varies radially. Depending on the processing conditions, disordered structure
Fig. 1. A sub-micron tubular CVD carbon with an outer diameter and an inner diameter of |0.2 and |0.15 mm, respectively.
0008-6223 / 01 / $ – see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S0008-6223( 00 )00194-9
836
J.-M. Ting, N.Z. Huang / Carbon 39 (2001) 835 – 839
Fig. 2. A broken end of CVD carbon fiber where the core remains intact.
[13] and polycrystalline [10] structure may be found near the hollow center. Also, either better-ordered or lessordered structure may be seen when moving radially outward toward the fiber surface. Occasionally, sp 3 structure can be obtained [14]. Therefore variation in the diameter often leads to fibers / tubes with different physical properties. Investigation of fractured cross sessions of CVD carbon fiber indicates that the core exhibits a much higher stiffness [15]. Fig. 2 shows a broken end of such CVD carbon fiber where the core remains intact after the fiber was broken. Although CVD carbon fiber has been investigated in the past decades and intensive studies on CNT are being carried out, less research effort on the thickening behavior of these tubular carbon has been made. As mentioned above, CVD carbon fiber can have different diameters, leading to the differences in the microstructure and therefore the properties. It is thus realized that the control of fiber diameter can be a part of microstructure engineering. Such control relies on an understanding of the growth kinetics and mechanisms. As a result, the objective of this study was to investigate the thickening behavior of CVD fiber. Effects of growth parameters including gaseous composition, temperature, and time were examined.
2. Experimental A 1-inch horizontal tubular furnace was used for the growth of CVD carbon fiber. Growth of the fiber was performed using a technique similar to those described elsewhere [16,17]. In short, the carbon fibers were grown through the pyrolysis of a hydrocarbon gas. In this study, the hydrocarbon gas used was either methane or propane. The catalyst used was nano-sized iron particles with an average diameter of 100620 nm. Various concentrations of the hydrocarbon, balanced by hydrogen, were used. The hydrocarbon concentration ranged from 17 to 83%. The
growth temperatures were 8008C, 9008C, 10008C, 11008C, 12008C, 13008C, and 13008C, which were determined by the furnace set point. In each experiment, the hydrocarbon / hydrogen gas mixture at atmospheric pressure was introduced to the growth tube when it reached the desired temperature. Prior to the admission of the gas mixture, the growth tube was purged with argon, vacuumed, and kept at a pressure less than 1310 23 Torr. The growth time was varied from less than 5 to 60 min. As the thickening of CVD carbon fiber follows a lengthening stage, a minimum growth time was selected for each growth condition such that the following characterization were all pertinent to the thickening of the fibers [3,13]. Kinetic study shows that thickening of CVD carbon fiber starts at a time very near the end of lengthening [18]. Carbon fibers produced were examined using scanning electron microscopy (SEM).
3. Results and discussion CVD fibers with various diameters were produced. In general, these CVD carbon fibers exhibit typical smooth surfaces. However, at temperatures of 1100 and 12008C, rough or pitted surface morphologies were observed, as shown in Figs. 3 and 4, respectively. Fig. 3 shows SEM micrographs of such CVD fibers obtained at a methane concentration of 40% and various growth times. Granular morphology is seen on the surfaces of both the 5-min (Fig. 3A) and 10-min (Fig. 3B) fibers. The grains are larger on the 10-min fiber, indicating the growth of them with time. As the growth time is further increased, coalescence occurs, leaving pits on the surface, as shown in Fig. 3C. When propane was used as the hydrocarbon source, a similar morphology was also observed. Fig. 4 shows a carbon fiber with pitted surface. The fiber was grown using a propane concentration of 33% and a temperature of 12008C for 30 min. Although the exact mechanism is not known, such morphologies are attributed to the high thickening rates as discussed below. Effects of temperature on the thickening rate of CVD fibers were then investigated for 40% methane and 33% propane. Fibers with different diameters were determined using SEM micrographs of fibers obtained at various growth times. When methane was used as the hydrocarbon source, fiber thickening was not observed at 800 and 9008C, and was not significant at 10008C. Fiber ‘thickening’ at 9008C is shown in Fig. 5A. It appears that at 800 and 9008C, fibers were at the so-called lengthening stage 3 and therefore the diameters are close to that of the catalyst particles. As the temperature was increased, thickening was observed, although the rate was insignificant at 10008C, as shown in Fig. 5A. Data analysis indicates that the thickening rate at 10008C is merely 0.4 nm / min, which is the slope of the straight line. As the temperature further increases, significant thickening was observed and the rates vary as shown in Fig. 5B. It appears that the rate increases
J.-M. Ting, N.Z. Huang / Carbon 39 (2001) 835 – 839
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Fig. 3. Surface morphologies of fibers obtained at a methane concentration of 40% and a temperature of 11008C. The growth times are, respectively, (A) 5 min, (B) 10 min, and (C) 30 min.
Fig. 4. A carbon fiber with pitted surface. The fiber was grown at 12008C using a propane concentration of 33% for 30 min.
and then decreases as the temperature varies from 1100 to 13008C. The highest thickening rate, 238 nm / min, was obtained at 11008C, as indicated in Fig. 5B. Such a variation of thickening rate as a function of temperature was also observed when propane was used as the carbon source. When propane was used as the hydrocarbon source, fiber thickening was not observed at 8008C. Thickening took place as the temperature was equal to or greater than 9008C, as shown in Fig. 6. The highest thickening rate, 266 nm / min, occurred at 12008C. For comparison, the thickening rates or the slopes obtained from Figs. 5 and 6 are shown in Figs. 7 and 8, respectively, as a function of temperature. Four-parameter log normal curve fitting was used to analyze that data shown in Figs. 7 and 8. It is clear that the thickening rate increases and then decreases as the temperature raises from 800 to 13008C. The rates peak at temperatures near 1100 and 12008C when methane and propane were used as the hydrocarbon sources, respectively. It was further found that hydrocarbon concentration
838
J.-M. Ting, N.Z. Huang / Carbon 39 (2001) 835 – 839
Fig. 7. Thickening rate as a function of temperature (40% methane concentration). (Dashed line represents curve fitting).
Fig. 5. Thickening of CVD fibers at (A) 900 and 10008C, and (B) 1100–13008C. The methane concentration used was 40%. (Dashed lines are linear fits). Fig. 8. Thickening rate as a function of temperature (33% propane concentration). (Dashed line represents curve fitting).
Fig. 6. Thickening of CVD fibers at various temperatures and a propane concentration of 33%. (Dashed lines are linear fits).
exhibits similar effect on the thickening rate. Various methane and propane concentrations were respectively used for fiber growth at the peak temperatures of 1100 and 12008C (Figs. 7 and 8). The thickening rates were determined as before and are shown in Fig. 9 as a function of hydrocarbon concentration. It is obvious that the rates peaks at concentrations of 40% methane and 30% propane, respectively. As noted above, at a temperature of 11008C and a concentration of 49% methane; and at 12008C when 33% was used, rough or pitted surface morphologies were observed (Figs. 3 and 4). These growth conditions are those when the highest thickening rates were found (Figs. 7, 8 and 9). The morphologies shown in Figs. 3 and 4 are therefore attributed to the high CVD thickening rates [19].
J.-M. Ting, N.Z. Huang / Carbon 39 (2001) 835 – 839
Fig. 9. Thickening rate as a function of hydrocarbon concentration. (Dashed lines represent curve fitting).
4. Conclusion Thickening of CVD carbon fiber was studied. It was found that the thickening rate increases and then decreases as the CVD temperature raises from 800 to 13008C. The rates peak at temperatures near 1100 and 12008C when methane and propane were used as the hydrocarbon sources, respectively. It was also found that hydrocarbon concentration exhibits similar effect on the thickening rate. The thickening rates peak at concentrations of 40% methane and 30% propane, respectively. At these peak rates, CVD fibers exhibit rough are pitted surface, which are not commonly seen.
Acknowledgements This work was sponsored by the National Science Council in Taiwan under Contract [ NSC 88-2216-E-006018.
References [1] Chwastiak S, Barr JB, Didchenko R. Carbon 1979;17(1):49– 53.
839
[2] Hamada T, Nishida T, Sajiki Y, Matsumoto M, Endo M. J Mater Res 1987;2(6):850–7. [3] Tibbetts GG, Endo M, Beetz Jr. CP. SAMPE J 1986;5:22–8. [4] Lake ML, Ting JM. In: Burchell T, editor, Carbon materials for advanced technologies, New York: Elsevier, 1999, pp. 139–68. [5] Heremans J, Beetz Jr. CP. Phys Rev 1985;B32(4):1981–6. [6] Cheng HM, Li F, Su G, Pan HY, Sun LL, Dresselhaus MS. Appl Phys Lett 1998;73(22):3282–4. ˜ ´ [7] Benito A, Maniette Y, Munoz E, Martınez MT. Carbon 1999;36(5-6):681–3. [8] Chen P, Wu X, Lin J, Li H, Tan KL. Carbon 2000;38(1):139–43. [9] Ting JM, Lan BC, Chen YM, Huang NZ. Proceedings, 5th annual microelectromechanical system meeting. National Cheng Kung University (Tainan. Taiwan): National Cheng Kung University, 1999; 105–110. [10] Ting JM, Huang NZ, Lan BC. J Mater Sci 1999;34(21):5233–5. [11] Lake ML, Ting JM, Alig RL. Proceedings, 8th annual conf. on materials technology. Southern Illinois University (Illinois, USA): Southern Illinois University, 1992:55–61. [12] Ebbsen TW. Nature 1996;381(20):678–80. [13] Oberlin A, Endo M, Koyama T. Carbon 1976;14(2):133–5. [14] Anderson DP, Ting JM, Lake ML, Alig RL. Extended abstract, 22nd biennial conf. on carbon. UC San Diego (California, USA): American Carbon Society; 1995: 304– 305. [15] Ting JM, Guth JR. Extended abstract, 22nd biennial. conf. on carbon. UC San Diego (California, USA): American Carbon Society, 1995; 296–297. [16] Tibbetts GG. In: Figueiredo JL, Bernardo CA, Baker RTK, ¨ Huttinger KJ, editors, Carbon fibers, filaments, and composites, The Netherlands: Kluwer Academic Publishers, 1990, pp. 73–94. [17] Ting JM, Lake ML. In: Upadhya, editor, Processing, Fabrication, and Applications of Advanced Composites, Ohio: ASM International, 1993:117–127. [18] Endo M, Koyoma T. Kotai Butsuri 1977;12:1–32. [19] Smith DL. In: Thin-film deposition: principles & practice, New York: McGraw-Gill, 1995, pp. 119–219.