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Synthesis of Fe–C60 complex by ion irradiation
Nuclear Instruments and Methods in Physics Research B 310 (2013) 18–22
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Synthesis of Fe–C60 complex by ion irradiation Hidekazu Minezaki a,⇑, Kosuke Oshima a, Takashi Uchida b, Toru Mizuki b, Richard Racz c, Masayuki Muramatsu d, Toyohisa Asaji e, Atsushi Kitagawa d, Yushi Kato f, Sandor Biri c, Yoshikazu Yoshida a,b a
Graduate School of Engineering, Toyo University, 2100 Kujirai, Kawagoe, Saitama 350-8585, Japan Bio-Nano Electronics Research Centre, Toyo University, 2100 Kujirai, Kawagoe, Saitama 350-8585, Japan Institute of Nuclear Research (ATOMKI), H-4026, Debrecen, Bem tér 18/C, Hungary d National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan e Oshima National College of Maritime Technology, 1091-1 Komatsu Suou Oshima City, Oshima, Yamaguchi 742-2193, Japan f Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka 565-0871, Japan b c
a r t i c l e
i n f o
Article history: Received 18 September 2012 Received in revised form 26 March 2013 Available online 29 May 2013 Keywords: Endohedral fullerenes Ion irradiation LDI-TOF-MS HPLC
a b s t r a c t In order to synthesize the Fe@C60 complex, iron ion beam irradiated to C60 thin films. The energy of the irradiated iron ions was controlled from 50 eV to 250 eV. The dose of that was controlled from 6.67 1012 to 6.67 1014 ions/cm2. By the analysis of the surface of the iron ion irradiated C60 thin films using laser desorption/ionization time-of-flight mass spectrometry, we could confirm the peak with mass/charge of 776. The mass/charge of 776 corresponds to Fe + C60. We obtained the maximum intensity of the peak with mass/charge of 776 under the irradiation iron ion energy and the dose were 50 eV and 3.30 1013 ions/cm2, respectively. Then, the separation of the material with mass of 776 was performed by using high performance liquid chromatography. We could separate the Fe + C60 from the iron ion irradiated C60 thin film. As a result, we could synthesize the Fe + C60 complex as a new material. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction A special electron cyclotron resonance (ECR) ion source (ECRIS) was developed by our team for the production of new materials on nano-scale [1–3]. One of our main targets is the production of endohedral fullerenes, i.e. having at least one additional atom within a fullerene cage. Among others, for example we expect an endohedral iron-fullerene (Fe@C60) can be applied as a contrast material for magnetic resonance imaging. Endohedral fullerenes can be produced (1) during the fullerene fabrication process (using arc discharge, laser vaporization, etc.) [4], or (2) by incorporating other materials to the open-cage fullerene (chemical processing) [5], or (3) by collision reaction of the fullerene molecules with a different material (collision processing) [6–9]. Such synthesis (3) can be taken place in the plasma or by particle–surface interactions using ion beam. Using the ECR plasma, our authors reported an endohedral nitrogen-fullerene (N@C60) production in the nitrogen-C60 mixture plasma, by the collision reaction of those ions or neutrals in the plasma and on the internal surface of the plasma chamber [6]. Abe et al. have reported the N@C60 production by the nitrogen plasma irradiation to the C60 at ion energy ranged from ⇑ Corresponding author. E-mail address: [email protected] (H. Minezaki). 0168-583X/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nimb.2013.05.015
0 to 200 eV [7]. As a result, they confirmed that the energy necessary for the synthesis of the N@C60 is higher than 20 eV. Watanabe et al. have reported an endohedral xenon-fullerene (Xe@C60) production by Xe ion irradiation to the C60 thin film at the ion energy of 30, 34, and 38 keV [8]. The Xe@C60 was synthesized by step-by-step deceleration of the Xe ion within the C60 thin film, and the ion energy and the dose were confirmed as important parameters in synthesis of the Xe@C60. Reinke et al. studied the feasibility of a Fe@C60 using the Fe ion beam of the ion energy ranged from 60 to 380 eV, followed by the surface characterization with the X-ray photoelectron spectroscopy [9]. The paper concludes with an indication the absence of sizable amount of the Fe@C60. Altogether, the Fe@C60 has not been clearly synthesized yet. We have recently reported about the Fe+ beam irradiation to the C60 thin film [10], and confirmed the presence of the peak with a mass/charge of 776 (Fe + C60) by time-of-flight mass spectrometry. However, quantity of the Fe + C60 was very low, and that material could not be confirmed that the Fe is encapsulated within the C60 or stuck to surface of that. In this study, the single-charged Fe ion (Fe+) beam irradiated to the C60 thin films. The ion energy of the Fe+ beam was controlled from 50 to 250 eV, and the dose of that was controlled from 6.67 1012 to 6.67 1014 ions/cm2. The surface of the Fe+-irradiated C60 thin films was investigated by laser desorption/ionization
H. Minezaki et al. / Nuclear Instruments and Methods in Physics Research B 310 (2013) 18–22
time-of-flight mass spectrometry (LDI-TOF-MS), and the separation of the material was performed by high performance liquid chromatography (HPLC). 2. Experimental 2.1. Experimental setup and material Fig. 1 shows a schematic of a Bio-Nano ECRIS with a beam transportation system (a), a deceleration system (b) [1,2]. In the irradiation experiments a pre-prepared 10 nm-thick C60 thin film is set up on the deceleration electrode. Then the Fe plasma is generated in the Bio-Nano ECRIS by using an induction heating (IH) oven for evaporation [3]. The Fe+ beam was extracted from the ECRIS forming the ion energy of 5 keV. The C60 thin film is irradiated by Fe+ ions. The deceleration system consists of a beam restriction electrode, a suppressor electrode a deceleration electrode. The beam restriction electrode restricts the ion beam by a20 mm of the hole. The deceleration electrode decelerates the ion beam extracted at 5 kV by applying the voltage of 4.75–4.95 kV. The suppressor electrode attracts the secondary electron emitted from the target by the ion beam irradiation. The dose and the ion energy of the Fe+ beam are varied in this experiment. The irradiation conditions of the Fe+ beam are as follows: the ion energy of 50, 80, 100, 150, 200 and 250 eV, the Fe+ beam intensity of 40 nA, and the irradiation time of 60, 180, 300, 420, 600, 1800, 3000, 4200, and 6000 s. The dose of the Fe+ beam was calculated by the beam size (15 15 mm2) and the irradiation time. Then, the doses of Fe+ were calculated to be 6.67 1012, 2.00 1013, 3.30 1013, 4.67 1013, 6.67 1013, 2.00 1014, 3.30 1014, 4.67 1014, and 6.67 1014 ions/cm2. The parameters of the ECRIS for production of the Fe+ beam are as follows; microwave frequency of 9.75 GHz, microwave power of 10 W, mirror coils current ranged from 424 to 500 A (maximum axial magnetic field strength ranged from 0.37 to 0.44 T), Fe temperature of 1250 °C, pressure of 1.0 10 5 Pa, extraction voltage of 5.0 kV.
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2.2. Analysis method The surface of the Fe+-irradiated C60 thin films are investigated by LDI-TOF-MS (Bruker Daltonics, Autoflex 2), and the separation of the synthesized material is investigated by HPLC (Shimadzu Co., prominence). The separated material after the HPLC is analyzed again by the LDI-TOF-MS. The LDI-TOF-MS measured an area of 4 4 mm2 at the center of the Fe+-irradiated C60 thin films. We have performed a numerical simulation of Fe ion trajectories in the C60 thin film at collision energies of 50 to 250 eV using the SRIM code [11]. Since at these small energies projection range was only 1–2 monolayers of the C60 film, the topmost surface of the Fe+-irradiated C60 films were analyzed by LDI-TOF-MS. The HPLC data were taken with a 5 PYE (250 mm 4.6 I.D. mm, Nacalai Tesque, INC.) column with the toluene as the solvent and the flow rate of 0.5 ml/min. The solution dissolved 1 lg of the Fe+-irradiated C60 thin film in the 1.75 ml of the toluene and the 0.05 ml of that is injected to the column. The HPLC chromatogram was measured by optical absorption. Optical absorption of the solution was detected at 312 nm. In analysis of HPLC system, the fullerene was separated by the molecular geometry [12,13]. Therefore, at HPLC analysis, the solution was eluted the fraction. The eluted fraction was dropped on a Si substrate and analyzed again by using the LDI-TOF-MS. 3. Results and discussion 3.1. LDI-TOF-MS analysis of the surface of the irradiated C60 thin films and optimization of irradiation conditions Fig. 2 shows the LDI-TOF-MS spectra: an non-irradiated C60 thin film (a), a Fe+-irradiated C60 thin film (b). The Fe+-irradiation conditions of Fig. 1 (b) were the ion energy of 50 eV and the dose of 3.30 1013 ions/cm2. We could observe the peaks of the C60, C58,
Fig. 1. Schematic drawing: Bio-Nano ECRIS with beam transportation system (a), deceleration system (b).
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H. Minezaki et al. / Nuclear Instruments and Methods in Physics Research B 310 (2013) 18–22
Fig. 2. LDI-TOF-MS spectra: non-irradiated C60 thin film (a), Fe+-irradiated C60 thin film (b). Irradiation conditions of the Fe+-irradiated C60 thin film were the ion energy of 50 eV and the dose of 3.30 1013 ions/cm2.
and O + C60. In addition, we could observe the Fe + C60 peak from Fig. 1 (b). This peak could not observe from Fig. 1 (a). Fig. 3 shows the ion energy dependence of the relative intensity ratio of a Fe + C60 to C60 (hereinafter, R). The dose of these samples were 6.67 1012 and 6.67 1013 ions/cm2. The R value tended to increase with decreasing the ion energy at the both conditions. The R value became high at the ion energy of 50 eV in each dose. According to the molecular dynamics simulation of Neyts et al. [14], in the case of a nickel (Ni) implantation to the C60 molecule (which is close to the Fe by size and mass), the value of energy for the surface sticking of the C60 was 10 to 90 eV, and the C60 was broken more than 90 eV. It can be considered that the same phenomenon occurs with the result of our experiment as shown in Fig. 3. Therefore, the R value decreases with increasing the ion energy. In addition, the case of 50 eV, it is thought that the Fe + C60 is encapsulated Fe within the C60 or stuck to C60 surface. Fig. 4 shows the dose dependence of the R value. The ion energy of these samples were 50 eV. We could observe the Fe + C60 peak in all samples except for the sample obtained with the dose of 6.67 104 ions/cm2. The R value increased for the dose from 6.67 1012 to 3.30 1013 ions/cm2, and it decreased for the dose from 3.30 1013 to 6.67 1014 ions/cm2. The R value reached the maximum value at 3.30 1013 ions/cm2. Fig. 5 shows the LDI-TOF-MS spectrum of the Fe+-irradiated C60 thin film with the dose of 6.67 1014 ions/cm2. We could confirm the peaks with
Fig. 3. Ion energy dependence of relative intensity ratio of Fe + C60 to C60 (R). These samples were performed at the dose of 6.67 1012 ions/cm2 or 6.67 1013 ions/ cm2 and the ion energy of 50–250 eV. The error bar is shown by standard error.
Fig. 4. Dose dependence of relative intensity ratio of Fe + C60 to C60 (R). These samples were performed at the ion energy of 50 eV and the dose of 6.67 1012 ions/cm2 to 6.67 1014 ions/cm2. The error bar is shown by standard error.
the mass/charge smaller than 600 and the mass/charge larger than 1000. As for the peak with the mass/charge smaller than 600, these peaks were fragment of C60 (hereinafter, C60-fragment peaks) such as C50 and C48. As for the peak with the mass/charge larger than 1000, it is thought that these peaks are the polymer (hereinafter, C60-polymer peaks) such as the C60 + C60-fragment and the C60fragment + C60-fragment. It seems that the C60-fragment peak and the C60-polymer peak are synthesized by collision of the C60 and the Fe+. These peaks increased with increasing the dose. Therefore, it is thought that the Fe + C60 was broken by collision of Fe+ in the range more than 3.30 1013 ions/cm2 in Fig. 4. As that result, it supposed that the Fe + C60 peak decreased with increasing the dose. 3.2. HPLC analysis of the irradiated C60 thin film Fig. 6 shows the HPLC chromatograms; the non-irradiated C60 thin film (a), and the Fe+-irradiated C60 thin film (b). The condition of the Fe+-irradiated C60 thin film used sample of the optimum conditions (ion energy of 50 eV, dose of 3.30 1013 ions/cm2) in the previous section. Compared with the non-irradiated and the Fe+irradiated C60 thin film, the difference between the two chromatograms could not be confirmed. Then, we could observe the peaks at retention time of 10.7 min and 11.7 min in each chromatogram. In the non-irradiated C60 thin film, using LDI-TOF-MS, we confirmed that the peaks of 10.7 min and 11.7 min were C60 and O + C60, respectively. We eluted the fraction I, II and III in Fig. 6, and they were analyzed by the LDI-TOF-MS. Fig. 7 shows the LDI-TOF-MS spectra of the fraction I: the nonirradiated C60 thin film (a), the Fe+-irradiated C60 thin film (b). We could observe the peaks of the C60, C58, and O + C60. It is thought that the C58 was generated by laser irradiation during the LDITOF-MS analysis. As for the O + C60, it is thought that O adsorbed to the C60, because the fraction I was dried in air. In addition, we could observe the Fe + C60 peak again in the spectrum of the Fe+irradiated C60 thin film. Although a detailed structure of the Fe + C60 is not known, we could synthesize a Fe–C60 complex. Compared with the R value before and after HPLC analysis, it decreased after the HPLC analysis. The R value before and after HPLC analysis were 0.101 and 0.014, respectively. In this experiment, we used the C60 with 10 layers, but the Fe+ beam irradiated only one layer in the case of the ion energy of 50 eV. The Fe + C60 in 10 layers was calculated on the assumption that the C60 thin film has crystal structure, and calculated the R value was approximately 0.01. Therefore, we consider that the R value decreased at after the HPLC analysis
H. Minezaki et al. / Nuclear Instruments and Methods in Physics Research B 310 (2013) 18–22
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Fig. 5. LDI-TOF-MS spectrum of Fe+-irradiated C60 thin film. Irradiation conditions of the Fe+-irradiated C60 thin film were the ion energy of 50 eV and the dose of 6.67 1014 ions/cm2. The peaks with the mass/charge smaller than 600 are the C60 fragment peak, and the peaks with the mass/charge larger than 1000 are C60 polymer peak.
makes sense. As for the fraction II, Only the O + C60 peak was observed. As for the fraction III, the peak was not detected. We could confirm that the adsorption material was excluded from the Fe+ irradiated C60 thin film by using the HPLC and LDI-TOF-MS. However, the detailed structure of the Fe–C60 complex was not known. Therefore, the detailed structural analysis of the Fe-C60 complex will be needed in the future. 4. Conclusions
Fig. 6. HPLC chromatograms: non-irradiated C60 thin film (a), Fe+-irradiated C60 thin film (b). Irradiation conditions of the Fe+-irradiated C60 thin film were ion energy of 50 eV and dose of 3.30 1013 ions/cm2. The HPLC data are taken with a 5 PYE (250 mm 4.6 I.D. mm) column. The solution dissolved 1 lg of the Fe+irradiated C60 thin film in 1.75 ml of toluene and the 0.05 ml of that is injected to the column. Optical absorption of the solution was detected at 312 nm.
We synthesized the Fe–C60 complex by the Fe+ irradiation to the C60 thin film. By the analysis of the surface of the Fe+-irradiated to C60 thin films using the LDI-TOF-MS, the Fe + C60 peak could be confirmed. In addition, in order to optimize the Fe + C60, the dose and the ion energy of the Fe+ beam were varied. We confirmed that the R value became highest at the ion energy of 50 eV and the dose of 3.30 1013 ions/cm2. By the separation of the material with the mass of the Fe + C60 was performed by the HPLC, the Fe + C60 peak was confirmed again in the LDI-TOF-MS spectrum of the material. In addition, we confirmed that the adsorption material is excluded from the Fe+ irradiated C60 thin film by using the HPLC and LDI-TOF-MS. And we could synthesize the Fe–C60 complex as new material. Acknowledgements Part of this study has been supported by a Grant for the 21st Century Center of Excellence Program from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan since 2003, a Grant for the High-Tech Research Center Fund from MEXT, Japan from 2006 to 2010, and a Grant for the Programme for the Strategic Research Foundation at Private Universities S1101017 organized by the MEXT, Japan, since April 2011. This work was partly supported by the TAMOP 4.2.2.A-11/1/KONV-2012-0036 project, which is co-financed by the European Union and European Social Fund. References
Fig. 7. LDI-TOF-MS spectra of the fraction I: non -irradiated C60 thin film (a), Fe+irradiated C60 thin film (b). Irradiation conditions of this sample were the ion energy of 50 eV and the dose of 3.30 1013 ions/cm2.
[1] T. Uchida, H. Minezaki, Y. Yoshida, S. Biri, A. Kitagawa, M. Muramatsu, T. Asaji, K. Tanaka, Y. Kato, Proc. of the 18th International Workshop on ECRIS, Chicago, IL, 2008, 27–31, (http://accelconf.web.cern.ch/AccelConf/ecris08/papers/ moco-c01.pdf). [2] K. Tanaka, M. Muramatsu, T. Uchida, S. Biri, T. Asaji, K. Shima, T. Hanajiri, A. Kitagawa, Y. Kato, Y. Yoshikazu, AIP Conf. Proc. 1066 (2008) 525–528.
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[3] T. Uchida, H. Minezaki, K. Tanaka, M. Muramatsu, T. Asaji, Y. Kato, A. Kitagawa, S. Biri, Y. Yoshikazu, Rev. Sci. Instrum. 81 (2010) 02A306. [4] Y. Chai, T. Cuo, C. Jin, R.E. Haufler, L.P.F. Chibante, J. Fure, L. Wang, J.M. Alford, R.E. Smalley, J. Phys. Chem. 95 (1991) 7564. [5] K. Komatsu, M. Murata, Y. Murata, Science 307 (2005) 14. [6] S. Biri, E. Fekete, A. Kitagawa, M. Muramatsu, A. Janossy, J. Palinkas, Rev. Sci. Instrum. 77 (2006) 03A314. [7] S. Abe, G. Sata, T. Kaneko, T. Hirata, R. Hatakeyama, K. Yokoo, S. Ono, K. Omote, Y. Kasama, Jpn. J. Appl. Phys. B 10 (45) (2006) 8340–8343. [8] S. Watanabe, N.S. Ishioka, H. Shimomura, H. Muramatsu, T. Sekine, Nuc. Instrum. Methods Phys. Res. B 206 (2006) 399–402.
[9] P. Reinke, S. Eyhusen, M. Büttner, P. Oelhafen, Appl. Phys. Lett. 84 (2004) 4373. [10] H. Minezaki, T. Uchida, K. Tanaka, M. Muramatsu, T. Asaji, A. Kitagawa, Y. Kato, S. Biri, Y. Yoshida, Rev. Sci. Instrum. 83 (2012) 02A346. [11] J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Pergamon Press, 1958. [12] S.T. Wan, W.H. Zhang, T. Nakane, D.Z. Xu, M. Inakuma, H. Shinohara, K. Kobayashi, S. Nagase, J. Am. Chem. Soc. 120 (1998) 6806. [13] N. Tagmatarchis, E. Aslanis, K. Prassides, H. Shinohara, Chem. Mater. 13 (2001) 2374–2379. [14] E.C. Neyts, A. Bogaerts, Carbon 47 (2009) 1028–1033.
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Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Synthesis of Fe–C60 complex by ion irradiation Hidekazu Minezaki a,⇑, Kosuke Oshima a, Takashi Uchida b, Toru Mizuki b, Richard Racz c, Masayuki Muramatsu d, Toyohisa Asaji e, Atsushi Kitagawa d, Yushi Kato f, Sandor Biri c, Yoshikazu Yoshida a,b a
Graduate School of Engineering, Toyo University, 2100 Kujirai, Kawagoe, Saitama 350-8585, Japan Bio-Nano Electronics Research Centre, Toyo University, 2100 Kujirai, Kawagoe, Saitama 350-8585, Japan Institute of Nuclear Research (ATOMKI), H-4026, Debrecen, Bem tér 18/C, Hungary d National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan e Oshima National College of Maritime Technology, 1091-1 Komatsu Suou Oshima City, Oshima, Yamaguchi 742-2193, Japan f Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka 565-0871, Japan b c
a r t i c l e
i n f o
Article history: Received 18 September 2012 Received in revised form 26 March 2013 Available online 29 May 2013 Keywords: Endohedral fullerenes Ion irradiation LDI-TOF-MS HPLC
a b s t r a c t In order to synthesize the Fe@C60 complex, iron ion beam irradiated to C60 thin films. The energy of the irradiated iron ions was controlled from 50 eV to 250 eV. The dose of that was controlled from 6.67 1012 to 6.67 1014 ions/cm2. By the analysis of the surface of the iron ion irradiated C60 thin films using laser desorption/ionization time-of-flight mass spectrometry, we could confirm the peak with mass/charge of 776. The mass/charge of 776 corresponds to Fe + C60. We obtained the maximum intensity of the peak with mass/charge of 776 under the irradiation iron ion energy and the dose were 50 eV and 3.30 1013 ions/cm2, respectively. Then, the separation of the material with mass of 776 was performed by using high performance liquid chromatography. We could separate the Fe + C60 from the iron ion irradiated C60 thin film. As a result, we could synthesize the Fe + C60 complex as a new material. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction A special electron cyclotron resonance (ECR) ion source (ECRIS) was developed by our team for the production of new materials on nano-scale [1–3]. One of our main targets is the production of endohedral fullerenes, i.e. having at least one additional atom within a fullerene cage. Among others, for example we expect an endohedral iron-fullerene (Fe@C60) can be applied as a contrast material for magnetic resonance imaging. Endohedral fullerenes can be produced (1) during the fullerene fabrication process (using arc discharge, laser vaporization, etc.) [4], or (2) by incorporating other materials to the open-cage fullerene (chemical processing) [5], or (3) by collision reaction of the fullerene molecules with a different material (collision processing) [6–9]. Such synthesis (3) can be taken place in the plasma or by particle–surface interactions using ion beam. Using the ECR plasma, our authors reported an endohedral nitrogen-fullerene (N@C60) production in the nitrogen-C60 mixture plasma, by the collision reaction of those ions or neutrals in the plasma and on the internal surface of the plasma chamber [6]. Abe et al. have reported the N@C60 production by the nitrogen plasma irradiation to the C60 at ion energy ranged from ⇑ Corresponding author. E-mail address: [email protected] (H. Minezaki). 0168-583X/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nimb.2013.05.015
0 to 200 eV [7]. As a result, they confirmed that the energy necessary for the synthesis of the N@C60 is higher than 20 eV. Watanabe et al. have reported an endohedral xenon-fullerene (Xe@C60) production by Xe ion irradiation to the C60 thin film at the ion energy of 30, 34, and 38 keV [8]. The Xe@C60 was synthesized by step-by-step deceleration of the Xe ion within the C60 thin film, and the ion energy and the dose were confirmed as important parameters in synthesis of the Xe@C60. Reinke et al. studied the feasibility of a Fe@C60 using the Fe ion beam of the ion energy ranged from 60 to 380 eV, followed by the surface characterization with the X-ray photoelectron spectroscopy [9]. The paper concludes with an indication the absence of sizable amount of the Fe@C60. Altogether, the Fe@C60 has not been clearly synthesized yet. We have recently reported about the Fe+ beam irradiation to the C60 thin film [10], and confirmed the presence of the peak with a mass/charge of 776 (Fe + C60) by time-of-flight mass spectrometry. However, quantity of the Fe + C60 was very low, and that material could not be confirmed that the Fe is encapsulated within the C60 or stuck to surface of that. In this study, the single-charged Fe ion (Fe+) beam irradiated to the C60 thin films. The ion energy of the Fe+ beam was controlled from 50 to 250 eV, and the dose of that was controlled from 6.67 1012 to 6.67 1014 ions/cm2. The surface of the Fe+-irradiated C60 thin films was investigated by laser desorption/ionization
H. Minezaki et al. / Nuclear Instruments and Methods in Physics Research B 310 (2013) 18–22
time-of-flight mass spectrometry (LDI-TOF-MS), and the separation of the material was performed by high performance liquid chromatography (HPLC). 2. Experimental 2.1. Experimental setup and material Fig. 1 shows a schematic of a Bio-Nano ECRIS with a beam transportation system (a), a deceleration system (b) [1,2]. In the irradiation experiments a pre-prepared 10 nm-thick C60 thin film is set up on the deceleration electrode. Then the Fe plasma is generated in the Bio-Nano ECRIS by using an induction heating (IH) oven for evaporation [3]. The Fe+ beam was extracted from the ECRIS forming the ion energy of 5 keV. The C60 thin film is irradiated by Fe+ ions. The deceleration system consists of a beam restriction electrode, a suppressor electrode a deceleration electrode. The beam restriction electrode restricts the ion beam by a20 mm of the hole. The deceleration electrode decelerates the ion beam extracted at 5 kV by applying the voltage of 4.75–4.95 kV. The suppressor electrode attracts the secondary electron emitted from the target by the ion beam irradiation. The dose and the ion energy of the Fe+ beam are varied in this experiment. The irradiation conditions of the Fe+ beam are as follows: the ion energy of 50, 80, 100, 150, 200 and 250 eV, the Fe+ beam intensity of 40 nA, and the irradiation time of 60, 180, 300, 420, 600, 1800, 3000, 4200, and 6000 s. The dose of the Fe+ beam was calculated by the beam size (15 15 mm2) and the irradiation time. Then, the doses of Fe+ were calculated to be 6.67 1012, 2.00 1013, 3.30 1013, 4.67 1013, 6.67 1013, 2.00 1014, 3.30 1014, 4.67 1014, and 6.67 1014 ions/cm2. The parameters of the ECRIS for production of the Fe+ beam are as follows; microwave frequency of 9.75 GHz, microwave power of 10 W, mirror coils current ranged from 424 to 500 A (maximum axial magnetic field strength ranged from 0.37 to 0.44 T), Fe temperature of 1250 °C, pressure of 1.0 10 5 Pa, extraction voltage of 5.0 kV.
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2.2. Analysis method The surface of the Fe+-irradiated C60 thin films are investigated by LDI-TOF-MS (Bruker Daltonics, Autoflex 2), and the separation of the synthesized material is investigated by HPLC (Shimadzu Co., prominence). The separated material after the HPLC is analyzed again by the LDI-TOF-MS. The LDI-TOF-MS measured an area of 4 4 mm2 at the center of the Fe+-irradiated C60 thin films. We have performed a numerical simulation of Fe ion trajectories in the C60 thin film at collision energies of 50 to 250 eV using the SRIM code [11]. Since at these small energies projection range was only 1–2 monolayers of the C60 film, the topmost surface of the Fe+-irradiated C60 films were analyzed by LDI-TOF-MS. The HPLC data were taken with a 5 PYE (250 mm 4.6 I.D. mm, Nacalai Tesque, INC.) column with the toluene as the solvent and the flow rate of 0.5 ml/min. The solution dissolved 1 lg of the Fe+-irradiated C60 thin film in the 1.75 ml of the toluene and the 0.05 ml of that is injected to the column. The HPLC chromatogram was measured by optical absorption. Optical absorption of the solution was detected at 312 nm. In analysis of HPLC system, the fullerene was separated by the molecular geometry [12,13]. Therefore, at HPLC analysis, the solution was eluted the fraction. The eluted fraction was dropped on a Si substrate and analyzed again by using the LDI-TOF-MS. 3. Results and discussion 3.1. LDI-TOF-MS analysis of the surface of the irradiated C60 thin films and optimization of irradiation conditions Fig. 2 shows the LDI-TOF-MS spectra: an non-irradiated C60 thin film (a), a Fe+-irradiated C60 thin film (b). The Fe+-irradiation conditions of Fig. 1 (b) were the ion energy of 50 eV and the dose of 3.30 1013 ions/cm2. We could observe the peaks of the C60, C58,
Fig. 1. Schematic drawing: Bio-Nano ECRIS with beam transportation system (a), deceleration system (b).
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Fig. 2. LDI-TOF-MS spectra: non-irradiated C60 thin film (a), Fe+-irradiated C60 thin film (b). Irradiation conditions of the Fe+-irradiated C60 thin film were the ion energy of 50 eV and the dose of 3.30 1013 ions/cm2.
and O + C60. In addition, we could observe the Fe + C60 peak from Fig. 1 (b). This peak could not observe from Fig. 1 (a). Fig. 3 shows the ion energy dependence of the relative intensity ratio of a Fe + C60 to C60 (hereinafter, R). The dose of these samples were 6.67 1012 and 6.67 1013 ions/cm2. The R value tended to increase with decreasing the ion energy at the both conditions. The R value became high at the ion energy of 50 eV in each dose. According to the molecular dynamics simulation of Neyts et al. [14], in the case of a nickel (Ni) implantation to the C60 molecule (which is close to the Fe by size and mass), the value of energy for the surface sticking of the C60 was 10 to 90 eV, and the C60 was broken more than 90 eV. It can be considered that the same phenomenon occurs with the result of our experiment as shown in Fig. 3. Therefore, the R value decreases with increasing the ion energy. In addition, the case of 50 eV, it is thought that the Fe + C60 is encapsulated Fe within the C60 or stuck to C60 surface. Fig. 4 shows the dose dependence of the R value. The ion energy of these samples were 50 eV. We could observe the Fe + C60 peak in all samples except for the sample obtained with the dose of 6.67 104 ions/cm2. The R value increased for the dose from 6.67 1012 to 3.30 1013 ions/cm2, and it decreased for the dose from 3.30 1013 to 6.67 1014 ions/cm2. The R value reached the maximum value at 3.30 1013 ions/cm2. Fig. 5 shows the LDI-TOF-MS spectrum of the Fe+-irradiated C60 thin film with the dose of 6.67 1014 ions/cm2. We could confirm the peaks with
Fig. 3. Ion energy dependence of relative intensity ratio of Fe + C60 to C60 (R). These samples were performed at the dose of 6.67 1012 ions/cm2 or 6.67 1013 ions/ cm2 and the ion energy of 50–250 eV. The error bar is shown by standard error.
Fig. 4. Dose dependence of relative intensity ratio of Fe + C60 to C60 (R). These samples were performed at the ion energy of 50 eV and the dose of 6.67 1012 ions/cm2 to 6.67 1014 ions/cm2. The error bar is shown by standard error.
the mass/charge smaller than 600 and the mass/charge larger than 1000. As for the peak with the mass/charge smaller than 600, these peaks were fragment of C60 (hereinafter, C60-fragment peaks) such as C50 and C48. As for the peak with the mass/charge larger than 1000, it is thought that these peaks are the polymer (hereinafter, C60-polymer peaks) such as the C60 + C60-fragment and the C60fragment + C60-fragment. It seems that the C60-fragment peak and the C60-polymer peak are synthesized by collision of the C60 and the Fe+. These peaks increased with increasing the dose. Therefore, it is thought that the Fe + C60 was broken by collision of Fe+ in the range more than 3.30 1013 ions/cm2 in Fig. 4. As that result, it supposed that the Fe + C60 peak decreased with increasing the dose. 3.2. HPLC analysis of the irradiated C60 thin film Fig. 6 shows the HPLC chromatograms; the non-irradiated C60 thin film (a), and the Fe+-irradiated C60 thin film (b). The condition of the Fe+-irradiated C60 thin film used sample of the optimum conditions (ion energy of 50 eV, dose of 3.30 1013 ions/cm2) in the previous section. Compared with the non-irradiated and the Fe+irradiated C60 thin film, the difference between the two chromatograms could not be confirmed. Then, we could observe the peaks at retention time of 10.7 min and 11.7 min in each chromatogram. In the non-irradiated C60 thin film, using LDI-TOF-MS, we confirmed that the peaks of 10.7 min and 11.7 min were C60 and O + C60, respectively. We eluted the fraction I, II and III in Fig. 6, and they were analyzed by the LDI-TOF-MS. Fig. 7 shows the LDI-TOF-MS spectra of the fraction I: the nonirradiated C60 thin film (a), the Fe+-irradiated C60 thin film (b). We could observe the peaks of the C60, C58, and O + C60. It is thought that the C58 was generated by laser irradiation during the LDITOF-MS analysis. As for the O + C60, it is thought that O adsorbed to the C60, because the fraction I was dried in air. In addition, we could observe the Fe + C60 peak again in the spectrum of the Fe+irradiated C60 thin film. Although a detailed structure of the Fe + C60 is not known, we could synthesize a Fe–C60 complex. Compared with the R value before and after HPLC analysis, it decreased after the HPLC analysis. The R value before and after HPLC analysis were 0.101 and 0.014, respectively. In this experiment, we used the C60 with 10 layers, but the Fe+ beam irradiated only one layer in the case of the ion energy of 50 eV. The Fe + C60 in 10 layers was calculated on the assumption that the C60 thin film has crystal structure, and calculated the R value was approximately 0.01. Therefore, we consider that the R value decreased at after the HPLC analysis
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Fig. 5. LDI-TOF-MS spectrum of Fe+-irradiated C60 thin film. Irradiation conditions of the Fe+-irradiated C60 thin film were the ion energy of 50 eV and the dose of 6.67 1014 ions/cm2. The peaks with the mass/charge smaller than 600 are the C60 fragment peak, and the peaks with the mass/charge larger than 1000 are C60 polymer peak.
makes sense. As for the fraction II, Only the O + C60 peak was observed. As for the fraction III, the peak was not detected. We could confirm that the adsorption material was excluded from the Fe+ irradiated C60 thin film by using the HPLC and LDI-TOF-MS. However, the detailed structure of the Fe–C60 complex was not known. Therefore, the detailed structural analysis of the Fe-C60 complex will be needed in the future. 4. Conclusions
Fig. 6. HPLC chromatograms: non-irradiated C60 thin film (a), Fe+-irradiated C60 thin film (b). Irradiation conditions of the Fe+-irradiated C60 thin film were ion energy of 50 eV and dose of 3.30 1013 ions/cm2. The HPLC data are taken with a 5 PYE (250 mm 4.6 I.D. mm) column. The solution dissolved 1 lg of the Fe+irradiated C60 thin film in 1.75 ml of toluene and the 0.05 ml of that is injected to the column. Optical absorption of the solution was detected at 312 nm.
We synthesized the Fe–C60 complex by the Fe+ irradiation to the C60 thin film. By the analysis of the surface of the Fe+-irradiated to C60 thin films using the LDI-TOF-MS, the Fe + C60 peak could be confirmed. In addition, in order to optimize the Fe + C60, the dose and the ion energy of the Fe+ beam were varied. We confirmed that the R value became highest at the ion energy of 50 eV and the dose of 3.30 1013 ions/cm2. By the separation of the material with the mass of the Fe + C60 was performed by the HPLC, the Fe + C60 peak was confirmed again in the LDI-TOF-MS spectrum of the material. In addition, we confirmed that the adsorption material is excluded from the Fe+ irradiated C60 thin film by using the HPLC and LDI-TOF-MS. And we could synthesize the Fe–C60 complex as new material. Acknowledgements Part of this study has been supported by a Grant for the 21st Century Center of Excellence Program from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan since 2003, a Grant for the High-Tech Research Center Fund from MEXT, Japan from 2006 to 2010, and a Grant for the Programme for the Strategic Research Foundation at Private Universities S1101017 organized by the MEXT, Japan, since April 2011. This work was partly supported by the TAMOP 4.2.2.A-11/1/KONV-2012-0036 project, which is co-financed by the European Union and European Social Fund. References
Fig. 7. LDI-TOF-MS spectra of the fraction I: non -irradiated C60 thin film (a), Fe+irradiated C60 thin film (b). Irradiation conditions of this sample were the ion energy of 50 eV and the dose of 3.30 1013 ions/cm2.
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