- Email: [email protected]
High-resolution transmission electron microscopic and electron diffraction studies of C60 single crystal films before and after electron-beam irradiation
CARBON
8 1 ( 2 0 1 5 ) 8 4 2 –8 4 6
Available at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/carbon
Letter to the Editor
High-resolution transmission electron microscopic and electron diffraction studies of C60 single crystal films before and after electron-beam irradiation Hideki Masuda
a,1
, Jun Onoe
a,* ,
Hidehiro Yasuda
b
a
Research Laboratory for Nuclear Reactors and Department of Nuclear Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8550, Japan b Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
We observed single crystal C60 films before and after 3 kV electron-beam irradiation, using
Received 14 April 2014
high-resolution transmission electron microscopy and electron diffraction (ED). Compari-
Accepted 16 September 2014
son between the experimental and simulated ED patterns demonstrates a mixture of
Available online 28 September 2014
body-centered orthorhombic and hexagonal close packed-monoclinic based one˚ well reprodimensional C60 polymer models with the intermolecular distance of 9.28 A duces the experimental ED results. 2014 Elsevier Ltd. All rights reserved.
Nanocarbon allotropes such as fullerenes, carbon nanotubes (CNTs), and graphenes have been extensively investigated and they exhibit novel properties differing from e.g. diamond and graphite, thus being expected to fabricate electronic devices beyond those based on silicon materials [1]. We found that one-dimensional (1D) uneven peanut-shaped C60 polymer is formed by electron-beam (EB) irradiation of a pristine C60 film [2], and exhibits not only physical properties arising from 1D metal but also the geometrical curvature effects on electronic properties [3], which have been a big puzzle in quantum mechanics since 1950s. Basically, the EB-induced structural transformation of C60 strongly depends on a kinetic energy of incident electrons.
In the case of EB with a high kinetic energy (ca. 100 keV and more), C60 are elastically interacted with incident electrons and thus destroyed to form amorphous carbon [4]. On the other hand, in the case of EB with a low kinetic energy (less than 10 keV), C60 are inelastically interacted with incident electrons and thus sometimes damaged and sometimes polymerized with each other [5,6]. Besides EB incident energy, the interactions with substrates should be considered for a few C60 layers [7]. In our previous work [6], we examined the evolution of infrared (IR) spectra of C60 films with respect to EB irradiation time, using in situ high-resolution IR spectroscopy and firstprinciples density-functional calculations, and found semi-
* Corresponding author: Current address: Department of Physical Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan. E-mail address: [email protected] (J. Onoe). 1 Current address: National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan. http://dx.doi.org/10.1016/j.carbon.2014.09.049 0008-6223/ 2014 Elsevier Ltd. All rights reserved.
CARBON
8 1 (2 0 1 5) 8 4 2–84 6
843
Fig. 1 – Schematic illustration of the 1D uneven peanutshaped C60 polymer (lower) with a cross-linked structure of the P08 C120 isomer (upper) obtained from the general Stone–Wales rearrangement. (A colour version of this figure can be viewed online.)
quantitatively that the 1D uneven peanut-shaped C60 polymer has a waist cross-linked structure close to that of the P08 peanut-shaped C120 isomer (Fig. 1) obtained from the general Stone–Wales transformation. In addition, we examined the dependence of C60 polymerization on an incident energy of EB in the range of 3–7 kV. IR spectra obtained for 5 and 7 kV EB irradiation of C60 films showed the same product as for 3 kV EB irradiation. However, when 5 and 7 kV EBs were continued to irradiate C60 films for a long time after the 1D polymer formation, the 1D peanut-shaped polymer was proceeded not to be 1D polymers with a more coalesced linkage than that of the P08 C120 but to be amorphous carbons [6]. Although we already obtained several facts [8,9] indicating the 1D metallic peanut-shaped C60 polymer as well as Tomonaga–Luttinger liquid behavior [3], we have not obtained the experimental results directly supporting the 1D geometric structure so far. In the present study, we have examined the geometric structure of the C60 polymer single crystal (SC) film formed by EB irradiation of a C60 SC film, using HR transmission electron microscope (TEM) and electron diffraction (ED) in combination with ED simulations of 1D C60 polymer SC models. A C60 SC film (50 nm thick) was formed on a mica substrate (20-mm wide and 30-mm long) at 473 K (±0.1 K) by thermal evaporation of C60 powder (99.98% pure) at 623 K (±0.1 K) in an ultrahigh vacuum (UHV) chamber (base pressure: 10–6 Pa). Thereafter, the C60 SC film was irradiated with 3 kV EB (electron dose: 1.2 · 1018 m 2 s 1) at room temperature. We confirmed that all C60 molecules were completely polymerized, using in situ IR spectroscopy. We next took the film out of the chamber, and then ripped the film off the substrate by putting it into pure water. Subsequently, the film thus ripped was mounted on a copper (Cu) grid, and observed using HRTEM and ED apparatus (Hitachi HF-2000 and H-800, respectively).
Fig. 2 – (a, b) HRTEM images of the pristine and EB-irradiated C60 single crystal films taken at the Scherzer focus condition. Insets show the FFT patterns of individual corresponding HRTEM images. The arrows show the bright spots corresponding to the fringes with a width of 0.9 nm. (c, d) ED patterns of the pristine and EB-irradiated C60 single crystal films. Scale is calibrated with pristine C60 sample. In (c), the two weak spots indicated by E1 and E2 (which correspond to 1/3 and 2/3 of 422 series, respectively) are attributed to twins due to the stacking faults formed on the (1 1 1)FCC surface of the film. (e) Intensity profile of individual ED patterns from the center (S) to the right edge on the [2 2 0]FCC (E) in the red rectangular area shown in (c). Note that the lateral axis denotes a reciprocal space (not indicates the distance in a real space). (A colour version of this figure can be viewed online.)
Since 200 kV EB (electron dose: 1.5 · 1020 m 2 s 1) was focused on the films for HRTEM observation, electron-irradiated damage such as destroy of C60 cage is significantly included in HRTEM images during the observation time. This results in the difficulty of direct observation of 1D peanut-shape structure at this stage. On the contrary, since the ED patterns were recorded by defocusing EB (electron dose: 1.2 · 1019 m 2 s 1) over the whole area of the samples, they remained unchanged during ED measurement time. Fig. 2(a) shows the HRTEM image and fast Fourier-transformed (FFT) pattern of the pristine C60 SC film with the [1 1 1]FCC orientation, though some defects are introduced at the center of the image. Correspondingly, small spots
844
CARBON
8 1 ( 2 0 1 5 ) 8 4 2 –8 4 6
Fig. 3 – (a) FCC (grey) and BCO (red) structural models of C60 single crystal, whereas (b) HCP (grey) and HCP-m (red) models of C60 single crystal. Each blue band line shows the 1D direction of C60–C60 polymerization. (a) We set the 1D C60 polymer along the [ 1 1 0]FCC (in-plane of (1 1 1)FCC). The ˚ lattice constant of the pristine C60 FCC unit cell is a = 14.17 A ˚) [14]. The di between adjacent C60 molecules (10.0 A ˚ judging from the experimental ED decreases to 9.3 A patterns shown in Fig. 2. The BCO model has the lattice ˚ , b = 9.28 A ˚ , and c = 14.17 A ˚, constant of a = 10.02 A ˚, respectively, whereas the HCP-m has that of a = 9.28 A ˚ , and c = 16.36 A ˚ , respectively. (A colour version of b = 9.84 A this figure can be viewed online.)
appeared besides the main spots of 220 series. Fig. 2(b) shows the HRTEM image and FFT pattern of the EB-irradiated C60 SC film. Despite the threefold symmetry disappeared, vertical fringes with an interval of 0.5 nm and horizontal fringes with that of 0.9 nm appeared, which is wider than that of Fig. 2(a). In the FFT pattern of Fig. 2(b), the bright spots shown by arrows appeared at the position corresponding to horizontal wide fringes in the image. Fig. 2(c) shows the ED pattern of the C60 SC film with the [1 1 1]FCC orientation. The weak spots corresponding to twins due to the stacking faults appeared. Fig. 2(d) shows the ED pattern of the EB-irradiated C60 SC film. This pattern shows three new features: (1) the spot of 220 series is still intense and becomes an extended doublet (the extension of the spot along one given direction has been observed for 1D crystal strain [10]), (2) the spot E1 becomes one of the main spots in this pattern, which implies that the crystal structure of the EB-irradiated C60 SC film becomes oriented to both [1 1 1]FCC and [0 0 1]HCP, and (3) each spot becomes an arc-like stretched line with a rotation angle of ca. 9.2, which shows a slight loss of crystal orientation. The intensity profile (see Fig. 2(e)) of both ED patterns esti˚, mated the intermolecular distance di to be 10.0 and 9.3 A ˚ for the 1D C60 polymer is longer respectively. The di of 9.3 A ˚ ) of the P08 C120 isomer. This may be because than that (8.7 A adjacent C60 molecules are pulled to each other on both sides on the contrary to the C120. Although a small peak appeared in the intensity profile of the EB-irradiated C60, it attributes to a part of the broadening of the arc-like spots which correspond to the stacking faults.
Fig. 4 – Schematic illustration of a mixture of BCO and HCP-m structure models for 1D C60 polymer. Colored open circles indicate the positions of C60 molecules. Blue band line shows the 1D direction of C60–C60 polymerization. In the bird’s-eye view, each layer named as A, B, and C is (1 1 1)FCC induced an orientational plane. Each open circle indicates the position of C60 molecules and each blue band shows 1D direction for polymerization. In the bird’s-eye view, one stacking fault is introduced as a BCBC stacking that can be identified to be HCP-m. (A colour version of this figure can be viewed online.)
CARBON
8 1 (2 0 1 5) 8 4 2–84 6
845
˚ (see Fig. 2) on Fig. 5 – Simulated ED patterns of the BCO- (a) and HCP-m- (b) based 1D C60 polymer models with the di of 9.28 A three possible polymerization directions on (1 1 1)FCC. Both models reproduce the doublet spots. (a) BCO model does not reproduce the E1 spots, whereas (b) HCP-m one well reproduces the whole ED pattern.
Given that the polymerization proceeds along one direction in the (1 1 1)FCC plane of the C60 SC film with no stacking faults, the crystal structure should change to body-centered orthorhombic (BCO) structure (see Fig. 3(a)). However, there exists a stacking mismatch of 8% estimated from the two ˚ (pristine) and 9.28 A ˚ (polyexperimental di values of 10.02 A mer). This implies that a stacking fault is induced every 12 BCO layers, which changes the crystal structure to hexagonal close-packed (HCP)-based monoclinic (HCP-m) (see Fig. 3(b)). In fact, the spots indicated by arrows in inset of Fig. 3(b) and labeled as E1 in Fig. 3(d) showed that the BCO contains stacking faults. Fig. 4 shows a mixture model of BCO and HCP-m 1D C60 polymer from several views. The side view indicates that the stacking faults play a role of relaxing the crystal strains generated by polymerization. The top view explains the arclike spot shape by the fluctuation of polymer directions after lattice reconstruction. The orientation slightly changes upon stacking. When C60 molecules in the threefold symmetrical (1 1 1)FCC layer are polymerized to form 1D C60 polymer with ˚ along one direction, the symmetry is broken to di = 9.28 A change the angle between adjacent polymerization directions from 60.00 to 61.87 (shown in layer A of the top view). Therefore, at least five layers should be stacked helically along the same direction in order to obtain the angle distribution of 9.2 for the arc-like spots that are due to the helical stacking of the 1D C60 polymers. Fig. 5 shows the simulated ED patterns of BCO (a) and HCP-m (b) based 1D C60 polymer models with three possible polymerization directions on (1 1 1)FCC, obtained using the QSTEM code [11]. Here, the precision of ED obtained experi˚ , whereas that of ED simulation is 0.01 A ˚. mentally is 0.1 A The BCO model does not reproduce the E1 spots, whereas the HCP-m one well reproduces the whole ED pattern, though both models reproduce the doublet spots. However, since the simulated BCO pattern is completely overlapped with the simulated HCP-m one, it is difficult to exclude the BCO model at this stage.
In summary, we have investigated the structure of pristine and EB-irradiated C60 SC films, using HRTEM and ED, and demonstrated that the mixture of BCO- and HCP-m-based 1D peanut-shaped C60 polymer models with an intermolecu˚ well explain the experimental ED results lar distance of 9.28 A of the EB-irradiated C60 SC film.
Acknowledgments This work was supported both by ‘‘Advanced Characterization Nanotechnology Platform (MEXT)’’ at Osaka University and by the Collaborative Research Fund of J-Power.
R E F E R E N C E S
[1] Guisinger NP, Arnold MS. Beyond silicon: carbon-based nanotechnology. MRS Bull 2010;35(04):273–9. [2] Onoe J, Nakayama T, Aono M, Hara T. Structural and electrical properties of an electron-beam-irradiated C60 film. Appl Phys Lett 2003;82(4):595–7. [3] Onoe J, Ito T, Shima H, Yoshioka H, Kimura S. Observation of Riemannian geometric effects on electronic states. Europhys Lett 2012;98:27001. [4] Seraphin S, Zhou D, Jiao J. Electron-beam-induced structural changes in crystalline C60 and C70. J Mater Res 1993;8(8):1895–9. [5] Zhao YB, Poirier DM, Pechman RJ, Weaver JH. Electron simulated polymerization of solid C60. Appl Phys Lett 1994;64(5):577–9. [6] Takashima A, Nishii T, Onoe J. Formation process and electron-beam incident energy dependence of onedimensional uneven peanut-shaped C60 polymer studied using in situ high-resolution infrared spectroscopy and density-functional calculations. J Phys D Appl Phys 2012;45(48):485302. [7] Hunt MRC, Schmidt J, Palmer RE. Electron-beam damage of C60 films on hydrogen-passivated Si(1 0 0). Appl Phys Lett 1998;72(3):323–5.
846
CARBON
8 1 ( 2 0 1 5 ) 8 4 2 –8 4 6
[8] Toda Y, Ryuzaki S, Onoe J. Femtosecond carrier dynamics in an electron-beam-irradiated C60 film. Appl Phys Lett 2008;92:094102. [9] Onoe J, Takashima A, Toda Y. Infrared phonon anomaly of one-dimensional metallic peanut-shaped C60 polymer. Appl Phys Lett 2010;97:241911. [10] Che J, Burger C, Toki S, Rong L, Hsiao BS, Amnuaypornsri S, et al. Crystal and crystallites structure of natural rubber and
synthetic cis-1,4-polyisoprene by a new two dimensional wide angle X-ray diffraction simulation method. I. Straininduced crystallization. Macromolecules 2013;46(11): 4520–8. [11] Koch C. [Ph.D. thesis]. Arizona State University; 2002.
8 1 ( 2 0 1 5 ) 8 4 2 –8 4 6
Available at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/carbon
Letter to the Editor
High-resolution transmission electron microscopic and electron diffraction studies of C60 single crystal films before and after electron-beam irradiation Hideki Masuda
a,1
, Jun Onoe
a,* ,
Hidehiro Yasuda
b
a
Research Laboratory for Nuclear Reactors and Department of Nuclear Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8550, Japan b Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
We observed single crystal C60 films before and after 3 kV electron-beam irradiation, using
Received 14 April 2014
high-resolution transmission electron microscopy and electron diffraction (ED). Compari-
Accepted 16 September 2014
son between the experimental and simulated ED patterns demonstrates a mixture of
Available online 28 September 2014
body-centered orthorhombic and hexagonal close packed-monoclinic based one˚ well reprodimensional C60 polymer models with the intermolecular distance of 9.28 A duces the experimental ED results. 2014 Elsevier Ltd. All rights reserved.
Nanocarbon allotropes such as fullerenes, carbon nanotubes (CNTs), and graphenes have been extensively investigated and they exhibit novel properties differing from e.g. diamond and graphite, thus being expected to fabricate electronic devices beyond those based on silicon materials [1]. We found that one-dimensional (1D) uneven peanut-shaped C60 polymer is formed by electron-beam (EB) irradiation of a pristine C60 film [2], and exhibits not only physical properties arising from 1D metal but also the geometrical curvature effects on electronic properties [3], which have been a big puzzle in quantum mechanics since 1950s. Basically, the EB-induced structural transformation of C60 strongly depends on a kinetic energy of incident electrons.
In the case of EB with a high kinetic energy (ca. 100 keV and more), C60 are elastically interacted with incident electrons and thus destroyed to form amorphous carbon [4]. On the other hand, in the case of EB with a low kinetic energy (less than 10 keV), C60 are inelastically interacted with incident electrons and thus sometimes damaged and sometimes polymerized with each other [5,6]. Besides EB incident energy, the interactions with substrates should be considered for a few C60 layers [7]. In our previous work [6], we examined the evolution of infrared (IR) spectra of C60 films with respect to EB irradiation time, using in situ high-resolution IR spectroscopy and firstprinciples density-functional calculations, and found semi-
* Corresponding author: Current address: Department of Physical Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan. E-mail address: [email protected] (J. Onoe). 1 Current address: National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan. http://dx.doi.org/10.1016/j.carbon.2014.09.049 0008-6223/ 2014 Elsevier Ltd. All rights reserved.
CARBON
8 1 (2 0 1 5) 8 4 2–84 6
843
Fig. 1 – Schematic illustration of the 1D uneven peanutshaped C60 polymer (lower) with a cross-linked structure of the P08 C120 isomer (upper) obtained from the general Stone–Wales rearrangement. (A colour version of this figure can be viewed online.)
quantitatively that the 1D uneven peanut-shaped C60 polymer has a waist cross-linked structure close to that of the P08 peanut-shaped C120 isomer (Fig. 1) obtained from the general Stone–Wales transformation. In addition, we examined the dependence of C60 polymerization on an incident energy of EB in the range of 3–7 kV. IR spectra obtained for 5 and 7 kV EB irradiation of C60 films showed the same product as for 3 kV EB irradiation. However, when 5 and 7 kV EBs were continued to irradiate C60 films for a long time after the 1D polymer formation, the 1D peanut-shaped polymer was proceeded not to be 1D polymers with a more coalesced linkage than that of the P08 C120 but to be amorphous carbons [6]. Although we already obtained several facts [8,9] indicating the 1D metallic peanut-shaped C60 polymer as well as Tomonaga–Luttinger liquid behavior [3], we have not obtained the experimental results directly supporting the 1D geometric structure so far. In the present study, we have examined the geometric structure of the C60 polymer single crystal (SC) film formed by EB irradiation of a C60 SC film, using HR transmission electron microscope (TEM) and electron diffraction (ED) in combination with ED simulations of 1D C60 polymer SC models. A C60 SC film (50 nm thick) was formed on a mica substrate (20-mm wide and 30-mm long) at 473 K (±0.1 K) by thermal evaporation of C60 powder (99.98% pure) at 623 K (±0.1 K) in an ultrahigh vacuum (UHV) chamber (base pressure: 10–6 Pa). Thereafter, the C60 SC film was irradiated with 3 kV EB (electron dose: 1.2 · 1018 m 2 s 1) at room temperature. We confirmed that all C60 molecules were completely polymerized, using in situ IR spectroscopy. We next took the film out of the chamber, and then ripped the film off the substrate by putting it into pure water. Subsequently, the film thus ripped was mounted on a copper (Cu) grid, and observed using HRTEM and ED apparatus (Hitachi HF-2000 and H-800, respectively).
Fig. 2 – (a, b) HRTEM images of the pristine and EB-irradiated C60 single crystal films taken at the Scherzer focus condition. Insets show the FFT patterns of individual corresponding HRTEM images. The arrows show the bright spots corresponding to the fringes with a width of 0.9 nm. (c, d) ED patterns of the pristine and EB-irradiated C60 single crystal films. Scale is calibrated with pristine C60 sample. In (c), the two weak spots indicated by E1 and E2 (which correspond to 1/3 and 2/3 of 422 series, respectively) are attributed to twins due to the stacking faults formed on the (1 1 1)FCC surface of the film. (e) Intensity profile of individual ED patterns from the center (S) to the right edge on the [2 2 0]FCC (E) in the red rectangular area shown in (c). Note that the lateral axis denotes a reciprocal space (not indicates the distance in a real space). (A colour version of this figure can be viewed online.)
Since 200 kV EB (electron dose: 1.5 · 1020 m 2 s 1) was focused on the films for HRTEM observation, electron-irradiated damage such as destroy of C60 cage is significantly included in HRTEM images during the observation time. This results in the difficulty of direct observation of 1D peanut-shape structure at this stage. On the contrary, since the ED patterns were recorded by defocusing EB (electron dose: 1.2 · 1019 m 2 s 1) over the whole area of the samples, they remained unchanged during ED measurement time. Fig. 2(a) shows the HRTEM image and fast Fourier-transformed (FFT) pattern of the pristine C60 SC film with the [1 1 1]FCC orientation, though some defects are introduced at the center of the image. Correspondingly, small spots
844
CARBON
8 1 ( 2 0 1 5 ) 8 4 2 –8 4 6
Fig. 3 – (a) FCC (grey) and BCO (red) structural models of C60 single crystal, whereas (b) HCP (grey) and HCP-m (red) models of C60 single crystal. Each blue band line shows the 1D direction of C60–C60 polymerization. (a) We set the 1D C60 polymer along the [ 1 1 0]FCC (in-plane of (1 1 1)FCC). The ˚ lattice constant of the pristine C60 FCC unit cell is a = 14.17 A ˚) [14]. The di between adjacent C60 molecules (10.0 A ˚ judging from the experimental ED decreases to 9.3 A patterns shown in Fig. 2. The BCO model has the lattice ˚ , b = 9.28 A ˚ , and c = 14.17 A ˚, constant of a = 10.02 A ˚, respectively, whereas the HCP-m has that of a = 9.28 A ˚ , and c = 16.36 A ˚ , respectively. (A colour version of b = 9.84 A this figure can be viewed online.)
appeared besides the main spots of 220 series. Fig. 2(b) shows the HRTEM image and FFT pattern of the EB-irradiated C60 SC film. Despite the threefold symmetry disappeared, vertical fringes with an interval of 0.5 nm and horizontal fringes with that of 0.9 nm appeared, which is wider than that of Fig. 2(a). In the FFT pattern of Fig. 2(b), the bright spots shown by arrows appeared at the position corresponding to horizontal wide fringes in the image. Fig. 2(c) shows the ED pattern of the C60 SC film with the [1 1 1]FCC orientation. The weak spots corresponding to twins due to the stacking faults appeared. Fig. 2(d) shows the ED pattern of the EB-irradiated C60 SC film. This pattern shows three new features: (1) the spot of 220 series is still intense and becomes an extended doublet (the extension of the spot along one given direction has been observed for 1D crystal strain [10]), (2) the spot E1 becomes one of the main spots in this pattern, which implies that the crystal structure of the EB-irradiated C60 SC film becomes oriented to both [1 1 1]FCC and [0 0 1]HCP, and (3) each spot becomes an arc-like stretched line with a rotation angle of ca. 9.2, which shows a slight loss of crystal orientation. The intensity profile (see Fig. 2(e)) of both ED patterns esti˚, mated the intermolecular distance di to be 10.0 and 9.3 A ˚ for the 1D C60 polymer is longer respectively. The di of 9.3 A ˚ ) of the P08 C120 isomer. This may be because than that (8.7 A adjacent C60 molecules are pulled to each other on both sides on the contrary to the C120. Although a small peak appeared in the intensity profile of the EB-irradiated C60, it attributes to a part of the broadening of the arc-like spots which correspond to the stacking faults.
Fig. 4 – Schematic illustration of a mixture of BCO and HCP-m structure models for 1D C60 polymer. Colored open circles indicate the positions of C60 molecules. Blue band line shows the 1D direction of C60–C60 polymerization. In the bird’s-eye view, each layer named as A, B, and C is (1 1 1)FCC induced an orientational plane. Each open circle indicates the position of C60 molecules and each blue band shows 1D direction for polymerization. In the bird’s-eye view, one stacking fault is introduced as a BCBC stacking that can be identified to be HCP-m. (A colour version of this figure can be viewed online.)
CARBON
8 1 (2 0 1 5) 8 4 2–84 6
845
˚ (see Fig. 2) on Fig. 5 – Simulated ED patterns of the BCO- (a) and HCP-m- (b) based 1D C60 polymer models with the di of 9.28 A three possible polymerization directions on (1 1 1)FCC. Both models reproduce the doublet spots. (a) BCO model does not reproduce the E1 spots, whereas (b) HCP-m one well reproduces the whole ED pattern.
Given that the polymerization proceeds along one direction in the (1 1 1)FCC plane of the C60 SC film with no stacking faults, the crystal structure should change to body-centered orthorhombic (BCO) structure (see Fig. 3(a)). However, there exists a stacking mismatch of 8% estimated from the two ˚ (pristine) and 9.28 A ˚ (polyexperimental di values of 10.02 A mer). This implies that a stacking fault is induced every 12 BCO layers, which changes the crystal structure to hexagonal close-packed (HCP)-based monoclinic (HCP-m) (see Fig. 3(b)). In fact, the spots indicated by arrows in inset of Fig. 3(b) and labeled as E1 in Fig. 3(d) showed that the BCO contains stacking faults. Fig. 4 shows a mixture model of BCO and HCP-m 1D C60 polymer from several views. The side view indicates that the stacking faults play a role of relaxing the crystal strains generated by polymerization. The top view explains the arclike spot shape by the fluctuation of polymer directions after lattice reconstruction. The orientation slightly changes upon stacking. When C60 molecules in the threefold symmetrical (1 1 1)FCC layer are polymerized to form 1D C60 polymer with ˚ along one direction, the symmetry is broken to di = 9.28 A change the angle between adjacent polymerization directions from 60.00 to 61.87 (shown in layer A of the top view). Therefore, at least five layers should be stacked helically along the same direction in order to obtain the angle distribution of 9.2 for the arc-like spots that are due to the helical stacking of the 1D C60 polymers. Fig. 5 shows the simulated ED patterns of BCO (a) and HCP-m (b) based 1D C60 polymer models with three possible polymerization directions on (1 1 1)FCC, obtained using the QSTEM code [11]. Here, the precision of ED obtained experi˚ , whereas that of ED simulation is 0.01 A ˚. mentally is 0.1 A The BCO model does not reproduce the E1 spots, whereas the HCP-m one well reproduces the whole ED pattern, though both models reproduce the doublet spots. However, since the simulated BCO pattern is completely overlapped with the simulated HCP-m one, it is difficult to exclude the BCO model at this stage.
In summary, we have investigated the structure of pristine and EB-irradiated C60 SC films, using HRTEM and ED, and demonstrated that the mixture of BCO- and HCP-m-based 1D peanut-shaped C60 polymer models with an intermolecu˚ well explain the experimental ED results lar distance of 9.28 A of the EB-irradiated C60 SC film.
Acknowledgments This work was supported both by ‘‘Advanced Characterization Nanotechnology Platform (MEXT)’’ at Osaka University and by the Collaborative Research Fund of J-Power.
R E F E R E N C E S
[1] Guisinger NP, Arnold MS. Beyond silicon: carbon-based nanotechnology. MRS Bull 2010;35(04):273–9. [2] Onoe J, Nakayama T, Aono M, Hara T. Structural and electrical properties of an electron-beam-irradiated C60 film. Appl Phys Lett 2003;82(4):595–7. [3] Onoe J, Ito T, Shima H, Yoshioka H, Kimura S. Observation of Riemannian geometric effects on electronic states. Europhys Lett 2012;98:27001. [4] Seraphin S, Zhou D, Jiao J. Electron-beam-induced structural changes in crystalline C60 and C70. J Mater Res 1993;8(8):1895–9. [5] Zhao YB, Poirier DM, Pechman RJ, Weaver JH. Electron simulated polymerization of solid C60. Appl Phys Lett 1994;64(5):577–9. [6] Takashima A, Nishii T, Onoe J. Formation process and electron-beam incident energy dependence of onedimensional uneven peanut-shaped C60 polymer studied using in situ high-resolution infrared spectroscopy and density-functional calculations. J Phys D Appl Phys 2012;45(48):485302. [7] Hunt MRC, Schmidt J, Palmer RE. Electron-beam damage of C60 films on hydrogen-passivated Si(1 0 0). Appl Phys Lett 1998;72(3):323–5.
846
CARBON
8 1 ( 2 0 1 5 ) 8 4 2 –8 4 6
[8] Toda Y, Ryuzaki S, Onoe J. Femtosecond carrier dynamics in an electron-beam-irradiated C60 film. Appl Phys Lett 2008;92:094102. [9] Onoe J, Takashima A, Toda Y. Infrared phonon anomaly of one-dimensional metallic peanut-shaped C60 polymer. Appl Phys Lett 2010;97:241911. [10] Che J, Burger C, Toki S, Rong L, Hsiao BS, Amnuaypornsri S, et al. Crystal and crystallites structure of natural rubber and
synthetic cis-1,4-polyisoprene by a new two dimensional wide angle X-ray diffraction simulation method. I. Straininduced crystallization. Macromolecules 2013;46(11): 4520–8. [11] Koch C. [Ph.D. thesis]. Arizona State University; 2002.