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Selective growth of double-walled carbon nanotubes on gold films
Materials Letters 72 (2012) 78–80
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Selective growth of double-walled carbon nanotubes on gold films Yifeng Fu a, b, Si Chen a, c, Johan Bielecki d, Aleksandar Matic d, Teng Wang a, Li-Lei Ye e, Johan Liu a, c,⁎ a
Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Göteborg, Sweden FOAB Elektronik AB, S:t Jörgens väg 8, SE-422 49 Hisings Backa, Sweden c Key Laboratory of Advanced Display and System Applications and SMIT Center, School of Automation and Mechanical Engineering, Box 282, No. 149 Yan Chang Road, Yan Chang Campus, Shanghai University, Shanghai 200072, China d Department of Applied Physics, Chalmers University of Technology, SE-41296 Göteborg, Sweden e SHT Smart High Tech AB, Fysikgränd 3, SE-412 96 Göteborg, Sweden b
a r t i c l e
i n f o
Article history: Received 28 October 2011 Accepted 7 December 2011 Available online 14 December 2011 Keywords: Carbon nanotubes Selective growth Double-walled Gold film Field emission
a b s t r a c t Growth of high-quality vertical aligned carbon nanotube (CNT) structures on silicon supported gold (Au) films by thermal chemical vapor deposition (TCVD) is presented. Transmission electron microscopy (TEM) images show that the growth is highly selective. Statistical study reveals that 79.4% of the as-grown CNTs are double-walled. The CNTs synthesized on Au films are more porous than that synthesized on silicon substrates under the same conditions. Raman spectroscopy and electrical characterization performed on the asgrown double-walled CNTs (DWNTs) indicate that they are competitive with those CNTs grown on silicon substrates. Field emission tests show that closed-ended DWNTs have lower threshold field than those open-ended. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Double-walled carbon nanotube (DWNT) is the thinnest multiwalled CNT (MWNT) composed of two nested nanotubes. Due to the special geometrical structure, DWNTs exhibit different physical performance from their single-walled and multi-walled counterparts, e.g. they are thermally more stable than SWNTs [1] and mechanically more flexible than MWNTs [2]. In a DWNT, the two graphitic walls only interact with each other, making the DWNT an ideal objective for investigating the interaction between different walls of CNTs [3]. In some applications where both the outer tube and inner tube characteristics are crucial, DWNTs can offer unique advantages that other CNTs cannot [4]. DWNTs have been prepared by post-growth selection [5–7], controlled synthesize from single-walled CNTs and C60 [8], and selective growth using engineered/mixed catalysts [2,9–12] by CVD or arc discharge process. In this letter, we report a new method which enables the highly selective growth of DWNTs on silicon supported Au films without any catalyst engineering. Statistical study shows that the selectivity of DWNTs is about 79.4%. The quality of the as-grown DWNTs is confirmed by Raman spectra and electrical characterization.
2.1. CNT growth
⁎ Corresponding author at: Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Göteborg, Sweden. Tel.: + 46 31 772 3067. E-mail addresses: [email protected] (Y. Fu), [email protected] (S. Chen), [email protected] (J. Bielecki), [email protected] (A. Matic), [email protected] (T. Wang), [email protected] (L.-L. Ye), [email protected] (J. Liu). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.12.026
The CNT growth process starts with the preparation of the Au films and catalyst layer on a p-type silicon wafer. Prior to the catalyst deposition, a 1 μm thick Au film was sputtered onto the wafer as an underlayer. Al2O3/Fe with a thickness of 10/1 nm was then evaporated onto the Au film by electron beam evaporation, acting as CNT catalyst. Patterning of the catalyst layer was realized by standard photolithography and lift-off processes. Afterwards, the samples with Au film and patterned catalyst layer were put into a commercial CNT growth system (Black Magic ΙΙ, Aixtron) for CNT synthesis [13]. The samples were first placed on a graphite heater which was heated up to 500 °C for catalyst reduction and annealing and stayed there for 3 min in an environment of 692 standard cubic centimeter (sccm) hydrogen (H2). The heater temperature was then elevated to 700 °C in about 10 s. At the same time 200 sccm acetylene (C2H2) flow was introduced to start the CNT growth. The height of the CNTs was controlled by varying the growth time. After the growth was finished, the samples were cooled down to room temperature in 1000 sccm nitrogen (N2) flow. The CNT growth was also performed on bare silicon substrates with the same catalytic and growth conditions as a comparison. Fig. 1(a) shows a scanning electron microscopy (SEM) image of the synthesized CNT bundles standing on the Au film. 2.2. CNT characterization SEM (JEOL JSM-6301F) was used to characterize the morphology of CNTs synthesized on Au films and TEM (Tecnai T20 FEI) was used
Y. Fu et al. / Materials Letters 72 (2012) 78–80
79
Fig. 1. (a) CNT bundles grown on the Au film. (b) TEM image of the as-grown DWNTs on Au films.
to observe their wall structures. Statistical study was carried out to analyze the wall number distribution of the CNTs. Raman spectroscopy (Dilor-XY800, 514 nm laser line of an Ar/Kr laser) was used to examine the quality of the CNTs. Electrical characterization was performed on a Keithley 4200 multimeter equipped with a probe station to examine the current– voltage (I–V) response of the CNT bundles synthesized on Au films. One probe contacted the Au film on the substrate near the bundle to be measured and the other probe was placed on the top of the CNT bundle. In order to examine the field emission behavior of the DWNT synthesized on Au films with and without a cap at the tip, oxygen (O2) plasma etching (BatchTop m/91) with 50 W power was carried out for 5 min to open the ends. Field emission tests were subsequently performed both on the open-ended and closed-ended DWNTs under a cathode-to-anode distance of 1.1 mm at 5.4 × 10 − 7 Torr.
and supporting surfaces [15], the adhesion and wettability of catalyst on substrates [16], etc. Further investigation will be performed to identify which factor is responsible for the DWNT growth in our case. Locally magnified captures on the sidewalls and top views of the CNT bundles synthesized on Au film and Si surface are shown in Fig. 3(a–f). It can be seen that the DWNTs synthesized on the Au
3. Results and discussion Fig. 1(a) shows that the CNT bundles synthesized on the Au film are well aligned. Randomly selected CNTs observed in the TEM shows that 50 out of 63, i.e. 79.4% are double-walled. This is one of the highest selectivity ever reported [2,8–11]. More detailed wall distribution of the CNTs synthesized on Au films is displayed in Fig. 2. A typical wall structure of the DWNTs is shown in Fig. 1(b). For comparison, the CNTs grown on bare Si surface under the same conditions as the growth on Au films were also investigated in a TEM. The wall distribution is presented in Fig. 2, which shows a much more uniform distribution of CNT walls and triple-walled CNTs is mostly visible in the material. It has been reported that the CNT growth varies dramatically on different substrates possibly due to the different nucleation of CNTs around catalyst particles [14], the alloying between catalyst
Fig. 2. Number of wall distributions of the CNTs synthesized on Au films and bare Si surfaces.
Fig. 3. (a) A DWNT bundle synthesized on Au film. (b) Top view of the DWNT bundle. (c) Sidewall of the DWNT bundle. (d) A CNT bundle synthesized on bare silicon substrate. (e) Top view of the CNT bundle. (f) Sidewall of the CNT bundle. (g) Raman spectra of the CNTs synthesized on Si surface and Au films.
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Y. Fu et al. / Materials Letters 72 (2012) 78–80
4. Conclusions In summary, the selective growth of DWNTs on Au films has been demonstrated and the selectivity is about 79.4% which is one of the highest ever reported. Compared to the CNTs grown on bare silicon, we found that these DWNTs are more porous. However, Raman spectra and electrical characterization indicate that the DWNTs are competitive with those CNTs grown on silicon substrates and assembled by post-growth transfer processes. We attribute this to the good contact between DWNTs and the conductive substrate (Au film). Field emission tests show that the closed-ended DWNTs are easier to be activated than those open-ended. The work reported in this letter provides a new method to synthesize DWNTs on conductive substrates as a fundamental material in electronic applications [20].
Acknowledgements This work was supported by EU programs “Thema-CNT”, “Smartpower”, “Nanotec”, “Nanocom”, “Nanoteg”, “Mercure”, and the Swedish National Science Foundation (VR) under the project “on-chip cooling using thermo-electrical device with the contract no: 20095042. This work was also carried out within the Sustainable Production Initiative and the Production Area of Advance at Chalmers. J.L. also acknowledges the support from the Chinese Ministry of Science and Technology for the International Science and Technology Cooperation program of China (No. 2010DFA14450). Y.F. is grateful to Dr. Zonghe Lai at MC2, Chalmers University of Technology, for the help on TEM characterization. Y.F. also appreciates Mr. Ying-Pin Wu from National Taiwan University and Dr. Qiu-Hong Hu from LightLab Sweden AB for their help on the field emission tests.
References Fig. 4. (a) I–V response of a DWNT bundle synthesized on Au film. (b) Field emission tests of DWNTs synthesized on Au films before and after O2 plasma etching.
films are more porous than those CNTs synthesized on bare silicon substrates. Raman spectra of the DWNTs and the CNTs on Si surface are shown in Fig. 3(g). The D, G and 2D peaks are located at ~ 1335 cm − 1, ~1573 cm − 1 and ~ 2669 cm − 1 respectively. For the DWNTs grown on Au films, the D-to-G peak-height ratio (ID/IG) is about 1.40 compared to 1.26 for those CNTs grown on bare silicon, which indicates that the quality of the DWNTs is close to those CNTs synthesized on Si surface [17]. Electrical characterization result of the DWNTs synthesized on Au films is shown in Fig. 4(a). The approximately linear I–V curve shows that the electrical resistance is about 430 Ω for a DWNT bundle 50 μm in diameter and 157 μm high, i.e. a resistivity of 5.375 × 10 − 3 Ω m, which is at the same level as the CNTs grown on bare silicon substrates and assembled by post-growth transfer processes [18,19]. The field emission test results on DWNTs are displayed in Fig. 4(b). According to the cathode-to-anode distance and the height of the DWNTs, the distance between the DWNT tips and the anode is about 943 μm. As the applied voltage between cathode and anode was increased, the emission was detected at 250 V (0.27 V/μm) and 360 V (0.38 V/μm) for DWNTs with and without caps, respectively. That means the DWNTs with closed ends have lower threshold field than the open-ended DWNTs.
[1] Kim YA, Muramatsu H, Hayashi T, Endo M, Terrones M, Dresselhaus MS. Chem Phys Lett 2004;398:87–92. [2] Yamada T, Namai T, Hata K, Futaba DN, Mizuno K, Fan J, et al. Nat Nanotechnol 2006;1:131–6. [3] Guo Z, Chang T, Guo X, Gao H. Phys Rev Lett 2011;107:105502. [4] Jung YC, Muramatsu H, Fujisawa K, Kim LH, Hayashi T, Kim YA, et al. Small 2011;7: 3292–7. [5] Endo M, Muramatsu H, Tayashi T, Kim YA, Terrones M, Dresselhaus MS. Nature 2005;433:476. [6] Kim YA, Muramatsu H, Hayashi T, Endo M, Terrones M, Dresselhaus MS. Chem Vap Deposition 2006;12:327–30. [7] Kim JH, Kataoka M, Kim YA, Shimamoto D, Muramatsu H, Hayashi T, et al. Appl Phys Lett 2008;93:223107. [8] Bandow S, Takizawa M, Hirahara K, Yudasaka M, Iijima S. Chem Phys Lett 2001;337:48–54. [9] Lyu SC, Liu BC, Lee CJ, Kang HK, Yang CW. Chem Mater 2003;15:3951–4. [10] Lyu SC, Lee TJ, Yang CW, Lee CJ. Chem Commun 2003:1404–5. [11] Dunens OM, MacKenzie KJ, Harris AT. Ind Eng Chem Res 2010;49:4031–5. [12] Hutchison JL, Kiselev NA, Krinichnaya EP, Krestinin AV, Loutfy RO, Morawsky AP, et al. Carbon 2001;39:761–70. [13] Fu Y, Qin Y, Wang T, Chen S, Liu J. Adv Mater 2010;22:5039–42. [14] Cao A, Ci L, Li D, Wei B, Xu C, Liang J, et al. Chem Phys Lett 2001;335:150–4. [15] Nessim GD, Seita M, O'Brien KP, Hart AJ, Bonaparte RK, Mitchell RR, et al. Nano Lett 2009;9:3398–405. [16] Matthews KD, Lemaitre MG, Kim T, Chen H, Shim M, Zuo J-M. J Appl Phys 2006;100:044309. [17] Ferrari AC, Meyer JC, Scardaci V, Casiraghi C, Lazzeri M, Mauri F, et al. Phys Rev Lett 2006;97:187401. [18] Wang T, Carlberg B, Jönsson M, Jeong G, Campbell EEB, Liu J. Appl Phys Lett 2007;91:093123. [19] Jiang H, Zhu L, Moon K, Wong CP. Nanotechnology 2007;18:125203. [20] Shimada T, Sugai T, Ohno Y, Kishimoto S, Mizutani T, Yoshida H, et al. Appl Phys Lett 2004;84:2412–4.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Selective growth of double-walled carbon nanotubes on gold films Yifeng Fu a, b, Si Chen a, c, Johan Bielecki d, Aleksandar Matic d, Teng Wang a, Li-Lei Ye e, Johan Liu a, c,⁎ a
Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Göteborg, Sweden FOAB Elektronik AB, S:t Jörgens väg 8, SE-422 49 Hisings Backa, Sweden c Key Laboratory of Advanced Display and System Applications and SMIT Center, School of Automation and Mechanical Engineering, Box 282, No. 149 Yan Chang Road, Yan Chang Campus, Shanghai University, Shanghai 200072, China d Department of Applied Physics, Chalmers University of Technology, SE-41296 Göteborg, Sweden e SHT Smart High Tech AB, Fysikgränd 3, SE-412 96 Göteborg, Sweden b
a r t i c l e
i n f o
Article history: Received 28 October 2011 Accepted 7 December 2011 Available online 14 December 2011 Keywords: Carbon nanotubes Selective growth Double-walled Gold film Field emission
a b s t r a c t Growth of high-quality vertical aligned carbon nanotube (CNT) structures on silicon supported gold (Au) films by thermal chemical vapor deposition (TCVD) is presented. Transmission electron microscopy (TEM) images show that the growth is highly selective. Statistical study reveals that 79.4% of the as-grown CNTs are double-walled. The CNTs synthesized on Au films are more porous than that synthesized on silicon substrates under the same conditions. Raman spectroscopy and electrical characterization performed on the asgrown double-walled CNTs (DWNTs) indicate that they are competitive with those CNTs grown on silicon substrates. Field emission tests show that closed-ended DWNTs have lower threshold field than those open-ended. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Double-walled carbon nanotube (DWNT) is the thinnest multiwalled CNT (MWNT) composed of two nested nanotubes. Due to the special geometrical structure, DWNTs exhibit different physical performance from their single-walled and multi-walled counterparts, e.g. they are thermally more stable than SWNTs [1] and mechanically more flexible than MWNTs [2]. In a DWNT, the two graphitic walls only interact with each other, making the DWNT an ideal objective for investigating the interaction between different walls of CNTs [3]. In some applications where both the outer tube and inner tube characteristics are crucial, DWNTs can offer unique advantages that other CNTs cannot [4]. DWNTs have been prepared by post-growth selection [5–7], controlled synthesize from single-walled CNTs and C60 [8], and selective growth using engineered/mixed catalysts [2,9–12] by CVD or arc discharge process. In this letter, we report a new method which enables the highly selective growth of DWNTs on silicon supported Au films without any catalyst engineering. Statistical study shows that the selectivity of DWNTs is about 79.4%. The quality of the as-grown DWNTs is confirmed by Raman spectra and electrical characterization.
2.1. CNT growth
⁎ Corresponding author at: Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Göteborg, Sweden. Tel.: + 46 31 772 3067. E-mail addresses: [email protected] (Y. Fu), [email protected] (S. Chen), [email protected] (J. Bielecki), [email protected] (A. Matic), [email protected] (T. Wang), [email protected] (L.-L. Ye), [email protected] (J. Liu). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.12.026
The CNT growth process starts with the preparation of the Au films and catalyst layer on a p-type silicon wafer. Prior to the catalyst deposition, a 1 μm thick Au film was sputtered onto the wafer as an underlayer. Al2O3/Fe with a thickness of 10/1 nm was then evaporated onto the Au film by electron beam evaporation, acting as CNT catalyst. Patterning of the catalyst layer was realized by standard photolithography and lift-off processes. Afterwards, the samples with Au film and patterned catalyst layer were put into a commercial CNT growth system (Black Magic ΙΙ, Aixtron) for CNT synthesis [13]. The samples were first placed on a graphite heater which was heated up to 500 °C for catalyst reduction and annealing and stayed there for 3 min in an environment of 692 standard cubic centimeter (sccm) hydrogen (H2). The heater temperature was then elevated to 700 °C in about 10 s. At the same time 200 sccm acetylene (C2H2) flow was introduced to start the CNT growth. The height of the CNTs was controlled by varying the growth time. After the growth was finished, the samples were cooled down to room temperature in 1000 sccm nitrogen (N2) flow. The CNT growth was also performed on bare silicon substrates with the same catalytic and growth conditions as a comparison. Fig. 1(a) shows a scanning electron microscopy (SEM) image of the synthesized CNT bundles standing on the Au film. 2.2. CNT characterization SEM (JEOL JSM-6301F) was used to characterize the morphology of CNTs synthesized on Au films and TEM (Tecnai T20 FEI) was used
Y. Fu et al. / Materials Letters 72 (2012) 78–80
79
Fig. 1. (a) CNT bundles grown on the Au film. (b) TEM image of the as-grown DWNTs on Au films.
to observe their wall structures. Statistical study was carried out to analyze the wall number distribution of the CNTs. Raman spectroscopy (Dilor-XY800, 514 nm laser line of an Ar/Kr laser) was used to examine the quality of the CNTs. Electrical characterization was performed on a Keithley 4200 multimeter equipped with a probe station to examine the current– voltage (I–V) response of the CNT bundles synthesized on Au films. One probe contacted the Au film on the substrate near the bundle to be measured and the other probe was placed on the top of the CNT bundle. In order to examine the field emission behavior of the DWNT synthesized on Au films with and without a cap at the tip, oxygen (O2) plasma etching (BatchTop m/91) with 50 W power was carried out for 5 min to open the ends. Field emission tests were subsequently performed both on the open-ended and closed-ended DWNTs under a cathode-to-anode distance of 1.1 mm at 5.4 × 10 − 7 Torr.
and supporting surfaces [15], the adhesion and wettability of catalyst on substrates [16], etc. Further investigation will be performed to identify which factor is responsible for the DWNT growth in our case. Locally magnified captures on the sidewalls and top views of the CNT bundles synthesized on Au film and Si surface are shown in Fig. 3(a–f). It can be seen that the DWNTs synthesized on the Au
3. Results and discussion Fig. 1(a) shows that the CNT bundles synthesized on the Au film are well aligned. Randomly selected CNTs observed in the TEM shows that 50 out of 63, i.e. 79.4% are double-walled. This is one of the highest selectivity ever reported [2,8–11]. More detailed wall distribution of the CNTs synthesized on Au films is displayed in Fig. 2. A typical wall structure of the DWNTs is shown in Fig. 1(b). For comparison, the CNTs grown on bare Si surface under the same conditions as the growth on Au films were also investigated in a TEM. The wall distribution is presented in Fig. 2, which shows a much more uniform distribution of CNT walls and triple-walled CNTs is mostly visible in the material. It has been reported that the CNT growth varies dramatically on different substrates possibly due to the different nucleation of CNTs around catalyst particles [14], the alloying between catalyst
Fig. 2. Number of wall distributions of the CNTs synthesized on Au films and bare Si surfaces.
Fig. 3. (a) A DWNT bundle synthesized on Au film. (b) Top view of the DWNT bundle. (c) Sidewall of the DWNT bundle. (d) A CNT bundle synthesized on bare silicon substrate. (e) Top view of the CNT bundle. (f) Sidewall of the CNT bundle. (g) Raman spectra of the CNTs synthesized on Si surface and Au films.
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Y. Fu et al. / Materials Letters 72 (2012) 78–80
4. Conclusions In summary, the selective growth of DWNTs on Au films has been demonstrated and the selectivity is about 79.4% which is one of the highest ever reported. Compared to the CNTs grown on bare silicon, we found that these DWNTs are more porous. However, Raman spectra and electrical characterization indicate that the DWNTs are competitive with those CNTs grown on silicon substrates and assembled by post-growth transfer processes. We attribute this to the good contact between DWNTs and the conductive substrate (Au film). Field emission tests show that the closed-ended DWNTs are easier to be activated than those open-ended. The work reported in this letter provides a new method to synthesize DWNTs on conductive substrates as a fundamental material in electronic applications [20].
Acknowledgements This work was supported by EU programs “Thema-CNT”, “Smartpower”, “Nanotec”, “Nanocom”, “Nanoteg”, “Mercure”, and the Swedish National Science Foundation (VR) under the project “on-chip cooling using thermo-electrical device with the contract no: 20095042. This work was also carried out within the Sustainable Production Initiative and the Production Area of Advance at Chalmers. J.L. also acknowledges the support from the Chinese Ministry of Science and Technology for the International Science and Technology Cooperation program of China (No. 2010DFA14450). Y.F. is grateful to Dr. Zonghe Lai at MC2, Chalmers University of Technology, for the help on TEM characterization. Y.F. also appreciates Mr. Ying-Pin Wu from National Taiwan University and Dr. Qiu-Hong Hu from LightLab Sweden AB for their help on the field emission tests.
References Fig. 4. (a) I–V response of a DWNT bundle synthesized on Au film. (b) Field emission tests of DWNTs synthesized on Au films before and after O2 plasma etching.
films are more porous than those CNTs synthesized on bare silicon substrates. Raman spectra of the DWNTs and the CNTs on Si surface are shown in Fig. 3(g). The D, G and 2D peaks are located at ~ 1335 cm − 1, ~1573 cm − 1 and ~ 2669 cm − 1 respectively. For the DWNTs grown on Au films, the D-to-G peak-height ratio (ID/IG) is about 1.40 compared to 1.26 for those CNTs grown on bare silicon, which indicates that the quality of the DWNTs is close to those CNTs synthesized on Si surface [17]. Electrical characterization result of the DWNTs synthesized on Au films is shown in Fig. 4(a). The approximately linear I–V curve shows that the electrical resistance is about 430 Ω for a DWNT bundle 50 μm in diameter and 157 μm high, i.e. a resistivity of 5.375 × 10 − 3 Ω m, which is at the same level as the CNTs grown on bare silicon substrates and assembled by post-growth transfer processes [18,19]. The field emission test results on DWNTs are displayed in Fig. 4(b). According to the cathode-to-anode distance and the height of the DWNTs, the distance between the DWNT tips and the anode is about 943 μm. As the applied voltage between cathode and anode was increased, the emission was detected at 250 V (0.27 V/μm) and 360 V (0.38 V/μm) for DWNTs with and without caps, respectively. That means the DWNTs with closed ends have lower threshold field than the open-ended DWNTs.
[1] Kim YA, Muramatsu H, Hayashi T, Endo M, Terrones M, Dresselhaus MS. Chem Phys Lett 2004;398:87–92. [2] Yamada T, Namai T, Hata K, Futaba DN, Mizuno K, Fan J, et al. Nat Nanotechnol 2006;1:131–6. [3] Guo Z, Chang T, Guo X, Gao H. Phys Rev Lett 2011;107:105502. [4] Jung YC, Muramatsu H, Fujisawa K, Kim LH, Hayashi T, Kim YA, et al. Small 2011;7: 3292–7. [5] Endo M, Muramatsu H, Tayashi T, Kim YA, Terrones M, Dresselhaus MS. Nature 2005;433:476. [6] Kim YA, Muramatsu H, Hayashi T, Endo M, Terrones M, Dresselhaus MS. Chem Vap Deposition 2006;12:327–30. [7] Kim JH, Kataoka M, Kim YA, Shimamoto D, Muramatsu H, Hayashi T, et al. Appl Phys Lett 2008;93:223107. [8] Bandow S, Takizawa M, Hirahara K, Yudasaka M, Iijima S. Chem Phys Lett 2001;337:48–54. [9] Lyu SC, Liu BC, Lee CJ, Kang HK, Yang CW. Chem Mater 2003;15:3951–4. [10] Lyu SC, Lee TJ, Yang CW, Lee CJ. Chem Commun 2003:1404–5. [11] Dunens OM, MacKenzie KJ, Harris AT. Ind Eng Chem Res 2010;49:4031–5. [12] Hutchison JL, Kiselev NA, Krinichnaya EP, Krestinin AV, Loutfy RO, Morawsky AP, et al. Carbon 2001;39:761–70. [13] Fu Y, Qin Y, Wang T, Chen S, Liu J. Adv Mater 2010;22:5039–42. [14] Cao A, Ci L, Li D, Wei B, Xu C, Liang J, et al. Chem Phys Lett 2001;335:150–4. [15] Nessim GD, Seita M, O'Brien KP, Hart AJ, Bonaparte RK, Mitchell RR, et al. Nano Lett 2009;9:3398–405. [16] Matthews KD, Lemaitre MG, Kim T, Chen H, Shim M, Zuo J-M. J Appl Phys 2006;100:044309. [17] Ferrari AC, Meyer JC, Scardaci V, Casiraghi C, Lazzeri M, Mauri F, et al. Phys Rev Lett 2006;97:187401. [18] Wang T, Carlberg B, Jönsson M, Jeong G, Campbell EEB, Liu J. Appl Phys Lett 2007;91:093123. [19] Jiang H, Zhu L, Moon K, Wong CP. Nanotechnology 2007;18:125203. [20] Shimada T, Sugai T, Ohno Y, Kishimoto S, Mizutani T, Yoshida H, et al. Appl Phys Lett 2004;84:2412–4.