- Email: [email protected]
Production of electrically conductive paper by adding carbon nanotubes
CARBON
4 6 (2 0 0 8) 1 6 9–17 1
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/carbon
Production of electrically conductive paper by adding carbon nanotubes Takahide Oya*, Toshio Ogino Graduate School of Engineering, Yokohama National University, Tokiwadai 79-5, Hodogaya-ku, Yokohama 240-8501, Japan
A R T I C L E I N F O
Article history: Received 21 June 2007 Accepted 26 October 2007 Available online 1 November 2007
Recently, fabricating applied functional electric devices (nanodevices) that are based on nanotechnology is gaining prominence for novel information-processing devices. Many researchers consider that nanodevices, for instance, quantum dot devices, single-electron circuit devices, magnetic-flux quantum circuit devices, and so on, will be devices which have several functions. Carbon nanotubes (CNTs) [1] have also been focused on as novel devices because the CNTs are not only suitable as wires in devices but also as data processing objects. In a piece of recent research on fabricating CNT devices, various functional devices and fabrication methods for making network formations were proposed [2,3]. Furthermore, very interesting research on the fabrication of CNT sheets has been reported [4]. Such CNT sheets will have applications that include light emitting diodes, high-strength cables, and substrates that are suitable for observing the behavior of biomolecules. However, manufacturing difficulties mean that these sheets will not be ready for use in the near future. Therefore, we developed a simple method for making CNT sheets that is based on a traditional method for making Japanese washi paper. We make electrically conductive washi that contains CNTs (CNT-washi). Our CNT-washi is made following an advanced traditional washi making method that combines paper fibers and CNTs. In the CNT-washi, the CNTs are located in apertures between paper fibers and also on the fibers. The CNT-washi has high electrical conductivity because of the CNTs that were added. The electrical conductivity of the paper can be easily set by controlling the amount of added CNTs. Therefore, standard
paper sizes can be made. These features mean that our CNT-washi method of making paper can be used to easily fabricate electrically conductive sheets. To make our CNT-washi, we combined a traditional washi paper making process and a CNT-dispersing process that uses a surfactant in pure water. The actual method we used is as follows: (1) Cut paper products into small pieces. (2) Macerate the cut paper in pure water and disentangle the paper fibers from the macerated paper. (3) Make the pulp suspension by soaking the fibers in pure water. We prepared 300 mg of pulp material and soaked it in 150 ml of pure water for the suspension. (4) Prepare the CNT suspension. Here, we adopted a general method that involved using sodium dodecyl sulfate (SDS) to make the CNTs disperse [5,6]. We used 1, 3, 5, and 7 mg measures of single-walled CNTs that were made using a HiPco method and 10 mg of SDS to make CNT suspension. This gave us CNT suspensions with four different concentrations of CNTs. We added the different suspension to 10 ml of pure water. We used ultrasonication for 15 min to disperse the CNTs. (5) Mix the CNT suspension with the pulp suspension to make a mixed suspension. (6) Pour the mixed suspension into a petri dish and use a tray-screen to scoop the paper fibers containing the CNTs from the suspension. (7) Dry the contents of the tray-screen.
* Corresponding author: Fax: +81 45 338 1157. E-mail address: [email protected] (T. Oya). 0008-6223/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2007.10.027
170
CARBON
4 6 ( 2 0 0 8 ) 1 6 9 –1 7 1
To scoop paper fibers containing CNTs from the mixed suspension, we used a circular tray-screen with a diameter of 6 cm. We made two or three sheets of paper with a thickness of about 0.2 mm from the prepared suspension. We observed the surface of the CNT-washi by scanning electron microscopy (SEM) and determined the molecular structure by Raman spectroscopy. We measured the electrical conductivity of the CNT-washi with a semiconductor parameter analyzer using a four-probe method. Fig. 1a shows normal washi made by a traditional paper making method that, with the exception of step (4) and (5), follows steps (1)–(7). Fig. 1b shows our CNT-washi. We used 5 mg of CNTs for CNT-washi in Fig. 1b. Our CNT-washi is gray because of the added CNTs. To determine its detailed formation using SEM, we observed the surfaces of our CNT-washi paper. SEM images of our CNT-washi are shown in Fig. 2. Fig. 2a shows an image of normal washi surface for reference. The paper fibers are intertwined. As shown in Fig. 2b and c, there are CNTs on the paper fibers and in the apertures between the paper fibers. Some CNTs seem to form suspended bridges with paper fibers. In addition to the SEM observations, we observed Raman spectra to prove that CNTs were in our paper (Fig. 3). We used a laser to generate a 532-nm wave to excite the CNT-washi. In
Fig. 2 – SEM images of (a) normal washi, (b) CNT-washi, and (c) enlargement of (b).
Fig. 1 – (a) Normal washi and (b) CNT-washi.
Fig. 3, we use ‘‘#’’ to indicate Raman peaks that may result from paper fibers (cellulose) because these peaks appeared on the curves for both the normalwashi and the CNT-washi. Furthermore, we observed Raman peaks of both a G- and a D-band, and a radial breathing mode (RBM) generated from CNTs on the curve of the paper. The SEM images and the Raman spectra proved that the CNTs are in the CNT-washi.
CARBON
171
4 6 (2 0 0 8) 1 6 9–17 1
Table 2 – Averaged resistance values for five types of CNT-washi Amount of used CNTs (mg) 0 (Normal washi) 1 3 5 7
Fig. 3 – Raman spectra of CNT-washi and normal washi.
Table 1 – Resistance values at 10 measured points on CNT-washi Measured points Point Point Point Point Point Point Point Point Point Point
1 2 3 4 5 6 7 8 9 10
Resistance (kX/square) 8.624 10.429 9.534 9.366 14.551 6.872 11.028 8.262 12.125 10.510
Next, we used a four-probe method to measure the electrical conductivity of the normal washi and the CNT-washi papers with a semiconductor parameter analyzer. We randomly chose ten measuring points on the paper and averaged these values. As shown in Table 1, our CNT-washi (with 5 mg of CNTs) shows low values: 5–15 kX/square and an averaged value of 10.13 kX/square. We made two sheets of paper from each mixture of CNTs (0, 1, 3, 5, and 7 mg) and 300 mg of pulp. The averaged resistance values for all the CNT-washi papers that we made are shown in Table 2. These results show that adding CNTs to the pulp mixture greatly improves the electrical conductivity of the washi. The results also show that the conductivity can be set by controlling the amount of the CNTs added to the pulp mixture. In conclusion, we showed a newer simple method that is suitable for making electrically conductive paper (CNT-washi). Our CNT-washi is made from a mixture of a pulp suspension and a dispersed CNT suspension. A screen-tray is used to scoop up paper fibers that contain CNTs. This pulp mixture
Averaged resistance (X/square) >1010 >1010 2.07 · 106 1.01 · 104 2.74 · 103
is dried and in the process becomes paper. The CNTs are spread all over the CNT-washi on the paper fibers and in apertures between the paper fibers. The CNT-washi has higher electrically conductivity than normal washi because of the added CNTs. However, the conductivity of CNT-washi is not uniform. Now, we think that the non-uniform conductivity of our paper is applicable to an artifact-metrics system [7]. Artifact-metrics is an authentication technology for articles and is used to prove the intrinsic physical patterns on them. Therefore, the non-uniform conductivity on our paper is highly suitable for the artifact-metrics because of its randomness. In addition to the conductivity, our CNT-washi should have a unique photoluminescence property because of the added CNTs [8]. This property is expected to change with every fabrication of the paper because the CNT arrayed patterns in our papers change. Thus the photoluminescence property is also suit for the artifact-metrics. We are now considering developing security cards as an application of our CNT-washi with artifact-metrics system. Our paper is suitable for making not only cards, but also the system itself. We expect security CNT-washi cards to have a strong effect on the development of these systems.
R E F E R E N C E S
[1] Iijima S. Helical microtubeles of graphitic carbon. Nature 1991;354:56–8. [2] Tsukagoshi K, Yoneya N, Uryu S, Aoyagi Y, Kanda A, Ootuka Y, et al. Carbon nanotube devices for nanoelectronics. Physica B 2002;323:107–14. [3] Homma Y, Kobayashi Y, Ogino T, Yamashita T. Growth of suspended carbon nanotube networks on 100-nm-scale silicon pillars. Appl Phys Lett 2002;81:2261–3. [4] Zhang M, Fang S, Zakhidov AA, Lee SB, Aliev AE, Williams CD, et al. Strong, transparent, multifunctional, carbon nanotube sheets. Science 2005;309:1215–9. [5] Jiang L, Gao L, Sun J. Production of aqueous colloidal dispersions of carbon nanotubes. J Coll Interf Sci 2003;260:89–94. [6] O’Connell MJ, Bachilo SM, Huffman CB, Moore VC, Strano MS, Haroz EH, et al. Band gap fluorescence from individual single-walled carbon nanotubes. Science 2002;297:593–6. [7] Matsumoto H, Takeuchi I, Hoshino H, Sugahara T, Matsumoto T. An artifact-metric system which utilizes inherent texture. IPSJ J 2001;42:1992–2005. [8] Bachilo SM, Strano MS, Kittrell C, Hauge RH, Smalley RE, Weisman RB. Structure-assigned optical spectra of singlewalled carbon nanotubes. Science 2002;298:2361–6.
4 6 (2 0 0 8) 1 6 9–17 1
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/carbon
Production of electrically conductive paper by adding carbon nanotubes Takahide Oya*, Toshio Ogino Graduate School of Engineering, Yokohama National University, Tokiwadai 79-5, Hodogaya-ku, Yokohama 240-8501, Japan
A R T I C L E I N F O
Article history: Received 21 June 2007 Accepted 26 October 2007 Available online 1 November 2007
Recently, fabricating applied functional electric devices (nanodevices) that are based on nanotechnology is gaining prominence for novel information-processing devices. Many researchers consider that nanodevices, for instance, quantum dot devices, single-electron circuit devices, magnetic-flux quantum circuit devices, and so on, will be devices which have several functions. Carbon nanotubes (CNTs) [1] have also been focused on as novel devices because the CNTs are not only suitable as wires in devices but also as data processing objects. In a piece of recent research on fabricating CNT devices, various functional devices and fabrication methods for making network formations were proposed [2,3]. Furthermore, very interesting research on the fabrication of CNT sheets has been reported [4]. Such CNT sheets will have applications that include light emitting diodes, high-strength cables, and substrates that are suitable for observing the behavior of biomolecules. However, manufacturing difficulties mean that these sheets will not be ready for use in the near future. Therefore, we developed a simple method for making CNT sheets that is based on a traditional method for making Japanese washi paper. We make electrically conductive washi that contains CNTs (CNT-washi). Our CNT-washi is made following an advanced traditional washi making method that combines paper fibers and CNTs. In the CNT-washi, the CNTs are located in apertures between paper fibers and also on the fibers. The CNT-washi has high electrical conductivity because of the CNTs that were added. The electrical conductivity of the paper can be easily set by controlling the amount of added CNTs. Therefore, standard
paper sizes can be made. These features mean that our CNT-washi method of making paper can be used to easily fabricate electrically conductive sheets. To make our CNT-washi, we combined a traditional washi paper making process and a CNT-dispersing process that uses a surfactant in pure water. The actual method we used is as follows: (1) Cut paper products into small pieces. (2) Macerate the cut paper in pure water and disentangle the paper fibers from the macerated paper. (3) Make the pulp suspension by soaking the fibers in pure water. We prepared 300 mg of pulp material and soaked it in 150 ml of pure water for the suspension. (4) Prepare the CNT suspension. Here, we adopted a general method that involved using sodium dodecyl sulfate (SDS) to make the CNTs disperse [5,6]. We used 1, 3, 5, and 7 mg measures of single-walled CNTs that were made using a HiPco method and 10 mg of SDS to make CNT suspension. This gave us CNT suspensions with four different concentrations of CNTs. We added the different suspension to 10 ml of pure water. We used ultrasonication for 15 min to disperse the CNTs. (5) Mix the CNT suspension with the pulp suspension to make a mixed suspension. (6) Pour the mixed suspension into a petri dish and use a tray-screen to scoop the paper fibers containing the CNTs from the suspension. (7) Dry the contents of the tray-screen.
* Corresponding author: Fax: +81 45 338 1157. E-mail address: [email protected] (T. Oya). 0008-6223/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2007.10.027
170
CARBON
4 6 ( 2 0 0 8 ) 1 6 9 –1 7 1
To scoop paper fibers containing CNTs from the mixed suspension, we used a circular tray-screen with a diameter of 6 cm. We made two or three sheets of paper with a thickness of about 0.2 mm from the prepared suspension. We observed the surface of the CNT-washi by scanning electron microscopy (SEM) and determined the molecular structure by Raman spectroscopy. We measured the electrical conductivity of the CNT-washi with a semiconductor parameter analyzer using a four-probe method. Fig. 1a shows normal washi made by a traditional paper making method that, with the exception of step (4) and (5), follows steps (1)–(7). Fig. 1b shows our CNT-washi. We used 5 mg of CNTs for CNT-washi in Fig. 1b. Our CNT-washi is gray because of the added CNTs. To determine its detailed formation using SEM, we observed the surfaces of our CNT-washi paper. SEM images of our CNT-washi are shown in Fig. 2. Fig. 2a shows an image of normal washi surface for reference. The paper fibers are intertwined. As shown in Fig. 2b and c, there are CNTs on the paper fibers and in the apertures between the paper fibers. Some CNTs seem to form suspended bridges with paper fibers. In addition to the SEM observations, we observed Raman spectra to prove that CNTs were in our paper (Fig. 3). We used a laser to generate a 532-nm wave to excite the CNT-washi. In
Fig. 2 – SEM images of (a) normal washi, (b) CNT-washi, and (c) enlargement of (b).
Fig. 1 – (a) Normal washi and (b) CNT-washi.
Fig. 3, we use ‘‘#’’ to indicate Raman peaks that may result from paper fibers (cellulose) because these peaks appeared on the curves for both the normalwashi and the CNT-washi. Furthermore, we observed Raman peaks of both a G- and a D-band, and a radial breathing mode (RBM) generated from CNTs on the curve of the paper. The SEM images and the Raman spectra proved that the CNTs are in the CNT-washi.
CARBON
171
4 6 (2 0 0 8) 1 6 9–17 1
Table 2 – Averaged resistance values for five types of CNT-washi Amount of used CNTs (mg) 0 (Normal washi) 1 3 5 7
Fig. 3 – Raman spectra of CNT-washi and normal washi.
Table 1 – Resistance values at 10 measured points on CNT-washi Measured points Point Point Point Point Point Point Point Point Point Point
1 2 3 4 5 6 7 8 9 10
Resistance (kX/square) 8.624 10.429 9.534 9.366 14.551 6.872 11.028 8.262 12.125 10.510
Next, we used a four-probe method to measure the electrical conductivity of the normal washi and the CNT-washi papers with a semiconductor parameter analyzer. We randomly chose ten measuring points on the paper and averaged these values. As shown in Table 1, our CNT-washi (with 5 mg of CNTs) shows low values: 5–15 kX/square and an averaged value of 10.13 kX/square. We made two sheets of paper from each mixture of CNTs (0, 1, 3, 5, and 7 mg) and 300 mg of pulp. The averaged resistance values for all the CNT-washi papers that we made are shown in Table 2. These results show that adding CNTs to the pulp mixture greatly improves the electrical conductivity of the washi. The results also show that the conductivity can be set by controlling the amount of the CNTs added to the pulp mixture. In conclusion, we showed a newer simple method that is suitable for making electrically conductive paper (CNT-washi). Our CNT-washi is made from a mixture of a pulp suspension and a dispersed CNT suspension. A screen-tray is used to scoop up paper fibers that contain CNTs. This pulp mixture
Averaged resistance (X/square) >1010 >1010 2.07 · 106 1.01 · 104 2.74 · 103
is dried and in the process becomes paper. The CNTs are spread all over the CNT-washi on the paper fibers and in apertures between the paper fibers. The CNT-washi has higher electrically conductivity than normal washi because of the added CNTs. However, the conductivity of CNT-washi is not uniform. Now, we think that the non-uniform conductivity of our paper is applicable to an artifact-metrics system [7]. Artifact-metrics is an authentication technology for articles and is used to prove the intrinsic physical patterns on them. Therefore, the non-uniform conductivity on our paper is highly suitable for the artifact-metrics because of its randomness. In addition to the conductivity, our CNT-washi should have a unique photoluminescence property because of the added CNTs [8]. This property is expected to change with every fabrication of the paper because the CNT arrayed patterns in our papers change. Thus the photoluminescence property is also suit for the artifact-metrics. We are now considering developing security cards as an application of our CNT-washi with artifact-metrics system. Our paper is suitable for making not only cards, but also the system itself. We expect security CNT-washi cards to have a strong effect on the development of these systems.
R E F E R E N C E S
[1] Iijima S. Helical microtubeles of graphitic carbon. Nature 1991;354:56–8. [2] Tsukagoshi K, Yoneya N, Uryu S, Aoyagi Y, Kanda A, Ootuka Y, et al. Carbon nanotube devices for nanoelectronics. Physica B 2002;323:107–14. [3] Homma Y, Kobayashi Y, Ogino T, Yamashita T. Growth of suspended carbon nanotube networks on 100-nm-scale silicon pillars. Appl Phys Lett 2002;81:2261–3. [4] Zhang M, Fang S, Zakhidov AA, Lee SB, Aliev AE, Williams CD, et al. Strong, transparent, multifunctional, carbon nanotube sheets. Science 2005;309:1215–9. [5] Jiang L, Gao L, Sun J. Production of aqueous colloidal dispersions of carbon nanotubes. J Coll Interf Sci 2003;260:89–94. [6] O’Connell MJ, Bachilo SM, Huffman CB, Moore VC, Strano MS, Haroz EH, et al. Band gap fluorescence from individual single-walled carbon nanotubes. Science 2002;297:593–6. [7] Matsumoto H, Takeuchi I, Hoshino H, Sugahara T, Matsumoto T. An artifact-metric system which utilizes inherent texture. IPSJ J 2001;42:1992–2005. [8] Bachilo SM, Strano MS, Kittrell C, Hauge RH, Smalley RE, Weisman RB. Structure-assigned optical spectra of singlewalled carbon nanotubes. Science 2002;298:2361–6.