Synthesis of Fe–C60 complex by ion irradiation

https://doi.org/10.1016/j.nimb.2013.05.015Get rights and content

Highlights

  • The Fe+ beam was irradiated to the C60 thin films.

  • The Fe+-irradiated C60 thin films were analyzed by LDI-TOF-MS and by HPLC.

  • The peak with mass/charge of 776 was observed in the Fe+-irradiated C60 thin film.

  • We could synthesize the Fe–C60 complex as a new material.

Abstract

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.

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], [2], [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], [7], [8], [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 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 time-of-flight mass spectrometry (LDI-TOF-MS), and the separation of the material was performed by high performance liquid chromatography (HPLC).

Section snippets

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

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, 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

Conclusions

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

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

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