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Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces
DIAMAT-06498; No of Pages 5 Diamond & Related Materials xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond
Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces Kun'ichi Miyazawa a,⁎, Shuichi Shimomura b, Takatsugu Wakahara a, Masaru Tachibana c a b c
Fullerene Engineering Group, Materials Processing Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan Carbon Composite Materials Group, Materials Processing Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan Department of Materials System Science, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027, Japan
a r t i c l e
i n f o
Article history: Received 7 October 2015 Received in revised form 25 October 2015 Accepted 27 October 2015 Available online xxxx Keywords: C60 microtube AAO Vertical growth DLLIP TEM Fullerene nanowhisker
a b s t r a c t C60 microtubes (C60MTs) were vertically grown on an AAO membrane, and the joint interfaces between the C60MTs and the AAO membrane were investigated by FIB-SEM and TEM for the first time. No cracking was observed along the joint interfaces between the C60MTs and the AAO membrane. C60 nanowhiskers were found to continuously grow into the alumina nanotubes of the AAO membrane from the bottom of the C60MTs, indicating strong bonding between the AAO membrane and the C60MTs. © 2015 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
C60 microtubes (C60MTs) are tubular needle-like crystals composed of C60 molecules, and they have diameters that are greater than 1 μm. C60MTs can be vertically grown on anodic aluminum oxide (AAO) membranes using the diaphragm liquid–liquid interfacial precipitation method (DLLIP method) [1–3]. In the DLLIP method, C60MTs can be synthesized by slowly injecting isopropyl alcohol (IPA) through an AAO membrane into a C60-saturated toluene solution. The vertically grown C60MTs can reach lengths of 500 μm [1]. The AAO membranes are composed of ordered alumina nanotubes, and can be formed by anodizing aluminum thin foils in suitable acidic media such as oxalic acid, phosphoric acid and sulfuric acid [4,5]. In our previous paper [2], very good wettability was observed between the formed C60 nuclei and the AAO membrane as a result of the DLLIP process. A longitudinal section of the C60MT-AAO joint interface prepared by a focused ion beam (FIB) system was examined by scanning electron microscopy (SEM) and showed no cracks along the joint interface [2]; however, details of this interface were not presented. Hence, the current paper seeks to further investigate the microstructure of C60MT-AAOs by preparing longitudinal sections of the joint interface for transmission electron microscopy (TEM) and to discuss the joining mechanism between the C60MTs and the AAO membrane.
C60MTs synthesized in our previous paper [2] were used in the present research. An AAO membrane (Whatman Anodisc, 25-mm diameter, USA) with vertically grown C60MTs was mounted on the aluminum stage of an FIB system (FIB-SEM, Hitachi NB5000, Japan) equipped with a Ga source, side-entry goniometer stage, SEM and energy dispersive X-ray spectroscopy system (EDX, Bruker QUANTAX, USA). The acceleration voltage of the Ga ion beam was set at 40 kV. Next, thin plates containing C60MT-AAO membrane joints were cut out of the specimen by a Ga ion beam and then mounted on a halfmoon-shaped copper mesh of the side entry goniometer stage, using a molybdenum probe, where the thin plates were further milled by the Ga ion beam into thin foils. Tungsten deposition was used to affix the thin plate specimens to the copper mesh and to protect the upper surface of the specimens. The prepared thin foil specimens were observed by the FIB-SEM and a transmission electron microscope (TEM, JEM4010, JEOL, Japan) with an acceleration voltage of 400 kV.
⁎ Corresponding author. E-mail address: [email protected] (K. Miyazawa).
3. Results and discussion A SEM image of the AAO membrane that was used to synthesize the vertically grown C60MTs is shown in Fig. 1(a). The pores of AAO membrane were approximated by ellipses, and the size distribution of
http://dx.doi.org/10.1016/j.diamond.2015.10.027 0925-9635/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: K. Miyazawa, et al., Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces, Diamond Relat. Mater. (2015), http://dx.doi.org/10.1016/j.diamond.2015.10.027
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K. Miyazawa et al. / Diamond & Related Materials xxx (2015) xxx–xxx
Fig. 1. SEM image of the AAO membrane used in the present experiment, (b) pore diameter distribution for the enclosed rectangular area in (a), and (c) the scheme used to calculate the wall thickness of alumina nanotubes in the AAO membrane.
Fig. 2. SEM images of (a) fractured C60MTs grown on an AAO membrane, (b) an enlarged image of the fractured C60MTs remaining on an AAO membrane, and (c) a fractured C60MT with a lower cup-shaped fracture surface and an upper cone-shaped fracture surface.
pores in the rectangular area enclosed by the white lines was obtained as shown in Fig. 1(b), where the diameter of a pore was calculated as the geometric mean of the major axis and the minor axis of the pore. The average diameter of the 207 pores of Fig. 1(a) was calculated to be 218 ± 46 nm. Further, the average thickness T of pore walls was calculated by using the hexagonal close-packed structure model of Fig. 1(c) for the two-dimensional pore arrays. The side length E of the regular hexagons was calculated using the average area occupied by one hexagon that can be known from the number of pores contained in the rectangular area. As the result, the value of T was calculated to be 110 nm. Fig. 2(a) presents a SEM image of the C60MTs that were artificially fractured using sharp tweezers. As shown in the magnified image of Fig. 2(b), the fracture occurred within the body of the C60MTs and not at the joint interface. Fig. 2(c) displays a C60MT exhibiting a set of cupshaped fractures on the bottom surface and a cone-shaped upper
fracture surface. For the case shown in Fig. 2(b), the fracture arose in the body of the C60MT, and these observations show that the C60MTs and the AAO membrane form strong bonded joint interfaces. To elucidate the bonding mechanism, longitudinal sections of the C60MT-AAO membrane joint interfaces were prepared by FIB-SEM. Fig. 3 shows the longitudinal sections of eight different C60MT-AAO membrane joints that were mounted on the edge of a half-moonshaped copper mesh, where only one section was removed from each C60MT-AAO joint. The images show the thin foils after thinning by FIB-SEM. Fig. 4 displays enlarged SEM images of the thin foil samples that are shown in Fig. 3; each image in Fig. 4 corresponds to the sample with the same label in Fig. 3. Although Fig. 4(d, e, h) have no open cracks on the side of C60, Fig. 4(a, b, c, f, g) shows vertical cracks. It is believed that those cracks were formed by the finite surface tension of thin foils during the thinning process. However, there is also a possibility that
Fig. 3. SEM images of the longitudinal thin foil sections cut out of eight different C60MT-AAO membrane joints and mounted on the edge of a half-moon-shaped copper mesh.
Please cite this article as: K. Miyazawa, et al., Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces, Diamond Relat. Mater. (2015), http://dx.doi.org/10.1016/j.diamond.2015.10.027
K. Miyazawa et al. / Diamond & Related Materials xxx (2015) xxx–xxx
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Fig. 4. Enlarged SEM images of the cross-sections shown in Fig. 3. The surfaces of the specimens were coated with a thin film of tungsten for protection during the FIB thinning process.
the cracks are inherent to the C60MTs because similar features were observed running along the growth axis of the C60MTs from our previous paper [2]. Fig. 5(a) presents a SEM image of a joint interface. No cracking is observed along the joint interface. The vertical long holes that are marked by 1, 2 and 3 were opened by the thinning process using the Ga ion beam. The outer diameter, d, of the alumina nanotube is shown to be 253 nm. Fig. 5(b), (c) and (d) displays the EDX maps for carbon (C), aluminum (Al) and oxygen (O), respectively. The columnar distributions of Al and O for the AAO membrane are observed at the lower side of the specimen. Although a uniform distribution of C is observed on the side of the C60MT, columnar distributions of C
are also observed on the side of the AAO membrane, suggesting that C60 molecules diffused into the alumina nanotubes during the DLLIP process. The thin foils were characterized by TEM, and Fig. 6(a) shows a cross-sectional image of a C60MT–AAO membrane joint interface. Although the crack indicated by the white arrow is obliquely running toward the joint interface, no cracking along the joint interface is observed. It is surprising that fine needles of C60 (C60 nanowhiskers, C60NWs) continuously grow into the alumina nanotubes across the joint interface, which is suggested by the EDX image of Fig. 5(b). C60NW and the wall of an alumina nanotube are indicated by the red arrows in Fig. 6(a).
Fig. 5. (a) SEM image of a thin foil cut out of a C60MT–AAO membrane joint. SEM–EDX analyses for (b) carbon, (c) aluminum and (d) oxygen.
Please cite this article as: K. Miyazawa, et al., Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces, Diamond Relat. Mater. (2015), http://dx.doi.org/10.1016/j.diamond.2015.10.027
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K. Miyazawa et al. / Diamond & Related Materials xxx (2015) xxx–xxx
Fig. 6. (a) Cross-sectional TEM image of a C60MT-AAO joint interface and (b) magnified region of (a).
In the vicinity of the joint interface (marked by 1), the C60 matrix is observed to be well bonded to the wall of the alumina nanotube (Fig. 6(b)). However, it is found that the C60NW is not attached to the wall of alumina nanotube at location 2. This observation reveals that the adhesive force between the C60MT and the AAO membrane is mainly generated in the regions where the surface of the C60NWs and the wall of alumina nanotubes are in intimate contact. This interpenetrating structure between the C60NWs and the alumina nanotubes must form strong C60MT–AAO joint interfaces. The C60MT–AAO joint interface was further investigated by TEM at higher magnifications. Fig. 7(a) shows a TEM image for a C60MT–AAO joint interface, which is indicated by the red dashed line. It is clear that the matrix of the C60MT was heavily damaged by the Ga ion beam milling and the high energy electron beam from TEM. Literature [6] informs that the final polishing using Ga ion beams with energies down to 1–2 keV is recommended in order to remove the damaged zones of specimens. However, the fast Fourier transform (FFT) patterns of Fig. 7(c) and (e) for rectangular regions 1 and 2 (Fig. 7(a)) indicate
that the remaining intact structures are crystalline, as evidenced by the appearance of dotted patterns. The rectangular region 2 marks a part of a C60NW that grew into the AAO membrane. Fig. 7(b) and (d) are partially enlarged images of rectangular regions 1 and 2. The FFT patterns of (c) and (e) could be indexed as the face-centered cubic (fcc) structure of C60 with lattice constant a = 1.38 ± 0.02 nm, which is 2.8% shorter than the lattice constant a = 1.4166 nm of pristine C60 [7]. The reduced lattice constant was likely caused by electron beam-induced polymerization during the TEM observation [8,9]. The 220 dots in the FFT patterns suggest that the growth axis of the C60MT is along the [1 1 0] close-packed direction and that the C60 crystal grew in the same direction across the C60MT–AAO joint interface. Fig. 8 (a) displays the head of a C60NW growing into an alumina nanotube. Although the magnified image of the rectangular region 1 (Fig. 8(b)) indicates that the C60NW was heavily damaged by the FIB thinning process and the TEM electron beam irradiation, the FFT (Fig. 8(c)) presents a dotted pattern showing the crystalline nature of the intact structure. These data reveal that the growth direction of the
Fig. 7. TEM images for the area containing the C60MT–AAO joint interface indicated by the red dashed line. The FFT patterns (c) and (e) are from rectangular regions 1 and 2 of image (a), respectively. Images (b) and (d) are the partially enlarged images of areas 1 and 2, respectively.
Please cite this article as: K. Miyazawa, et al., Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces, Diamond Relat. Mater. (2015), http://dx.doi.org/10.1016/j.diamond.2015.10.027
K. Miyazawa et al. / Diamond & Related Materials xxx (2015) xxx–xxx
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Fig. 8. (a) TEM image showing the head of a C60NW that grew into an AAO nanotube. The FFT patterns (c) and (e) are from rectangular regions 1 and 2 of (a), respectively. Images (b) and (d) are partially enlarged images of areas 1 and 2, respectively.
C60NW is along the [1 1 0] direction, as is observed in Fig. 7. The magnified image in Fig. 8(d) looks disordered to the eye. The diffuse FFT pattern (Fig. 8(e)) of the TEM image of the rectangular region 2 (Fig. 8(a)) shows that the alumina nanotube has an amorphous structure, as was reported in literature [10,11].
4. Conclusions (1) Longitudinal sections of C60MT–AAO joint interfaces were successfully prepared by FIB-SEM, and the bonding structure of the joint interfaces were clarified by SEM and TEM. (2) C60NWs are observed to grow into the alumina nanotubes along their [1 1 0] close-packed direction, which is the same as the growth direction of the C60MTs. (3) Strong bonding forces at the C60MT–AAO membrane joint interfaces are expected because of the interconnection between the C60NWs and the alumina nanotubes near the C60MT–AAO joint interface.
Prime novelty statement We have revealed the bonding structure between C60 microtube and AAO membrane by using transmission electron microscopy for the first time in the world.
Acknowledgments Portions of this research were supported by the Center of Materials Research for Low Carbon Emission (MEXT, Japan) and JSPS KAKENHI Grant number 26600007. References [1] S.I. Cha, K. Miyazawa, J.-D. Kim, Vertically well-aligned C60 microtube crystal array prepared using solution-based one-step process, Chem. Mater. 20 (2008) 1667–1669. [2] K. Miyazawa, R. Kuriyama, S. Shimomura, T. Wakahara, M. Tachibana, Growth and FIB-SEM analyses of C60 microtubes vertically synthesized on porous alumina membranes, J. Cryst. Growth 388 (2014) 5–11. [3] K. Miyazawa, Y. Kuwasaki, A. Obayashi, M. Kuwabara, C60 nanowhiskers formed by the liquid–liquid interfacial precipitation method, J. Mater. Res. 17 (2002) 83–88. [4] G.E.J. Poinern, N. Ali, D. Fawcett, Progress in nano-engineered anodic aluminum oxide membrane development, Materials 4 (2011) 487–526. [5] N. Taşaltin, S. Öztürk, H. Yüzer, Z.Z. Öztürk, Simple fabrication of highly ordered AAO nanotubes, J. Optoelectron. Biomed. Mater. 1 (2009) 79–84. [6] J. Mayer, L.A. Giannuzzi, T. Kamino, J. Michael, TEM sample preparation and FIBinduced damage, MRS Bull. 32 (2007) 400–407. [7] D. McCready, M. Alnajjar, Powder Diffraction File No. 44–558, International Centre for Diffraction Data, Newton Square, PA, 1994. [8] K. Miyazawa, J. Minato, M. Fujino, T. Suga, Structural investigation of heat-treated fullerene nanotubes and nanowhiskers, Diam. Relat. Mater. 15 (2006) 1143–1146. [9] M. Nakaya, T. Nakayama, M. Aono, Fabrication and electron-beam-induced polymerization of C60 nanoribbon, Thin Solid Films 464-465 (2004) 327–330. [10] J.W. Diggle, T.C. Downie, C.W. Goulding, Anodic oxide films on aluminum, Chem. Rev. 69 (1969) 365–405. [11] F. Le Coz, L. Arurault, S. Fontorbes, V. Vilar, L. Datas, P. Winterton, Chemical composition and structural changes of porous templates obtained by anodising aluminium in phosphoric acid electrolyte, Surf. Interface Anal. 42 (2010) 227–233.
Please cite this article as: K. Miyazawa, et al., Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces, Diamond Relat. Mater. (2015), http://dx.doi.org/10.1016/j.diamond.2015.10.027
Contents lists available at ScienceDirect
Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond
Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces Kun'ichi Miyazawa a,⁎, Shuichi Shimomura b, Takatsugu Wakahara a, Masaru Tachibana c a b c
Fullerene Engineering Group, Materials Processing Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan Carbon Composite Materials Group, Materials Processing Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan Department of Materials System Science, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027, Japan
a r t i c l e
i n f o
Article history: Received 7 October 2015 Received in revised form 25 October 2015 Accepted 27 October 2015 Available online xxxx Keywords: C60 microtube AAO Vertical growth DLLIP TEM Fullerene nanowhisker
a b s t r a c t C60 microtubes (C60MTs) were vertically grown on an AAO membrane, and the joint interfaces between the C60MTs and the AAO membrane were investigated by FIB-SEM and TEM for the first time. No cracking was observed along the joint interfaces between the C60MTs and the AAO membrane. C60 nanowhiskers were found to continuously grow into the alumina nanotubes of the AAO membrane from the bottom of the C60MTs, indicating strong bonding between the AAO membrane and the C60MTs. © 2015 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
C60 microtubes (C60MTs) are tubular needle-like crystals composed of C60 molecules, and they have diameters that are greater than 1 μm. C60MTs can be vertically grown on anodic aluminum oxide (AAO) membranes using the diaphragm liquid–liquid interfacial precipitation method (DLLIP method) [1–3]. In the DLLIP method, C60MTs can be synthesized by slowly injecting isopropyl alcohol (IPA) through an AAO membrane into a C60-saturated toluene solution. The vertically grown C60MTs can reach lengths of 500 μm [1]. The AAO membranes are composed of ordered alumina nanotubes, and can be formed by anodizing aluminum thin foils in suitable acidic media such as oxalic acid, phosphoric acid and sulfuric acid [4,5]. In our previous paper [2], very good wettability was observed between the formed C60 nuclei and the AAO membrane as a result of the DLLIP process. A longitudinal section of the C60MT-AAO joint interface prepared by a focused ion beam (FIB) system was examined by scanning electron microscopy (SEM) and showed no cracks along the joint interface [2]; however, details of this interface were not presented. Hence, the current paper seeks to further investigate the microstructure of C60MT-AAOs by preparing longitudinal sections of the joint interface for transmission electron microscopy (TEM) and to discuss the joining mechanism between the C60MTs and the AAO membrane.
C60MTs synthesized in our previous paper [2] were used in the present research. An AAO membrane (Whatman Anodisc, 25-mm diameter, USA) with vertically grown C60MTs was mounted on the aluminum stage of an FIB system (FIB-SEM, Hitachi NB5000, Japan) equipped with a Ga source, side-entry goniometer stage, SEM and energy dispersive X-ray spectroscopy system (EDX, Bruker QUANTAX, USA). The acceleration voltage of the Ga ion beam was set at 40 kV. Next, thin plates containing C60MT-AAO membrane joints were cut out of the specimen by a Ga ion beam and then mounted on a halfmoon-shaped copper mesh of the side entry goniometer stage, using a molybdenum probe, where the thin plates were further milled by the Ga ion beam into thin foils. Tungsten deposition was used to affix the thin plate specimens to the copper mesh and to protect the upper surface of the specimens. The prepared thin foil specimens were observed by the FIB-SEM and a transmission electron microscope (TEM, JEM4010, JEOL, Japan) with an acceleration voltage of 400 kV.
⁎ Corresponding author. E-mail address: [email protected] (K. Miyazawa).
3. Results and discussion A SEM image of the AAO membrane that was used to synthesize the vertically grown C60MTs is shown in Fig. 1(a). The pores of AAO membrane were approximated by ellipses, and the size distribution of
http://dx.doi.org/10.1016/j.diamond.2015.10.027 0925-9635/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: K. Miyazawa, et al., Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces, Diamond Relat. Mater. (2015), http://dx.doi.org/10.1016/j.diamond.2015.10.027
2
K. Miyazawa et al. / Diamond & Related Materials xxx (2015) xxx–xxx
Fig. 1. SEM image of the AAO membrane used in the present experiment, (b) pore diameter distribution for the enclosed rectangular area in (a), and (c) the scheme used to calculate the wall thickness of alumina nanotubes in the AAO membrane.
Fig. 2. SEM images of (a) fractured C60MTs grown on an AAO membrane, (b) an enlarged image of the fractured C60MTs remaining on an AAO membrane, and (c) a fractured C60MT with a lower cup-shaped fracture surface and an upper cone-shaped fracture surface.
pores in the rectangular area enclosed by the white lines was obtained as shown in Fig. 1(b), where the diameter of a pore was calculated as the geometric mean of the major axis and the minor axis of the pore. The average diameter of the 207 pores of Fig. 1(a) was calculated to be 218 ± 46 nm. Further, the average thickness T of pore walls was calculated by using the hexagonal close-packed structure model of Fig. 1(c) for the two-dimensional pore arrays. The side length E of the regular hexagons was calculated using the average area occupied by one hexagon that can be known from the number of pores contained in the rectangular area. As the result, the value of T was calculated to be 110 nm. Fig. 2(a) presents a SEM image of the C60MTs that were artificially fractured using sharp tweezers. As shown in the magnified image of Fig. 2(b), the fracture occurred within the body of the C60MTs and not at the joint interface. Fig. 2(c) displays a C60MT exhibiting a set of cupshaped fractures on the bottom surface and a cone-shaped upper
fracture surface. For the case shown in Fig. 2(b), the fracture arose in the body of the C60MT, and these observations show that the C60MTs and the AAO membrane form strong bonded joint interfaces. To elucidate the bonding mechanism, longitudinal sections of the C60MT-AAO membrane joint interfaces were prepared by FIB-SEM. Fig. 3 shows the longitudinal sections of eight different C60MT-AAO membrane joints that were mounted on the edge of a half-moonshaped copper mesh, where only one section was removed from each C60MT-AAO joint. The images show the thin foils after thinning by FIB-SEM. Fig. 4 displays enlarged SEM images of the thin foil samples that are shown in Fig. 3; each image in Fig. 4 corresponds to the sample with the same label in Fig. 3. Although Fig. 4(d, e, h) have no open cracks on the side of C60, Fig. 4(a, b, c, f, g) shows vertical cracks. It is believed that those cracks were formed by the finite surface tension of thin foils during the thinning process. However, there is also a possibility that
Fig. 3. SEM images of the longitudinal thin foil sections cut out of eight different C60MT-AAO membrane joints and mounted on the edge of a half-moon-shaped copper mesh.
Please cite this article as: K. Miyazawa, et al., Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces, Diamond Relat. Mater. (2015), http://dx.doi.org/10.1016/j.diamond.2015.10.027
K. Miyazawa et al. / Diamond & Related Materials xxx (2015) xxx–xxx
3
Fig. 4. Enlarged SEM images of the cross-sections shown in Fig. 3. The surfaces of the specimens were coated with a thin film of tungsten for protection during the FIB thinning process.
the cracks are inherent to the C60MTs because similar features were observed running along the growth axis of the C60MTs from our previous paper [2]. Fig. 5(a) presents a SEM image of a joint interface. No cracking is observed along the joint interface. The vertical long holes that are marked by 1, 2 and 3 were opened by the thinning process using the Ga ion beam. The outer diameter, d, of the alumina nanotube is shown to be 253 nm. Fig. 5(b), (c) and (d) displays the EDX maps for carbon (C), aluminum (Al) and oxygen (O), respectively. The columnar distributions of Al and O for the AAO membrane are observed at the lower side of the specimen. Although a uniform distribution of C is observed on the side of the C60MT, columnar distributions of C
are also observed on the side of the AAO membrane, suggesting that C60 molecules diffused into the alumina nanotubes during the DLLIP process. The thin foils were characterized by TEM, and Fig. 6(a) shows a cross-sectional image of a C60MT–AAO membrane joint interface. Although the crack indicated by the white arrow is obliquely running toward the joint interface, no cracking along the joint interface is observed. It is surprising that fine needles of C60 (C60 nanowhiskers, C60NWs) continuously grow into the alumina nanotubes across the joint interface, which is suggested by the EDX image of Fig. 5(b). C60NW and the wall of an alumina nanotube are indicated by the red arrows in Fig. 6(a).
Fig. 5. (a) SEM image of a thin foil cut out of a C60MT–AAO membrane joint. SEM–EDX analyses for (b) carbon, (c) aluminum and (d) oxygen.
Please cite this article as: K. Miyazawa, et al., Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces, Diamond Relat. Mater. (2015), http://dx.doi.org/10.1016/j.diamond.2015.10.027
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K. Miyazawa et al. / Diamond & Related Materials xxx (2015) xxx–xxx
Fig. 6. (a) Cross-sectional TEM image of a C60MT-AAO joint interface and (b) magnified region of (a).
In the vicinity of the joint interface (marked by 1), the C60 matrix is observed to be well bonded to the wall of the alumina nanotube (Fig. 6(b)). However, it is found that the C60NW is not attached to the wall of alumina nanotube at location 2. This observation reveals that the adhesive force between the C60MT and the AAO membrane is mainly generated in the regions where the surface of the C60NWs and the wall of alumina nanotubes are in intimate contact. This interpenetrating structure between the C60NWs and the alumina nanotubes must form strong C60MT–AAO joint interfaces. The C60MT–AAO joint interface was further investigated by TEM at higher magnifications. Fig. 7(a) shows a TEM image for a C60MT–AAO joint interface, which is indicated by the red dashed line. It is clear that the matrix of the C60MT was heavily damaged by the Ga ion beam milling and the high energy electron beam from TEM. Literature [6] informs that the final polishing using Ga ion beams with energies down to 1–2 keV is recommended in order to remove the damaged zones of specimens. However, the fast Fourier transform (FFT) patterns of Fig. 7(c) and (e) for rectangular regions 1 and 2 (Fig. 7(a)) indicate
that the remaining intact structures are crystalline, as evidenced by the appearance of dotted patterns. The rectangular region 2 marks a part of a C60NW that grew into the AAO membrane. Fig. 7(b) and (d) are partially enlarged images of rectangular regions 1 and 2. The FFT patterns of (c) and (e) could be indexed as the face-centered cubic (fcc) structure of C60 with lattice constant a = 1.38 ± 0.02 nm, which is 2.8% shorter than the lattice constant a = 1.4166 nm of pristine C60 [7]. The reduced lattice constant was likely caused by electron beam-induced polymerization during the TEM observation [8,9]. The 220 dots in the FFT patterns suggest that the growth axis of the C60MT is along the [1 1 0] close-packed direction and that the C60 crystal grew in the same direction across the C60MT–AAO joint interface. Fig. 8 (a) displays the head of a C60NW growing into an alumina nanotube. Although the magnified image of the rectangular region 1 (Fig. 8(b)) indicates that the C60NW was heavily damaged by the FIB thinning process and the TEM electron beam irradiation, the FFT (Fig. 8(c)) presents a dotted pattern showing the crystalline nature of the intact structure. These data reveal that the growth direction of the
Fig. 7. TEM images for the area containing the C60MT–AAO joint interface indicated by the red dashed line. The FFT patterns (c) and (e) are from rectangular regions 1 and 2 of image (a), respectively. Images (b) and (d) are the partially enlarged images of areas 1 and 2, respectively.
Please cite this article as: K. Miyazawa, et al., Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces, Diamond Relat. Mater. (2015), http://dx.doi.org/10.1016/j.diamond.2015.10.027
K. Miyazawa et al. / Diamond & Related Materials xxx (2015) xxx–xxx
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Fig. 8. (a) TEM image showing the head of a C60NW that grew into an AAO nanotube. The FFT patterns (c) and (e) are from rectangular regions 1 and 2 of (a), respectively. Images (b) and (d) are partially enlarged images of areas 1 and 2, respectively.
C60NW is along the [1 1 0] direction, as is observed in Fig. 7. The magnified image in Fig. 8(d) looks disordered to the eye. The diffuse FFT pattern (Fig. 8(e)) of the TEM image of the rectangular region 2 (Fig. 8(a)) shows that the alumina nanotube has an amorphous structure, as was reported in literature [10,11].
4. Conclusions (1) Longitudinal sections of C60MT–AAO joint interfaces were successfully prepared by FIB-SEM, and the bonding structure of the joint interfaces were clarified by SEM and TEM. (2) C60NWs are observed to grow into the alumina nanotubes along their [1 1 0] close-packed direction, which is the same as the growth direction of the C60MTs. (3) Strong bonding forces at the C60MT–AAO membrane joint interfaces are expected because of the interconnection between the C60NWs and the alumina nanotubes near the C60MT–AAO joint interface.
Prime novelty statement We have revealed the bonding structure between C60 microtube and AAO membrane by using transmission electron microscopy for the first time in the world.
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Please cite this article as: K. Miyazawa, et al., Transmission electron microscopy analysis of vertically grown C60 fullerene microtube-AAO membrane joint interfaces, Diamond Relat. Mater. (2015), http://dx.doi.org/10.1016/j.diamond.2015.10.027