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Silver Nanowires as Templates for Preparation of Amorphous Carbon Nanotubes
Journal of Colloid and Interface Science 225, 254–256 (2000) doi:10.1006/jcis.2000.6835, available online at http://www.idealibrary.com on
LETTER TO THE EDITOR Silver Nanowires as Templates for Preparation of Amorphous Carbon Nanotubes
In this report, we describe a novel method for preparing amorphous carbon nanotubes (ACNT) from silver nanowires using a carbon replica technique. ACNT size and shape are determined by the template silver nanowire. Interspaces between carbon grains present in the ACNT wall cause the wall to act as a permeable membrane through which reactants pass freely. Simple chemical modifications can be used to modify the diameter of the silver filaments within. We anticipate that this method will prove useful in preparing a wide variety of nanometer-sized filaments, perhaps with the replica itself able to serve as a template in casting nanomaterials of assorted shapes. °C 2000 Academic Press Key Words: amorphous carbon; nanotubes; silver nanowires.
Carbon nanotubes (1, 2) are generating much interest because of their potential applications in high-performance nanoscale materials (3, 4) and electronic devices (5, 6). Strong interest in carbon nanotubes first emerged in the nanotechnology (7) field when it was shown that different kinds of materials with potentially interesting properties can be inserted into the core volumes of nanotubes. The inner cavities of carbon nanotubes can also serve as nanoscale test tubes and templates (8–10) or be utilized for controlled production of encapsulated nanostructures. However, problems remain to be solved, such as the controlled filling of the tubes and the modification of materials in the carbon nanotubes. In the production of fullerene nanotubes, it is problematic that amorphous carbon always appears. However, if a nanotube is composed completely of amorphous carbon, the tube manifests wholly different properties. In this report, we describe a method for the preparation of such amorphous carbon nanotubes (ACNTs). Silver nanowires serve as templates in a carbon replica technique. Amorphous carbon nanotubes are produced. The ACNT wall acts as a permeable membrane which permits reactants to pass through freely. When nanometersized filaments are encapsulated in the tubes, they can easily be modified by chemical reaction in solution.
EXPERIMENTAL
1. The Growth of Silver Nanowire Templates Silver nanowires were prepared to serve as templates of ACNTs. For this, a photographic emulsion of AgBr (11) was used to coat a film. This film was exposed for 5 s to fluorescent light. Dilute D-76 developer (1/20 concentration) was used to develop the film for 8 min, and F-11 fixer was used for 10 min to 0021-9797/00 $35.00
C 2000 by Academic Press Copyright ° All rights of reproduction in any form reserved.
remove undeveloped AgBr. Last, the coating layer on the film was rinsed with deionized water at 40◦ C, collected into test tubes, and then centrifuged. This centrifugation step was repeated four times at 40◦ C to remove all superfluous gelatin, yielding a pure silver nanowire deposit. A few drops of deionized water were then added to produce an aqueous suspension.
2. Preparation of ACNTs A collodion film was prepared on a small piece of glass and then dried. A few drops of aqueous silver nanowire suspension were placed onto the film. Silver nanowires were then replicated via carbon evaporation. A high-vacuum evaporator (HITACH Hus5GB) was employed in this process. The evaporated carbon formed the wall of the ACNT. The sample containing ACNT was cut into small squares and dipped into a fixing bath composed of Na2 SO3 (anhydrous) 10 g, Na2 S2 O3 · 5H2 O 250 g, and deionized water added up to 1000 ml. The solution was agitated slightly. During this step, the sample pieces separated from the glass base and floated in solution. The collodion was removed in ethyl alcohol, and the film pieces were once again immersed in the fixing bath. After 3–5 h, the film pieces were transferred to a copper grid lacking carbon film for TEM and HREM analysis. The instruments used here were an HITACH-800 transmission electron microscope and a JEOL-2010 high-resolution transmission electron microscope.
RESULTS AND DISCUSSION Figure 1 shows the electron micrograph of silver nanowire templates. The average nanowire is about 25 nm in diameter and several micrometers in length. Following the carbon replica method and more than 5 h of fixation, the empty carbon nanotube appeared in exactly the same shape as the silver nanowires which had formed prior to the fixation step. We noticed greatly reduced silver nanowire diameters following different fixation times. In the case of a 3-h fixation, some ACNTs contained the modified thinner silver filaments (see Fig. 2). HREM was used for observation of the fine structure of ACNT walls. The inset in Fig. 2 shows an HREM image of an ACNT wall which lacks fringes for a crystalline but only contains some disordered fine carbon grains. A selected area electron diffraction (SAED) of the empty part of an ACNT demonstrates a diffuse ring pattern characteristic of amorphous materials (see Fig. 3). These two results confirm that the ACNT is composed completely of amorphous carbon rather than graphite. The string seen in Fig. 2 is a postfixation silver nanowire whose diameter is less than 10 nm. Subsequently, a high-resolution transmission electron microscope (HREM) was employed to observe the fine structures of the string. Figure 4 shows the fine structure of the string within the ACNT. It has a diameter of only 4 nm and is much thinner than it was originally. In this picture, the nanocrystal lattice fringes are spaced apart from each other by 0.236 and 0.204 nm. These
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LETTER TO THE EDITOR
255
FIG. 3. A selected area electron diffraction (SAED) of the empty part of an ACNT shows a series of diffuse rings.
FIG. 1. TEM photo of silver nanowires formed after development of silver halide crystals for 8 min. The diameter of the nanowires is about 25 nm and the length is several micrometers.
findings are in agreement with the (111) and (200) planes of silver crystalline, respectively. Obviously, the size and shape of the ACNT depend on the original silver filament. Due to interspaces present among carbon grains in the wall of the nanotube, the wall can act as a permeable membrane that allows reactants to pass through freely. Therefore, the silver nanowires in the ACNTs were eroded gradually by Na2 S2 O3 during fixation. This reaction can be written as in Eq. [1].
FIG. 2. TEM photo after sample was developed for 8 min, replicated, and then fixed for 3 h. Amorphous carbon nanotubes containing thin strings can be seen. Inset shows an HREM image of the ACNT wall.
If KCN was used instead of Na2 S2 O3 , empty ACNTs appeared quickly because CN− reacts more strongly than S2 O− 3 with silver: 3− 4Ag + 8S2 O2− + 4OH− . 3 + O2 + 2H2 O = 4[Ag(S2 O3 )2 ]
[1]
It is particularly interesting that the nanowires can be modified through the wall of the ACNT by chemical species in solution. We think it is likely that this method can also be used to cast nanomaterials of various form from replicated ACNTs. We anticipate that ACNTs will prove of benefit to the field of nanotechnology in the preparation and modification of many kinds of nanoscale filaments.
FIG. 4. The HREM photo of “thin string” in the ACNT. The strings formed after extended fixation are much thinner than the original nanowire.
256
LETTER TO THE EDITOR
ACKNOWLEDGMENTS
11. Liu, S. W., Yue, J., Fu, S. L., and Kobayashi, H., Imag. Sci. J. 46, 69 (1998).
The authors acknowledge Professor Shuyuan Zhang for his assistance on HREM. The research was supported by the Chinese Academy of Sciences and the Natural Science Foundation of China (NNSFC 29743002).
Suwen Liu*,1 Jun Yue* Tanhong Cai* Karen L. Anderson†
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Iijima, S., Nature 354, 56 (1991). Ebbesen, T. W., and Ajayan, P. M., Nature 358, 220 (1991). Ebbesen, T. W., Phys. Today 49, 26 (1996). Treacy, M. M. J., Ebbesen, T. W., and Gibbson, J. M., Nature 381, 678 (1996). De Heer, W. A., Chatelian, A., and Ugarte, J. M., Science 270, 1179 (1996). Service, R. F., Science 271, 1232 (1996). Ruoff, R. S., Nature 372, 731 (1994). Ugarte, D., Chatelian, A., and de Heer, W. A., Science 274, 1897 (1996). Han, W. G., Fan, S. S., Li, Q. Q., and Hu, Y. D., Science 277, 1287 (1997). Sloan, J., Wright, D. M., Woo, H.-G., Bailey, S., et al., Chem. Commun., 699 (1999).
* Department of Applied Chemistry University of Science and Technology of China Hefei, Anhui 230026 People’s Republic of China †Department of Life Sciences Bar-Ilan University Ramat-Gan 52900 Israel Received December 10, 1999; accepted March 13, 2000
1 To
whom correspondence should be addressed.
LETTER TO THE EDITOR Silver Nanowires as Templates for Preparation of Amorphous Carbon Nanotubes
In this report, we describe a novel method for preparing amorphous carbon nanotubes (ACNT) from silver nanowires using a carbon replica technique. ACNT size and shape are determined by the template silver nanowire. Interspaces between carbon grains present in the ACNT wall cause the wall to act as a permeable membrane through which reactants pass freely. Simple chemical modifications can be used to modify the diameter of the silver filaments within. We anticipate that this method will prove useful in preparing a wide variety of nanometer-sized filaments, perhaps with the replica itself able to serve as a template in casting nanomaterials of assorted shapes. °C 2000 Academic Press Key Words: amorphous carbon; nanotubes; silver nanowires.
Carbon nanotubes (1, 2) are generating much interest because of their potential applications in high-performance nanoscale materials (3, 4) and electronic devices (5, 6). Strong interest in carbon nanotubes first emerged in the nanotechnology (7) field when it was shown that different kinds of materials with potentially interesting properties can be inserted into the core volumes of nanotubes. The inner cavities of carbon nanotubes can also serve as nanoscale test tubes and templates (8–10) or be utilized for controlled production of encapsulated nanostructures. However, problems remain to be solved, such as the controlled filling of the tubes and the modification of materials in the carbon nanotubes. In the production of fullerene nanotubes, it is problematic that amorphous carbon always appears. However, if a nanotube is composed completely of amorphous carbon, the tube manifests wholly different properties. In this report, we describe a method for the preparation of such amorphous carbon nanotubes (ACNTs). Silver nanowires serve as templates in a carbon replica technique. Amorphous carbon nanotubes are produced. The ACNT wall acts as a permeable membrane which permits reactants to pass through freely. When nanometersized filaments are encapsulated in the tubes, they can easily be modified by chemical reaction in solution.
EXPERIMENTAL
1. The Growth of Silver Nanowire Templates Silver nanowires were prepared to serve as templates of ACNTs. For this, a photographic emulsion of AgBr (11) was used to coat a film. This film was exposed for 5 s to fluorescent light. Dilute D-76 developer (1/20 concentration) was used to develop the film for 8 min, and F-11 fixer was used for 10 min to 0021-9797/00 $35.00
C 2000 by Academic Press Copyright ° All rights of reproduction in any form reserved.
remove undeveloped AgBr. Last, the coating layer on the film was rinsed with deionized water at 40◦ C, collected into test tubes, and then centrifuged. This centrifugation step was repeated four times at 40◦ C to remove all superfluous gelatin, yielding a pure silver nanowire deposit. A few drops of deionized water were then added to produce an aqueous suspension.
2. Preparation of ACNTs A collodion film was prepared on a small piece of glass and then dried. A few drops of aqueous silver nanowire suspension were placed onto the film. Silver nanowires were then replicated via carbon evaporation. A high-vacuum evaporator (HITACH Hus5GB) was employed in this process. The evaporated carbon formed the wall of the ACNT. The sample containing ACNT was cut into small squares and dipped into a fixing bath composed of Na2 SO3 (anhydrous) 10 g, Na2 S2 O3 · 5H2 O 250 g, and deionized water added up to 1000 ml. The solution was agitated slightly. During this step, the sample pieces separated from the glass base and floated in solution. The collodion was removed in ethyl alcohol, and the film pieces were once again immersed in the fixing bath. After 3–5 h, the film pieces were transferred to a copper grid lacking carbon film for TEM and HREM analysis. The instruments used here were an HITACH-800 transmission electron microscope and a JEOL-2010 high-resolution transmission electron microscope.
RESULTS AND DISCUSSION Figure 1 shows the electron micrograph of silver nanowire templates. The average nanowire is about 25 nm in diameter and several micrometers in length. Following the carbon replica method and more than 5 h of fixation, the empty carbon nanotube appeared in exactly the same shape as the silver nanowires which had formed prior to the fixation step. We noticed greatly reduced silver nanowire diameters following different fixation times. In the case of a 3-h fixation, some ACNTs contained the modified thinner silver filaments (see Fig. 2). HREM was used for observation of the fine structure of ACNT walls. The inset in Fig. 2 shows an HREM image of an ACNT wall which lacks fringes for a crystalline but only contains some disordered fine carbon grains. A selected area electron diffraction (SAED) of the empty part of an ACNT demonstrates a diffuse ring pattern characteristic of amorphous materials (see Fig. 3). These two results confirm that the ACNT is composed completely of amorphous carbon rather than graphite. The string seen in Fig. 2 is a postfixation silver nanowire whose diameter is less than 10 nm. Subsequently, a high-resolution transmission electron microscope (HREM) was employed to observe the fine structures of the string. Figure 4 shows the fine structure of the string within the ACNT. It has a diameter of only 4 nm and is much thinner than it was originally. In this picture, the nanocrystal lattice fringes are spaced apart from each other by 0.236 and 0.204 nm. These
254
LETTER TO THE EDITOR
255
FIG. 3. A selected area electron diffraction (SAED) of the empty part of an ACNT shows a series of diffuse rings.
FIG. 1. TEM photo of silver nanowires formed after development of silver halide crystals for 8 min. The diameter of the nanowires is about 25 nm and the length is several micrometers.
findings are in agreement with the (111) and (200) planes of silver crystalline, respectively. Obviously, the size and shape of the ACNT depend on the original silver filament. Due to interspaces present among carbon grains in the wall of the nanotube, the wall can act as a permeable membrane that allows reactants to pass through freely. Therefore, the silver nanowires in the ACNTs were eroded gradually by Na2 S2 O3 during fixation. This reaction can be written as in Eq. [1].
FIG. 2. TEM photo after sample was developed for 8 min, replicated, and then fixed for 3 h. Amorphous carbon nanotubes containing thin strings can be seen. Inset shows an HREM image of the ACNT wall.
If KCN was used instead of Na2 S2 O3 , empty ACNTs appeared quickly because CN− reacts more strongly than S2 O− 3 with silver: 3− 4Ag + 8S2 O2− + 4OH− . 3 + O2 + 2H2 O = 4[Ag(S2 O3 )2 ]
[1]
It is particularly interesting that the nanowires can be modified through the wall of the ACNT by chemical species in solution. We think it is likely that this method can also be used to cast nanomaterials of various form from replicated ACNTs. We anticipate that ACNTs will prove of benefit to the field of nanotechnology in the preparation and modification of many kinds of nanoscale filaments.
FIG. 4. The HREM photo of “thin string” in the ACNT. The strings formed after extended fixation are much thinner than the original nanowire.
256
LETTER TO THE EDITOR
ACKNOWLEDGMENTS
11. Liu, S. W., Yue, J., Fu, S. L., and Kobayashi, H., Imag. Sci. J. 46, 69 (1998).
The authors acknowledge Professor Shuyuan Zhang for his assistance on HREM. The research was supported by the Chinese Academy of Sciences and the Natural Science Foundation of China (NNSFC 29743002).
Suwen Liu*,1 Jun Yue* Tanhong Cai* Karen L. Anderson†
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Iijima, S., Nature 354, 56 (1991). Ebbesen, T. W., and Ajayan, P. M., Nature 358, 220 (1991). Ebbesen, T. W., Phys. Today 49, 26 (1996). Treacy, M. M. J., Ebbesen, T. W., and Gibbson, J. M., Nature 381, 678 (1996). De Heer, W. A., Chatelian, A., and Ugarte, J. M., Science 270, 1179 (1996). Service, R. F., Science 271, 1232 (1996). Ruoff, R. S., Nature 372, 731 (1994). Ugarte, D., Chatelian, A., and de Heer, W. A., Science 274, 1897 (1996). Han, W. G., Fan, S. S., Li, Q. Q., and Hu, Y. D., Science 277, 1287 (1997). Sloan, J., Wright, D. M., Woo, H.-G., Bailey, S., et al., Chem. Commun., 699 (1999).
* Department of Applied Chemistry University of Science and Technology of China Hefei, Anhui 230026 People’s Republic of China †Department of Life Sciences Bar-Ilan University Ramat-Gan 52900 Israel Received December 10, 1999; accepted March 13, 2000
1 To
whom correspondence should be addressed.