K., Kondo

K., Niwase

K.G., Nakamura

T., Homae

English

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   - 1 - TuP.11 Version date: 10, August 2005  Polymerized phase and amorphous diamond synthesized from  C60 fullerene by shock compression  K. Niwase a, T.Homae b,*, K.G. Nakamura b, K.Kondo b a Hyogo University of Teacher Education, Yashiro-cho, Hyogo 673-1494, Japan. bMaterials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama, 226-8503, Japan.  Abstract C60 fullerene films were shock compressed to 23 and 52 GPa. Both the recovered samples exhibit fracture into platelets and broad photoluminescence, of which intensity increases with increasing the pressure. At 23 GPa, a characteristic single broad band appears at 1560-1570 cm-1, which is similar to the one found for three-dimensional (3D) polymerized C60 fullerene under high-pressure-high-temperature treatment. At 52 GPa, on the other hand, the single broad band has disappeared and a diamond peak sometimes appears, depending on the platelets.   Keywords: C60 fullerene, Shock compression, Polymerization, Diamond   Corresponding author K. Niwase Hyogo University of Teacher Education, Yashiro-cho, Hyogo 673-1494, Japan. Phone: +81-795-44-2210, Fax: +81-795-44-2210,  e-mail: niwase@sci.hyogo-u.ac.jp ――――――――――――――――――――――――――――― *Present address: Research Center for Explosion Safety, Advanced Industrial  Science and Technology, Tsukuba, Ibaraki, 305-8565, Japan   - 2 - 1. Introduction    Shock compression and rapid quenching (SCARQ) technique is a unique method to generate new interesting carbon materials [1-3]. Hirai et al. have found a transparent carbon product from C60 fullerene [2]. This product has a characteristic features, exhibiting σ-electron state in sp3 hybridization by electron energy loss spectroscopy (EELS) and a diffuse pattern by electron diffractometry. Then, it was judged as amorphous in the long-range order and diamond in short-range order and labeled as "amorphous diamond". Recently, broadband photoluminescence for the amorphous diamond has been reported [4]. High-pressure-high-temperature (HPHT) treatment for solid C60, on the other hand, also allows us to create a new carbon material such as superhard fullerite materials [5-8]. The superhard fullerites have features similar to the amorphous diamond fabricated by the SCARQ technique in the structure and physical properties, but there exists some essential differences. The superhard samples did not include both diamond and the so-called "collapsed fullerite" carbon state. The molecules in the HPHT samples are suggested to either create 3D polymers with crystalline and amorphous structures or a cellular nanostructure of sp2- and sp3-hybridized carbon atoms under different high pressure, high temperature and shear deformation conditions [5].  The aim of this study is to investigate polymerization of C60 fullerene by SCARQ at a pressure lower than the formation of amorphous diamond.  2. Experimental      We used a commercial grade C60 fullerene purified to 99.9 % as a starting material. Gold disks of 12 mm in diameter and 100 μm in thickness were utilized for rapid quenching after shock compression. C60 films of approximately 4.5 and 4.0 μm in thickness were prepared by vacuum deposition on the gold disks. Nondeposited gold disks were superimposed on the C60 deposited gold disks, making sandwiches. They were inserted into capsules made of stainless steel. Then the capsules were put into a protective assembly and subjected to shock loading from a flyer accelerated by a powder gun. The flyer velocities were estimated to 1.09 and 1.65 km/s, corresponding to a shock pressure of 23 and 52 GPa, respectively. The samples recovered from the capsules were investigated by scanning electron microscopy (SEM) and micro-Raman spectroscopy.     - 3 -  3. Results and discussion     Figures 1(a) and 1(b) show SEM micrographs of a recovered sample shock compressed to 23 GPa. A part of gold foil of the sandwiched sample was stripped and then dark areas corresponding to the C60 deposited area can be seen. In Fig. 1(a), we observe division of the dark areas by bright lines, indicating an occurrence of fracture into platelets due to the shock compression. Similar bright lines can be seen on the surface of gold foil. Figure 1(b) shows a magnified view of the area denoted by a square in Fig. 1(a). One can see the correspondence between platelets sticked to the gold foil and the bright squares in the dark area where the platelets were stripped off. The size of platelets ranged from several μm to several tens of μm. Optically most of the platelets looks dark blue. The recovered sample after shock compression at 52 GPa, on the other hand, was also divided into platelets but mostly transparent, as reported before [1-4]. An oblique view of the platelets on the gold foil for the 23 GPa sample is shown in Fig. 2. There exist breaches in the platelets. The bright lines on the gold foil are seen to be ridges formed between the platelets.     Figure 3 compares Raman spectra for a pristine C60 deposited film, and the two recovered samples shock compressed to 23 and 52 GPa. Raman measurements were done in the same condition for the samples in order to compare the relative intensity. At 23 GPa, photoluminescence can be seen as an increase of the Raman intensity, compared to the background intensity of the pristine C60 fullerene, over a wide range of 500-7000 cm-1. The sharp peaks observed at Raman shift of 1469 cm-1 on Ag2 pentagonal pinching mode of a C60 fullerene crystal disappeared and single intense broad at 1560-1570 cm-1 appeared instead, as denoted by an arrow. Other broad peaks at 3000, 4500 and 6300 cm-1 can change the peak positions and the intensities, depending on the platelets. Then, we guess the three peaks do not reflect the internal structure but originate in interference between the incident and the reflected laser beams. At 52 GPa, on the other hand, the single broad band observed at 23 GPa had disappeared and the intensity of the photoluminescence at a peak of 3000 cm-1 significantly increased over the wide range of 500-7000 cm-1. A broad diamond peak sometimes appeared at around 1320-1330 cm-1, depending on the platelets. The absence of Raman peaks of C60 fullerene and graphite peaks, and the appearance of broad diamond peak and the broad photoluminescence inidicate that this sample is in a transient state from amorphous    - 4 - diamond [2] to nanocrystalline diamond [3].     In HPHT studies, it has been reported that one intense broad band at 1560-1570 cm-1, which was assigned to a characteristic peak of 3D polymerization of C60 fullerene [9], appears in conditions 9.5-13 GPa and 300-1560 ℃, although the conditions are still rather controversial [8]. The 3D polymer can reach a hardness near to, or even greater than, that of diamond [5-8]. One should note that the SCARQ sample at 23 GPa in the present study exhibits a similar single broad band at 1560-1570 cm-1, suggesting 3D polymerization. A fracture into platelets for the SCARQ sample seen in Figs. 1 and 2 also suggests the formation of some hard material. Nevertheless, the highest pressure on the observation of the characteristic Raman band for the 3D polymerization by HPHT treatment reported so far is 13 GPa, which is significantly lower than 23 GPa of SCARQ.     Photoluminescence, on the other hand, is also a characteristic feature on the SCARQ specimens [4]. Probably, the photoluminescence should relate to some defective sites in the samples, because pristine C60 fullerene, diamond and graphite do not show such a type of photoluminescence. By utilizing other experimental methods, a variety of defective sites can be induced into carbon materials. High energy particle irradiation will produce point defects or defect clusters in the bulk materials [10-12] and ball milling will also make defective sites mechanically [13]. However, no photoluminescence has been reported so far for such the defective graphite or diamond specimens. Photoluminescence barely appears for chemical vapor deposited (CVD) diamond [14] and ultrafine explosive diamond [15]. Notably, no photoluminescence has been reported for the HPHT samples, suggesting some difference in the defective structures between SCARQ and HPHT samples.     One should remember that the SCARQ technique generates adequately high pressure and temperature for an extremely short duration within a fraction of a microsecond, and also quenches transformed phases with cooling rates of 106 to 1010 K/s [16]. Then, a transformed phase from single crystals of the initial C60 fullerene would be quenched in more defective structure, and (P,T) condition on the products may be different from that of the HPHT treatment due to the short duration.     In conclusion, we have found a characteristic Raman feature which suggests 3D polymerization and photoluminescence for a SCARQ sample. Further experimental investigations at pressures lower than the critical pressure for the synthesis of    - 5 - amorphous diamond by SCARQ technique are needed to clarify the nature of the polymerized materials and the formation mechanism.  Acknowledgements This research was partly supported by Nippon Sheet Glass Foundation for Materials Science and Engineering, and Collaborative Research Project of Materials and Structures Laboratory, Tokyo Institute of Technology.  References  [1] H.Hirai and K.Kondo, Science 253 (1991) 772. [2] H.Hirai, K.Kondo, N.Yoshizawa, and Me.Shiraishi, Appl.Phys.Lett. 64 (1994) 1797. [3] H.Hirai, K.Kondo, M.Kim, H.Koinuma, K.Kurashima and Y.Bando, Appl. Phys.Lett. 71 (1997) 3016. [4] T.Homae, K.Wakabayashi, K.G.Nakamura, K.Kondo, M.Yoshida, J.Mater.Sci.Lett. 20 (2001) 1107. [5] V.D.Blank, S.G.Buga, N.R.Serebryanaya, G.A.Dubitsky, S.N.Sulyanov, M.Yu.Popov, V.N.Denisov, A.N.Ivlev, B.N.Mavrin, Phys. Lett. A 220 (1996) 149. [6] V.V.Brazhkin, A.G.Lyapin, S.V.Popova, R.N.Voloshin and Yu. V.Antonov, S.G. Lyapin, Yu.A.Kluev, A.M.Natetov, Phys. Rev. B 56 (1997) 11465. [7] V.D.Blank, G.A.Dubitsky,N.R.Serebryanaya, B.N.Mavrin,  V.N.Denisov, S.G.Buga, L.A.Chernozatonskii, Physica B, 339 (2003) 39. [8] T.Horikawa, K.Suito, M.Kobayashi and R.Oshima, J.J.A.P., 44 (2005) 3141. [9] L.A.Chernozatonskii, N.R.Serebryanaya, B.N.Mavrin, Chem. Phys. Lett. 316 (2000) 199. [10] K.Niwase and T.Tanabe, Mater. Trans. JIM 34 (1993) 1111. [11] K. Nakamura and M.Kitajima, Phys. Rev. B 45 (1992) 78. [12] K.Niwase, Y.Kakimoto, I.Tanaka and T.Tanabe, Nucl.Instr.Meth. Phys. Res. B 91 (1994) 78. [13] K.Niwase, T.Tanaka, Y.Kakimoto, K.N.Ishihara and P.H.Shingu, Mater.Trans., JIM 36 (1995) 282. [14] L.Bergman, M.T.Mcclure, J.T.Glass and R.J.Nemanich, J.Appl.Phys. 76 (1994) 3020.    - 6 - [15] E.D.Obraztsova, K.G.Korotushenko, S.M.Pimenov, V.G.Ralchenko, A.A.Smolin, V.I.Konov and E.N.Loubnin, Nanostruc. Mater. 6 (1995) 827. [16] K. Kondo, Diamond and Related Materials 5 (1996) 13.     - 7 -  List of figure captions  Fig.1 SEM micrographs of a sample recovered from a shock compression to 23 GPa. A part of gold foil of the sample was stripped. Dark and bright areas correspond to the areas of C60 fullerene deposition and gold foils, respectively. Photo (b) is a magnified view of area denoted by a square in photo (a).   Fig.2 An oblique view of platelets on a gold foil. The bright lines appeared on the gold foil are ridges formed between the platelets.  Fig. 3 Raman spectra for pristine C60 fullerene, and samples recovered from a shock compression to 23 and 52 GPa. Broad photoluminescence can be seen for both the recovered samples as an increase of the Raman intensity over a wide range of 500-7000 cm-1. At 23 GPa, the sharp peaks observed for pristine C60 fullerene disappeared and single broad band at 1560-1570 cm-1 appeared as denoted by an arrow. At 52 GPa the single broad band has disappeared.     - 8 -   Fig. 1 K. Niwase et al.     Fig. 2 K. Niwase et al.        - 9 -  Fig. 3 K. Niwase et al.  

Polymerized phase and amorphous diamond synthesized from C60 fullerene by shock compression

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Polymerized phase and amorphous diamond synthesized from C60 fullerene by shock compression

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