(Invited) Novel Synthesis Procedure for Endohedral-Fullerenes Using Laser Ablation Plasma from Solid Material and Vaporized Fullerenes
Authors: Sakakita Hajime , Itagaki Hirotomo , Fujiwara Yutaka , Minowa Yuki , Kim Jaeho , Ikehara Yuzuru , Kaneko Toshiro , IIzumi Yoko , Okazaki Toshiya 
Published: May 2020

Since a fullerene was discovered in 1985, fullerene has attracted much attentions [1]. A unique feature of the fullerene that has the spherical structure with hollow interior allows a fullerene to accommodate any other atoms and molecules. Especially, the fullerenes containing other atoms which is called as endohedral fullerene have been expected to be applied in medical uses, electronics systems and so on [2]. In many cases, endohedral fullerenes have been synthesized by ion implantation, co-vaporization of carbon and metal atoms [3], or ion plasma irradiation technique for non-metal material [4]. However, these procedures have remained several issues. One of the critical issues is low production rate for endohedral fullerene synthesize due to difficulties in controlling a physical and a chemical property during synthesizing process. To increase the production efficiency of endohedral fullerene, it is required to optimize elementary process between fullerenes and injected atoms.
Under these situations, we recently developed a novel procedure to synthesize endohedral fullerenes that induce the collision of vaporized fullerenes and ablated particles produced by the laser ablation of a solid material. Here, a Q-switched Nd:YAG Laser (Continuum, Powerlite DLS8000) with a wavelength of 1064 nm, a pulse-width of 9 ns, a laser energy of up to 1 J, and a pulse-frequency of up to 10Hz was used. Laser light was focused to be 50 m in diameter on the target surface. In this procedure, N@C60 was synthesized using the ablation of boron nitride material. From the previous studies [4], it is quite important for encapsulated particles to have about 100 eV. Optical emission spectrum of ablated particles by a polychromator (Bunkokeiki, CT-1000) with an intensified CCD detector (Princeton Instruments, PI-Max) was measured, and Doppler shift of the spectrum was estimated. The result showed that the kinetic energy of nitrogen ions was in the range of 20 to 65 eV by controlling the energy of the incident laser beam. The synthesis of N@C60 was conducted with a nitrogen kinetic energy of 65 eV, fullerenes vaporizing temperature of 800 degree Celsius, and a total reaction time of one hour. By optimizing the kinetic energy of ablated particles, synthesis of N@C60 was succeeded [5]. Existence of N@C60 in the toluene solution was confirmed by an electron spin resonance measurement (Elexsys E500, Bruker) without purification by high performance liquid chromatography [6]. The purity of produced N@C60 was two orders of magnitude higher than that achieved using alternative physical synthetic methods that use solid materials, such as arc discharge and co-evaporation methods. However, the purity must be increased by at least two orders of magnitude for the commercial use. Therefore, it is necessary to enhance the purity by optimizing experimental conditions such as laser energy, laser wavelength, amount of ion flux with appropriate energy, repetition rate of laser pulses, laser duration time, area of the laser ablation, and so on. In the meeting, novel synthesis procedure for endohedral-fullerenes using laser ablation plasma from solid material and vaporized fullerenes will be presented.
Acknowledgments
This study was financially supported by JSPS KAKENHI Grant No. 25287157 from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
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